Enzymatic glucose biosensor based on CeO2 nanorods synthesized by non-isothermal precipitation

Cerium oxide nanorods (CeO(2) NRs) were synthesized without templates through a low cost and simple non-isothermal precipitation method. The structure and morphology of CeO(2) NRs were characterized by X-ray diffraction and transmission electron microscopy. The CeO(2) NRs films, deposited on indium tin oxide (ITO)-coated glass substrates through electrophoretic deposition, were used for the immobilization of glucose oxidase (GOx). Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the CeO(2) NRs/ITO and GOx/CeO(2) NRs/ITO electrodes. The GOx/CeO(2) NRs/ITO electrode exhibits a linear range for the detection of glucose from 2 to 26 mM (correlation coefficient: 0.99) at 1-2s response time. Biosensor sensitivity is 0.165 μA mM(-1) cm(-2) with 100 μM detection limit. The anti-interference ability of the biosensor was also examined. The mediator-less application of CeO(2) NRs for glucose sensing was demonstrated.     

The use of differential measurements with a glucose biosensor for interference compensation during glucose determinations by flow injection analysis

A novel detection system for the determination of glucose in the presence of clinically important interferents, based on the use of dual sensors and flow-injection analysis (FIA), is described. The normalisation methodology involves measurement of the interference signal at a reference sensor; this signal can then be subtracted from the glucose sensor signal (post-run) to give a corrected measurement of the glucose concentration. The detection system consists of a thin layer cell with dual glassy carbon working electrodes. One electrode was surface modified to act asglucose biosensor by immobilisation of glucose oxidase (GOx) (from Aspergillus niger) with 1% glutaraldehyde and bovine serum albumin. The second electrode (glucose oxidase omitted) was utilised to measure the interference signal responding only to electroactive species present in the injected sample. A computer controlled multichannel potentiostat was used for potential application and current monitoring duties. The sensor responses were saved in ASCII format to facilitate post-run analysis in Microsoft Excel. Cyclic voltammetry (CV) was utilised to investigate the manner in which the interference signal contributed to the total signal obtained at the biosensor in the presence of glucose. The kinetic parameters I_max and the apparent Michaelis-Menten constant, K′_m, were calculated for the sensor operating under flow-injection conditions.     

The potential use of hydrazine as an alternative to peroxidase in a biosensor: comparison between hydrazine and HRP-based glucose sensors

The potential use of hydrazine sulfate was examined for the catalytic reduction of enzymatically generated H2O2 in a biosensor system. The performance of the hydrazine-based sensor was compared with an HRP-based glucose sensor as a model of a biosensor. Hydrazine and HRP were covalently immobilized onto a conducting polymer layer with glucose oxidase. The direct electron transfer reactions of the immobilized hydrazine and HRP onto the poly-5,2':5,2'-terthiophene-3'-carboxylic acid (poly-TTCA) layer were investigated by using cyclic voltammetric method and the electron transfer rate constants were determined. The glucose oxidase- and hydrazine-immobilized sensor efficiently reduced the enzymatically generated H2O2 at -0.15 V versus Ag/AgCl. The surface of this GOx/hydrazine/poly-TTCA-based glucose sensor was characterized by QCM, SEM, and ESCA. Glucose-sensing properties were studied using cyclic voltammetric and chronoamperometric techniques. Various experimental parameters were optimized according to the amount of hydrazine, pH, the temperature, and the applied potential. A linear calibration plot was obtained in the concentration range between 0.1 and 15.0 mM, and the detection limit was determined to be 40.0+/-7.0 microM. Interferences from other biological compounds were studied. The long-term stability of the GOx/hydrazine sensor was better than that of the one based on a GOx/HRP biosensor. The proposed glucose sensor was successfully applied to human whole blood and urine samples for the detection of glucose.     

Critical assessment of the Quartz Crystal Microbalance with Dissipation as an analytical tool for biosensor development and fundamental studies: Metallophthalocyanine-glucose oxidase biocomposite sensors

One of the challenges in electrochemical biosensor design is gaining a fundamental knowledge of the processes underlying immobilisation of the molecules onto the electrode surface. This is of particular importance in biocomposite sensors where concerns have arisen as to the nature of the interaction between the biological and synthetic molecules immobilised. We examined the use of the Quartz Crystal Microbalance with Dissipation (QCM-D) as a tool for fundamental analyses of a model sensor constructed by the immobilisation of cobalt(II) phthalocyanine (TCACoPc) and glucose oxidase (GOx) onto a gold-quartz electrode (electrode surface) for the enhanced detection of glucose. The model sensor was constructed in aqueous phase and covalently linked the gold surface to the TCACoPc, and the TCACoPc to the GOx, using the QCM-D. The aqueous metallophthalocyanine (MPc) formed a multi-layer over the surface of the electrode, which could be removed to leave a monolayer with a mass loading that compared favourably to the theoretical value expected. Analysis of frequency and dissipation plots indicated covalent attachment of glucose oxidase onto the metallophthalocyanine layer. The amount of GOx bound using the model system compared favourably to calculations derived from the maximal amperometric functioning of the electrochemical sensor (examined in previously-published literature, Mashazi, P.N., Ozoemena, K.I., Nyokong, T., 2006. Electrochim. Acta 52, 177-186), but not to theoretical values derived from dimensions of GOx as established by crystallography. The strength of the binding of the GOx film with the TCACoPc layer was tested by using 2% SDS as a denaturant/surfactant, and the GOx film was not found to be significantly affected by exposure to this. This paper thus showed that QCM-D can be used in order to model essential processes and interactions that dictate the functional parameters of a biosensor.     

Immobilization of glucose oxidase on electrodeposited nickel oxide nanoparticles: direct electron transfer and electrocatalytic activity

For the first time glucose oxidase (GOx) was successfully co-deposited on nickel-oxide (NiO) nanoparticles at a glassy carbon electrode. In this paper we present a simple fabrication method of biosensor which can be easily operated without using any specific reagents. Cyclic voltammetry was used for electrodeposition of NiO nanoparticle and GOx immobilization. The direct electron transfer of immobilized GOx displays a pair of well defined and nearly reversible redox peaks with a formal potential (E(0')) of -0.420 V in pH 7 phosphate buffer solution and the response shows a surface controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (k(s)) of GOx immobilized on NiO film glassy carbon electrode are 9.45 x 10(-13)mol cm(-2) and 25.2+/-0.5s(-1), indicating the high enzyme loading ability of the NiO nanoparticles and great facilitation of the electron transfer between GOx and NiO nanoparticles. The biosensor shows excellent electrocatalytical response to the oxidation of glucose when ferrocenmethanol was used as an artificial redox mediator. Furthermore, the apparent Michaelis-Menten constant 2.7 mM, of GOx on the nickel oxide nanoparticles exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. In addition, this glucose biosensor shows fast amperometric response (3s) with the sensitivity of 446.2nA/mM, detection limit of 24 microM and wide concentration range of 30 microM to 5mM. This biosensor also exhibits good stability, reproducibility and long life time.     

Multilayer assembly of positively charged polyelectrolyte and negatively charged glucose oxidase on a 3D Nafion network for detecting glucose

In this paper, a novel amperometric glucose biosensor was constructed by alternative self-assembly of positively charged poly(diallydimethylammonium chloride) (PDDA) and negatively charged glucose oxidase (GOx) onto a 3D Nafion network via electrostatic adsorption. The amount of Nafion in the electrode and the number of the (PDDA/GOx)_n multilayers were optimized to develop a sensitive and selective glucose biosensor. Under optimal conditions, the glucose biosensor with (PDDA/GOx)₅ multilayers exhibited remarkable electrocatalytic activity, capable of detecting glucose with enhanced sensitivity of 9.55 μA/mM cm² and a commendably low detection limit of 20 μM (S/N = 3). A linear response range of 0.05–7 mM (a linear correlation coefficient of 0.9984, n = 20) was achieved. In addition, the glucose biosensor demonstrated superior selectivity towards glucose over some interferents, such as ascorbic acid (AA) and uric acid (UA), at an optimized detection potential of 0.6 V versus Ag/AgCl reference.     

Interfacial electron transfer of glucose oxidase on poly(glutamic acid)-modified glassy carbon electrode and glucose sensing

The interfacial electron transfer of glucose oxidase (GOx) on a poly(glutamic acid)-modified glassy carbon electrode (PGA/GCE) was investigated. The redox peaks measured for GOx and flavin adenine dinucleotide (FAD) are similar, and the anodic peak of GOx does not increase in the presence of glucose in a mediator-free solution. These indicate that the electroactivity of GOx is not the direct electron transfer (DET) between GOx and PGA/GCE and that the observed electroactivity of GOx is ascribed to free FAD that is released from GOx. However, efficient electron transfer occurred if an appropriate mediator was placed in solution, suggesting that GOx is active. The PGA/GCE-based biosensor showed wide linear response in the range of 0.5–5.5 mM with a low detection limit of 0.12 mM and high sensitivity and selectivity for measuring glucose.     

Electrochemical studies of glucose oxidase immobilized on glutathione coated gold nanoparticles

Glutathione (L-gamma-glutamyl-L-cysteinyl-L-glycine; GSH) forms a surface monolayer on gold nanoparticles by tethering via sulfur bonds (Au:GSH). In the present study, glucose oxidase (GOx; EC 1.1.3.4) was immobilized by covalent chemical coupling reactions on to Au:GSH nanoparticles and the enzyme coupled nanoparticles formed a stable colloid (stable for several weeks) in water. The immobilized enzyme was investigated for electrochemical characteristics to monitor the FAD (prosthetic group of the GOx) redox potentials. Various concentrations of substrate (glucose) were added to check the oxidation characteristics. It was observed that with increase in substrate concentrations, the oxidation rate increased proportionally with the current. The present study demonstrated that GOx was effectively coupled to the gold nanoparticle (Au:GSH). The coupled nanoparticle system could be used in a potential biosensor application. Similarly, other enzymes (e.g., horseradish peroxidase) could be immobilized to the Au:GSH nanoparticles via the peptide arm (GSH) to achieve the desired characteristics needed for a specific application in biosensor.     

An autoclavable glucose biosensor for microbial fermentation monitoring and control

The design, construction, and characterization of a prototype-regenerable glucose biosensor based on the reversible immobilization of glucose oxidase (GOx) using cellulose binding domain (CBD) technology is described. GOx, chemically linked to CBD, is immobilized by binding to a cellulose matrix on the sensor-indicating electode. Enzyme immobilization can be reversed by perfusing the cellulose matrix with a suitable eluting solution. An autocavable sensor membrane system is employed which is shown to be practical for use in real microbial fermentations. The prototype glucose biosensor was used without failure or deterioration during fed-batch fermentations of Escherichia coli reaching a maximum cell density of 85 g (dry weight)/L. Medium glucose concentration based on sensor output correlated closely with off-line glucose analysis and was controlled manually at 0.44 +/- 0.2 g/L for 2 h based on glucose sensor output. The sensor enzyme component could be eluted and replaced without interrupting the fermentation. To our knowledge, no other in situ biosensor has been used for such an extended period of time in such a high-cell-density fermentation. (c) 1995 John Wiley & Sons, Inc.     

Amperometric glucose biosensor based on layer-by-layer covalent attachment of AMWNTs and IO(4)(-)-oxidized GOx

Multi-wall carbon nanotubes (MWNTs) functionalized with amino groups were prepared via silane treatment using 3-aminopropyltrimethoxysilane (APS) as a silane-coupling agent. The resultant amino terminated MWNTs (AMWNTs) were applied to construct glucose biosensors with IO(4)(-)-oxidized glucose oxidase (IO(4)(-)-oxidized GOx) through the layer-by-layer (LBL) covalent self-assembly method without any cross-linker. Scanning electron microscopy (SEM) indicated that the assembled AMWNTs were almost in a form of small bundles or single nanotubes, and the surface density increased uniformly with the number of GOx/AMWNTs bilayers. From the analysis of voltammetric signals, a linear increment of the coverage of GOx per bilayer was estimated. The resulting biosensor showed excellent catalytic activity towards the electroreduction of dissolved oxygen at low overvoltage, based on which glucose concentration was monitored conveniently. The enzyme electrode exhibited good electrocatalytic response towards the glucose and that response increased with the number of GOx/AMWNTs bilayers, suggesting that the analytical performance such as sensitivity and detection limit of the glucose biosensors could be tuned to the desired level by adjusting the number of deposited GOx/AMWNTs bilayers. The biosensor constructed with four bilayers of GOx/AMWNTs showed high sensitivity of 7.46muAmM(-1)cm(-2) and the detection limit of 8.0muM, with a fast response less than 10s. Because of relative low applied potential, the interference from other electro-oxidizable compounds was minimized, which improved the selectivity of the biosensors. Furthermore, the obtained enzyme electrodes also showed remarkable stability due to the covalent interaction between the GOx and AMWNTs.     

Preserved enzymatic activity of glucose oxidase immobilized on unmodified electrodes for glucose detection

Glucose sensing electrodes have been realized by immobilizing glucose oxidase (GOx) on unmodified edge plane of highly oriented pyrolytic graphite (epHOPG) and the native oxide of heavily doped silicon (SiO2/Si). Both kinds of electrode show direct interfacial electron transfer due to the redox process of the immobilized GOx. The measured formal potential of the redox process agrees with that of the native enzyme, suggesting that the immobilized GOx has retained its enzymatic activity. The electron transfer rates of the GOx immobilized electrode are 2s(-1) for GOx/epHOPG electrode and 7.9s(-1) for GOx/SiO2/Si electrode, which are greater than those for which GOx is immobilized on modified electrodes, probably due to the fact that the enzyme makes direct contact to electrode surface. The preservation of the enzymatic activity of the immobilized GOx has been confirmed by observing the response of the GOx/epHOPG and GOx/SiO2/Si electrodes to glucose with a detection limit of 0.050 mM. The response signals the catalyzed oxidation of glucose and, therefore, confirms that the immobilized GOx retained its enzymatic activity. The properties of the electrode as a glucose sensor are presented.     

Miniaturized glucose biosensor modified with a nitric oxide-releasing xerogel microarray

An enzyme-based glucose biosensor modified to release nitric oxide (NO) via a xerogel microarray is reported. The biosensor design is as follows: (1) glucose oxidase (GOx) is immobilized in a methyltrimethoxysilane (MTMOS) xerogel layer; (2) a blended polyurethane/hydrophilic polyurethane coating prevents enzyme leaching and imparts selectivity for glucose; and (3) micropatterned xerogel lines (5 microm wide) separated by distances of 5 or 20 microm provide NO-release capability. This configuration allows for increased glucose sensitivity relative to sensors modified with NO-releasing xerogel films since significant portions of the sensor surface remain unmodified. Glucose diffusion to the GOx layer is thus less inhibited. The micropatterned NO-releasing biosensors generate sufficient NO levels to reduce both Pseudomonas aeruginosa and platelet adhesion without significantly compromising the enzymatic activity of GOx. The glucose response, linearity and stability of the NO-releasing micropatterned sensors are reported.     

A biosensor based on the self-entrapment of glucose oxidase within biomimetic silica nanoparticles induced by a fusion enzyme

We constructed a fusion protein (GOx-R5) consisting of R5 (a polypeptide component of silaffin) and glucose oxidase (GOx) that was expressed in Pichia pastoris. Silaffin proteins are responsible for the formation of a silica-based cell matrix of diatoms, and synthetic variants of the R5 protein can perform silicification in vitro[1]. GOx secreted by P. pastoris was self-immobilized (biosilicification) in a pH 5 citric buffer using 0.1 M tetramethoxysilane as a silica source. This self-entrapment property of GOx-R5 was used to immobilize GOx on a graphite rod electrode. An electric cell designed as a biosensor was prepared to monitor the glucose concentrations. The electric cell consisted of an Ag/AgCl reference electrode, a platinum counter electrode, and a working electrode modified with poly(neutral red) (PNR)/GOx/Nafion. Glucose oxidase was immobilized by fused protein on poly(neutral red) and covered by Nafion to protect diffusion to the solution. The morphology of the resulting composite PNR/GOx/Nafion material was analyzed by scanning electron microscopy (SEM). This amperometric transducer was characterized electrochemically using cyclic voltammetry and amperometry in the presence of glucose. An image produced by scanning electron microscopy supported the formation of a PNR/GOx complex and the current was increased to 1.58 μA cm⁻¹ by adding 1 mM glucose at an applied potential of −0.5 V. The current was detected by way of PNR-reduced hydrogen peroxide, a product of the glucose oxidation by GOx. The detection limit was 0.67 mM (S/N = 3). The biosensor containing the graphite rod/PNR/GOx/Nafion detected glucose at various concentrations in mixed samples, which contained interfering molecules. In this study, we report the first expression of R5 fused to glucose oxidase in eukaryotic cells and demonstrate an application of self-entrapped GOx to a glucose biosensor.     

Supramolecular architecture based on the self-assembling of multiwall carbon nanotubes dispersed in polyhistidine and glucose oxidase: Characterization and analytical applications for glucose biosensing

We report for the first time the development of a sensitive and selective glucose biosensor based on the self-assembling of multiwall carbon nanotubes (MWCNTs) dispersed in polyhistidine (Polyhis) and glucose oxidase (GOx) on glassy carbon electrodes (GCE). The supramolecular architecture was characterized by SEM, FT-IR and electrochemical techniques. The optimum multistructure was obtained with five (MWCNT-Polyhis/GOx) bilayers and one layer of Nafion as anti-interferent barrier. The sensitivity at 0.700V was (1.94±0.03) mAM(-1) (r=0.9991), with a linear range between 0.25 and 5.00mM, a detection limit of 2.2μM and a quantification limit of 6.7μM with minimum interference from lactose (1.5%), maltose (5.7%), galactose (1.2%), ascorbic acid (1.0%), and uric acid (3.3%). The biocatalytic layer demonstrated to be highly reproducible since the R.S.D. for 10 successive amperometric calibrations using the same surface was 3.6%. The sensitivity of the biosensor after 15 day storage at 4°C remained at 90% of its original value. The combination of the excellent dispersing properties and polycationic nature of polyhistidine, the stability of the MWCNT-Polyhis dispersion, the electrocatalytic properties of MWCNTs, the biocatalytic specificity of GOx, and the permselective properties of Nafion have allowed building up a sensitive, selective, robust, reproducible and stable glucose amperometric biosensor for the quantification of glucose in milk samples.     

Application of hydrophobic palladium nanoparticles for the development of electrochemical glucose biosensor

An amperometric glucose biosensor based on an n-alkylamine-stabilized palladium nanoparticles (PdNPs)-glucose oxidase (GOx) modified glassy carbon (GC) electrode has been successfully fabricated. PdNPs were initially synthesized by a biphase mixture of water and toluene method using n-alkylamines (dodecylamine, C??-NH? and octadecylamine, C??-NH?) as stabilizing ligands. The performance of the PdNPs-GOx/GC biosensor was studied by cyclic voltammetry. The optimum working potential for amperometric measurement of glucose in pH 7.0 phosphate buffer solution is -0.02 V (vs. Ag/AgCl). The analytical performance of the biosensor prepared from C??-PdNPs-GOx is better than that of C??-PdNPs-GOx. The C??-PdNPs-GOx/GC biosensor exhibits a fast response time of ca. 3s, a detection limit of 3.0 μM (S/N=3) and a linear range of 3.0 μM-8.0 mM. The linear dependence of current density with glucose concentration is 70.8 μA cm?2 mM?1. The biosensor shows good stability, repeatability and reproducibility. It has been successfully applied to determine the glucose content in human blood serum samples.     

Electrodeposition of polypyrrole-multiwalled carbon nanotube-glucose oxidase nanobiocomposite film for the detection of glucose

A nanobiocomposite film consisted of polypyrrole (PPy), functionalized multiwalled carbon nanotubes (cMWNTs), and glucose oxidase (GOx) were electrochemically synthesized by electrooxidation of 0.1M pyrrole in aqueous solution containing appropriate amounts of cMWNTs and GOx. Potentiostatic growth profiles indicate that the anionic cMWNTs is incorporated within the growing PPy-cMWNTs nanocomposite for maintaining its electrical neutrality. The morphology of the PPy-cMWNTs nanocomposite was characterized by scanning electron microscopy (SEM). The PPy-cMWNTs nanocomposite was deposited homogeneously onto glassy carbon electrode. The amperometric responses vary proportionately to the concentration of hydrogen peroxide at the PPy-cMWNTs nanocomposite modified electrode at an operating potential of 0.7V versus Ag/AgCl (3M). The results indicate that the electroanalytical PPy-cMWNTs-GOx nanobiocomposite film was highly sensitive and suitable for glucose biosensor based on GOx function. The GOx concentration within the PPy-cMWNTs-GOx nanobiocomposite and the film thickness are crucial for the performance of the glucose biosensor. The amperometric responses of the optimized PPy-cMWNTs-GOx glucose biosensor (1.5 mgmL(-1) GOx, 141 mCcm(-2) total charge) displayed a sensitivity of 95 nAmM(-1), a linear range up to 4mM, and a response time of about 8s.     

Glucose Biosensor Based on a Glassy Carbon Electrode Modified with Polythionine and Multiwalled Carbon Nanotubes

A novel glucose biosensor was fabricated. The first layer of the biosensor was polythionine, which was formed by the electrochemical polymerisation of the thionine monomer on a glassy carbon electrode. The remaining layers were coated with chitosan-MWCNTs, GOx, and the chitosan-PTFE film in sequence. The MWCNTs embedded in FAD were like “conductive wires” connecting FAD with electrode, reduced the distance between them and were propitious to fast direct electron transfer. Combining with good electrical conductivity of PTH and MWCNTs, the current response was enlarged. The sensor was a parallel multi-component reaction system (PMRS) and excellent electrocatalytic performance for glucose could be obtained without a mediator. The glucose sensor had a working voltage of −0.42 V, an optimum working temperature of 25°C, an optimum working pH of 7.0, and the best percentage of polytetrafluoroethylene emulsion (PTFE) in the outer composite film was 2%. Under the optimised conditions, the biosensor displayed a high sensitivity of 2.80 µA mM⁻¹ cm⁻² and a low detection limit of 5 µM (S/N = 3), with a response time of less than 15 s and a linear range of 0.04 mM to 2.5 mM. Furthermore, the fabricated biosensor had a good selectivity, reproducibility, and long-term stability, indicating that the novel CTS+PTFE/GOx/MWCNTs/PTH composite is a promising material for immobilization of biomolecules and fabrication of third generation biosensors.     

Offline glucose biomonitoring in yeast culture by polyamidoamine/cysteamine-modified gold electrodes

This article deals with the use of pyranose oxidase (PyOx) and glucose oxidase (GOx) enzymes in amperometric biosensor design and their application in monitoring fermentation processes with the combination of flow injection analysis (FIA). The amperometric studies were carried out at -0.7 V by following the oxygen consumption due to the enzymatic reactions for both batch and FIA modes. Optimization studies (enzyme amounts and pH) and analytical parameters such as linearity, repeatability, effect of interference, storage, and operational stabilities have been studied. Under optimized conditions, for the PyOx-based biosensor, linear graph was obtained from 0.025 to 0.5 mM glucose in phosphate buffer (50 mM) at pH 7.0 with the equation of y = 3.358x + 0.028 and R(2) = 0.998. Linearity was found to be 0.01-1.0 mM in citrate buffer (50 mM and pH 4.0) with the equation of y = 1.539x + 0.181 and R(2) = 0.992 for the GOx biosensor. Finally, these biosensor configurations were further evaluated in a conventional flow injection system. Results from batch experiments provide a guide to design sensitive, stable, and interference-free biosensors for FIA mode. Biosensor stability, dynamic range, and repeatability were also studied in FIA conditions, and the applicability for the determination of glucose in fermentation medium could be successfully demonstrated. The FIA-combined glucose biosensor was used for the offline monitoring of yeast fermentation. The obtained results correlated well with HPLC measurements.     

Nanocrystalline diamond modified gold electrode for glucose biosensing

Boron-doped diamond has drawn much attention in electrochemical sensors. However there are few reports on non-doped diamond because of its weak conductivity. Here, we reported a glucose biosensor based on electrochemical pretreatment of non-doped nanocrystalline diamond (N-NCD) modified gold electrode for the selective detection of glucose. N-NCD was coated on gold electrode and glucose oxidase (GOx) was immobilized onto the surfaces of N-NCD by forming amide linkages between enzyme amine residues and carboxylic acid groups on N-NCD. The anodic pretreatment of N-NCD modified electrode not only promoted the electron transfer rate in the N-NCD thin film, but also resulted in a dramatic improvement in the reduction of the dissolved oxygen. This performance could be used to detect glucose at negative potential through monitoring the current change of oxygen reduction. The biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents, such as ascorbic acid (AA), acetaminophen (AP) and uric acid (UA). A wide linear calibration range from 10 microM to 15 mM and a low detection limit of 5 microM were achieved for the detection of glucose.     

Evaluation of glucose sensitive affinity binding assay entrapped in fluorescent dissolved‐core alginate microspheres

The feasibility of dissolved‐core alginate‐templated fluorescent microspheres as “smart tattoo” glucose biosensors was investigated in simulated interstitial fluid (SIF). The sensor works on the principle of competitive binding and fluorescence resonance energy transfer. The sensor consists of multilayer thin film coated alginate microspheres incorporating dye‐labeled glucose receptor and competing ligand within the partially dissolved alginate core. In this study, different approaches for the sensing and detection chemistry were studied, and the response of encapsulated reagents was compared with the solution‐phase counterparts. The glucose sensitivity of the encapsulated TRITC‐Con A/FITC‐dextran (500 kDa) assay in DI water was estimated to be 0.26%/mM glucose while that in SIF was observed to be 0.3%/mM glucose. The glucose sensitivity of TRITC‐apo‐GOx/FITC‐dextran (500 kDa) assay was estimated to be 0.33%/mM glucose in DI water and 0.5%/mM glucose in SIF and both demonstrated a response in the range of 0–50 mM glucose. Therefore, it is hypothesized that the calcium ion concentration outside the microsphere (in the SIF) does not interfere with the response sensitivity. The sensor response was observed to exhibit a maximum response time of 120 s. The system further exhibited a sensitivity of 0.94%/mM glucose with a response in range of 0–50 mM glucose, using near‐infrared dyes (Alexa Fluor‐647‐labeled dextran as donor and QSY‐21‐conjugated apo‐GOx as acceptor), thereby making the sensor more amenable to in vivo use, when implanted in scattering tissue. Biotechnol. Bioeng. 2009; 104: 1075–1085. © 2009 Wiley Periodicals, Inc.