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Analytica Chimica Acta (v.697, #1-2)

Editorial Board (pp. iii).

Nanoparticle-assisted MALDI-TOF MS combined with seed-layer surface preparation for quantification of small molecules by Yi-Chi Ho; Mei-Chun Tseng; Ying-Wei Lu; Chun-Cheng Lin; Yu-Ju Chen; Ming-Ren Fuh (pp. 1-7).

Display Omitted► Matrix-conjugated magnetic nanoparticles combined with seed-layer method was developed as a new platform for the rapid identification and quantification of small molecule in urine samples by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. ► By applying this new strategy, determination of 7-aminoflunitrazepam in urine was successfully achieved with good precision (RSD<10%) and accuracy (95.0–115.5%).Despite the advantages of simplicity and high-throughput detection that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has over other methods, quantitative analysis of low-molecular-weight analyte is hampered by interference from matrix-derived background noise and signal fluctuation due to the inhomogeneous MALDI sample surface. Taking advantage of improved sample homogeneity through matrix-conjugated magnetic nanoparticles (matrix@MNP) and the seed-layer method, we report a new strategy for the rapid identification and quantification of drugs in urine samples, using morphine and 7-aminoflunitrazepam (7-aminoFM2) as model compounds. To our knowledge, this is the first attempt using the seed-layer method for small molecule analysis. By applying the proposed seed-layer method, which was specifically optimized for the 2,5-dihydroxybenzoic acid@MNP (DHB@MNP) matrix, homogeneous sample crystallization examined by microscopy analysis was obtained that generated reproducible MALDI signals (RSD<10.0%). For urine sample analysis, simple liquid–liquid extraction as a sample pretreatment step effectively reduced the ion suppression effect caused by the endogenous components in urine; good recoveries (82–90%) were obtained with a small ion suppression effect (<14% of signal decrease). This newly developed method demonstrated good quantitation linearity over a range of 50–2000ngmL⁻¹ ( R²>0.996) with reduced signal variation (RSD<10.0%). The detection limit is 30ngmL⁻¹ with good precision (intra-day, 2.0–9.3%; inter-day, 5.0–10.0%) and accuracy (intra-day, 95.0–106.0%; inter-day, 103.0–115.5%). The nanoparticle-assisted MALDI-TOF MS combined with seed-layer surface preparation provides a rapid, efficient and accurate platform for the quantification of small molecules in urine samples.

Keywords: Nanoparticle; Quantification; Seed-layer method; Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS); Small molecules

Automated optimization and construction of chemometric models based on highly variable raw chromatographic data by Nikolai A. Sinkov; Brandon M. Johnston; P. Mark L. Sandercock; James J. Harynuk (pp. 8-15).

► Introduce deuterated alkane ladder for retention time alignment. ► Automated feature selection for chemometric modelling of raw GC/MS data. ► Compare deuterated ladder with conventional feature-based alignment. ► Application to successful detection of gasoline in simulated fire debris.Direct chemometric interpretation of raw chromatographic data (as opposed to integrated peak tables) has been shown to be advantageous in many circumstances. However, this approach presents two significant challenges: data alignment and feature selection. In order to interpret the data, the time axes must be precisely aligned so that the signal from each analyte is recorded at the same coordinates in the data matrix for each and every analyzed sample. Several alignment approaches exist in the literature and they work well when the samples being aligned are reasonably similar. In cases where the background matrix for a series of samples to be modeled is highly variable, the performance of these approaches suffers. Considering the challenge of feature selection, when the raw data are used each signal at each time is viewed as an individual, independent variable; with the data rates of modern chromatographic systems, this generates hundreds of thousands of candidate variables, or tens of millions of candidate variables if multivariate detectors such as mass spectrometers are utilized. Consequently, an automated approach to identify and select appropriate variables for inclusion in a model is desirable. In this research we present an alignment approach that relies on a series of deuterated alkanes which act as retention anchors for an alignment signal, and couple this with an automated feature selection routine based on our novel cluster resolution metric for the construction of a chemometric model. The model system that we use to demonstrate these approaches is a series of simulated arson debris samples analyzed by passive headspace extraction, GC–MS, and interpreted using partial least squares discriminant analysis (PLS-DA).

Keywords: Chemometrics; Data alignment; Retention anchor; GC–MS; PLS-DA; Forensics; Arson

Sensitive electrochemical immunoassay of carcinoembryonic antigen with signal dual-amplification using glucose oxidase and an artificial catalase by Juan Tang; Dianping Tang; Qunfang Li; Biling Su; Bin Qiu; Guonan Chen (pp. 16-22).

A new dual-amplification strategy of electrochemical signal based on the catalytic recycling of the product was developed for the antigen–antibody interaction by glucose oxidase-conjugated gold–silver hollow microspheres coupled with an artificial catalase, Prussian blue nanoparticles, on a graphene-based immunosensing platform.Display Omitted► We designed an electrochemical immunoassay of carcinoembryonic antigen with signal dual-amplification. ► A new signal tag with glucose oxidase-conjugated gold–silver hollow microspheres. ► An artificial catalase, Prussian blue nanoparticles, on a graphene-based sensing platform. ► Comparative study of the electrochemical immunoassay by using various signal tags and sensing platforms.A new dual-amplification strategy of electrochemical signal based on the catalytic recycling of the product was developed for the antigen–antibody interaction by glucose oxidase (GOD)- conjugated gold–silver hollow microspheres (AuAgHSs) coupled with an artificial catalase, Prussian blue nanoparticles (PB), on a graphene-based immunosensing platform. The first signal amplification introduced in this study was based on the labeled GOD on the AuAgHSs toward the catalytic oxidation of glucose. The generated H₂O₂ was catalytically reduced by the immobilized PB on the graphene nanosheets with the second amplification. With a sandwich-type immunoassay format, carcinoembryonic antigen (CEA) was monitored as a model analyte by using the synthesized AuAgHSs as labels in pH 6.0 phosphate buffer containing 10mM glucose. Under optimal conditions, the electrochemical immunosensor exhibited a wide dynamic range of 0.005–50ngmL⁻¹ with a low detection limit (LOD) of 1.0pgmL⁻¹ CEA (at 3 σ). Both the intra- and inter-assay coefficients of variation (CVs) were lower than 10%. The specificity and stability of the immunosensor were acceptable. In addition, the assay was evaluated for clinical serum specimens, and received a good correlation with those obtained by the referenced electrochemiluminescent (ECL).

Keywords: Gold–silver hollow microspheres; Graphene-Prussian blue hybrid nanosheets; Carcinoembryonic antigen; Electrochemical immunosensor; Signal dual-amplification

Spectroelectrochemical determination of the electron consumption by Viliam Kolivoška; Miroslav Gál; Štěpánka Lachmanová; Michal Valášek; Magdaléna Hromadová; Lubomír Pospíšil (pp. 23-26).

Display Omitted► Measurements of UV–vis spectra as a function of charge yield rapidly and in a small volume the number of exchanged electrons. ► The determination of n is based on the calibration procedure using the ferrocene oxidation and the methyl viologen reduction. ► This method eliminates problems of side reactions of intermediates with the parent form by using a thin layer optical cell.Measurements of UV–vis spectra as a function of the consumed charge in an optically transparent thin layer cell (OTTLE) offer a fast, small-volume and reliable method for the determination of the number of electrons n exchanged in the redox reaction. The determination of n is based on the calibration procedure using the ferrocene oxidation and the methyl viologen reduction. Virtues of this method are demonstrated on the determination of n of two oligomers of ‘extended viologens’ with multiple redox centers and correspondingly large n. The described method eliminates problems of side reactions of reactive intermediates with the parent oxidized form, which often impede a reliable estimation of n by the established coulometric method.

Keywords: Coulometry; Spectroelectrochemistry; Number of electrons; Electrolysis

Direct electrochemistry of horseradish peroxidase immobilized on electrografted 4-ethynylphenyl film via click chemistry by Qin Ran; Ru Peng; Cong Liang; Siqiu Ye; Yuezhong Xian; Wenjing Zhang; Litong Jin (pp. 27-31).

Hydrogen peroxide biosensor was developed based on electrochemically assisted aryldiazonium salt chemistry and click chemistry.Display Omitted► A simple, versatile two-step approach, which is based on electrochemically assisted aryldiazonium salt chemistry and Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC) reaction has been developed for covalent redox proteins immobilization and biosensing for the first time. In this work, azido group modified HRP was covalently grafted on 4-ethylnylphenyl diazonium compound via CuAAC reaction and a novel electrochemical hydrogen peroxide biosensor was successfully fabricated.In this paper, a simple two-step approach for redox protein immobilization was introduced. Firstly, alkynyl-terminated film was formed on electrode surface by electrochemical reduction of 4-ethylnylphenyl (4-EP) diazonium compound. Then, horseradish peroxidase (HRP) modified with azido group was covalently immobilized onto the electrografted film via click reaction. Reflection absorption infrared (RAIR) spectroscopy and electrochemical methods were used to characterize the modification process. The results indicate that HRP retains its native structure and shows fast direct electron transfer. Moreover, the immobilized HRP shows excellent electrocatalytic reduction activity toward H₂O₂ with a linear range of 5.0×10⁻⁶ to 9.3×10⁻⁴molL⁻¹.

Keywords: Click chemistry; Diazonium salts; Direct electron transfer; Horseradish peroxidase; Biosensor

Extraction and analysis of avermectines in agricultural soils by microwave assisted extraction and ultra high performance liquid chromatography coupled to tandem mass spectrometry by J. Raich-Montiu; M.D. Prat; M. Granados (pp. 32-37).

Display Omitted► Avermectines in agricultural soils. ► Extraction by using microwave assisted extraction. ► Analysis by using UHPLC–MS/MS ► Soil physico-chemical properties and aging influence on extraction.A method for the analysis of avermectines (abamectine, doramectine and ivermectine) in soils has been developed. The analytes are extracted with acetonitrile/water (90:10) by using microwave assisted extraction. The extract is cleaned-up through solid phase extraction with Oasis HLB cartridges and analyzed by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC–MS/MS). Separation is obtained in 3min. Extraction of analytes from the soil, that is the most critical point, has been studied in detail, and the effect of soil composition and aging time on the analytes recovery has been investigated.

Keywords: UHPLC–MS/MS; Avermectines; Soils; Extraction techniques; Environmental analysis

Recovery of phosphonate surface contaminants from glass using a simple vacuum extractor with a solid-phase microextraction fiber by Gary S. Groenewold; Jill R. Scott; Catherine Rae (pp. 38-47).

.Display Omitted► A field vacuum extractor (FVE) nondestructively samples surface-adsorbed organics. ► The FVE creates a modest vacuum over the surface, volatilizing surface organics. ► A solid phase microextraction fiber (SPME) collects volatilized organics. ► The SPME is easily analyzed using GC/MS. ► The FVE enables collection chemical signatures from hard-to-sample surfaces.Recovery of chemical contaminants from fixed surfaces for analysis can be challenging, particularly if it is not possible to acquire a solid sample to be taken to the laboratory. A simple device is described that collects semi-volatile organic compounds from fixed surfaces by creating an enclosed volume over the surface, then generating a modest vacuum. A solid-phase microextraction (SPME) fiber is then inserted into the evacuated volume where it functions to sorb volatilized organic contaminants. The device is based on a syringe modified with a seal that is used to create the vacuum, with a perforable plunger through which the SPME fiber is inserted. The reduced pressure speeds partitioning of the semi-volatile compounds into the gas phase and reduces the boundary layer around the SPME fiber, which enables a fraction of the volatilized organics to partition into the SPME fiber. After sample collection, the SPME fiber is analyzed using conventional gas chromatography/mass spectrometry. The methodology has been used to collect organophosphorus compounds from glass surfaces, to provide a simple test for the functionality of the devices. Thirty minute sampling times (Δ T_vac) resulted in fractional recovery efficiencies that ranged from 10⁻³ to >10⁻², and in absolute terms, collection of low nanograms was demonstrated. Fractional recovery values were positively correlated to the vapor pressure of the compounds being sampled. Fractional recovery also increased with increasing Δ T_vac and displayed a roughly logarithmic profile, indicating that an operational equilibrium is being approached. Fractional recovery decreased with increasing time between exposure and sampling; however, recordable quantities of the phosphonates could be collected three weeks after exposure.

Keywords: Surface sampling; Surface extraction; GC/MS; SPME; Surface contamination

A broad-spectrum equine urine screening method for free and enzyme-hydrolysed conjugated drugs with ultra performance liquid chromatography/tandem mass spectrometry by Colton H.F. Wong; Francis P.W. Tang; Terence S.M. Wan (pp. 48-60).

► A high throughput screening method for 140 free and enzyme-hydrolysed conjugated drugs. ► Detection of drugs which are prone to decomposition during hydrolysis. ► Detection of drugs using polarity switching. ► Easily expandable to accommodate more target analytes.The authors’ laboratory at one time employed four liquid chromatography/mass spectrometric (LC/MS) methods for the detection of a large variety of drugs in equine urine. Drug classes covered by these methods included anti-diabetics, anti-ulcers, cyclooxygenase-2 (COX-2) inhibitors, sedatives, corticosteroids, anabolic steroids, sulfur diuretics, xanthines, etc. With the objective to reduce labour and instrumental workload, a new ultra performance liquid chromatography/tandem mass spectrometric (UPLC/MS/MS) method has been developed, which encompasses all target analytes detected by the original four LC/MS methods. The new method has better detection limits than the superseded methods. In addition, it covers new target analytes that could not be adequately detected by the four LC/MS methods.The new method involves solid-phase extraction (SPE) of two aliquots of equine urine using two Abs Elut Nexus cartridges. One aliquot of the urine sample is treated with β-glucuronidase before subjecting to SPE. A second aliquot of the same urine sample is processed directly using another SPE cartridge, so that drugs that are prone to decomposition during enzyme hydrolysis can be preserved. The combined eluate is analysed by UPLC/MS/MS using alternating positive and negative electrospray ionisation in the selected-reaction-monitoring mode. Exceptional chromatographic separation is achieved using an UPLC system equipped with a UPLC^® BEH C18 column (10cmL×2.1mm ID with 1.7μm particles). With this newly developed UPLC/MS/MS method, the simultaneous detection of 140 drugs at ppb to sub-ppb levels in equine urine can be achieved in less than 13min inclusive of post-run equilibration. Matrix interference for the selected transitions at the expected retention times is minimised by the excellent UPLC chromatographic separation. The method has been validated for recovery and precision, and is being used regularly in the authors’ laboratory as an important component of the array of screening methods for doping control analyses of equine urine samples.

Keywords: Equine; Urine; Doping control; Ultra performance liquid chromatography/tandem mass spectrometry

Highly sensitive detection of clenbuterol using competitive surface-enhanced Raman scattering immunoassay by Guichi Zhu; Yongjun Hu; Jiao Gao; Liang Zhong (pp. 61-66).

Schemes of SERS nanoprobes preparation (a) and competitive SERS immunoassay for clenbuterol (b).Display Omitted► A new method for clenbuterol detection by the use of a competitive SERS immunoassay has been developed. ► 4,4′-Dipyridyl is chosen as the Raman reporter due to its fast-labeled, nontoxic and bifunctional properties. ► The present method could detect clenbuterol over a wide dynamic concentration range and exhibit significant specificity in real samples. ► The technique is more sensitive and simpler than the conventional method ELISA.In this report, we present a novel approach to detect clenbuterol based on competitive surface-enhanced Raman scattering (SERS) immunoassay. Herein, a SERS nanoprobe that relies on gold nanoparticle (GNP) is labeled by 4,4′-dipyridyl (DP) and clenbuterol antibody, respectively. The detection of clenbuterol is carried out by competitive binding between free clenbuterol and clenbuterol-BSA fastened on the substrate with their antibody labeled on SERS nanoprobes. The present method allows us to detect clenbuterol over a much wider concentration range (0.1–100pgmL⁻¹) with a lower limit of detection (ca. 0.1pgmL⁻¹) than the conventional methods. Furthermore, by the use of this new competitive SERS immunoassay, the clenbuterol-BSA (antigen) is chosen to fasten on the substrate instead of the clenbuterol antibody, which could reduce the cost of the assay. Results demonstrate that the proposed method has the wide potential applications in food safety and agonist control.

Keywords: Clenbuterol; Surface-enhanced Raman scattering; Competitive; Label; Immunoassay

Monitoring of alcoholic fermentation using near infrared and mid infrared spectroscopies combined with electronic nose and electronic tongue by S. Buratti; D. Ballabio; G. Giovanelli; C.M. Zuluanga Dominguez; A. Moles; S. Benedetti; N. Sinelli (pp. 67-74).

Application of non destructive methods for the monitoring of red wine fermentation in correlation with the evolution of chemical parameters.Display Omitted► We monitored time-related changes in red wine fermentation process. ► NIR and MIR spectroscopies, electronic nose and tongue were applied. ► Data were kinetically modelled to identify critical points during fermentation. ► NIR, MIR electronic nose and tongue were able to follow the fermentation process. ► The models agreed with the evolution of chemical parameters.Effective fermentation monitoring is a growing need due to the rapid pace of change in the wine industry, which calls for fast methods providing real time information in order to assure the quality of the final product. The objective of this work is to investigate the potential of non-destructive techniques associated with chemometric data analysis, to monitor time-related changes that occur during red wine fermentation. Eight micro-fermentation trials conducted in the Valtellina region (Northern Italy) during the 2009 vintage, were monitored by a FT-NIR and a FT-IR spectrometer and by an electronic nose and tongue. The spectroscopic technique was used to investigate molecular changes, while electronic nose and electronic tongue evaluated the evolution of the aroma and taste profile during the must-wine fermentation. Must-wine samples were also analysed by traditional chemical methods in order to determine sugars (glucose and fructose) consumption and alcohol (ethanol and glycerol) production. Principal Component Analysis was applied to spectral, electronic nose and electronic tongue data, as an exploratory tool, to uncover molecular, aroma and taste modifications during the fermentation process. Furthermore, the chemical data and the PC1 scores from spectral, electronic nose and electronic tongue data were modelled as a function of time to identify critical points during fermentation. The results showed that NIR and MIR spectroscopies are useful to investigate molecular changes involved in wine fermentation while electronic nose and electronic tongue can be applied to detect the evolution of taste and aroma profile. Moreover, as demonstrated through the modeling of NIR, MIR, electronic nose and electronic tongue data, these non destructive methods are suitable for the monitoring of must-wine fermentation giving crucial information about the quality of the final product in agreement with chemical parameters. Although in this study the measurements were carried out in off-line mode, in future these non destructive techniques could be valid and simple tools, able to provide in-time information about the fermentation process and to assure the quality of wine.

Keywords: Alcoholic fermentation; Near infrared spectroscopy; Mid infrared spectroscopy; Electronic nose; Electronic tongue; Red wine

Integration of fiber optic-particle plasmon resonance biosensor with microfluidic chip by Wei-Ting Hsu; Wen-Hsin Hsieh; Shu-Fang Cheng; Chung-Ping Jen; Chao-Ching Wu; Cheng-Han Li; Chia-Yu Lee; Wan-Yun Li; Lai-Kwan Chau; Chang-Yue Chiang; Shaw-Ruey Lyu (pp. 75-82).

Display Omitted► Fiber optic-particle plasmon resonance biosensor has been integrated with microfluidic chip. ► Integration reduces response time. ► Integration improves detection limit. ► Fiber optic-particle plasmon resonance measurement alleviates the demand on precise optical alignment.This article reports the integration of the fiber optic-particle plasmon resonance (FO-PPR) biosensor with a microfluidic chip to reduce response time and improve detection limit. The microfluidic chip made of poly(methyl methacrylate) had a flow-channel of dimensions 4.0cm×900μm×900μm. A partially unclad optical fiber with gold or silver nanoparticles on the core surface was placed within the flow-channel, where the volume of the flow space was about 14μL. Results using sucrose solutions of various refractive indexes show that the refractive index resolution improves by 2.4-fold in the microfluidic system. The microfluidic chip is capable of delivering a precise amount of biological samples to the detection area without sample dilution. Several receptor/analyte pairs were chosen to examine the biosensing capability of the integrated platform: biotin/streptavidin, biotin/anti-biotin, DNP/anti-DNP, OVA/anti-OVA, and anti-MMP-3/MMP-3. Results show that the response time to achieve equilibrium can be shortened from several thousand seconds in a conventional liquid cell to several hundred seconds in a microfluidic flow-cell. In addition, the detection limit also improves by about one order of magnitude. Furthermore, the normalization by using the relative change of transmission response as the sensor output alleviate the demand on precise optical alignment, resulting in reasonably good chip-to-chip measurement reproducibility.

Keywords: Biosensor; Fiber optic-particle plasmon resonance (FO-PPR); Microfluidic chip; Gold nanoparticle; Silver nanoparticle

Curcumin induced nanoscale CD44 molecular redistribution and antigen–antibody interaction on HepG2 cell surface by Mu Wang; Yuxia Ruan; Xiaobo Xing; Qian Chen; Yuan Peng; Jiye Cai (pp. 83-89).

Display Omitted► In this study, we investigate the changes of CD44 expression and distribution on HepG2 cells after curcumin treatment. ► We find curcumin is able to change the morphology and ultrastructure of HepG2 cells. ► Curcumin can reduce the expression of CD44 molecules and induce the nanoscale molecular redistribution on cell surface. ► The binding force between CD44-modified AFM tip and the HepG2 cell surface decreases after curcumin-treatment.The cell surface glycoprotein CD44 was implicated in the progression, metastasis and apoptosis of certain human tumors. In this study, we used atomic force microscope (AFM) to monitor the effect of curcumin on human hepatocellular carcinoma (HepG2) cell surface nanoscale structure. High-resolution imaging revealed that cell morphology and ultrastructure changed a lot after being treated with curcumin. The membrane average roughness increased (10.88±4.62nm to 129.70±43.72nm) and the expression of CD44 decreased (99.79±0.16% to 75.14±8.37%). Laser scanning confocal microscope (LSCM) imaging showed that CD44 molecules were located on the cell membrane. The florescence intensity in control group was weaker than that in curcumin treated cells. Most of the binding forces between CD44 antibodies and untreated HepG2 cell membrane were around 120–220pN. After being incubated with curcumin, the major forces focused on 70–150pN (10μM curcumin-treated) and 50–120pN (20μM curcumin-treated). These results suggested that, as result of nanoscale molecular redistribution, changes of the cell surface were in response to external treatment of curcumin. The combination of AFM and LSCM could be a powerful method to detect the distribution of cell surface molecules and interactions between molecules and their ligands.

Keywords: Curcumin; Atomic force microscope; CD44 molecule; Redistribution; Force measurement

Enhanced electrochemiluminescence from luminol at multi-walled carbon nanotubes decorated with palladium nanoparticles: A novel route for the fabrication of an oxygen sensor and a glucose biosensor by Behzad Haghighi; Somayyeh Bozorgzadeh (pp. 90-97).

Display Omitted► Glassy carbon electrode was modified with Pd nanoparticles decorated MWCNTs. ► Modified GCE showed sensitizing effect on luminol-O₂ and luminol-H₂O₂ ECL reactions. ► The sensitized ECL reactions were conducted at neutral media. ► Dissolved O₂, luminol, H₂O₂ and glucose were determined using the proposed modified GCE.Incorporation of palladium nanoparticles on the surface of multi-walled carbon nanotubes and modification of glassy carbon electrode with the prepared nano-hybrid material led to the fabrication of a novel electrode. The modified electrode showed attractive electrocatalytic activity and sensitizing effect on luminol–O₂ and luminol–H₂O₂ electrochemiluminescence (ECL) reactions at neutral media. The sensitized luminol–O₂ and luminol–H₂O₂ reactions were successfully applied for the ECL determination of dissolved O₂ and glucose, respectively. Under the optimal conditions for luminol–O₂ system, the ECL signal intensity of luminol was linear with the concentration of dissolved oxygen in the range between 0.08 and 0.94mM ( r=0.9996) and for luminol–H₂O₂ system, the ECL signal intensity of luminol was linear with the concentration of glucose in the range between 0.1 and 1000μM ( r=0.9998). The limits of detection (S/N=3) for dissolved oxygen and glucose were 0.02mM and 54nM, respectively. The relative standard deviations (RSD) for repetitive measurements of 0.50mM oxygen ( n=10) and 10μM glucose ( n=30) were 3.5% and 0.3%, respectively. Also, under the optimal conditions for luminol–H₂O₂ system, the ECL signal intensity of luminol was linear with the concentration of H₂O₂ in the range between 1nM and 0.45mM ( r=0.9997). The limit of detection (S/N=3) for H₂O₂ detection was 0.5nM and the relative standard deviation for repetitive measurements of 10μM H₂O₂ ( n=10) was 0.8%.

Keywords: Electrochemiluminescence; Multi-walled carbon nanotubes; Palladium nanoparticles; Luminol; Oxygen; Glucose

Chronocoulometric determination of urea in human serum using an inkjet printed biosensor by Suman; Emmet O’Reilly; Michele Kelly; Aoife Morrin; Malcolm R. Smyth; Anthony J. Killard (pp. 98-102).

.Display Omitted► A urease biosensor was fabricated using inkjet and screen printing. ► Polyaniline nanoparticles were inkjet printed onto screen-printed electrodes. ► Urease enzyme was also deposited using inkjet printing. ► Ammonium could be measured using chronocoulometry in the range 0.1–100mM. ► Urea was measured in serum from 2 to 12mM ( r²=0.98) and correlated well with spectrophotometry (0.85).A biosensor for the determination of urea in human serum was fabricated using a combination of inkjet printed polyaniline nanoparticles and inkjet printed urease enzyme deposited sequentially onto screen-printed carbon paste electrodes. Chronocoulometry was used to measure the decomposition of urea via the doping of ammonium at the polyaniline-modified electrode surface at −0.3V vs. Ag/AgCl. Ammonium could be measured in the range from 0.1 to 100mM. Urea could be measured by the sensor in the range of 2–12mM ( r²=0.98). The enzyme biosensor was correlated against a spectrophotometric assay for urea in 15 normal human serum samples which yielded a correlation coefficient of 0.85. Bland–Altman plots showed that in the range of 5.8–6.6mM urea, the developed sensor had an average positive experimental bias of 0.12mM (<2% RSD) over the reference method.

Keywords: Urea; Polyaniline; Nanoparticle; Inkjet; Chronocoulometry

Erratum to “Monitoring of diisopropyl fluorophosphate hydrolysis by fluoride-selective polymeric films using absorbance spectroscopy” [Anal. Chim. Acta 667 (2010) 119–122] by Madhumati Ramanathan; Lin Wang; James R. Wild; Mark E. Meyerhoff; Aleksandr L. Simonian (pp. 103-103).

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Analytica Chimica Acta (v.697, #1-2)