Sensors & Actuators: B. Chemical (v.155, #1)

Locked nucleic acids biosensor for detection of BCR/ABL fusion gene using benzoate binuclear copper (II) complex as hybridization indicator by Liqing Lin; Jie Kang; Shaohuang Weng; Jinghua Chen; Ailin Liu; Xinhua Lin; Yuanzhong Chen (1-7).
Benzoate binuclear copper (II) complex, [Cu2(C7H5O2)4(C2H6O)2] (abbreviated as CuR2) was prepared and its interaction with double-stranded salmon sperm DNA (dsDNA) in pH 7.4 phosphate buffer solution was studied by electrochemical experiments at the Au electrode (AuE). It was revealed that CuR2 presented an excellent electrochemical activity on AuE and could bind with dsDNA by intercalation mode. The CuR2 was further utilized as a new indicator in the fabrication of an electrochemical DNA biosensor for detection of BCR/ABL fusion gene. The biosensor based on nanogold (NG) modified AuE was developed by using thiolated-hairpin locked nucleic acids (LNA) as the capture probe for hybridization with BCR/ABL fusion gene. The results indicated this new method has excellent specificity for single-base mismatch and complementary after hybridization. The constructed electrochemical DNA biosensor achieved a detection limit of 1.0 × 10−10  M for complementary target DNA with a good stability.
Keywords: CuR2; DNA hybridization; BCR/ABL fusion gene; Locked nucleic acids; Electrochemical biosensor;

Our major goal in developing intelligent quality sensors is to detect bacterial pathogens such as Salmonella in the packaged beef. Olfactory sensing of specific volatile organic compounds released by the bacterial pathogens is one of the unique ways for determining contamination in food products. This work aims at developing a biomimetic piezoelectric olfactory sensor for detecting specific gases (alcohols) at low concentrations.The computational simulation was used to determine the biomimetic peptide-based sensing material to be deposited on the quartz crystal microbalance (QCM) sensor. Tripos/Sybyl®8.0 was used to predict the binding site of an olfactory receptor and determine the binding affinity as well as orientation of the selected ligands (specific molecules) to the olfactory receptor. The designed polypeptide sequence based on the simulation program was synthesized and used as a sensing layer in the QCM crystal. The developed QCM sensors were sensitive to 1-hexanol as well as 1-pentanol as predicted by the simulation algorithm. The estimated lower detection limits of the QCM sensors for detecting 1-hexanol and 1-pentanol were 2–3 ppm and 3–5 ppm, respectively. This study demonstrates the applicability of simulation-based peptide sequence that mimics the olfactory receptor for sensing specific gases.
Keywords: Food safety; Salmonella contamination; Piezoelectric sensor; Alcohols; Molecular simulation;

In2O3  +  xBaO (x  = 0.5–5 at.%) – A novel material for trace level detection of NO x in the ambient by Chander Shekhar; K.I. Gnanasekar; E. Prabhu; V. Jayaraman; T. Gnanasekaran (19-27).
Indium oxide (In2O3) doped with 0.5–5 at.% of Ba was examined for their response towards trace levels of NO x in the ambient. Crystallographic phase studies, electrical conductivity and sensor studies for NO x with cross interference for hydrogen, petroleum gas (PG) and ammonia were carried out. Bulk compositions with x  ≤ 1 at.% of Ba exhibited high response towards NO x with extremely low cross interference for hydrogen, PG and ammonia, offering high selectivity. Thin films of 0.5 at.% Ba doped In2O3 were deposited using pulsed laser deposition technique using an excimer laser (KrF) operating at a wavelength of (λ) 248 nm with a fluence of ∼3 J/cm2 and pulsed at 10 Hz. Thin film sensors exhibited better response towards 3 ppm NO x quite reliably and reproducibly and offer the potential to develop NO x sensors (Threshold limit value of NO2 and NO is 3 and 25 ppm, respectively).
Keywords: In2O3; Ba doping; Electrical conductivity; Sensor studies for NO x ; H2; Petroleum gas and NH3; Thin films; Pulsed laser deposition;

Chemo-sensitivity of latex-based films containing segregated networks of carbon nanotubes by J. Lu; J.F. Feller; B. Kumar; M. Castro; Y.S. Kim; Y.T. Park; J.C. Grunlan (28-36).
In contrast to conventional hydrophobic Conductive Polymer nanoComposites (CPCs) used to design vapor sensors, which are mostly soluble in organic solvents, monodispersed acrylate copolymer latexes present the double advantage of being more sensitive and selective towards polar vapors such as water. A hierarchically structured latex based CPC film was obtained by co-dispersion of an aqueous acrylic emulsion with multiwalled carbon nanotubes (CNTs), followed by spray layer by layer (sLbL) assembly. The analysis of CPC films morphology by AFM and TEM show that a segregated network of CNT as been achieved by partial coalescence of latex nanoparticles and homogeneously assembled in 3D. Transducer sensitivity was investigated as a function of CNT content, latex glass transition temperature (T g), organic vapor nature and vapor concentration. The source of the high sensitivity and selectivity observed for these latex-based composites towards water vapor is assumed to mainly result from ionic interaction of SDS with water molecules offering interesting perspectives of development. The different diffusion regimes through the CPC transducer are visualized, modeled and interpreted with the Langmuir–Henry-Clustering (LHC) model, showing that only water is reaching a clustering mode at high vapor concentration. Finally it is believed that the unique hierarchical architecture of BA latex–CNT sensors is responsible for their quick, stable and reproducible responses to vapors.
Keywords: Vapor sensor; Acrylate latex; Carbon nanotubes; Segregated network; Chemo-resistive response; Conductive Polymer nanoComposites; Spray layer by layer assembly;

Design and performances of a mid-infrared CH4 detection device with novel three-channel-based LS-FTF self-adaptive denoising structure by Wei-Lin Ye; Chuan-Tao Zheng; Xin Yu; Cong-Xin Zhao; Zhan-Wei Song; Yi-Ding Wang (37-45).
A novel mid-infrared (MIR) CH4 concentration detection device using three-channel-based least-square fast transverse filtering (LS-FTF) self-adaptive denoising structure was proposed. By introducing an additional noise-channel besides the traditional detection-channel and reference-channel, the noises can be well removed using the LS-FTF denoising algorithm. The detection procedure was described, and the key modules including the optical part and electrical part were designed and fabricated. Thorough experiments performed for the fabricated device show that the absolute detection error is less than 5%, and by quantifying the detected voltage using software, the minimum detection level is 8 ppm and the detection sensitivity is 9 ppm within the detection range of 8–1000 ppm. The measured maximum response time is less than 10 s, and the absolute detection error with temperature-compensation is less than 5%. The proposed three-channel-based LS-FTF denoising structure can also be adapted to other similar detection systems for noise elimination.
Keywords: Mid-infrared; Gas detection; LS-FTF; Detection sensitivity; Detection error;

Cu2+ chemosensing behaviour of self-organized micro-array structures of a donor–acceptor bichromophoric compound anchored onto Ag nanoisland films by T. Del Rosso; E. Giorgetti; G. Margheri; A. Rindi; M. Muniz-Miranda; A. Carloni; F. Pavone; P. Fabbrizzi; S. Cicchi (46-52).
This work reports on the Cu2+ chemosensing behaviour of self-organized micro-array structures of a novel donor–acceptor bichromophoric compound anchored onto Ag nanoisland films. The system exhibits quenching of the fluorescence in the presence of Cu2+ ions, with detection range extending from 2 × 10−8  M up to 3 × 10−6  M and limit of detection (LOD) of 8 × 10−9  M. The quenching of fluorescence is accompanied by a quenching of SERS signal from the metal-organic structure, which is consistent with an electron transfer between the copper cation and the organic moiety. The self-organization property of the sensing complexes into micrometric arrays offers great potential for miniaturization and future development of Cu2+ detection systems based on real-time observation of fluorescence or SERS quenching by fluorescence microscopy or microRaman spectroscopy.
Keywords: Copper chemosensors; Fluorescence quenching; Raman quenching; Metal nanoisland films; SERS;

A simple, low-cost technique for fabrication of high performance optical fiber oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of an optical fiber with ORMOSIL composite xerogel films film sequestered with luminophore platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) prepared by a sol–gel process. The composite xerogels studied are 3,3,3-trifluoropropyltrimethoxysliane (TFP-TriMOS) or n-propyltrimethoxysilane (n-propyl-TriMOS)/tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS). Results show that, expect for PtTFPP-doped TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels show the high sensitivity and linear Stern–Volmer relationship which indicate the homogenous environment of the luminophore. The sensitivities of the two oxygen sensors are quantified in terms of the ratio I N2/I O2, where I N2 and I O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the PtTFPP-doped TFP-TriMOS/TEOS/Octyl-triEOS and n-propyl-TriMOS/TEOS/Octyl-triEOS oxygen sensors have sensitivities of 101 and 155, respectively. The experimental results confirm that the current oxygen sensors exhibit the linear Stern–Volmer plots and high-sensitive based on the oxygen indicator embedded in TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels.
Keywords: Optical fiber; Oxygen sensor; Sol–gel; PtTFPP;

This paper demonstrates and systematically characterizes the enrichment of biomolecular compounds using aptamer-functionalized surfaces within a microfluidic device. The device consists of a microchamber packed with aptamer-functionalized microbeads and integrated with a microheater and temperature sensor to enable thermally controlled binding and release of biomolecules by the aptamer. We first present an equilibrium binding-based analytical model to understand the enrichment process. The characteristics of the aptamer–analyte binding and enrichment are then experimentally studied, using adenosine monophosphate (AMP) and a specific RNA aptamer as a model system. The temporal process of AMP binding to the aptamer is found to be primarily determined by the aptamer-AMP binding kinetics. The temporal process of aptamer-AMP dissociation at varying temperatures is also obtained and observed to occur relatively rapidly (<2 s). The specificity of the enrichment is next confirmed by performing selective enrichment of AMP from a sample containing biomolecular impurities. Finally, we investigate the enrichment of AMP by either discrete or continuous introduction of a dilute sample into the microchamber, demonstrating enrichment factors ranging from 566 to 686×, which agree with predictions of the analytical model.
Keywords: Aptamer; Enrichment; Microfluidic; Solid phase capture; Isocratic elution;

Carbon nanotube based sensors for the detection of viruses by M. Bhattacharya; S. Hong; D. Lee; T. Cui; S.M. Goyal (67-74).
Carbon nanotube biosensors were assembled using a layer-by-layer (LBL) technique exploiting the chemical functionalization on nanotubes to tailor their interactions with viruses and antiviral antibodies. Gold electrodes were patterned in the form of resistors onto a Si/SiO2 substrate, followed by stepwise LBL assembly to change the resistivity of the channel. Polyelectrolyte multilayer films were prepared by the sequential electrostatic adsorption of poly(diallyldimethylammonium chloride), poly(styrene sulfonate), and functionalized single-walled carbon nanotubes. Viral antibodies were successfully immobilized between the electrodes and the binding of antibodies to the surface was enhanced by coating with poly(l-lysine). An antigen specific to the immobilized antibody was captured on these devices. The coupled antibody–antigen complex changed the conductance of the device and this change was related to the antigen concentration. The two factors affecting the performance of the device were the number of layers and the channel length between the electrodes. We were able to detect conductance change for a viral antigen with a titer of 102  TCID50/ml (50% tissue culture infective dose).
Keywords: Carbon nanotubes; Biosensors; Viruses;

A biosensor based on the immobilization of lactate oxidase (LOx) on a glassy carbon electrode modified with laponite/chitosan hydrogels for the quantification of l-lactate in alcoholic beverages and dairy products is presented. Ferrocene–methanol (FcMe) is used as artificial mediator. The purpose of this work is to determine the best hydrogel composition from the analytical point of view. The characterization of the hydrogels was carried out by CV, amperometry and EIS. According to permeabilities and charge transfer resistances for ferrocyanide (used as molecular probe) as well as the enzymatic behavior of the enzyme for l-lactate, the best laponite/chitosan mass ratio found was 25/50. The distinct features of the bioelectrode are its long stability, its ability to reject or minimize most interferents including ascorbic acid, and its excellent analytical response, which allowed the reduction of the enzyme content below 0.5 U, for a sensitivity of (0.326 ± 0.003) A cm−2  M−1, with a time response lower than 5 s and a detection limit of (3.8 ± 0.2) × 10−6  M. Our l-lactate biosensor was validated by comparison with a standard spectroscopic method.
Keywords: Lactate biosensor; Laponite/chitosan hydrogel; Ferrocene–methanol; Wine; Beer; Dairy products;

Potential of 5,10,15,20-Tetrakis(3′,5′-di-tertbutylphenyl)porphyrinatocopper(II) for a multifunctional sensor by Z. Ahmad; M.H. Sayyad; M. Yaseen; K.C. Aw; M. M-Tahir; M. Ali (81-85).
An organic compound 5,10,15,20-Tetrakis(3′,5′-di-tertbutylphenyl)porphyrinatocopper(II) (TDTPPCu) is synthesized and studied as an active material for multifunctional capacitive sensor. The capacitance of the device as a function of illumination, humidity and temperature has been investigated. It is observed that the capacitance increases by 4.7 times from the dark condition under an illumination of 3850 lx. The capacitance is also changed 9.5 times with the increase in relative humidity (RH) from 30% to 95%. No change in capacitance appeared below critical temperature 120 °C. Based on the experimental results for the multifunctional sensor a mathematical model has been developed. The model is mainly based on the assumption that the capacitive response of the sensor is associated with dielectric polarization. The sensors are simulated using this model. The simulated results match well with experimental results.
Keywords: Multifunctional sensor; Metalloporphyrin; Capacitance; 5,10,15,20-Tetrakis(3′,5′-di-tertbutylphenyl)porphyrinatocopper(II);

Novel C-doped WO3 microtubes (MTs) were successfully synthesized by a facile infiltration and calcination process using the cotton fibers as templates. The prepared MTs were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), N2 adsorption and desorption measurements and ultraviolet–visible spectroscopy. XPS spectra show the carbon was doped into the lattice of the WO3 phase, resulting in a decrease of the band gap of the C-doped WO3 MTs from 2.45 eV to 2.12 eV. Moreover, the WO3 MTs were assembled by nanoparticles in size of ca. 40 nm and had larger specific surface area (21.3 m2/g) due to existence of meso/macro-pores inside them. At low operating temperature of 90 °C, the gas sensor based on the C-doped WO3 MTs had a detected limit of 50 ppb to the toluene gas (response of 2.0). The enhancement of toluene sensing performance of C-doped WO3 MTs was attributed to a larger surface area and higher porosity, which arises from its unique MTs. Furthermore, the band gap reduction and a new intragap band formation for C-doped WO3 MTs were proposed as the reason for the decrease in optimal operating temperature.
Keywords: C-doped WO3; Microtubes; Toluene; Ultrahigh sensitivity; Low operating temperature;

Amorphous cyclic olefin copolymers (COCs) are beginning to be used for making microfluidic devices for life science applications. Typically, both micro-scale and nano-scale channels are imprinted onto the copolymer by hot embossing. However, optimal manufacturing process conditions will only be possible if the COCs thermo-mechanical behavior is experimentally well characterized, mathematically modeled, and implemented in a numerical simulation. We have conducted large-strain compression experiments on two commercial grades of COCs: TOPAS-8007, and TOPAS-6015 in a wide temperature, and strain rate range. A constitutive theory and numerical implementation developed by Srivastava et al. was applied to model the behavior of TOPAS. We have employed that numerical implementation, together with the material parameters for TOPAS determined here, to predict the response of TOPAS in the following microfluidic fabrication operations: (i) micro-scale hot embossing on TOPAS-8007 to replicate a micro-chip; and (ii) for sealing the channels in the micro-chip: (a) thermal bonding of an embossed chip of TOPAS-8007 with a cover plate of TOPAS-8007; and (b) thermal bonding of an embossed chip of TOPAS-6015 with a cover plate of TOPAS-8007. We show that the model can provide a simulation capability for estimation of the processing parameters for hot embossing and thermal bonding.
Keywords: COC; Thermo-mechanical behavior; Hot embossing; Thermal bonding; Finite elements; Numerical simulations;

Electro-chemical operation of ionic polymer–metal composites by Doyeon Kim; Kwang J. Kim; Jae-do Nam; Viljar Palmre (106-113).
Currently, there is a major engineering challenge associated with ionic polymer–metal composites (IPMCs) that needs to be resolved before they can be vastly adopted in current and future engineering markets—relaxation of the IPMC actuator under a DC voltage. In this article, we rigorously discuss the potential origin of the relaxation phenomena of IPMCs that can be related to electro-chemically induced surface reactions with electrodes. Our measured voltammograms and deflection data of IPMCs revealed that the relaxation phenomena of the IPMC actuators are primarily caused by the overpotential of the surface electrodes. The overpotential values of ca. +1 V were clearly noted for many IPMC samples. We believe that the relaxation of IPMCs originate from the platinum oxide formation during actuation—a key surface reaction. The IPMC solvated with a typical ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) as a solvent, showed a larger bending, but there was no relaxation during actuation because there was no platinum oxide formation.
Keywords: Ionic polymer–metal composite; IPMC; Actuator; Relaxation;

Sensitive amperometric determination of chemical oxygen demand using Ti/Sb–SnO2/PbO2 composite electrode by Chuanjun Ma; Feng Tan; Huimin Zhao; Shuo Chen; Xie Quan (114-119).
A novel Ti/Sb–SnO2/PbO2 composite electrode was fabricated for COD determination. The new electrode configuration improved the sensitivity of the amperometric method apparently. Effects of common experimental parameters, such as applied potential, pH and concentration of the electrolyte on its analytical performance were investigated. A linear range of 0.5–200 mg L−1 COD and a detection limit (a signal-to-noise ratio of 3) of 0.3 mg L−1 were achieved under optimized conditions. The experiments for detecting COD in model samples and real samples were carried out to evaluate the electrode's performance. The obtained results were in good agreement with those determined by the standard dichromate method, with a relative error less than 12%.
Keywords: Chemical oxygen demand; Ti/Sb–SnO2/PbO2 electrode; Amperometric detection;

Pure diamond-like carbon (DLC) thin films and boron-doped DLC thin films have been deposited on silicon substrates using femtosecond pulsed laser. The amorphous carbon materials (DLC), have been deposited at room temperature by ablating graphite targets with an amplified Ti:sapphire laser of 800 nm wavelength and a pulse duration of 150 fs in high vacuum conditions. Doping with boron has been performed by ablating alternatively graphite and boron targets.In this study, the DLC films were used as working electrodes for the electrochemical detection of trace heavy metals namely, Cd2+, Pb2+, Ni2+ and Hg2+, by using square wave anodic stripping voltammetry (SWASV) technique. Four metals were detected at −1.3 V deposition potential, and 90 s deposition time. The DLC films have been characterized by multiwavelength Raman spectrometry and high resolution scanning electron microscopy. The effect of the boron doping on the electrochemical behavior has been shown. The a-C:B 8%/Si3N4 electrode gives the more sensitive detection. The four metals are detected simultaneously with a detection limit of 1 μg/L or 2 μg/L and a dynamic range from 1 or 2 to 25 μg/L for every metal, as presented in third table of this article. The different sensitivities obtained are 6.2, 20.0, 1.2 and 6.6 μA/ppb or μA μg−1  L for Cd2+, Pb2+, Ni2+ and Hg2+, respectively.
Keywords: Boron-doped DLC; Femtosecond Pulsed laser deposition; Heavy metal; Aquare wave anodic stripping voltammetry;

Fabrication and gas-sensing properties of hierarchically porous ZnO architectures by Jiarui Huang; Youjie Wu; Cuiping Gu; Muheng Zhai; Yufeng Sun; Jinhuai Liu (126-133).
Hierarchically three-dimensional (3D) porous ZnO architectures are synthesized by a template-free, economical aqueous solution method combined with subsequent calcination. First, the precursors of interlaced and monodisperse basic zinc nitrate (BZN) nanosheets are prepared. Then calcination of the precursors produces hierarchically 3D porous ZnO architectures composed of interlaced ZnO nanosheets with high porosity resulting from the thermal decomposition of the precursors. The products are characterized by X-ray diffraction, thermogravimetric–differential thermalgravimetric analysis, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller N2 adsorption–desorption analyses. The BET surface area of the hierarchically porous ZnO nanostructures was calculated to be 12.8 m2  g−1. Compared with ZnO rods, the as-prepared porous ZnO nanosheets exhibit a good response and reversibility to some organic gases, such as ethanol and acetone. The responses to 100 ppm ethanol and acetone are 24.3 and 31.6, respectively, at a working temperature of 320 °C. These results show that the porous ZnO architectures are highly promising for gas sensor applications, as the gas diffusion and mass transportation in sensing materials are significantly enhanced by their unique structures. Moreover, it is believed that this solution-based approach can be extended to fabricate other porous metal oxide materials with a unique morphology or shape.
Keywords: Zinc oxide; Basic zinc nitrate; Nanosheets; Porous; Gas sensor;

We are introducing a macroporous Au–Pt hybrid 3D electrode to be used for enzyme-free glucose detection. The proposed hybrid electrode was fabricated with a three dimensional structure by electroplating platinum nanoparticles onto the surface of the coral-like macroporous Au. It was then physically analyzed by using field emission scanning electron microscopy (FESEM). The porosity and window pore size of the macroporous Au electrode were 50% and 100–300 nm, respectively. The diameters of the Pt nanoparticles ranged from 10 to 15 nm. Through cyclic voltammograms in a 1 M sulfuric acid solution, we confirmed that the hybrid electrode exhibited a much larger surface activation area with a roughness factor (RF) of 2024.7 than the macroporous Au electrode with a roughness of 46.07. The highly improved surface activation area was caused by the electroplated Pt nanoparticles. The hybrid electrode exhibited a much stronger electrocatalytic activity due to glucose oxidation than the macroporous Au electrode. At 0.4 V, it responded linearly to the glucose up to 20 mM in a neutral media with a detection limit of 0.025 mM and detection sensitivity of 39.53 μA mM−1  cm−2 without being affected by interfering species. It also showed a stable recovery response to the step changes of the glucose concentration.
Keywords: Macroporous Au; Au–Pt hybrid; Pt nanoparticles; Electroplating; Enzyme-free; Glucose;

An obviously enantioselective strategy for the recognition of mandelic acid (MA) enantiomers in the presence of Zn(II) ions on a l-cysteine (l-Cys) self-assembled gold electrode is described. The high recognition of MA was evaluated via electrochemical impedance spectroscopy and cyclic voltammetry. After the modified electrode interacted with R- or S-MA solution containing Zn(II) ions for 10 min, larger electrochemical response signals were observed for R-MA. Time dependencies of the enantioselective interaction for the modified electrode with the solitary Zn(II) solution and MA enantiomers solutions containing Zn(II) were also investigated. The results showed that the enantioselective recognition was caused by the selective formation of Zn complex with l-Cys and MA enantiomers. In addition, the enantiomeric composition of R- and S-MA enantiomer mixtures could be monitored by measuring the current responses of the sample.
Keywords: Electrochemical investigation; Enantioselective recognition; Mandelic acid; Zn(II) ions; l-Cysteine-modified electrode;

This paper presents a reusable polymer lab chip sensor for continuous and on-site heavy metal monitoring in nature. In particular, detection of lead (Pb(II)), which is the most common heavy metal pollutant, has been performed using the proposed lab chip sensor. The miniaturized lab chip sensor consists of a microfabricated silver working electrode that replaces the conventional mercury and bismuth electrodes, an integrated silver counter and quasi-reference electrode, and microfluidic channels. The proposed sensor targets on-site environmental monitoring in a continuous fashion without disturbing or contaminating the sensing environment when it is reused. The reusability of the miniaturized lab chip sensor was characterized through forty-three consecutive measurements in non-deoxygenating standard solutions inside the microchannels using square-wave anodic stripping voltammetry (SWASV). With only 13.5 μL of sample volume the sensor chip showed a correlation coefficient of 0.998 for the Pb(II) concentration range of 1–1000 ppb with the limit of detection of 0.55 ppb at 300 s deposition time. The peak potentials during the forty-three consecutive SWASV measurements showed a relative standard deviation of 1.0%, with a standard deviation of 0.005 V. The high repeatability and linearity of the sensor over the large, three orders of magnitude, dynamic range of 1–1000 ppb showed that the developed sensor chip can be reused for a variety of on-site measurements such as for soil pore water or groundwater, using only micro-volumes.
Keywords: Lead (Pb(II)); On-site measurement; Reusable polymer lab chip sensor; Silver electrode; Square-wave anodic stripping voltammetry (SWASV);

Functionalized graphene as an aqueous phase chemiresistor sensing material by Matthew Myers; James Cooper; Bobby Pejcic; Murray Baker; Burkhard Raguse; Lech Wieczorek (154-158).
Here we report on the successful detection of benzene, toluene, ethylbenzene, xylenes and cyclohexane dissolved in water at low ppm concentration levels using functionalized graphene in a microelectrode chemiresistor platform. The use of microelectrodes results in a small double layer capacitance that effectively impedes charge transfer through the solution and allows the resistance of the graphene film to be measured preferentially. Comparing the relative chemiresistor response between cyclohexane (a non-aromatic molecule) and aromatic compounds (e.g. toluene), we have deduced that the response mechanism is most likely due to film swelling and not doping through the direct interaction of the molecule with the graphene basal plane.
Keywords: Chemiresistor; BTEX; Graphene; Sensor; Electrochemical;

Effect of surface defects on biosensing properties of TiO2 nanotube arrays by Peng Xiao; Yunhuai Zhang; Guozhong Cao (159-164).
In this paper, highly ordered titania nanotube (TNT) arrays fabricated by anodization were annealed at different temperatures in CO to create different concentrations of surface defects. The samples were characterized by SEM, XRD and XPS. The results showed different concentrations of Ti3+ defects were doped in TNT arrays successfully. Furthermore, after co-immobilized with horseradish peroxidase (HRP) and thionine chloride (Th), TNT arrays was employed as a biosensor to detect hydrogen peroxide (H2O2) using an amperometric method. Cyclic voltammetry results and UV–Vis absorption spectra presented that with an increase of Ti3+ defects concentration, the electron transfer rate and enzyme adsorption amount of TNT arrays were improved largely, which could be ascribed to the creation of hydroxyl groups on TNT surface due to dissociative adsorption of water by Ti3+ defects. Annealing in CO at 500 °C appeared to be the most favorable condition to achieve desirable nanotube array structure and surface defects density (0.27%), thus the TNT arrays showed the largest adsorption amount of enzyme (9.16 μg/cm2), faster electron transfer rate (1.34 × 10−3  cm/s) and the best response sensitivity (88.5 μA/mM l−1).
Keywords: TiO2 nanotubes; Surface defects concentration; Annealing; Enzyme; Hydrogen peroxide;

Enhanced chemosensing of ammonia based on the novel molecular semiconductor-doped insulator (MSDI) heterojunctions by Yanli Chen; Marcel Bouvet; Thibaut Sizun; Guillaume Barochi; Jérôme Rossignol; Eric Lesniewska (165-173).
A series of new molecular semiconductor-doped insulator (MSDI) heterojunctions as conductimetric transducers to NH3 sensing were fabricated based on a novel semiconducting molecular material, an amphiphilic tris(phthalocyaninato) rare earth triple-decker complex, Eu2[Pc(15C5)4]2[Pc(OC10H21)8], quasi-Langmuir–Shäfer (QLS) film, as a top-layer, and vacuum-deposited and cast film of CuPc as well as copper tetra-tert-butyl phthalocyanine (CuTTBPc) QLS film as a sub-layer, named as MSDIs 1, 2 and 3, respectively. MSDIs 13 and respective sub-layers prepared from three different methods were characterized by X-ray diffraction, electronic absorption spectra and current–voltage (IV) measurements. Depending on the sub-layer film-forming method used, α-phase CuPc film structure, β-phase CuPc crystallites and H-type aggregates of CuTTBPc have been obtained, respectively. An increasing sensitivity to NH3 at varied concentrations in the range of 15–800 ppm, follows the order MSDI 2  < MSDI 3  < MSDI 1, revealing the effect of sub-layer film structures on sensing performance of the MSDIs. In particular, the time-dependent current plot of the MSDI 1, with α-phase CuPc film as a sub-layer, clearly shows an excellent separation of the different ammonia concentration levels and nearly complete reversibility and reproducibility even at room temperature, which is unique among the phthalocyanine-based ammonia sensors thus far reported in the literature. This provides a general method to improve sensor response of organic heterojunctions by controlling and tuning the film structure of sub-layer with appropriate fabrication techniques. On the other hand, the enhanced sensitivity, stability and reproducible response of the MSDI 1 heterostructure in comparison with the respective single-layer films have also been obtained. A judicious combination of materials and molecular architectures has led to enhanced sensing properties of the MSDI 1, in which control at the molecular level can be achieved.
Keywords: Molecular semiconductor; Triple-decker rare earth phthalocyanine complex; Heterojunction; Chemosensing; Ammonia;

Nanostructured hollow spheres of SnO2 with fine nanoparticles were synthesized by ultrasonic atomization. Thick film gas sensors were fabricated by screen printing technique. Different surface modified films (Fe2O3 modified SnO2) were obtained by dipping them into an aqueous solution (0.01 M) of ferric chloride for different intervals of time followed by firing at 500 °C. The structural and microstructural studies of the samples were carried out using XRD, SEM, and TEM. The sensing performance of pure and modified films was studied by exposing various gases at different operating temperatures. One of the modified sample exhibited high response (1990) to 1000 ppm of LPG at 350 °C. Optimum amount of Fe2O3 dispersed evenly on the surface, adsorption and spillover of LPG on Fe2O3 misfits and high capacity of adsorption of oxygen on nanostructured hollow spheres may be the reasons of high response.
Keywords: Ultrasonic atomization; Fe2O3 modified SnO2; Thick films; LPG sensing; Fast response; Quick recovery time;

On data analysis in PTR-TOF-MS: From raw spectra to data mining by Luca Cappellin; Franco Biasioli; Pablo M. Granitto; Erna Schuhfried; Christos Soukoulis; Fabrizio Costa; Tilmann D. Märk; Flavia Gasperi (183-190).
Recently the coupling of proton transfer reaction ionization with a time-of-flight mass analyser (PTR-TOF-MS) has been proposed to realise a volatile organic compound (VOC) detector that overcomes the limitations in terms of time and mass resolution of the previous instrument based on a quadrupole mass analysers (PTR-Quad-MS). This opens new horizons for research and allows for new applications in fields where the rapid and sensitive monitoring and quantification of volatile organic compounds (VOCs) is crucial as, for instance, environmental sciences, food sciences and medicine. In particular, if coupled with appropriate data mining methods, it can provide a fast MS-nose system with rich analytical information. The main, perhaps even the only, drawback of this new technique in comparison to its precursor is related to the increased size and complexity of the data sets obtained. It appears that this is the main limitation to its full use and widespread application. Here we present and discuss a complete computer-based strategy for the data analysis of PTR-TOF-MS data from basic mass spectra handling, to the application of up-to date data mining methods. As a case study we apply the whole procedure to the classification of apple cultivars and clones, which was based on the distinctive profiles of volatile organic compound emissions.
Keywords: Proton transfer reaction-mass spectrometry; Time of flight; Data analysis; Data mining; Volatile organic compounds;

Pt nanoparticle-supported multiwall carbon nanotube electrodes for amperometric hydrogen detection by Duc-Duong La; Chi Kwan Kim; Tae Sun Jun; Yongju Jung; Gi Hun Seong; Jaebum Choo; Yong Shin Kim (191-198).
Platinum nanoparticles (Pt NPs) were grown directly on multiwall carbon nanotubes (MWNTs) using a wet chemical reduction process. Gas permeable Pt NP-supported MWNT (Pt/MWNT) electrodes were then formed on microporous PTFE membranes through the vacuum-filtration of a Pt/MWNT solution. The potential use of these electrodes in amperometric hydrogen sensor applications was assessed. Various material analysis methods such as SEM, TEM and XRD were employed in order to characterize the morphologies and microstructures of the Pt/MWNT nanocomposites. The electrodes exhibited a nanoporous interwoven surface morphology as a result of Pt agglomerates attached to the MWNTs. From the XRD and TEM measurements, individual polygonal Pt NPs were confirmed to have polycrystalline face-centered cubic (fcc) structures and very small particle sizes of 2–7 nm. The electrode fabrication process was sequentially optimized by adjusting the MWNT content, H2PtCl6 concentration, NaBH4 concentration, and the drying temperature. At optimized conditions, the Pt/MWNT electrode displayed a high sensitivity greater than 200 μA/ppm, a fairly good selectivity to interfering CO species, and an excellent linear response over the wide concentration range of 5–1000 ppm. Furthermore, the performances of the electrodes were found to be better than those of binary NP-supported MWNT systems (Pt–Pd/MWNT, Pt–Zn/MWNT, Pt–Ni/MWNT and Pt–ZnO/MWNT).
Keywords: Hydrogen sensor; Amperometric gas sensor; Pt/MWNT nanocomposites; Electrochemical sensor;

Urea-SCR systems (selective catalytic reduction) are required to meet future NO x emission standards of heavy-duty and light-duty vehicles. It is a key factor to control the SCR systems and to monitor the catalysts’ functionalities to achieve low emissions. The novel idea of this study is to apply commercially available SCR catalyst materials based on vanadia-doped tungsten–titania as gas sensing films for impedimetric thick-film exhaust gas sensor devices. The dependence of the impedance on the surrounding gas atmosphere, especially on the concentrations of NH3 and NO2, is investigated, as well as cross interferences from other components of the exhaust. The sensors provide a good NH3 sensitivity at 500 °C. The sensor behavior is explained in light of the literature combining the fields of catalysts and semiconducting gas sensors.
Keywords: V2O5; WO3; Anatase; Impedance spectroscopy; Zeolites;

Bioelectronic system for the control and readout of enzyme logic gates by Joshua Ray Windmiller; Padmanabhan Santhosh; Evgeny Katz; Joseph Wang (206-213).
In this work we describe the development of a novel microelectronic backbone configured specifically for the control of biocomputing systems applied to diagnostic merits. The operation of the sensor system is validated towards the rapid assessment of pathological conditions arising from soft tissue injury (STI) and abdominal trauma (ABT) using NAND and AND Boolean enzyme logic gates, respectively. The miniaturized 19 × 19 mm device employs a custom-designed three-electrode potentiostat coupled with an integrator, voltage amplifier, comparator, and digital logic and is easily interfaced with a screen-printed electrode contingent. By implementing an adjustable threshold comparator, a precise decision threshold could be established corresponding to pathological levels of the target biomarkers. As a result, a rapid amperometric analysis tendered the diagnosis in a straightforward ‘YES’/‘NO’ digital format via the illumination of a light emitting diode. Using low quiescent current voltage regulators, the device is able to achieve microwatt power operation and can be sustained by a single 3 V coin-cell battery for over 45 h under continuous use. The low-power, low-cost, and miniaturized device meets the requirements of field-deployable logic gate amperometric sensors. Such a reconfigurable micro-/bioelectronic logic-based multi-parameter sensing system shows considerable potential for the assessment of key analytes in a multitude of relevant clinical, security, and environmental applications where go/no-go readout, rapid measurement, device miniaturization, and extended longevity on battery power are key requirements.
Keywords: Enzyme logic; Potentiostat; Sensor; Screen-printed electrode; Chronoamperometry;

In vitro assessing the risk of drug-induced cardiotoxicity by embryonic stem cell-based biosensor by Qingjun Liu; Hui Yu; Zhou Tan; Hua Cai; Weiwei Ye; Ming Zhang; Ping Wang (214-219).
Drug-induced prolongation of ventricular repolarization with arrhythmia is a major concern in clinic safety pharmacology, and has been a common reason for the withdrawal of several promising drugs from the market. Therefore, novel techniques should be developed to evaluate cardiotoxicity of new drugs in preclinical research. A cardiomyocyte based biosensor was developed using the light addressable potentiometric sensor (LAPS). Mouse embryonic stem cells cultured on the surface of LAPS were induced to differentiate into synchronized spontaneity beating cardiomyocytes. Changes of extracellular potentials and cell shapes with their mechanical beatings could induce modulation of photocurrents in the LAPS system, and finally change the output of the sensor. With the characteristics of light addressability, LAPS can record cell clusters at any desired position. The sensor can be used to record the prolongation of ventricular action potentials with the cardiotoxicity induced by drugs such as amiodarone, levofloxacin, sparfloxacin, and noradrenaline. The quick and on time characteristics of the sensor were promising to establish a high-throughput platform for pharmacological toxicity investigation.
Keywords: Cell-based biosensor; Light addressable potentiometric sensor; Embryonic stem cell; Drug-induced cardiotoxicity;

Graphite oxide film-modified electrode as an electrochemical sensor for acetaminophen by Jinchun Song; Ji Yang; Junfen Zeng; Juan Tan; Li Zhang (220-225).
The graphite oxide (GO) was prepared via the chemical oxidation of natural graphite powder, and then used to modify the surface of glassy carbon electrode (GCE). The electrochemical behavior of acetaminophen was examined. In 0.01 mol L−1 HCl, an irreversible oxidation peak is observed for acetaminophen, and the peak current remarkably increases at the GO film-modified GCE. The influences of supporting electrolyte, amount of GO suspension, accumulation potential and time were studied on the oxidation peak current of acetaminophen. As a result, a new electrochemical method was developed for the detection of acetaminophen. The linear range is from 25 μg L−1 to 4 mg L−1, and the limit of detection is 6 μg L−1 based on three signal–noise ratio. Finally, it was successfully used to detect acetaminophen in tablets.
Keywords: Electrochemical sensor; Acetaminophen; Graphite oxide; Detection;

An optical humidity sensor based on Li3PO4 hollow nanospheres by Weixin Zhang; Lingling Chen; Zeheng Yang; Jing Peng (226-231).
Orthorhombic Li3PO4 hollow nanospheres and solid particles have been successfully prepared respectively via a simple neutralization reaction between H3PO4 and LiOH aqueous solutions, by just changing the adding sequence of H3PO4 and LiOH aqueous solutions (with PVP) in dropwise. Transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM) images display Li3PO4 hollow nanospheres with average diameters of about 400 nm and wall thickness of about 50 nm which is actually composed of nanoparticles with sizes of 20–50 nm, and Li3PO4 solid particles with lengths of 100–500 nm and widths of 100–250 nm. The photoluminescence (PL) properties of the samples reveal that the Li3PO4 hollow nanospheres show stronger PL intensity than the Li3PO4 solid particles. Furthermore, an adapted photoluminescence-type gas sensor based on Li3PO4 hollow nanospheres has been devised and its sensing property to humidity has also been investigated. This novel sensor exhibits good sensitivity, ideal linearity, quick response/recovery, and reliable repeatability in a very wide humidity range at room temperature.
Keywords: Li3PO4; Hollow nanosphere; Photoluminescence; Humidity sensing;

Ethanol sensing properties of LaCo x Fe1−x O3 nanoparticles: Effects of calcination temperature, Co-doping, and carbon nanotube-treatment by Caihui Feng; Shengping Ruan; Jiajing Li; Bo Zou; Junyu Luo; Weiyou Chen; Wei Dong; Fengqing Wu (232-238).
LaCo x Fe1−x O3 nanoparticles (x  = 0, 0.1, 0.2, and 0.3) are prepared by a sol–gel method, and the effects of calcination temperature, Co-doping, and carbon nanotube (CNT)-treatment on their ethanol sensing properties are investigated. The highest response is found based on the LaCo0.1Fe0.9O3 nanoparticles calcined at 600 °C, and the sensing properties of this sample can be further improved by adding CNT in the precursor. The responses of un-treated and CNT-treated LaCo0.1Fe0.9O3 nanoparticles are about 120.1 and 137.3–500 ppm ethanol at 140 °C, respectively. Simultaneously, by CNT -treatment, the response time is decreased from 56 to 10 s, and the recovery time is decreased from 95 to 35 s. The results not only make LaCo0.1Fe0.9O3 nanoparticles good candidates for fabricating practical gas sensors, but also provide a possible route for employing CNTs as a pore-forming agent.
Keywords: Gas sensors; Nanomaterials; Nanostructures; One dimension; Perovskite; Carbon nanotubes;

Signal changes for dye-complexed biomolecular interactions on waveguide-sensor chips by Subash C.B. Gopinath; Koichi Awazu; Makoto Fujimaki; Penmetcha K.R. Kumar (239-244).
We have previously made several modifications to the sensing chips of waveguide-mode sensors to permit detection of the interactions of several biomolecules at the 50-nM level. We further improved the sensitivity of this sensor by preparing a complex of a colored material with the target biomolecule. By using this strategy, we achieved a detection limit equivalent to 1 nM for the interactions of aptamers with proteins in the presence of Coomassie Brilliant Blue; this corresponds to an approximately fiftyfold increase in sensitivity. For comparison, we also evaluated the sensitivity of our system to another fluorescent dye, Hoechst 33258. These studies delineated the suitability of our color-sensitive sensor chips for the detection of interactions of biomolecules at low concentrations.
Keywords: Aptamer; Waveguide; Coomassie Brilliant Blue; Hoechst staining;

Synthesis, functionalization, and environmental stabilization of ZnO nanobridge transducers for gas and liquid-phase sensing by A.D. Mason; C.-C. Huang; S. Kondo; M.T. Koesdjojo; Y.H. Tennico; V.T. Remcho; J.F. Conley (245-252).
Three methods of functionalizing ZnO NW surfaces with biotin were demonstrated. Biotinylated ZnO NWs were found to dissolve during exposure to deionized (DI) water, so a chemical vapor deposition (CVD) process was developed for parylene-A, a common moisture barrier with an amine group which allows further functionalization. Parylene-A coated ZnO NWs were found to be resistant to dissolution. Electrical measurements on parylene-A coated nanobridge devices showed normal operation with higher dark current and an attenuated response to UV and O2, indicating the ability to modulate environmental sensitivity. This work demonstrates the novel use of parylene-A coatings as an encapsulation layer as well as a potential starting platform for general functionalization of ZnO NW devices for selective sensing.
Keywords: ZnO; Nanowires; Functionalization; Sensors;

A fluorescent chemosensor for cysteine based on naphthalimide derivative in aqueous solution by Yong-Fei Li; Chun-Yan Li; Fen Xu; Yu Zhou; Qi-Chang Xiao (253-257).
Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize cysteine (Cys) in aqueous solution. The fluorescence enhancement of 1 was attributed to the cyclization reaction of 1 with Cys by 1:1 binding stoichiometry, which has been utilized as the basis of fabrication of the Cys-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Cys indicated that the methods can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Cys-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Cys with a linear range covering from 3.9 × 10−8 to 1.4 × 10−5  M and a detection limit of 7.8 × 10−9  M. And the chemosensor shows excellent selectivity for Cys over other amino acids. Moreover, the response of the chemosensor toward Cys is fast (response time less than 3 min). In addition, the chemosensor has been used for determination of Cys in serum samples with satisfactory results.
Keywords: Fluorescence; Chemosensor; Cysteine; Naphthalimide;

In this paper, two fiber-optic interferometric humidity sensors based on silica/polymer microfiber knot resonators (SMKR/PMKR) are reported. These tiny humidity sensors are directly fabricated by using silica/polymer microfibers without any humidity-sensitive coating. The silica microfiber knot resonator sensor has a humidity sensitivity of ∼12 pm/10%-RH within a linearity range from 15%-RH to 60%-RH, while the polymer microfiber knot resonators sensor has a humidity sensitivity of ∼88 pm/10%-RH, with a linearity range from 17%-RH to 95%-RH. The temporal response of the PMKR sensor is <0.5 s. Such types of humidity sensors have advantages of easy fabrication, fast response, extremely compact size, stable and low cost, they would find potential applications in micro-scale humidity sensing.
Keywords: Optical fiber; Humidity sensors; Silica/polymer microfibers; Knot resonators;

We present the fabrication and characterization of new type of flexible gas sensors, composed mainly of a bottom ZnO conductive layer on metal foil, vertically aligned ZnO nanorod channel, and graphene-based top conductive electrode. Multiple cycling tests demonstrated the ZnO nanorods (NRs) and graphene (Gr) hybrid architectures accommodated the flexural deformation without mechanical or electrical failure for bending radius below 0.8 cm under the repeated bending and releasing up to 100 times. In addition, the hybrid architectures fabricated on glass substrate showed good optical transmittance larger than ∼70% for visible light, indicating potential application in transparent devices. Furthermore, our gas sensors demonstrated the ppm level detection of ethanol gas vapor with the sensitivity (resistance in air/resistance in target gas) as high as ∼9 for 10 ppm ethanol.
Keywords: Gas sensor; ZnO nanorod; Graphene; Nanorod-graphene hybrid architecture; Flexible device; Transparent device;

α-MoO3/TiO2 core/shell nanorods: Controlled-synthesis and low-temperature gas sensing properties by Yu-Jin Chen; Gang Xiao; Tie-Shi Wang; Fan Zhang; Yang Ma; Peng Gao; Chun-Ling Zhu; Endi Zhang; Zhi Xu; Qiu-hong Li (270-277).
Crystalline α-MoO3/TiO2 core/shell nanorods are fabricated by a hydrothermal method and subsequent annealing processes under H2/Ar flow and in the ambient atmosphere. The shell layer is composed of crystalline TiO2 particles with a diameter of 2–6 nm, and its thickness can be easily controlled in the range of 15–45 nm. The core/shell nanorods show enhanced sensing properties to ethanol vapor compared to bare α-MoO3 nanorods. The sensing mechanism is different from that of other one-dimensional metal oxide core/shell nanostructures due to very weak response of TiO2 nanoparticles to ethanol. The enhanced sensing properties can be explained by the change of type II heterojunction barrier formed at the interface between α-MoO3 and TiO2 in the different gas atmosphere. The present results demonstrate a novel sensing mechanism available for gas sensors with high performance.
Keywords: Heteronanostructures; Sensor; α-MoO3; TiO2; Ethanol sensing characteristics;

The low-voltage electromechanical actuation of polypyrrole (PPy) doped with di-(2-ethylhexyl)sulfosuccinate (DEHS) has been investigated. The PPy-DEHS has been prepared both chemically (cast as films from solution) and by more conventional electrochemical polymerization. Very large strains of ∼30% were obtained during slow-scan redox cycling of the electrochemically prepared PPy-DEHS films. In constrast, PPy-DEHS films cast from solutions of the chemically polymerized polymer gave actuation strains of ∼2.5%. The polymerization method was also found to have a significant effect on the structure, conductivity and mechanical properties of the PPy-DEHS materials. The conductivity of the electrochemically polymerized PPy-DEHS was 75 S cm−1, considerably higher than that found for the chemically derived polymer (7 S cm−1). The structure of the PPy-DEHS was further elucidated from UV–vis, Raman and FT-IR spectral studies which indicated that the conjugation length of the PPy could be increased significantly by varying the polymerization method. Films obtained by casting chemically prepared PPy-DEHS showed higher modulus (2.3 GPa) than electropolymerized PPy-DEHS (0.6 GPa), but were more brittle. Both materials were electroactive in acetonitrile/water electrolyte. The higher actuation strain observed in the electrochemically prepared films was attributed to a more open molecular structure (as indicated by the lower modulus) allowing for easier ion diffusion and a higher conductivity allowing easier charge transfer.
Keywords: Polypyrrole; Conducting polymer; e-Textile; Electropolymerization; Actuators;

Facile synthesis of hierarchical SnO2 semiconductor microspheres for gas sensor application by Lili Wang; Zheng Lou; Tong Zhang; Huitao Fan; Xiujuan Xu (285-289).
Hierarchical SnO2 microspheres were synthesized by a hydrothermal method at 140 °C using stannic chloride hydrate and sodium hydroxide as starting materials. The individual hierarchical SnO2 microsphere ranged from 700 to 900 nm in diameter. After these microspheres were heated at 600 °C for 2 h, the spheres were cross-linked into clusters by short SnO2 nanorods as revealed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Most importantly, SnO2 hierarchical microsphere sensor exhibits excellent selectivity and fast response to ethanol. Response and recovery times were 0.6 s and 11 s when the sensor was exposed to 50 ppm ethanol at an operating temperature of 300 °C. Thus, hierarchical structures play a significant role in the field of gas sensing.
Keywords: SnO2; Hierarchical structures; Ultra-high response; Gas sensing;

Optical fiber pH sensor based on lossy-mode resonances by means of thin polymeric coatings by C.R. Zamarreño; M. Hernáez; I. Del Villar; I.R. Matías; F.J. Arregui (290-297).
This work describes the fabrication of an optical fiber sensor with spectral response to pH based on the deposition of a thin polymeric coating on an optical fiber core. If the thin polymeric coating has a high refractive index real part and a non-null imaginary part, this permits a coupling of light to the modes guided in the polymeric coating originating optical resonances. These resonances are named by some authors as lossy-mode resonances (LMR) or guided-mode resonances. Moreover, the location of the resonances in the optical spectrum varies as a function of the coating thickness and refractive index. Hence, the utilization of the well-known poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) pH sensitive polymeric coating that presents a variation of the thickness with the pH of the solution (known as swelling/deswelling behaviour) permits the fabrication of optical fiber pH sensors based on wavelength detection. The fabrication of ready-to-use devices requires considering several aspects such as the adequate polymeric coating thickness or the selection of the resonance to be monitored. As a result, LMR-based optical fiber pH sensors with accuracy of ±0.001 pH units and an average sensitivity of 0.027 pH units/nm within the range between pH 3 and pH 6 have been obtained after an adequate design.
Keywords: Optical fiber; pH sensor; Lossy mode resonances; Polymeric coatings; Layer by layer;

Phthalocyanines as sensitive coatings for QCM sensors: Comparison of gas and liquid sensing properties by Mika Harbeck; Dilek D. Erbahar; Ilke Gürol; Emel Musluoğlu; Vefa Ahsen; Zafer Ziya Öztürk (298-303).
The quartz crystal microbalance (QCM) was used to investigate the liquid sensing properties of a set of phthalocyanines (Pcs) which were systematically varied by attaching the substituent 2,2,3,3-tetrafluoropropyloxy to different positions and by introducing a central metal ion (i.e. Ni2+, Zn2+, and Cu2+). The responses to low concentrations of organic compounds such as hydrocarbons and chlorocarbons dissolved in water were recorded. The materials were very sensitive to the tested compounds with detection limits in the lower parts-per-million range and they exhibited a good sensing performance as the sensors have been working fully reversibly and reliably over long periods of time. Besides, the influence of substitution pattern and choice of central metal ion on the liquid sensing properties of Pcs were studied for the first time. The results show that the responses differ notably from each other depending on the modifications made to the Pc. Finally, it is demonstrated that the gas and liquid sensing responses of the materials are highly correlated and can be linked to each other with the help of a basic physical model.
Keywords: Chemical sensor; Quartz crystal microbalance; Liquid sensing; Phthalocyanine; Organic pollutant; Response modeling;

A glucose oxidase immobilization platform for glucose biosensor using ZnO hollow nanospheres by Bin Fang; Cuihong Zhang; Guangfeng Wang; Meifang Wang; Yulan Ji (304-310).
A good route (template-directed synthetic route) for the fabrication of ZnO hollow nanospheres (ZnO-HNSPs) was proposed. ZnO hollow nanosphere is a wonderful platform to immobilize glucose oxidase for glucose biosensor owing to the high specific surface area and high isoelectric point (IEP). Along with nafion and glucose oxidase (GOD), a glucose sensor was designed. Nafion/ZnO-HNSPs/GOD/GCE displays higher catalytic activity toward the glucose oxidation than Nafion/ZnO nano-Flowers/GOD/GCE. Linear response was obtained over a concentration range from 5.0 × 10−3  mM to 13.15 mM with a detection limit of 1.0 μM (S/N = 3), and the sensitivity was 65.82 μA/(mM cm2). Satisfyingly, the Nafion/ZnO-HNSPs/GOD/GCE could effectively avoid the interferences from the common interfering species such as uric acid (UA), ascorbic acid (AA), dopamine (DA) and fructose. The Nafion/ZnO-HNSPs/GOD modified electrode allows high sensitivity, excellently selective, stable, and fast amperometric sensing of glucose and thus is promising for the future development of glucose sensors.
Keywords: ZnO; Hollow nanosphere; Glucose oxidase; Modified electrode; Glucose;

In this paper, we presented a carbon tetrachloride gas sensor with strong cataluminescence response based on Ag2Se nanomaterial, which was synthesized via the electrodeposition on the surface of Al foil by directly using a non-aqueous dimethyl sulfoxide (DMSO) solution with CH3COOAg and SeCl4. The deposited Ag2Se material was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Then, the prepared Ag2Se material along with the Al foil substrate was employed to design the carbon tetrachloride gas sensor. Under the optimized conditions, the present gas sensor exhibited a broad linear range of 0.9–228 μg mL−1, with a limit of detection of 0.3 μg mL−1 (S/N = 3). The proposed gas sensor showed good characteristics with high selectivity, fast response and long lifetime.
Keywords: Cataluminescence; Carbon tetrachloride; Gas sensor; Ag2Se; Electrodeposition;

Multi-enzyme layer-by-layer assembly for dual amplified ultrasensitive electronic detection of cancer biomarkers by Yun Xiang; Yuyong Zhang; Bingying Jiang; Yaqin Chai; Ruo Yuan (317-322).
The preparation and use of multi-enzyme layer-by-layer (LBL) assembled single wall carbon nanotube (SWCNT) composite labels for amplified ultrasensitive electrochemical detection of a cancer biomarker is described. The target protein, carcinoembryonic antigen (CEA), is sandwiched between an electrode surface-confined capture anti-CEA antibody and the secondary signal anti-CEA/enzyme-LBL/SWCNT bioconjugate. The dual biocatalytic signal amplification for CEA monitoring is achieved through both the numerous enzymes loaded on the CNTs and redox-recycling of the enzymatic products in the presence of the secondary enzyme and the corresponding substrate. Our novel dramatic signal amplification strategy, with a detection limit of 0.04 pg mL−1, shows about 2–4 orders of magnitude improvement in sensitivity for CEA detection compared with other universal signal amplified assays, which makes our signal amplification approach hold great potential applications in detection of ultra-trace protein biomarkers.
Keywords: Amplification; Carcinoembryonic antigen; Layer-by-layer assembly; Redox-recycling; Ultrasensitive immunosensor;

Alkaline apophosphatase (apoALP) was examined in flow bioanalytical systems as an immobilized bioligand for reversible recognition of zinc ions. For such investigations plastic open-tubular bioreactor coupled with spectrophotometric detector and potentiometric biosensor based on plasticized polymeric membrane ion-selective electrode were applied. Both biodevices contain covalently immobilized monomolecular layer of alkaline phosphatase (ALP) and operate according to the indirect biosensing scheme based on cofactor biorecognition by in situ generated apoenzymatic bioreceptor. An implementation of immobilized ALP into flow system enables automation of the developed bioanalytical procedure allowing multiple and reproducible apoenzyme formation/regeneration, analyte biorecognition as well as assays for recovered enzyme activity. Both developed bioanalytical systems offer relatively fast zinc biodetermination in the ppm range of concentrations. Additionally, effects from potential chelators and metal ions involving in holo–apo and apo–holo enzyme conversions were investigated. It was found, that the selectivity of the reported biosensing scheme is defined by alternative mechanisms for apoenzyme and holoenzyme formation. A model, clarifying such conversions, has been proposed and confirmed by simple analytical experiments performed under flow conditions.
Keywords: Apoenzyme; Coenzyme; Bioreactor; Biosensor; Bioreceptor; Alkaline phosphatase; Flow analysis;

Biomonitoring of methomyl pesticide by laccase inhibition on sensor containing platinum nanoparticles in ionic liquid phase supported in montmorillonite by Eduardo Zapp; Daniela Brondani; Iolanda C. Vieira; Carla W. Scheeren; Jairton Dupont; Antônio M.J. Barbosa; Valdir S. Ferreira (331-339).
This study focuses on the development and evaluation of a new biosensor for the determination of the pesticide methomyl, based on enzyme inhibition. Laccase (LAC) obtained from a genetically modified fungus (Aspergillus oryzae) was successfully immobilized in a new supported ionic liquid phase (SILP) based on platinum nanoparticles and the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (Pt–BMI·BF4) supported in montmorillonite, and subsequently applied in the construction of the biosensor. The process of inhibition by methomyl carbamate was performed using dopamine as a phenolic substrate to obtain the base signal. All measurements for the optimization and application of the biosensor were performed by square-wave voltammetry, and the best experimental conditions were obtained in acetate buffer solution (0.1 mol L−1, pH 5.5), with 0.5 units of enzyme and voltammetric parameters: 60 Hz of frequency, 100 mV of pulse amplitude and 8 mV of scan increment. The determination of methomyl in carrot and tomato samples using the proposed biosensor showed results consistent with those obtained by HPLC, verifying that the method developed can be used for the quantification of this pesticide.
Keywords: Biosensor; Laccase; Platinum nanoparticles; Ionic liquid; Pesticide; Methomyl;

In this study we synthesized Pt nanoparticles supported on carbon Vulcan (Pt/C), a cheap and high surface area carbon. Compared to the commercialized Pt/C, which showed a moderate activity towards the oxidation of H2O2 and a high catalytic activity to the interferences specially AP; the synthesized Pt/C illustrated a high activity towards the oxidation of H2O2 and negligible response towards the oxidation of the interferences at high applied potentials (>0.6 V). This difference in the catalytic behavior was attributed to the homogenous distribution of the synthesized Pt nanoparticles in the supporting carbon Vulcan as well as, to their relatively bigger size (8–9 nm) compared to (1–2 nm) estimated for the commercialized Pt/C. This particular and interesting behavior of the synthesized Pt/C was used to encapsulate glucose oxidase along with a small amount of Nafion for the manufacturing of a glucose sensor. The resulting glucose sensor has a high sensitivity of 1.25 μA/mM mm2, which compares very well with other glucose sensors based on precious metal nanoparticles and carbon nanotubes, an extended linear range up to 45 mM without using any outer polymer layer, low interference from endogenous species, short response time (<5 s), was stable for at least 1 month and, found to be dependable for glucose determination in human serum.
Keywords: Glucose sensor; Pt/C electrocatalyst; Sensor characteristics; Glucose measurements; Sensor evaluation in human serum;

Ammonia sensing characteristics of a Pt/AlGaN/GaN Schottky diode by Tai-You Chen; Huey-Ing Chen; Yi-Jung Liu; Chien-Chang Huang; Chi-Shiang Hsu; Chung-Fu Chang; Wen-Chau Liu (347-350).
The interesting ammonia sensing current–voltage (I–V) characteristics of a Pt/AlGaN/GaN Schottky diode are firstly studied and demonstrated. It is found that the ammonia sensitivity is increased by increasing the temperature. Yet, the sensitivity is decreased when the temperature is higher than 423 K. Experimentally, the studied device exhibits a good sensitivity of 13.1 under exposing to a relatively low concentration ammonia gas of 35 ppm NH3/air. In addition, the good sensing performance of the studied device is demonstrated over a wide operating temperature regime from 298 K to 473 K. A highest ammonia sensing response of 182.7 is found at 423 K while a 10,000 ppm NH3/air gas is introduced.
Keywords: AlGaN; Ammonia; Sensor; Schottky diode;

A novel method for label-free detection of ricin using liquid crystals supported on chemically functionalized surfaces by Ya-Bin Zhao; Jian-Hua Yu; Hong-Fei Zhao; Chao-Yang Tong; Pu-Hong Wang (351-356).
In this paper, we report a simple and novel liquid-crystal based sensor for ricin detection. The method relies on the use of liquid crystals (LCs) 5CB to amplify and report the presence of ricin captured by an affinity ligand. A merit of this approach is that the ricin can be imaged on the chemically functionalized surfaces and transduced into optical signal by using LCs, the optical signal caused by the orientational transition of the LCs could be easily identified with polarized light microscopy. In addition, the sensor exhibited high sensitivity with strong selectivity, experimental results showed that the minimum detection concentration was as low as 10 μg/mL, demonstrating the feasibility of using these devices to detect and positively identify ricin. Furthermore, the success of LC-based sensor reported here does not use complex instrumentations and does not involve any labeling steps.
Keywords: Liquid crystal; Ricin; Chemically functionalized surfaces; Label-free detection; Sensor;

Quantum dot (QD) functionalized graphene sheets (GS) were prepared and used as labels for the preparation of sandwich-type electrochemical immunosensors for the detection of a cancer biomarker (i.e., prostate specific antigen (PSA)). The primary anti-PSA antibody was also immobilized onto the GS. The immunosensor displayed a wide range of linear response (0.005–10 ng/mL), low detection limit (3 pg/mL), and good reproducibility, selectivity and stability. The immunosensor was used to detect PSA in patient serum samples with satisfactory results. Thus, this unique immunosensor may provide many applications in clinical diagnosis.
Keywords: Cancer biomarker; Graphene; Quantum dot; Prostate specific antigen;

Fast surface plasmon resonance imaging sensor using Radon transform by A. Karabchevsky; S. Karabchevsky; I. Abdulhalim (361-365).
Surface plasmon resonance (SPR) imaging technique is proposed in which a diverging laser beam at given frequency was used to illuminate the entire sensor surface in Kretschmann–Raether configuration. A pattern of dark intensity line on bright background is observed corresponding to the SPR dip at an angular range depending on the refractive index of the adjacent analyte and monitored by a two-dimensional CCD detector. A novel Radon transform based detection algorithm for the SPR line pattern is proposed, which is non sensitive to the laser speckle noise and improves the accuracy.
Keywords: Surface plasmon resonance; Imaging; Radon transform; Biosensing;

Gas sensing properties of p-type hollow NiO hemispheres prepared by polymeric colloidal templating method by Nam Gyu Cho; In-Sung Hwang; Ho-Gi Kim; Jong-Heun Lee; Il-Doo Kim (366-371).
This work presents a simple and versatile route to produce macroporous p-type metal oxide thin films. Two-dimensional arrays of p-type NiO films with a hollow hemisphere structure were fabricated by colloidal templating and RF-sputtering followed by a subsequent heat treatment. The diameter and shell thickness of the NiO hemisphere were 800 nm and 20 nm, respectively. X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the pure NiO phase with grain size of 10 nm was obtained at calcination temperatures that exceeded 450 °C. Close-packed arrays of hollow NiO hemispheres were found to exhibit p-type gas sensing properties against (CO, H2, C3H8, CH4, NO2, and C2H5OH), leading to significantly enhanced responses to C2H5OH (R gas /R air  = 5.0 at 200 ppm).
Keywords: Nickel oxide; Gas sensor; Nanostructure; Colloidal template; Hollow hemisphere;

Optical hydrogen sensing method using temperature-sensitive luminophore on porous palladium by Hirotaka Sakaue; Chih-Yung Huang; John P. Sullivan (372-374).
A new hydrogen sensing method of luminescence-based hydrogen sensors is presented. This method uses a porous palladium and temperature-sensitive luminophores of europium(III)thenoyltrifluoacetonate to selectively adsorbs hydrogen molecules that generates heat on the palladium surface. The luminophores translate this heat to the luminescent signal. This hydrogen sensing mechanism combines processes of hydrogen adsorption, thermal quenching, and excitation. The sensitivity of the resultant system is over 60 times better than that of the reflectance-based sensing system using a bulk palladium. The change in the luminescent signal increases as increasing the hydrogen concentration of the gas as well as the injection time.
Keywords: Hydrogen detection; Optical sensor; Luminescent technique; Temperature-sensitive paint;

Enhanced surface plasmon resonance detection of DNA hybridization based on ZnO nanorod arrays by Kyung Min Byun; Nak-Hyeon Kim; Yeong Hwan Ko; Jae Su Yu (375-379).
We demonstrated an enhanced surface plasmon resonance detection incorporating ZnO nanorod arrays (NRAs) built on a thin gold film. ZnO NRAs were fabricated by wet chemical growth method and used for the detection of DNA hybridization. Experimental results exhibited that ZnO NRAs provided a notable sensitivity improvement by more than 3 times, which is attributed to an increase in the surface reaction area. The measured sensitivity enhancement matched well with the numerical analyses based on the effective medium theory. Our approach is intended to show the feasibility and extend the applicability of the ZnO-based SPR biosensor to diverse biomolecular binding events.
Keywords: Surface plasmon resonance; Biosensor; ZnO nanorod; Sensitivity enhancement; Effective medium theory;

We present a digital dilution chip of 2 × 6 well array that is capable of changing the dilution ratio. We mixed the diluted samples with other samples by using inter-well valves. The previous continuous and digital dilution chips diluted samples that had a fixed dilution ratio depended on the structure of the branched microchannel or the volume of the well. The present chip can perform the programmable mixing process that selectively fills, merges, and splits the identical wells by controlling the inter-well valves. Thus, the present digital dilution chip can easily change the dilution ratio without any structural change. In this study, the present chip changed the dilution ratio, such as the linear or exponential ratio, within a 4.2% dilution difference. They were then mixed with other samples within a 3.4% mixing difference. In order to reduce the number of interconnection ports that transferred the pressure to inter-well valves, we also applied a latched ternary multiplexer and reduced nine interconnection ports of inter-well valves to five. By diluting the sample with different dilution ratios based on the well array, the present chip can be easier for users and more suitable to high-throughput screen systems.
Keywords: Dilution chip; Microfluidic multiplexer; Micro-valve;

UV initiated formation of polymer monoliths in glass and polymer microreactors by Jeremy A. Deverell; Thomas Rodemann; Jason A. Smith; Allan J. Canty; Rosanne M. Guijt (388-396).
Polymer monoliths with good flow-through properties were prepared by UV initiated polymerisation to form a support for heterogeneous palladium catalysis in glass and polymer microchips. Preparation of homogeneous polymer monoliths required investigation of different light source/photoinitiator combinations and manipulation of the polymerisation mixture to accommodate different channel dimensions. A deep UV (DUV) flood exposure lamp, UV tubes with respective outputs at 255 and 365 nm and a UV LED array with output at 365 nm were used to initiate the polymerisation. The spectra of light source and initiator were matched; 2,2-dimethoxy-2-phenylacetophenone (DMPAP) was selected for polymerisation in the DUV and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) was used for polymerisation in the near UV (NUV). This is the first report of the use of a BAPO-type photoinitiator for the formation of organic polymer monoliths. Only the DUV lamp and 365 nm UV LED array resulted in the formation of homogenous and continuous monoliths which were subsequently used to create continuous-flow microreactors in fused silica capillaries, borosilicate chips and in cyclic olefin copolymer (COC) capillaries and chips. All microreactors gave high to quantitative yields for the Suzuki–Miyaura's coupling of iodobenzene with 4-tolyl boronic acid. In addition to demonstrating the first polymer chip for heterogeneous Suzuki–Miyaura's catalysis, the UV LED array in combination with BAPO was found to be a suitable budget alternative to a DUV exposure source for monolith formation in devices with internal diameter of up to 2 mm.
Keywords: Polymer monolith; Photoinitiated polymerisation; UV LED; Heterogenous catalysis; Microreactor; Lab on a Chip;

Development of high throughput microfluidic cell culture chip for perfusion 3-dimensional cell culture-based chemosensitivity assay by Min-Hsien Wu; Yu-Han Chang; Yen-Ting Liu; Yan-Ming Chen; Shih-Siou Wang; Hsin-Yao Wang; Chao-Sung Lai; Tung-Ming Pan (397-407).
This study reports a microfluidic cell culture chip encompassing 36 microbioreactors for high throughput perfusion 3-dimensional (3D) cell culture-based chemosensitivity assays. Its advantages include the capability for multiplexed medium delivery, and the function for both efficient and high throughput micro-scale 3D culture construct preparation and loading. The results showed that the proposed medium pumping mechanism was able to provide a uniform pumping rates ranging from 1.2 to 3.9 μl h−1. In addition, the simple cell/hydrogel loading scheme has been proven to be able to carry out 3D cell culture construct preparation and loading precisely and efficiently. Furthermore, a chemosensitivity assay was successfully demonstrated using the proposed cell culture chip. The results obtained were also compared with the same evaluation based on a conventional 2D monolayer cell culture. It can be concluded that the choice of cell culture format can result in different chemosensitivity evaluation results. Overall, because of the nature of miniaturized perfusion 3D cell culture, the cell culture chip not only can provide stable, well-defined and more biologically relevant culture environments, but it also features low consumption of research resources. All these traits are found particularly useful for high-precision and high-throughput 3D cell culture-based assays.
Keywords: Microfluidics; Microbioreactors; Micropumps; Cell culture; Chemosensitivity;

Thin-film electrode based droplet detection for microfluidic systems by E.V. Moiseeva; A.A. Fletcher; C.K. Harnett (408-414).
We report on a droplet-producing microfluidic system with electrical impedance-based detection. The microfluidic devices are made of polydimethylsiloxane (PDMS) and glass with thin film electrodes connected to an impedance-monitoring circuit. Immiscible fluids containing the hydrophobic and hydrophilic phases are injected with syringe pumps and spontaneously break into water-in-oil droplet trains. When a droplet passes between a pair of electrodes in a medium having different electrical conductivity, the resulting impedance change signals the presence of the particle for closed-loop feedback during processing. The circuit produces a digital pulse for input into a computer control system. The droplet detector allows estimation of a droplet's arrival time at the microfluidic chip outlet for dispensing applications. Droplet detection is required in applications that count, sort, and direct microfluidic droplets. Because of their low cost and simplicity, microelectrode-based droplet detection techniques should find applications in digital microfluidics and in three-dimensional printing technology for rapid prototyping and biotechnology.
Keywords: Droplet microfluidics; PDMS; Lab on chip; Droplet detection circuit;

Suspending nanoliter droplet arrays for cell capture and copper ion stimulation by Hai-Fang Li; Yuan-Feng Pang; Jiang-Jiang Liu; Jin-Ming Lin (415-421).
In this paper, we developed a microdevice with raised cylinder arrays for capture of Chlorella vulgaris cells and kinetic analysis of stimulation. The cell solution was injected into the chip and held in the gaps between the opposite raised cylinders, forming 0.314 nL volume of suspending droplets. The number of the captured cells in each nanoliter suspending droplet could be controlled within five under our experiment conditions. When the stimulation reagent of copper ion (Cu2+) was injected into the chip and contacted with the suspending droplets, gradient concentration of Cu2+ stimulation to the captured C. vulgaris cells by free diffusion was formed. The bioabsorption kinetic process of C. vulgaris cells under continuous Cu2+ stimulation was investigated and the two-step bioabsorption process was revealed clearly. The Cu2+ toxicity accumulation effect on the cell was also studied by monitoring the fluorescence of cellular chlorophyll.
Keywords: Microchip; Cell capture; Cu2+ stimulation; Chlorella vulgaris cell;

Low-cost polymer microfluidic device for on-chip extraction of bacterial DNA by Kyu-Youn Hwang; Joon-Ho Kim; Kahp-Yang Suh; Jong Soo Ko; Nam Huh (422-429).
A polymer microfluidic device for on-chip extraction of bacterial DNA has been developed for molecular diagnostics. In order to manufacture a low-cost, disposable microchip, micropillar arrays of high surface-to-volume ratio (0.152 μm−1) were constructed on polymethyl methacrylate (PMMA) by hot embossing with an electroformed Ni mold, and their surface was modified with SiO2 and an organosilane compound in subsequent steps. To seal open microchannels, the organosilane layer on top plane of the micropillars was selectively removed through photocatalytic oxidation via TiO2/UV treatment at room temperature. As a result, the underlying SiO2 surface was exposed without deteriorating the organosilane layer coated on lateral surface of the micropillars that could serve as bacterial cell adhesion moiety. Afterwards, a plasma-treated PDMS substrate was bonded to the exposed SiO2 surface, completing the device fabrication. To optimize manufacturing throughput and process integration, the whole fabrication process was performed at 6 inch wafer-level including polymer imprinting, organosilane coating, and bonding. Preparation of bacterial DNA was carried out with the fabricated PDMS/PMMA chip according to the following procedure: bacterial cell capture, washing, in situ lysis, and DNA elution. The polymer-based microchip presented here demonstrated similar performance to Glass/Si chip in terms of bacterial cell capture efficiency and polymerase chain reaction (PCR) compatibility.
Keywords: Polymer-based microchip; Photocatalyst; Bacterial DNA; Organosilane; PCR;

A CMOS optical detection system for point-of-use luminescent oxygen sensing by Li Shen; Michael Ratterman; David Klotzkin; Ian Papautsky (430-435).
This work describes a stable and sensitive optical oxygen sensor based on a consumer CMOS image sensor array and polarization signal isolation. The consumer CMOS image sensor is inherently color discriminating, while the polarization is a wavelength-independent scheme for filtering excitation light. Combination of these two components generates a compact, multi-color detection system applicable to luminescence-based sensing. The optical system is applied to point-of-use oxygen sensing based on quenching of platinum octaethylporphine (PtOEP) luminophore. Sensitivity of the demonstrated portable oxygen sensor is comparable to that of benchtop spectroscopy-based systems. Taking advantage of the spatial resolution of the CMOS image sensor, an oxygen insensitive reference can be integrated to improve the reliability when powered by a battery. The low-cost and high sensitivity of the demonstrated optical sensing approach make it promising for point-of-use applications.
Keywords: Oxygen sensor; CMOS image sensor; Polarizerization signal isolation;