A glucose oxidase immobilization platform for glucose biosensor using ZnO hollow nanospheres

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

On-chip glucose biosensor based on enzyme entrapment with pre-reaction to lower interference in a flow injection system

In this study, poly(3,4-ethylenedioxythiophene), PEDOT, was electropolymerized on a sensing chip to entrap glucose oxidase (GOD). The interdigitated array (IDA) electrode and microfluidic channel of the sensing chip was fabricated by photolithography. The IDA electrodes consist of two working electrodes in which one (WE1) was the enzyme-modified electrode and the other was a Pt (WE2) for eliminating noise effect. The microfluidic channel was formed on etched silicon by PDMS (poly(dimethylsiloxane)). In the flow injection analysis, a 0.7 V (vs. Ag/AgCl) was set on enzyme electrode to detect the catalytic product, H₂O₂, and the sensing signal was calibrated using the passed charge rather than the peak current. The linear relationship between the charges and the glucose concentrations, ranging from 1 to 10 mM, was obtained with a sensitivity of 157 μC cm⁻² mM⁻¹. Besides, the response time and the recovery time were about 15 and 35-75 s, respectively. In real human sample test, the error of single-potential and bi-potential were about 140% and 13%, respectively, comparing to the standard value, indicating that the WE2 can lower the interference effect in this system.     

Study of an amperometric glucose sensor based on Pd-Ni/SiNW electrode

An amperometric glucose sensor based on Pd-Ni/SiNW electrode has been investigated. The silicon nanowire (SiNW) electrodes were first fabricated by chemical etching, and then nickel and palladium particles were deposited onto the surfaces of SiNWs via electroless co-plating technique followed by annealing in nitrogen atmosphere at 350 °C for 300 s. The morphology of Pd-Ni/SiNW electrode was characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The sensor performance was characterized by cyclic voltammetry (CV) and fixed potential amperometry techniques. In 0.1 M KOH alkaline medium with different glucose concentrations, the sensor shows an excellent sensitivity of 190.72 μA mM⁻¹ cm⁻² with the detection limit (S/N ratio = 3) of 2.88 μM. And it also exhibits superior anti-interference properties to the species including ascorbic acid (AA), uric acid (UA) and 4-acetamidophenol (AP). All results demonstrate that this Pd-Ni/SiNW electrode is a candidate with great potential for glucose detection.     

An amperometric glucose biosensor based on layer-by-layer GOx-SWCNT conjugate/redox polymer multilayer on a screen-printed carbon electrode

An amperometric glucose biosensor based on a multilayer made by layer-by-layer assembly of single-walled carbon nanotubes modified with glucose oxidase (GOx-SWCNT conjugates) and redox polymer (PVI-Os) on a screen-printed carbon electrode (SPCE) surface was developed. The SPCE surface was functionalized with a cationic polymer by electrodeposition of the PVI-Os, followed by alternating immersions in anionic GOx-SWCNT conjugate solutions and cationic PVI-O solutions. The purpose is to build a multilayer structure which is further stabilized through the electrodeposition of PVI-Os on the multilayer film. The electrochemistry of the layer-by-layer assembly of the GOx-SWCNT conjugate/PVI-Os bilayer was followed by cyclic voltammetry. The resultant glucose biosensor provided stable and reproducible electrocatalytic responses to glucose, and the electrocatalytic current for glucose oxidation was enhanced with an increase in the number of bilayers. The glucose biosensor displayed a wide linear range from 0.5 to 8.0 mM, a high sensitivity of 32 μA mM⁻¹ cm⁻², and a response time of less than 5 s. The glucose biosensor proved to be promising amperometric detectors for the flow injection analysis of glucose.     

One-pot electrodeposition of 3-aminopropyltriethoxysilane-chitosan hybrid gel film to immobilize glucose oxidase for biosensing

We report on the electrodeposition of a 3-aminopropyltriethoxysilane-chitosan (APTES-CS) hybrid gel film for in situ immobilization of glucose oxidase (GOx) on an Au or platinized Au (Pt_nano/Au) electrode for biosensing of glucose. Controllable electroreduction of p-benzoquinone is used to lift the electrode-surface pH for the GOx-APTES-CS codeposition, which was monitored by an electrochemical quartz crystal microbalance. The fabrication procedures of the biosensor and the parameters influencing the biosensing performance were optimized. The prepared porous GOx-APTES-CS/Pt_nano/Au and GOx-APTES-CS/Au electrodes can be used to detect the enzymatically generated H₂O₂ at 0.5 and 0.7 V vs SCE, respectively. The enzyme electrodes exhibited linear responses to glucose concentration from 0.2 μM to 8.2 mM (R = 0.998, at Pt_nano/Au substrate) and from 0.2 μM to 5.5 mM (R = 0.998, at Au substrate), with current sensitivities of 69.5 (Pt_nano/Au) and 65 (Au) μA mM⁻¹ cm⁻², respectively, and a detection limit of 0.2 μM (S/N = 3) was achieved for each electrode. The response time was less than 5 (Pt_nano/Au) or 8 (Au) s. It is striking that the enzyme electrodes remained their initial response sensitivity after storage for 5 (Au) and >6 (Pt_nano/Au) months in 0.10 M PBS (pH 7.0) at 4 °C.     

A coral-like macroporous gold-platinum hybrid 3D electrode for enzyme-free glucose detection

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

An electrochemical biosensor for determination of hydrogen peroxide using nanocomposite of poly(methylene blue) and FAD hybrid film

An electrochemical biosensor for determination of hydrogen peroxide (H₂O₂) has been developed by the hybrid film of poly(methylene blue) and FAD (PMB/FAD). The PMB/FAD hybrid film was performed in PBS (pH 7) containing methylene blue and FAD by cyclic voltammetry. Repeatedly scanning potential range of −0.6-1.1 V, FAD was immobilized on the electrode surface by electrostatic interaction while methylene blue was electropolymerized on electrode surface. This modified electrode was found surface confined and pH dependence. It showed good electrocatalytic reduction for H₂O₂, KBrO₃, KIO₃, and NaClO as well as electrocatalytic oxidation for NADH. At an applied potential of −0.45 V vs. Ag/AgCl, the sensor showed a rapid and linear response to H₂O₂ over the range from 0.1 μM to 960 μM, with a detection limit of 0.1 μM and a significant sensitivity of 1109 μA mM⁻¹ cm⁻² (S/N = 3). It presented excellent stability at room temperature, with a variation of response current less than 5% over 30 days.     

Targeting of multiple metabolites in neural cells monitored by using protein-based carbon nanotubes

Microdevices dedicated to monitor metabolite levels have recently enabled many applications in the field of cell analysis, to monitor cell growth and development of numerous cell lines. By combining the traditional technology used for electrochemical biosensors with nanoscale materials, it is possible to develop miniaturized metabolite biosensors with unique properties of sensitivity and detection limit. In particular, enzymes tend to adsorb onto carbon nanotubes and their optical or electrical activity can perturb the electronic properties. In the present work we propose multi-walled carbon nanotube-based biosensors to monitor a cell line highly sensitive to metabolic alterations, in order to evaluate lactate production and glucose uptake during different cell states. We achieve sensors for both lactate and glucose, with sensitivities of 40.1 μA mM⁻¹ cm⁻² and 27.7 μA mM⁻¹ cm⁻², and detection limits of 28 μM and 73 μM, respectively. This nano-biosensing technology is used to provide new information on cell line metabolism during proliferation and differentiation, which are unprecedented in cell biology.     

A novel electrochemiluminescence glucose biosensor based on alcohol-free mesoporous molecular sieve silica modified electrode

In this study, a thin-film glucose electrochemiluminescence (ECL) biosensor was developed. Ru(bpy)₃²⁺ was doped in alcohol-free low-volume shrinkage mesoporous silica sol-gel with PEG-400 as the template, and glucose dehydrogenase (GDH) was immobilized in polymer Resydrol. NADH, which is produced by the reaction of co-enzyme NAD⁺ and glucose catalyzed by glucose dehydrogenase, reacts with immobilized Ru(bpy)₃²⁺ to generate ECL emission. Among the three types of design including two-layer, mixed and sandwich configuration, the sandwich configuration showed the best sensitivity with the calibration range of 25-2000 μM and the limit of detection of 0.5 μM in a flow injection analysis of glucose. The alcohol-free mesoporous sol-gel and the sandwich design made the biosensor potentially applicable in flow-injection analysis of samples.     

Direct electron transfer of glucose oxidase at glassy carbon electrode modified with functionalized carbon nanotubes within a dihexadecylphosphate film

A glassy carbon electrode modified with functionalized multiwalled carbon nanotubes (CNTs) immobilized by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) in a dihexadecylphosphate film was prepared and characterized by cyclic voltammetry and scanning electron microscopy. It was used as a support for FAD or glucose oxidase (GOx) immobilization with EDC/NHS crosslinking agents. Cyclic voltammetry of GOx immobilized onto the surface of CNTs showed a pair of well-defined redox peaks, which correspond to the direct electron transfer of GOx, with a formal potential of −0.418 V vs. Ag/AgCl (3 M KCl) in 0.1 M phosphate buffer solution (pH 7.0). An apparent heterogeneous electron transfer rate constant of 1.69 s⁻¹ was obtained. The dependence of half wave potential on pH indicated that the direct electron transfer reaction of GOx involves a two-electron, two-proton transfer. The determination of glucose was carried out by square wave voltammetry and the developed biosensor showed good reproducibility and stability. The proposed method could be easily extended to immobilize and evaluate the direct electron transfer of other redox enzymes or proteins.     

Correlation between cell growth rate and glucose consumption determined by electrochemical monitoring

The electrochemical monitoring of glucose consumption is relevant for cell biology studies because of its wide detection range, high sensitivity and easy implementation. Whereas the glucose consumption and cell growth rate can be tightly correlated, they should also be cell population density dependent. In this work, we fabricated high sensitive enzyme electrodes for accurate monitoring of glucose consumption of cells in different growth stages. The performance of the fabricated device was firstly evaluated by cyclic voltammetry (CV) with p-benzoquinone (PBQ) as redox mediator, showing a linear response over a wide detection range (0.3-60 mM), a high sensitivity (1.61 ± 0.10 μA mM⁻¹ mm⁻² (n = 5)) and a low detection limit (80 μM). Then, daily glucose consumptions of NIH 3T3 cells in 24-well plates were determined for a period of 7 days. The results could be compared to the cell population growth curve, showing a close correlation but different behavior. We found that the increase of the glucose consumption took place prior the cell number increase but the glucose consumption per cell decreases linearly in the exponential growth stage of cells.     

Amperometric glucose biosensor based on integration of glucose oxidase with platinum nanoparticles/ordered mesoporous carbon nanocomposite

This article reports a new amperometric glucose biosensor based on ordered mesoporous carbon (OMC) supported platinum nanoparticles (Pt/OMC) modified electrode. The Pt/OMC nanocomposite modified electrode exhibited excellent electrocatalytic activities towards the reduction and oxidation of H₂O₂ as well. This feature allowed us to use it as bioplatform on which glucose oxidase (GOD) was immobilized by entrapment in electropolymerized pyrrole film for the construction of the glucose biosensor. The biosensor showed good analytical performances in terms of low detection (0.05 mM), high sensitivity (0.38 μA/mM) and wide linear range (0.05-3.70 mM). In addition, the effects of pH value, applied potential, electroactive interference and the stability of the biosensor were discussed. The applicability to blood analysis was also evaluated.     

Gold nanoparticles-coated eggshell membrane with immobilized glucose oxidase for fabrication of glucose biosensor

This work reports the fabrication and application of a glucose biosensor based on the catalytic effect of gold nanoparticles (AuNPs) on enzymatic reaction for blood glucose determination. AuNPs were initially in situ synthesized on the surface of an eggshell membrane (ESM) which was subsequently immobilized with glucose oxidase (GO_x) to produce a GO_x-AuNPs/ESM. The GO_x-AuNPs/ESM was positioned on the surface of an oxygen electrode to form a GO_x-AuNPs/ESM glucose biosensor. The effects of pH, concentration of phosphate buffer solution and amount of GO_x on the response of the GO_x-AuNPs/ESM glucose biosensor were studied in detail. AuNPs on GO_x/ESM can improve the calibration sensitivity (30% higher than GO_x/ESM without AuNPs), stability (87.3% of its initial response to glucose after 10-week storage) and shortens the response time (<30 s) of the glucose biosensor. The linear working range for the GO_x-AuNPs/ESM glucose biosensor is 8.33 μM to 0.966 mM glucose with a detection limit of 3.50 μM (S/N = 3). The biosensor has been successfully applied to determine the glucose in human blood serum samples and the results compared well to a standard spectrophotometric method commonly used in hospitals. Our work demonstrates that the developed GO_x-AuNPs/ESM glucose biosensor has potential in biomedical analysis.     

High-performance glucose sensor based on glucose oxidase encapsulated in new synthesized platinum nanoparticles supported on carbon Vulcan/Nafion composite deposited on glassy carbon

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

Electroanalytical detection of Pb, Cd and traces of Cr at micro/nano-structured bismuth film electrodes

A micro/nanoparticle (μ-NP) bismuth film electrode (BiFE) has been developed for the determination of lead and cadmium by anodic stripping voltammetry (ASV) and trace levels of chromium by adsorptive stripping voltammetry (AdSV). Chromium was detected in a flow cell. Bismuth was electrodeposited on a hydrated aluminum oxide template, which was previously coated on a glassy-carbon (GC) electrode. Then, the template was selectively removed by soaking the electrode in a 0.1 M NaOH solution for 30 min, leaving a dispersed bismuth film covering the electrode surface; such electrodeposits had a particulate appearance, which was observed by scanning electron microscopy (SEM). The voltammetric analyses from a chromium solution on a μ-NPs/BiFE provided a limit of detection (LOD) equal to 0.12 ng L⁻¹ (n = 6) and a slope of 0.27 μC/ng L⁻¹ (R² = 0.9903). The signals registered were more than 50 times higher than the peaks obtained from a conventional BiFE. The analysis of aqueous solutions of Cd and Pb gave also lower LOD and higher sensitivity against the conventional BiFe experiments.     

A novel bienzyme glucose biosensor based on three-layer Au-Fe3O4@SiO2 magnetic nanocomposite

The magnetic core-shell Au-Fe₃O₄@SiO₂ nanocomposite was prepared by layer-by-layer assembly technique and was used to fabricate a novel bienzyme glucose biosensor. Glucose oxidase (GOD) and horseradish peroxidase (HRP) were simply mixed with Au-Fe₃O₄@SiO₂ nanocomposite and cross-linked on the ITO magnetism-electrode with nafion (Nf) and glutaraldehyde (GA). The modified electrode was designated as Nf-GOD-HRP/Au-Fe₃O₄@SiO₂/ITO. The effects of some experimental variables such as the pH of supporting electrolyte, enzyme loading, the concentration of the mediator methylene blue (MB) and the applied potential were investigated. The electrochemical behavior of the biosensor was studied using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry. Under the optimized conditions, the biosensor showed a wide dynamic range for the detection of glucose with linear ranges of 0.05-1.0 mM and 1.0-8.0 mM, and the detection limit was estimated as 0.01 mM at a signal-to-noise ratio of 3. The biosensor exhibited a rapid response, good stability and anti-interference ability. Furthermore, the biosensor was successfully applied to detect glucose in human serum samples, showing acceptable accuracy with the clinical method.     

Electrochemical behaviors and determination of isoniazid at ordered mesoporous carbon modified electrode

In this work, an electrochemical sensor based on ordered mesoporous carbon (OMC) for the amperometric detection of isoniazid was developed. OMC was dispersed in a solution of Nafion, and the suspension was modified onto the surface of glassy carbon (GC) electrode. Cyclic voltammetry and amperometry were used to investigate the electrochemical behaviors of isoniazid on Nafion-OMC modified electrode (Nafion-OMC/GC). The results indicate that OMC can facilitate the electrochemical oxidation of isoniazid with a great decrease of overpotential in pH 7.0 phosphate buffer solution. The proposed biosensor provides excellent performance towards the determination of isoniazid with a high sensitivity of 0.031 μA/μM, a low detection limit of 8.4 × 10⁻⁸ M and wide linear range from 1.0 × 10⁻⁷ M to 3.7 × 10⁻⁴ M at +0.20 V vs. Ag/AgCl. The method was successfully applied to the determination of isoniazid tablets with satisfying results. All the results suggest that Nafion-OMC/GC electrode is a potential candidate for a stable and efficient electrochemical sensor to detect isoniazid.     

A CO2 sensor based upon a continuous-wave thermoelectrically-cooled quantum cascade laser

A CO₂ sensor based upon a continuous-wave thermoelectrically-cooled distributed feedback quantum cascade laser operating between 2305 and 2310 cm⁻¹ and a 54.2 cm long optical cell has been developed. Two approaches for direct absorption spectroscopy have been evaluated and applied for monitoring of the CO₂ concentration in gas lines and ambient laboratory air. In the first approach optical transmittance was derived from the single channel laser intensity, whilst in the second approach a ratio of signal and reference laser intensities (balanced detection) was used. The optimum residual absorption standard deviation was estimated to be 1.9 × 10⁻⁴ for 100 averages of 1 ms duration and 0.1 cm⁻¹ scans over the P(46) CO₂ absorption line of the ν₃ vibrational band at 2306.926 cm⁻¹. A CO₂ detection limit (1 standard deviation) of 36 ppb was estimated for 0.1 s average and balanced detection.     

Direct electrochemistry and electrocatalysis of hemoglobin immobilized into poly (lactic-co-glycolic acid)/room temperature ionic liquid composite film

A promising material of poly(lactic-co-glycolic acid) (PLGA) and, room temperature ionic liquid (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) was firstly used as an immobilization matrix to entrap proteins and its bioelectrochemical properties were studied. Direct electrochemistry and electrocatalytic behaviors of hemoglobin (Hb) entrapped in the PLGA/ILs composite film on the surface of glass carbon electrode were investigated. UV-vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the composite film. The obtained results demonstrated that the Hb molecule in the film kept its native structure and showed its good electrochemical behavior. A pair of well-defined redox peaks of Hb was obtained at the Hb/PLGA/ILs composite film-modified GC electrode through direct electron transfer between the protein and the underlying electrode. The proposed biosensor showed good reproducibility and high sensitivity to H₂O₂ with the detection limit of 2.37 × 10⁻⁷ M (S/N = 3). In the range of 5.0 × 10⁻⁶ to 8.05 × 10⁻³ M, the catalytic reduction current of H₂O₂ was proportional to its concentration. The apparent Michaelis-Menten constant of Hb in the PLGA/ILs composite film was estimated to be 0.069 mM, showing its high affinity.     

Carbon felt-based bioelectrocatalytic flow-through detectors: Highly sensitive amperometric determination of H2O2 based on a direct electrochemistry of covalently modified horseradish peroxidase using cyanuric chloride as a linking agent

Horseradish peroxidase (HRP) was chemically modified using cyanuric chloride (CC) as a linking agent onto a carbon felt (CF), which is a microelectrode ensemble of micro carbon fiber (>7 μm, diameter) with a random three-dimensional structure. The resulting HRP-modified CF (HRP-ccCF) exhibited well-defined redox waves based on the HRP heme Fe^III/Fe^II redox couple at −0.23 V vs. Ag/AgCl (at pH 7.0), while the HRP-adsorbed CF (HRP-CF) showed no apparent redox couple in the same potential range, indicating that the chemical modification of HRP via CC facilitated the direct electron transfer (DET) between HRP and CF. The apparent heterogeneous electron transfer rate constant k_s was estimated to be 35 s⁻¹. Cyclic voltammetry and electrochemical impedance spectroscopy revealed that the interfacial properties (i.e., structure, morphology of enzyme-layer) of covalently modified HRP (HRP-ccCF) and physically adsorbed HRP (HRP-CF) are different, resulting in the difference in the electron transfer properties. The HRP-ccCF was successfully used as a working electrode unit in bioelectrocatalytic flow-through detector for highly sensitive amperometric determination of H₂O₂. Under the optimized conditions (i.e., applied potential, 0 V vs. Ag/AgCl; carrier flow rate, 3.25 ml/min; and carrier pH 7.0), the cathodic peak current of H₂O₂ linearly increased up to 3 μM (sensitivity, 1.94 μA/μM; the detection limit, 0.08 μM [S/N = 3]) with sample through-put of ca. 90 samples/h.