Amperometric Glucose Biosensor Research Articles

Iodine-doped reduced graphene oxide and titanium dioxide nanocomposite as effective amperometric glucose biosensor

The current study fabricated a non-enzymatic glucose sensor based on iodine-doped reduced graphene oxide with titanium dioxide (I-rGO@TiO2) nanocomposite. Initially, the sol-gel and thermal reduction methods synthesized titanium dioxide (TiO2) nanoparticles and reduced graphene oxide (rGO). Then, the hydrothermal technique was utilized to synthesize a composite of I-rGO@TiO2 by combining I-rGO and TiO2 in a 1:4 ratio. The XRD spectrum and TEM images revealed that in the I-rGO@TiO2 nanocomposite, nanocrystalline anatase titanium is randomly distributed on the I-rGO sheets. Fourier transforms the infrared spectrum of nanocomposite shows the presence of titanium and oxygen bond characteristics peak between 400 and 850 cm−1. Iodine molecules peak at 100 cm−1 were obtained in Raman spectra. The AC conductivity and dielectric properties of the nanocomposite were analyzed. For the sensor fabrication, the indium tin oxide electrode surface is modified by I-rGO@TiO2, and the electrochemical performance was examined. At room temperature, the sensor demonstrated a wider linear detection range (0.5−10 mM). The lower detection limit of the sensor was 0.23 μM (S/N = 3), and the sensitivity was 221.69 μA mM−1 cm−2. The I-rGO@TiO2 nanocomposite shows a positive temperature coefficient via the thermal activation of charge carriers and a conductivity of 3.82 × 10−5 Ω−1m−1 at 200 °C. Additionally, the antibacterial properties was evaluated, and dose-dependent properties were observed towards E. coli and Bacillus subtilis bacterium.

Towards a Self-Powered Amperometric Glucose Biosensor Based on a Single-Enzyme Biofuel Cell.

This paper describes the study of an amperometric glucose biosensor based on an enzymatic biofuel cell consisting of a bioanode and a biocathode modified with the same enzyme-glucose oxidase (GOx). A graphite rod electrode (GRE) was electrochemically modified with a layer of Prussian blue (PB) nanoparticles embedded in a poly(pyrrole-2-carboxylic acid) (PPCA) shell, and an additional layer of PPCA and was used as the cathode. A GRE modified with a nanocomposite composed of poly(1,10-phenanthroline-5,6-dione) (PPD) and gold nanoparticles (AuNPs) entrapped in a PPCA shell was used as an anode. Both electrodes were modified with GOx by covalently bonding the enzyme to the carboxyl groups of PPCA. The developed biosensor exhibited a wide linear range of 0.15-124.00 mM with an R2 of 0.9998 and a sensitivity of 0.16 μA/mM. The limit of detection (LOD) and quantification (LOQ) were found to be 0.07 and 0.23 mM, respectively. The biosensor demonstrated exceptional selectivity to glucose and operational stability throughout 35 days, as well as good reproducibility, repeatability, and anti-interference ability towards common interfering substances. The studies on human serum demonstrate the ability of the newly designed biosensor to determine glucose in complex real samples at clinically relevant concentrations.

Green synthesis of silver nanoparticles and designing a new amperometric biosensor to determine glucose levels

The high-level of glucose in daily nutrition causes diabetes (Diabetes mellitus) and obesity. It is also important to determine glucose levels in food production processes for quality control methods. Biosensors are bio analytical devices that provides cheap, simple, analyses and have a fast response time. Silver nanoparticles are used to modify electrodes in bio-sensing glucose. The nanoparticles could be synthesized via the green synthesis technique. In this technique, plants could be used both reducing and stabilizing agents. Agricultural waste, an environmental problem, is increasing with the population. These wastes are a good natural source and have the potential for green synthesis of silver nanoparticles to use in biosensor applications. In this study, a new amperometric glucose biosensor was designed. For this purpose, carbon paste electrode (CPE) was modified by green synthesized waste tea based silver nanoparticles (WT-AgNPs) and the glucose oxidase enzyme was immobilized on MCPE by the cross-linking. Glucose determination was performed based on the reduction of hydrogen peroxide at +0.4 V versus Ag/AgCl. The linear working range was determined as 0.10–1.0 µM. In addition, the designed biosensor was applied to detect the amount of glucose in a commercial fruit juice. The results showed that the designed biosensor has low detection limit, very good reproducibility, selectivity, and almost long shelf life.

The Development of Reagentless Amperometric Glucose Biosensor Based on Gold Nanostructures, Prussian Blue and Glucose Oxidase.

Precise blood glucose detection plays a crucial role in diagnosing and medicating diabetes, in addition to aiding diabetic patients in effectively managing their condition. In this research, a first-generation reagentless amperometric glucose biosensor was developed by combining the graphite rod (GR) electrode modification by gold nanostructures (AuNS) and Prussian blue (PB) with glucose oxidase (GOx)-an enzyme that can oxidize glucose and produce H2O2. Firstly, AuNS was electrochemically deposited on the GR electrode (AuNS/GR), and then PB was electrochemically synthesized on the AuNS/GR electrode (PB/AuNS/GR). Finally, GOx was immobilized over the PB/AuNS nanocomposite with the assistance of Nafion (Nf) (Nf-GOx/PB/AuNS/GR). An application of PB in the design of a glucose biosensor enables an easy electrochemical reduction and, thus, the determination of the H2O2 produced during the GOx-catalyzed oxidation of glucose in the sample at a low operation potential of -0.05 V vs. Ag/AgCl/KCl3 mol L-1. In addition, AuNS increased the electrochemically active surface area, improved the GOx immobilization and ensured a higher analytical signal. The developed glucose biosensor based on the Nf-GOx/PB/AuNS/GR electrode exhibited a wide linear range, from 0.025 to 1 mmol L-1 of glucose, with a 0.0088 mmol L-1 limit of detection, good repeatability and high selectivity over electroactive interfering substances. The developed biosensor is convenient for the determination of glucose in the physiological environment.

Response surface methodology use in construction of polianiline-coated carbon paste electrode-based biosensor: Modification and characterization.

In this study, the effect of amperometric glucose biosensor construction and using conditions on the current response was investigated in detail applying experimental design. Polyaniline (PANI) was synthesized on the carbon paste electrode (CPE) surface using the cyclic voltammetry technique in sodium oxalate (NaOx ) electrolyte medium, and an amperometric biosensor was constructed by immobilizing glucose oxidase (GOD). Biosensor preparation (aniline, GOD and NaOx concentrations, and scan rate) and operating conditions (pH and applied potential) were optimized by Box-Behnken and optimal designs, respectively, via State Ease Design Expert 7.0.1.1 software. ANOVA analyses showed that among the biosensor preparation parameters, the NaOx concentration has the highest effect on the current measured in the presence of glucose, whereas in the optimization of pH and potential parameters applied in current measurement studies, it has been revealed that pH has a very high effect on the measured current. Several compounds, such as MWCNT, two different ionic liquids and two different organic molecules were added to carbon paste, and, among them, 2-cyanoethylpyrrole (CPy) enhanced the efficacy highly, most probably due to its polymerization in the paste and increasing the electron transfer rate of the CPE. Sucrose- and lactose-sensitive biosensors were also constructed by co-immobilizing GOD with invertase (INV) or β-galactosidase, respectively, onto modified CPE, and sensitivities to their substrates were shown by cyclic voltammetry and impedance analysis. CPy modification caused an increase in the current values, and also Imax /KM values increased approximately 11.8, 7.83, and 2.56 times for glucose-, sucrose-, and lactose-sensitive CPEs, respectively.

An Amperometric Glucose Biosensor Composed of Prussian Blue, Nafion, and Glucose Oxidase Studied by Flow Injection Analysis

The construction and characterization of a glucose biosensor has been implemented in an instrumental chemical analysis course to provide students experience with chemical sensing, electroanalytical methods, and flow injection analysis (FIA). The glucose biosensor was assembled on a glassy carbon electrode by depositing a layer of Prussian blue (PB) electrocatalyst followed by a layer of glucose oxidase (GOx) immobilized in a Nafion film. GOx catalyzed the oxidation of glucose in the presence of dissolved oxygen to yield gluconic acid and hydrogen peroxide. The hydrogen peroxide produced was then electrocatalytically reduced at the PB film with a mild applied potential. The measured cathodic current provided the analytical signal for the glucose biosensor, which was applied to the quantification of glucose levels in soft drinks using FIA techniques. This experiment exposes students to several electroanalytical methods, including amperometry, cyclic voltammetry, and chronocoulometry, as well as methods that are used to measure biosensor response, deposit the PB film, measure the PB film coverage, and examine its electrocatalytic properties. In addition, students gain experience with FIA and the application of an enzyme-based biosensor.

Tethering zwitterionic polymer coatings to mediated glucose biosensor enzyme electrodes can decrease sensor foreign body response yet retain sensor sensitivity to glucose

Foreign body response (FBR) is a major challenge that affects implantable biosensors and medical devices, including glucose biosensors, leading to a deterioration in device response over time. Polymer shields are often used to mitigate this issue. Zwitterionic polymers (ZPs) are a promising class of materials that reduce biofouling of implanted devices. A series of ZPs each containing tetherable epoxide functional groups was synthesised for application as a polymer shield for eventual application as implantable glucose biosensors. The polymer shields were initially tested for the ability to resist fibrinogen adsorption and fibroblast adhesion. All synthesised ZPs showed comparable behaviour to a commercial Lipidure ZP in resisting fibrinogen adsorption. Nafion, a common anionic shield used against electrochemical interferents, showed higher protein adsorption and comparable cell adhesion resistance as uncoated control surfaces. However, a poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) (MPC)-type ZP showed similar behaviour to Lipidure, with approximately 50% reduced fibrinogen adsorption and 80% decrease in fibroblast adhesion compared to uncoated controls. An MPC-coated amperometric glucose biosensor showed comparable current density and a 1.5-fold increase in sensitivity over an uncoated control biosensor, whereas all other polymer shields tested, including Lipidure, Nafion and a poly(ethyleneglycol) polymer, resulted in lower sensitivity and current density. Collectively, these characteristics make MPC-polymer shield coatings an appealing possibility for use in implantable glucose sensors and other implanted devices with the aim of reducing FBR while maintaining sensor performance.

Mathematical Modelling of Amperometric Glucose Biosensor Based on Immobilized Enzymes: New Approach of Taylors Series Method

Mathematical Modelling of Amperometric Glucose Biosensor Based on Immobilized Enzymes: New Approach of Taylors Series Method

Contrasting dose-dependent effects of acute intravenous methamphetamine on lateral hypothalamic extracellular glucose dynamics in male and female rats.

Glucose is the brain's primary energetic resource. The brain's use of glucose is dynamic, balancing delivery from the neurovasculature with local metabolism. Although glucose metabolism is known to differ in humans with and without methamphetamine use disorder (MUD), it is unknown how central glucose regulation changes with acute methamphetamine experience. Here, we determined how intravenous methamphetamine regulates extracellular glucose levels in a brain region implicated in MUD-like behavior, the lateral hypothalamus (LH). We measured extracellular LH glucose in awake adult male and female drug-naive Wistar rats using enzyme-linked amperometric glucose biosensors. Changes in LH glucose were monitored during a single session after: 1) natural nondrug stimuli (novel object presentation and a tail-touch), 2) increasing cumulative doses of intravenous methamphetamine (0.025, 0.05, 0.1, and 0.2 mg/kg), and 3) an injection of 60 mg of glucose. We found second-scale fluctuations in LH glucose in response to natural stimuli that differed by both stimulus type and sex. Although rapid, second-scale changes in LH glucose during methamphetamine injections were variable, slow, minute-scale changes following most injections were robust and resulted in a reduction in LH glucose levels. Dose and sex differences at this timescale indicated that female rats may be more sensitive to the impact of methamphetamine on central glucose regulation. These findings suggest that the effects of MUD on healthy brain function may be linked to how methamphetamine alters extracellular glucose regulation in the LH and point to possible mechanisms by which methamphetamine influences central glucose metabolism more broadly.NEW & NOTEWORTHY Enzyme-linked glucose biosensors were used to monitor lateral hypothalamic (LH) extracellular fluctuations during nondrug stimuli and intravenous methamphetamine injections in drug-naive awake male and female rats. Second-scale glucose changes occurred after nondrug stimuli, differing by modality and sex. Robust minute-scale decreases followed most methamphetamine injections. Sex differences at the minute-scale indicate female central glucose regulation is more sensitive to methamphetamine effects. We discuss likely mechanisms underlying these fluctuations, and their implications in methamphetamine use disorder.

An Oxygen Insensitive Amperometric Glucose Biosensor Based on An Engineered Cellobiose Dehydrogenase: Direct versus Mediated Electron Transfer Responses

AbstractCellobiose dehydrogenase (CDH) is capable of oxidizing cellobiose and related carbohydrates and generating electrical current at carbon‐based electrodes through direct electron transfer (DET) or mediated electron transfer (MET) mechanisms. As a result, CDHs have been utilized as biocatalysts in biosensors and biofuel cell anodes. A novel engineered ascomycetous Class II CDH with enhanced glucose activity was tested as a bioelectrocatalyst for application to DET or MET‐based glucose biosensors with the electrode component amount selection optimized for maximum current in 5 mM glucose solutions. The optimised DET biosensor showed a similar sensitivity and 3‐fold lower KM,app when compared to non‐optimised DET sensor based on the same engineered CDH. The optimized MET biosensor had a similar KM,app to non‐optimized MET biosensor. However, it showed 15‐fold improvement in jmax and 17‐fold improvement in sensitivity over the DET biosensor. The sensor signals are not affected by the presence of oxygen, although operation in artificial serum results in 43 % and 28 % lower sensitivity for the DET and MET sensors, respectively. While no individually tested potential interferent breaches a mean absolute relative difference of 20 % of the current, the cumulative co‐operative effect in complex media, such as artificial serum, decreases the glucose oxidation current signal.

Enhancement of Glucose Oxidase-Based Bioanode Performance by Comprising Spirulina platensis Microalgae Lysate

In this study, Spirulina platensis-based lysate was used as a biological redox mediator to design glucose oxidase (GOx) based biofuel cell bioanode. Chemically oxidized multi-walled carbon nanotubes (CNT) were deposited on carbon-electrode and were covered with eco-friendly algae cell-based lysate that facilitated the electron transfer and served as a biocompatible matrix for enzyme immobilization, which reduced the inactivation of GOx by CNT. The designed GC/PEI/CNT/S.p./GOx bioanode exhibited an open circuit potential (OCP) of −262 mV vs Ag/AgCl(3MKCl) in the presence of 12.5 mM of glucose. The maximum power output of the proposed bioanode was 21.8 times higher and reached 3.2 μW cm−2 at −51 mV vs Ag/AgCl(3MKCl) if the S. platensis cell lysate was used for bioanode design. The amperometric responses of GC/PEI/CNT/S.p./GOx bioelectrode towards the addition of glucose were linear at glucose concentrations ranging between 250 μM and 5 mM. These characteristics enable applying this bioanode as a part of biofuel cell and the electrode of an amperometric glucose biosensor, which response within 15 s, with a detection limit of 118 μM and a sensitivity of 15.09 μA mM−1 cm−2.

Optimization of Graphite-Mineral Oil Ratio With Response Surface Methodology in Glucose Oxidase Based Carbon Paste Electrode Design

In this study, construction of amperometric glucose biosensor was carried out by immobilizing of glucose oxidase (GOD) on carbon paste electrode (CPE) which was coated with polyaniline (PANI) by cyclic voltammetry technique. Since the current values to be measured depending on the glucose concentration will be affected by the graphite:mineral oil composition of the electrode, this parametres were optimized by response surface methodology (RSM). For this, State Ease Design Expert 8.0.7.1. (Serial Number: 0021-6578) software software was used applying Optimal Design. By using data obtained, Design Expert software suggested quadratic model to predict current values in terms of working parameters. In study, experimentally measured current values and predicted values by model were considerably found compatable and suitability of model was supported by ANOVA test.

An amperometric glucose biosensor based on electrostatic force induced layer-by-layer GOD/chitosan/pyrite on a glassy carbon electrode.

Pyrite (PR), as a representative sulfide mineral, possesses the advantages of abundancy, thermodynamic stability, non-toxicity and semi-conductivity. In this study, an amperometric glucose biosensor (GOD/CS/PR/GCE) based on layer-by-layer of glucose oxidase (GOD), chitosan (CS) and pyrite (PR) on a glassy carbon electrode (GCE) was fabricated through electrostatic force. In this research, PR suspension prepared in phosphate buffer (pH 5.5) was first immobilized on the GCE surface, which exhibits a negative charge. Then, positively charged CS was adsorbed on the PR/GCE by electrostatic force. Finally, negatively charged GOD was further modified on the CS/PR/GCE surface through electrostatic force again. The surface morphology and adsorbance mechanism were supported by field emission scanning electron microscopy, quartz crystal microbalance with dissipation and atomic force microscope. The step-by-step procedure gives both strong adhesion ability and good bioelectrocatalytic activity of GOD on the CS- and PR-modified electrode surface. The linear range of this GOD/CS/PR/GCE biosensor was achieved from 0.5 to 60mM with the linear regression equation of y = 0.897x - 0.3016 (R2 = 0.9996) and a limit of detection value of 50µM. This approach of using pyrite and chitosan as physically modified GOD to serve as electrostatic glues could be useful for designing better enzyme-based biosensors for a wide variety of practical applications.

Influence of enzyme immobilization and skin-sensor interface on non-invasive glucose determination from interstitial fluid obtained by magnetohydrodynamic extraction

We integrated a magnetohydrodynamic fluid extractor with an amperometric glucose biosensor to develop a wearable device for non-invasive glucose monitoring. Reproducible fluid extraction through the skin and efficient transport of the extracted fluid to the biosensor surface are prerequisites for non-invasive glucose monitoring. We optimized the enzyme immobilization and the interface layer between the sensing device and the skin. The monitoring device was evaluated by extracting fluid through porcine skin followed by glucose detection at the biosensor. The biosensor featured a screen-printed layer of Prussian Blue that was coated with a layer containing glucose oxidase. Both physical entrapment of glucose oxidase in chitosan and tethering of glucose oxidase to electrospun nanofibers were evaluated. Binding of glucose oxidase to nanofibers under mild conditions provided a stable biosensor with analytical performance suitable for accurate detection of micromolar concentrations of glucose. Hydrogels of varying thickness (95–2000 μm) as well as a thin (30 μm) nanofibrous polycaprolactone mat were studied as an interface layer between the biosensor and the skin. The effect of mass transfer phenomena at the biosensor-skin interface on the analytical performance of the biosensor was evaluated. The sensing device detected glucose extracted through porcine skin with an apparent (overall) sensitivity of −0.8 mA/(M·cm2), compared to a sensitivity of −17 mA/(M·cm2) for measurement in solution. The amperometric response of the biosensor correlated with the glucose concentration in the fluid that had been extracted through porcine skin with the magnetohydrodynamic technique.

Cascade amplification based on PEI-functionalized metal–organic framework supported gold nanoparticles/nitrogen–doped graphene quantum dots for amperometric biosensing applications

Robust and efficient multimodal catalysis platforms that possess high catalytic activity and enhanced electrical conductivity are preferred for enhancing the electrical analysis performance under a low overpotential. This report describes a function-switchable amperometric sensor for electrochemical monitoring hydrogen peroxide and glucose under relatively low overpotential based on PEI-functionalized metal–organic framework (P-MOF) supported gold nanoparticles/nitrogen-doped graphene quantum dots (AuNPs/N-GQDs) and glucose oxidase. AuNPs/N-GQDs with high peroxidase mimicking activity was anchored on the P-MOF modified electrode surface as H2O2 sensors, exhibiting a high sensitivity of 134.26 μA mM−1 cm−2 and a detection limit of 3.38 μM. Subsequently, AuNPs/N-GQDs-P-MOF used as a nanocarrier for glucose oxidase (GOx) to achieve “cascade nanoreactor” amplification for glucose detection. The amplified amperometric glucose biosensor showed excellent anti-interference ability, reproducibility, and a limit of detection as low as 0.7 μM (S/N = 3) with high sensitivity of 1512.4 μA mM−1 cm−2. In addition, the feasibility of the electrochemical biosensor for accurate and quantitative detection of glucose in human serum samples was confirmed with a recovery ranging from 93.2 to 99.3%. The strategy of combining AuNPs/N-GQDs-P-MOF and glucose oxidase for cascade catalysis in this work provides a simple yet efficient approach to prepare nanomaterial-based enzyme-mimics and enzymes hybrids with high performance, which holds great potential in biological and chemical applications of electrochemical devices and biosensing.

Lignosulfonate-assisted synthesis of platinum nanoparticles deposited on multi-walled carbon nanotubes for biosensing of glucose

It is presented in this work that lignosulfonate (LS) can be preferentially adsorbed on the surface of multi-walled carbon nanotubes (MWCNT) giving rise to the functional platform for platinum nanoparticles (NPt) deposition. The novel MWCNT/LS/NPt hybrid material has been characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS). The morphology of the MWCNT/LS/NPt electrodes has been investigated by atomic force microscopy (AFM). The electrochemical studies of MWCNT/LS/NPt hybrid material revealed strong electrocatalytic properties towards hydrogen peroxide. In addition, the effects of lignosulfonate amount adsorbed at the MWCNT on the voltammetric response of the hydrogen peroxide were discussed and used to select the optimal and effective conditions for the synthesis of the electrode material. An amperometric biosensor for glucose was developed based on the covalent linkage of glucose oxidase (GOx) at the MWCNT/LS/NPt. The enzyme electrode exhibited excellent electrocatalytic activity and rapid response for glucose. The linear range of the glucose determination was 50–1400 µM and LOD was quantified as 15.67 µM.

Extended Noninvasive Glucose Monitoring in the Interstitial Fluid Using an Epidermal Biosensing Patch.

An effective, noninvasive glucose monitoring technology could be a pivotal factor for addressing the major unmet needs for managing diabetes mellitus (DM). Here, we describe a skin-worn, disposable, wireless electrochemical biosensor for extended noninvasive monitoring of glucose in the interstitial fluid (ISF). The wearable platform integrates three components: a screen-printed iontophoretic electrode system for ISF extraction by reverse iontophoresis (RI), a printed three-electrode amperometric glucose biosensor, and an electronic interface for control and wireless communication. Prolonged on-body glucose monitoring of up to 8 h, including clinical trials conducted in individuals with and without DM, demonstrated good correlation between glucose blood and ISF concentrations and the ability to monitor dynamically changing glucose levels upon food consumption, with no evidence of skin irritation or discomfort. Such successful extended operation addresses the challenges reported for the GlucoWatch platform by using a lower RI current density at shorter extraction times, along with a lower measurement frequency. Such a noninvasive skin-worn platform could address long-standing challenges with existing glucose monitoring platforms.

Stainless steel 304 needle electrode for precise glucose biosensor with high signal-to-noise ratio

While accuracy and precision of human serum glucose measurements play a crucial role in determining treatments targeting glycemic control, electrochemical glucose meters widely used for blood sugar monitoring, have been facing issues of inaccuracy, making their application in medical decision-making difficult. Herein, we report a new amperometric glucose biosensor with extreme precision based on a stainless steel 304 (SS304) needle modified with glucose oxidase (GOx), chitosan, and Nafion. GOx and chitosan are immobilized on the surface of the SS304 needle and then covered with the Nafion layer. We focused on reducing electrochemical background signals and securing high signal-to-noise ratios associated with the electrode material, in contrast to most previous studies focusing on detection sensitivity enhancement. The SS304 needle was employed as a sensing electrode with H2O2, a product of GOx-catalysed oxidation reaction of glucose, owing to its convenient electrical properties with extremely shallow non-faradaic background currents under electrochemical conditions. We confirmed that the SS304 needle immobilized with glucose oxidase shows a distinct increase in current upon the addition of glucose at −0.10 V (vs. a saturated calomel electrode). The amperometric signal from the modified SS304 was specific to the serum glucose level without notable interference. It exhibits a strict linear correlation in the diabetic sugar level of 1–20 mM (y = 0.205x, R2 = 1.000) with an outstanding reproducibility (RSD = 4.4–6.8 %) and long-term storage stability. These results demonstrated that the SS304 electrode possesses great potential for electroanalytical biosensors based on the H2O2 content.

Measurements of working parameters of external mediators for biodetectors based on the polydopamine@magnetite nanoparticles

This paper describes the role of various external redox mediators in biodetector systems using bioinspired nanomaterials based on magnetite@polydopamine (Fe3O4@PDA), and their influence on the working parameters of the designed systems. The investigated mediators were hydroxy(methylferrocene, 1,4-benzoquinone, methylene blue, hydroquinone, and [Fe(CN)6]3-/4- redox couple. The amperometric glucose biosensor was fabricated by immobilizing glucose oxidase from Aspergillus niger (GOx) onto the Fe3O4@PDA nanomaterial, with the addition of a strictly defined amount of a specific external mediator. Among all tested mediators, the most favorable results were obtained for hydroxymethyl(ferrocene) with the integrated GC/Fe3O4@PDA-GOx system. The mediator exhibited ahigh linear amperometric response in a glucose concentration range from 1 to 20 mM, with a relatively high sensitivity of 139.71 μAmM−1 cm−2 and a limit of detection of 1.54 μM. Moreover, the system showed good stability over time, reproducibility, and resistance to interference.

(IMCS Second Place Best Paper Award) High-Density Immobilization of Tobacco Mosaic Virus Nanotubes As Enzyme Nanocarriers Onto Field-Effect Biosensor Structures

Introduction Viruses are not only infectious agents, they are also known as promising functional building blocks for application in nano- and biotechnologies. The tobacco mosaic virus (TMV) was the first studied plant virus and is widely distributed; it infects vegetables, like tomato, bell pepper, beans and other members of the family Solanaceae, while it is totally harmless for mammals [1]. It is one of the most studied plant viruses and its genome is completely sequenced, whereby genetical and chemical modification is easy. TMV has a nanotube-like shape with a length of 300 nm, an outer diameter of 18 nm and an inner diameter of 4 nm. Since it possesses a high chemical and physical robustness, it can be integrated with different electronic transducers for bio- and chemical sensing applications [2].Recently, we presented a TMV-based amperometric glucose biosensor [3] and a potentiometric penicillin biosensor [4]. TMV was used as enzyme nanocarrier for the enzyme glucose oxidase and penicillinase, respectively [3,4]. The sensitivity and detection limit of these biosensors, among others, depend on the density of TMVs on the sensor surface. The surface density of the immobilized TMVs is strongly influenced by the electrostatic interactions between the charged TMVs and sensor surface as well as by the inter-TMV-nanotubes repulsion, which could be changed by varying the pH value and the ionic strength of the TMV solution. In this study, we investigated an impact of the pH value and ionic strength of the TMV solution on the surface density of TMV nanotubes immobilized onto Ta2O5-gate capacitive field-effect electrolyte-insulator-semiconductor (EIS) sensors. Materials and Methods TMV particles modified with biotin-linker molecules (TMVBio), which serve as binding sites for streptavidin-conjugated enzymes, have been immobilized onto capacitive field-effect EIS sensors with Ta2O5 as transducer layer, as shown in Fig. 1. Immobilization was performed from TMVBiosolutions with different values of pH between pH 3.0 and pH 9.5 and ionic strength between 0.1 mM and 750 mM. The sensors have been electrochemically characterized before and after TMVBio immobilization by capacitance-voltage- and constant-capacitance methods, respectively. In addition, the density of the immobilized TMVs and morphology of the sensor surface has been investigated by means of scanning electron microscopy (SEM). Results and Conclusions The TMVBio density on the Ta2O5 sensor surface was influenced by varying the pH value (as exemplarily shown in Fig. 1) and ionic strength (not shown) of the TMVBio solution. The amplitude of the field-effect sensor signal correlates well with the density of the immobilized TMVBionanotubes. Thus, optimized conditions for the high-density immobilization of TMVBio nanotubes onto the Ta2O5 surface and thereby enhanced biosensing have been found. Details of the experiments and the obtained results will be presented and discussed. Acknowledgements The authors like to thank Dr. Claudia Koch and Rebecca Hummel, Stuttgart, for scientific and technical support.