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Analytica Chimica Acta (v.686, #1-2)

Editorial Board (pp. iii).

A single pump column-switching technique coupled with polystyrene-divinylbenzene–carbon nanotubes column for the determination of trace anions in different concentrated organic matrices by ion chromatography by Yingying Zhong; Wenfang Zhou; Haibao Zhu; Xueling Zeng; Mingli Ye; Peimin Zhang; Yan Zhu (pp. 1-8).

An ion chromatographic method with on-line sample pretreatment was developed for the trace analysis of seven common anions in concentrated matrices. The pretreatment column used in this study consisted of polystyrene-divinylbenzene (PS-DVB) and multi-walled carbon nanotubes (MWCNTs). It was too hydrophobic to retain different inorganic anions, but it showed a strong affinity for organic compounds. Thus, this chromatographic system could be used to detect trace anions in organic solvents, organic acids and relevant salts. The addition of MWCNTs decreased the surface areas of stationary phases and the retention times of organic matrices were shortened. Compared with conventional column-switching technique, only a single instrument (ICS2100) was needed in this system, including a pump, a conductivity detector, an eluent generator, a six-port valve and a ten-port valve. An electrochemical self-generating suppressor (ESGS) was adopted to convert the eluent of KOH into water for the matrix elimination. Two different eluent were employed in the chromatographic system, one for separation and the other for matrix elimination. The sample pretreatment and analysis were realized simultaneously. After optimization of this system, a calibration study was conducted by preparing and analyzing eight concentrations (between 5 and 5000μgL⁻¹) of mixture standards of seven anions in deionized water. The linearity was between 0.9990 and 0.9998, and the detection limits ranged from 0.41 to 3.17μgL⁻¹. A spiking study was performed on three representative organic chemicals with satisfactory recoveries between 88.1% and 118.5% when the concentrations of the matrices did not exceed 10gL⁻¹.

Keywords: Column-switching; Ion chromatography; Trace anion; Organic matrix; Polystyrene-divinylbenzene–carbon nanotubes column

Methods for measuring aptamer-protein equilibria: A review by Meng Jing; Michael T. Bowser (pp. 9-18).

Aptamers are single stranded DNA or RNA molecules that have been selected using in vitro techniques to bind target molecules with high affinity and selectivity, rivaling antibodies in many ways. In order to use aptamers in research and clinical applications, a thorough understanding of aptamer–target binding is necessary. In this article, we review methods for assessing aptamer–protein binding using separation based techniques such as dialysis, ultrafiltration, gel and capillary electrophoresis, and HPLC; as well as mixture based techniques such as fluorescence intensity and anisotropy, UV–vis absorption and circular dichroism, surface plasmon resonance, and isothermal titration calorimetry. For each method the principle, range of application and important features, such as sample consumption, experimental time and complexity, are summarized and compared.

Keywords: Aptamer; SELEX; Nucleic acids; Protein; Dissociation constant; Equilibrium constant

A review on the interrogation of peptide–metal interactions using electrospray ionization-mass spectrometry by Doug D. Carlton Jr.; Kevin A. Schug (pp. 19-39).

Over the years, protein interactions have been studied by many techniques to obtain a wide breadth of information. The large size and complexity of the macromolecules have caused difficulties for studying them by some techniques. In some cases, peptides, smaller and less complex biomolecules, have been found to be suitable models to mimic the interactions of entire proteins. The study of peptide–metal interaction, in particular, has proven to be fruitful to researchers across the science fields. One technique in particular, electrospray ionization-mass spectrometry (ESI-MS), has been shown to provide a great deal of information to these studies. The speed, sensitivity, and selectivity of MS, along with the information that can be interpreted from MS-based experiments, has driven this technique to the forefront for understanding the nature of peptide–metal complexes. MS has allowed researchers to identify the stoichiometry of peptide–metal complexes or even mixtures of complexes. The specific amino acids in which the metal cations are bound and the degree of association in these complexes can also be determined by MS experiments. The following review discusses the ESI process and how it is ideal for studying noncovalent interactions between peptides and metals. An investigation of the qualitative and quantitative information that has been determined by ESI-MS follows for readers to realize the versatility of this technique and the diversity of information that can be obtained by a variety of related methods.

Keywords: Peptide; Metal; Electrospray ionization; Mass spectrometry; Noncovalent interaction

Trace elemental analysis of airborne particulate matter using dynamic reaction cell inductively coupled plasma – mass spectrometry: Application to monitoring episodic industrial emission events by K. Suresh Kumar Danadurai; Shankararaman Chellam; Cin-Ty Lee; Matthew P. Fraser (pp. 40-49).

The elemental composition of airborne particles is being increasingly monitored since several metals have been implicated in adverse human health outcomes and environmental deterioration while simultaneously providing clues to the identity and strength of their emission sources. However, quantification of several elements and transition metals in ambient aerosols, which are typically present only at trace levels, is fraught with interferences using quadrupole inductively coupled plasma – mass spectrometry (q-ICP-MS). We report improved measurements of key aerosol elements including Al, V, Cr, Fe, Ni, Cu, and Zn in airborne coarse particulate matter (PM₁₀) by exploiting ion-molecule reactions in a dynamic reaction cell (DRC) with NH₃ as the cell gas. Numerous other elements (Na, Mg, Si, K, Ca, Sc, Ti, Mn, Co, Ga, As, Se, Rb, Sr, Zr, Mo, Cd, Sn, Sb, Cs, Ba, Pb, Th, and U) and lanthanoids (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), which are important trace components used for source apportionment studies, were also measured. Inter-laboratory comparison using sector field ICP-MS demonstrated the accuracy and precision of DRC-q-ICP-MS. This technique was used to determine the elemental composition of over 150 PM₁₀ samples collected from an industrialized region in Houston, TX. Samples were first digested using a combination of HF, HNO₃, and H₃BO₃ in two stages in a microwave oven each with set points of 200°C, 1.55MPa (225psig), and 20min dwell time. Trace metals were used to identify an episodic release of particles from a local source and subsequently track the atmospheric transport of the released particles. This establishes the inherent value of such measurements to developing air quality management strategies since emission events can significantly worsen air quality over a large area. Based on our findings, we recommend continuous independent monitoring of emissions to augment existing industry self-reporting regulatory requirements. Such environmental measurements will assist in establishing industrial regulatory compliance while simultaneously providing data necessary to develop scientifically defensible air quality management strategies.

Keywords: Atmospheric particulate matter; Dynamic reaction cell; ICP-MS; Rare earth elements; Industrial air pollution; Trace elements

Radiostrontium separation and measurement in a single step using plastic scintillators plus selective extractants. Application to aqueous sample analysis by H. Bagán; A. Tarancón; G. Rauret; J.F. García (pp. 50-56).

This study describes a new protocol for⁹⁰Sr determination in water samples based on the use of a selective extractant (DtBuCH18C6) and plastic scintillator microspheres. The proposed procedure unifies chemical separation and sample measurement preparation in a single step to reduce the effort, time and reagents required for analysis. In addition, the final measurement does not produce mixed waste. The minimum activity detectable for 10mL of sample solution is 0.46BqL⁻¹. Relative errors for the determination of⁹⁰Sr activity in drinking, sea and river waters are less than 4%.

Keywords: Plastic scintillation; Liquid scintillation; ⁹⁰; Sr/; ⁹⁰; Y; 4,4′(5′)-di-t-butylcyclohexano-18-crown-6; Extraction chromatography; Water samples

Principal component directed partial least squares analysis for combining nuclear magnetic resonance and mass spectrometry data in metabolomics: Application to the detection of breast cancer by Haiwei Gu; Zhengzheng Pan; Bowei Xi; Vincent Asiago; Brian Musselman; Daniel Raftery (pp. 57-63).

Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) are the two most commonly used analytical tools in metabolomics, and their complementary nature makes the combination particularly attractive. A combined analytical approach can improve the potential for providing reliable methods to detect metabolic profile alterations in biofluids or tissues caused by disease, toxicity, etc. In this paper,¹H NMR spectroscopy and direct analysis in real time (DART)-MS were used for the metabolomics analysis of serum samples from breast cancer patients and healthy controls. Principal component analysis (PCA) of the NMR data showed that the first principal component (PC1) scores could be used to separate cancer from normal samples. However, no such obvious clustering could be observed in the PCA score plot of DART-MS data, even though DART-MS can provide a rich and informative metabolic profile. Using a modified multivariate statistical approach, the DART-MS data were then reevaluated by orthogonal signal correction (OSC) pretreated partial least squares (PLS), in which the Y matrix in the regression was set to the PC1 score values from the NMR data analysis. This approach, and a similar one using the first latent variable from PLS-DA of the NMR data resulted in a significant improvement of the separation between the disease samples and normals, and a metabolic profile related to breast cancer could be extracted from DART-MS. The new approach allows the disease classification to be expressed on a continuum as opposed to a binary scale and thus better represents the disease and healthy classifications. An improved metabolic profile obtained by combining MS and NMR by this approach may be useful to achieve more accurate disease detection and gain more insight regarding disease mechanisms and biology.

Keywords: Metabolomics; Breast cancer; Nuclear magnetic resonance; Direct analysis in real time; Mass spectrometry; Partial least squares; Orthogonal signal correction; Human serum

Tracking diffusion of conditioning water in single wheat kernels of different hardnesses by near infrared hyperspectral imaging by Marena Manley; Gerida du Toit; Paul Geladi (pp. 64-75).

The combination of near infrared (NIR) hyperspectral imaging and chemometrics was used to follow the diffusion of conditioning water over time in wheat kernels of different hardnesses. Conditioning was attempted with deionised water (dH₂O) and deuterium oxide (D₂O). The images were recorded at different conditioning times (0–36h) from 1000 to 2498nm with a line scan imaging system. After multivariate cleaning and spectral pre-processing (either multiplicative scatter correction or standard normal variate and Savitzky–Golay smoothing) six principal components (PCs) were calculated. These were studied visually interactively as score images and score plots. As no clear clusters were present in the score plots, changes in the score plots were investigated by means of classification gradients made within the respective PCs. Classes were selected in the direction of a PC (from positive to negative or negative to positive score values) in almost equal segments. Subsequently loading line plots were used to provide a spectroscopic explanation of the classification gradients. It was shown that the first PC explained kernel curvature. PC3 was shown to be related to a moisture-starch contrast and could explain the progress of water uptake. The positive influence of protein was also observed. The behaviour of soft, hard and very hard kernels was different in this respect, with the uptake of water observed much earlier in the soft kernels than in the harder ones. The harder kernels also showed a stronger influence of protein in the loading line plots. Difference spectra showed interpretable changes over time for water but not for D₂O which had a too low signal in the wavelength range used. NIR hyperspectral imaging together with exploratory chemometrics, as detailed in this paper, may have wider applications than merely conditioning studies.

Keywords: Near infrared hyperspectral imaging; Image analysis; Wheat conditioning; Principal component analysis; Brushing; Classification gradient

Development of polymer-membrane based electrodes for suramin by Andrew Yu; Brandon Shepherd; Meghan Wagner; Jamie Clapper; Joan M. Esson (pp. 76-80).

The development of a polymer membrane-based electrode to measure the anionic drug suramin in buffered saline and biological samples is described. A large non-equilibrium, steady state EMF response is observed toward suramin, and judicious choice of the polymer membrane components allows for adjustment of the dynamic range of the electrode. The optimized membrane for use in the toxic suramin range consists of 25wt% tridodecylmethyl ammonium chloride, 55wt% bis-2-ethylhexyl sebacate, and 20wt% Pellethane. Although this electrode can be used to directly quantify suramin in human plasma, determination of suramin that is not affected by the background concentration of small anions is best achieved by simple potentiometric titrations with polycationic protamine monitored with a protamine-sensitive electrode.

Keywords: Suramin; Polymer membrane-based electrode; Polyanion-sensitive electrode; Potentiometry

Magnetic loading of tyrosinase-Fe₃O₄/mesoporous silica core/shell microspheres for high sensitive electrochemical biosensing by Shuo Wu; Hainan Wang; Shengyang Tao; Chan Wang; Lihui Zhang; Zhiguang Liu; Changgong Meng (pp. 81-86).

A new protocol is proposed for magnetic loading and sensitive electrochemical detection of phenol via the tyrosinase cross-linked mesoporous magnetic core/shell microspheres. The mesoporous magnetic microspheres, characterized by transmission electron microscopy, N₂ adsorption/desorption isotherms, and magnetic curve displays high capacity for enzyme immobilization and strong magnetism to adhere to the magnetic electrode surface without any additional adhesive reagent. The biosensor exhibits a wide linear response to phenol ranging from 1.0×10⁻⁹ to 1.0×10⁻⁵M, a high sensitivity of 78μAmM⁻¹, a low detection limit of 1nM, and a fast response rate (less than 5s). The proposed method is simple, rapid, inexpensive and convenient in electrode renewal, which is recommended as a promising experimental platform for wider applications in biosensing.

Keywords: Tyrosinase; Fe; ₃; O; ₄; /; m; SiO; ₂; core/shell mesoporous microspheres; Magnetic loading; Flow injection analysis; Amperometry

Application of ionic-liquid supported cloud point extraction for the determination of microcystin-leucine–arginine in natural waters by Shruti Pavagadhi; Chanbasha Basheer; Rajasekhar Balasubramanian (pp. 87-92).

A cloud point extraction method has been developed using an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMiM PF₆) for the determination of a widely studied cyanotoxin (microcystin leucine–arginine, MCLR) in natural waters. Extraction parameters such as sample pH, extraction temperature, extraction time, the amount of ionic liquid and the amount of extraction volume were investigated and optimized to achieve the maximum extraction efficiency. The results obtained indicated a good linearity with the correlation coefficient of 0.995 over the range of 0.5–50μgL⁻¹. The relative standard deviation (RSD) of the method was 7.5% ( n=6). The calculated method detection limit was 0.03μgL⁻¹ ( n=6). The practical applicability of the technique was demonstrated by analyzing water samples ( n=9) collected from three different sites in local reservoirs.

Keywords: Key words; Environmental applications; Microextraction; Microcystin-LR; Preconcentration; Ionic liquids

Analysis of trace metals (Cu, Cd, Pb, and Fe) in seawater using single batch nitrilotriacetate resin extraction and isotope dilution inductively coupled plasma mass spectrometry by Jong-Mi Lee; Edward A. Boyle; Yolanda Echegoyen-Sanz; Jessica N. Fitzsimmons; Ruifeng Zhang; Richard A. Kayser (pp. 93-101).

A simple and accurate low-blank method has been developed for the analysis of total dissolved copper, cadmium, lead, and iron in a small volume (1.3–1.5mL per element) of seawater. Pre-concentration and salt-separation of a stable isotope spiked sample are achieved by single batch extraction onto nitrilotriacetate (NTA)-type Superflow^® chelating resin beads (100–2400 beads depending on the element). Metals are released into 0.1–0.5M HNO₃, and trace metal isotope ratios are determined by ICPMS. The benefit of this method compared to our previous Mg(OH)₂ coprecipitation method is that the final matrix is very dilute so cone-clogging and matrix sensitivity suppression are minimal, while still retaining the high accuracy of the isotope dilution technique. Recovery efficiencies are sensitive to sample pH, number of resin beads added, and the length of time allowed for sample–resin binding and elution; these factors are optimized for each element to yield the highest recovery. The method has a low procedural blank and high sensitivity sufficient for the analysis of pM–nM open-ocean trace metal concentrations. Application of this method to samples from the Bermuda Atlantic Time-Series Study station provides oceanographically consistent Cu, Cd, Pb, and Fe profiles that are in good agreement with other reliable data for this site. In addition, the method can potentially be modified for the simultaneous analysis of multiple elements, which will be beneficial for the analysis of large number of samples.

Keywords: Seawater; Trace elements; Isotope dilution inductively coupled plasma mass spectrometry; Fe; Pb; Cd; Cu

Towards a selected reaction monitoring mass spectrometry fingerprint approach for the screening of oligosaccharidoses by John Sowell; Tim Wood (pp. 102-106).

The oligosaccharidoses are a group of metabolic disorders resulting from a deficiency in enzymes responsible for the catabolism of protein bound oligosaccharides and are typified by the accumulation of corresponding sugars in the urine. Screening is typically accomplished using thin layer chromatography. However, analyte specificity can be a problem and thus complicate interpretation of results. For this reason we developed a mixed mode liquid chromatography tandem mass spectrometry assay for the screening of the oligosaccharidoses which potentially mitigates many of the problems associated with thin layer chromatography. Samples from patients previously diagnosed with I-Cell disease, mannosidosis, Pompe, galactosialidosis, and fucosidosis were derivatized with 3-methyl-1-phenyl-2-pyrazolin-5-one and subjected to analysis by liquid chromatography tandem mass spectrometry. Results were compared to normal control samples. Preliminary results suggest that each oligosaccharidoses produces a unique selected reaction monitoring fingerprint and that the developed method may be an effective screening and diagnostic tool for these disorders.

Keywords: Liquid chromatography; Tandem mass spectrometry; Lysosomal storage disorders; Oligosaccharidoses

An improved method of ion exchange for nitrogen isotope analysis of water nitrate by Meng Xing; Weiguo Liu (pp. 107-114).

Nitrate nitrogen and oxygen isotopes have been widely used to trace the nitrogen biogeochemical cycle by identifying NO₃⁻ sources. An improved method of anion exchange was developed to measure δ¹⁵N-NO₃⁻ in fresh water by continuous-flow elemental analyzer/isotope ratio mass spectrometry (EA-IRMS). We used a custom-built exchange resin column, a peristaltic pump and the oven-drying method in our experiments. Consequently, the amount of Ag₂O used as a neutralizer was reduced, time was saved, and operation became simpler than before. Meanwhile, analytical precision remained identical to previous studies. KNO₃ solutions were prepared at 0.2, 5 and 25mg-NL⁻¹ from KNO₃ standard salt (δ¹⁵N=+6.27‰), and the average δ¹⁵N values of the solutions after having been absorbed on and subsequently stripped from anion columns were +6.62±0.22‰ ( n=6), +6.38±0.09‰ ( n=6), and +6.26±0.07‰ ( n=6), respectively. In addition, the “natural” water sample δ¹⁵N-NO₃⁻ showed consistency in comparison to standards, and the mean standard deviation by the different approaches was 0.08‰. Accordingly, by these improvements the anion exchange resin technique is demonstrated to be more suitable for measuring δ¹⁵N in NO₃⁻ than original techniques.

Keywords: Nitrate; Nitrogen isotope; Ion exchange; Water; δ; ¹⁵; N tracing approach

Gold nanoparticles based chemiluminescent resonance energy transfer for immunoassay of alpha fetoprotein cancer marker by Xiangyi Huang; Jicun Ren (pp. 115-120).

In this paper, we report a new strategy of chemiluminescence resonance energy transfer (CRET) by using gold nanoparticles (AuNPs) as efficient long-range energy acceptor in sandwich immunoassays. In the design of CRET system, we chose the highly sensitive chemiluminescence (CL) reaction of luminol and hydrogen peroxide catalysed by horseradish peroxidase (HRP) because the CL spectrum of luminol ( λ_max 425nm) partially overlaps with the visible absorption bands of AuNPs. On the basis of CRET strategy, we developed a sandwich immunoassay of alpha fetoprotein (AFP) cancer marker. In immunoassay, two antibodies (anti-AFP-1 and anti-AFP-2) were conjugated to AuNPs and horseradish peroxidase (HRP), respectively. The sandwich-type immunoreactions between the AFP (antigen) and the two different antibodies bridged the donors (luminol) and acceptors (AuNPs), which led to the occurrence of CRET from luminol to AuNPs upon chemiluminescent reaction. We observed that the quenching of chemiluminescence signal depended linearly on the AFP concentration within a range of concentration from 5 to 70ngmL⁻¹ and the detection limit of AFP was 2.5ngmL⁻¹. Our method was successfully applied for determination of AFP levels in sera from cancer patients, and the results were in good agreement with ELISA assays. This approach is expected to be extended to other assay designs, that is, using other antibodies, analytes, chemiluminescent substance, and even other metallic nanoparticles.

Keywords: Gold nanoparticles; Chemiluminescence resonance energy transfer; Luminol; Alpha fetoprotein

Determination of radon using solid state nuclear tracks wireless sensing method by Nan Du; Lifu Liao; Yongjun Xiao; Xilin Xiao; Zhiyuan Zhao; Yingwu Lin (pp. 121-125).

The aim of this paper is to develop a solid state nuclear tracks (SSNTs) wireless magnetoelastic sensing method for the determination of radon. In this method, wireless sensors for detecting radon are fabricated by coating polymethyl methacrylate (PMMA) film on the surface of magnetoelastic foils. The magnetoelastic sensing technique has the unique characteristic of being able to wirelessly detect resonance frequency shifts of a magnetoelastic foil in response to differences in the mass of foil. When the sensor is exposed to the environment containing radon, the PMMA film on the sensor is attacked by alpha-particles emitted from radon, generating latent SSNTs. After the sensor is chemically etched, the latent SSNTs in the PMMA film are enlarged and the sensor loses a certain mass, resulting in a shift in resonance frequency of the sensor. Consequently, the radon concentration can be determined by measuring the shift in resonance frequency. Under the conditions of the etchant concentration, etching temperature and etching time being 20% (w/w), 80°C and 18min, respectively, the linear range for the determination of radon is 1.20×10⁵ to 3.60337199×10⁶Bqm⁻³h with the detection limit of 20.3×10³Bqm⁻³h. The method has been applied for the determination of radon in air samples with satisfactory results.

Keywords: Radon; Wireless sensing; Solid state nuclear tracks; Magnetoelastic

Use of microperoxidase-11 to functionalize tin dioxide electrodes for the optical and electrochemical sensing of hydrogen peroxide by Yeni Astuti; Emmanuel Topoglidis; James R. Durrant (pp. 126-132).

In this paper, we employ microperoxidase MP-11 immobilized on mesoporous SnO₂ electrodes in order to study its peroxidase activity and reaction mechanism. We demonstrate the catalytic redox chemistry of the immobilized MP-11 via direct interfacial electron transfer without the use of electron mediators. By taking advantage from the optical transparency of the SnO₂ electrodes, optical absorbance spectroscopy is used in order to compliment the data information obtained from electrochemical techniques. The catalytic activity of the immobilized MP-11 is found to proceed via the Fenton reaction, yielding OH radical intermediates. We also demonstrate the viability of using this electrode system as a potential H₂O₂ biosensor with a sensitivity range of 0.05–30μM.

Keywords: Microperoxidase-11; Hydrogen peroxide; Biosensor; SnO; ₂; electrodes

A combined photocatalytic determination system for chemical oxygen demand with a highly oxidative reagent by Aiyong Zhang; Minghua Zhou; Qixing Zhou (pp. 133-143).

This study focuses on the proposal and validation of a combined photocatalytic (PC) system and a three-parameterized procedure for the determination of chemical oxygen demand (COD; PcCOD_combined), with a highly oxidative reagent utilized as a photoelectron scavenger and signal indicator. The PcCOD_combined was the functional combination of photon-efficient thin-layer photocatalytic oxidation, conventional bulk-phase photocatalytic oxidation and photocarrier-efficient high-activity photocatalytic reduction in one single photodigestion system, and consequently, this system possessed high photon-utilization efficiency, automatic stirring function and satisfactory determination characteristics. In comparison with the conventional one-parameterized procedure, the three-parameterized procedure introduces the blank and total photocatalytic reduction responses as two of the three significant analytical parameters. Under the optimized pH value of 3.0–4.5 and a rotating rate of 40rpm, the representative KMnO₄ species was used for the PcCOD_combined system as the combined high-activity oxidant, and a narrow and reliable analytical linear range of 0–260mgL⁻¹ was achieved during the 10min duration of the determinations. No observable interference of Cl⁻ was found at concentration of the ion up to 2000mgL⁻¹. A real sample analysis indicated that the measured values for the PcCOD_combined were all within a relative deviation below 5% of COD_Cr of the standard method, which further validates the practical feasibility of the proposed PcCOD_combined system.

Keywords: Environmental monitoring; Chemical oxygen demand (COD); Determination system; Determination procedure; Photocatalytic oxidation; Photocatalytic reduction

An enzyme-free quartz crystal microbalance biosensor for sensitive glucose detection in biological fluids based on glucose/dextran displacement approach by Dianping Tang; Qunfang Li; Juan Tang; Biling Su; Guonan Chen (pp. 144-149).

A sensitive and facile quartz crystal microbalance (QCM) biosensor for glucose detection in biological fluids was developed by means of a displacement-type assay mode between glucose and its analogy dextran for concanavalin A (ConA) binding sites on a graphene-based sensing platform. To construct such a displacement-based sensor, phenoxy-derived dextran (DexP) molecules were initially assembled onto the surface of graphene-coated QCM probe via π–π stacking interaction, and ConA molecules were then immobilized on the dextran through the dextran-ConA interaction. Upon addition of glucose, the analyte competed with the dextran for the ConA, and displaced it from the QCM probe, leading to a change in the frequency. Under optimal conditions, the frequency change relative to the basic resonant frequency was proportional to glucose concentration, and exhibited a dynamic range from 0.01 to 7.5mM with a low detection limit (LOD) of 5.0μM glucose (at 3 σ). The relative standard deviations (RSDs) were below 6.2% and 9.0% for the reproducibility and selectivity of the QCM glucose sensors, respectively. In addition, the assay system was evaluated with glucose spiking samples into the distilled water and blank cattle serum, receiving in excellent correlation with the referenced values.

Keywords: Displacement approach; Graphene nanosheets; Glucose; Nonenzyme biosensor; Quartz crystal microbalance

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Analytica Chimica Acta (v.686, #1-2)