A glucose biosensor based on chitosan–glucose oxidase–gold nanoparticles biocomposite formed by one-step electrodeposition

Amperometric biosensor based on coentrapment of enzyme and mediator by gold nanoparticles on indium–tin oxide electrode

A disposable pseudo-mediatorless amperometric biosensor has been fabricated for the determination of hydrogen peroxide (H2O2). In the current study, an indium-tin oxide (ITO) electrode was modified with thiol functional group by (3-mercaptopropyl)trimethoxysilane. The stable nano-Au-SH monolayer (AuS) was then prepared through covalent linking of gold nanoparticles and thiol groups on the surface of the ITO. The horseradish peroxidase (HRP) and tetramethyl benzidine (TMB) were finally coentrapped by the colloidal gold nanoparticles. The immobilized TMB was used as an electron transfer mediator that displayed a surface-controlled electrode process at a scan rate of less than 50mV/s. The biosensor was characterized by photometric and electrochemical measurements. The results showed that the prepared AuS monolayer not only could steadily immobilize HRP but also could efficiently retain HRP bioactivity. Parameters affecting the performance of the biosensor, including the concentrations of the immobilized TMB and HRP, the pH value, and the reaction temperature, were optimized. Under the optimized experimental conditions, H(2)O(2) could be determined in a linear calibration range from 0.005 to 1.5mM with a correlation coefficient of 0.998 (n=14) and a detection limit of 1microM at a signal/noise ratio of 3. The proposed method provides a new alternative to develop low-cost biosensors by using ITO film electrodes from industrial mass production.

Direct electrochemistry and electrocatalysis of hemoglobin entrapped in semi-interpenetrating polymer network hydrogel based on polyacrylamide and chitosan

Semi-interpenetrating polymer network (semi-IPN) hydrogel based on polyacrylamide (PAM) and chitosan was prepared to immobilize redox protein hemoglobin (Hb). The Hb-PAM-chitosan hydrogel film obtained has been investigated by scanning electron microscopy (SEM) and UV-VIS spectroscopy. UV-VIS spectroscopy showed that Hb kept its secondary structure similar to its native state in the Hb-PAM-chitosan hydrogel film. Cyclic voltammogram of Hb-PAM-chitosan film-modified glass carbon (GC) electrode showed a pair of well-defined and quasi-reversible redox peaks for Hb Fe(III)/Fe(II), indicating that direct electron transfer between Hb and GC electrode occurred. The electron-transfer rate constant was about 5.51 s(-1) in pH 7.0 buffers, and the formal potential (E degrees ') was -0.324 V (vs. SCE). The dependence of E degrees ' on solution pH indicated that one-proton transfer was coupled to each electron transfer in the direct electron-transfer reaction. Additionally, Hb in the semi-IPN hydrogel film retained its bioactivity and showed excellent electrocatalytic activity toward H(2)O(2). The electrocatalytic current values were linear with increasing concentration of H(2)O(2) in a wide range of 5-420 microM. The unique semi-IPN hydrogel would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.

A novel glucose biosensor based on immobilization of glucose oxidase in chitosan on a glassy carbon electrode modified with gold–platinum alloy nanoparticles/multiwall carbon nanotubes

A novel glucose biosensor was constructed, based on the immobilization of glucose oxidase (GOx) with cross-linking in the matrix of biopolymer chitosan (CS) on a glassy carbon electrode (GCE), which was modified with gold-platinum alloy nanoparticles (Au-PtNPs) by electrodeposition on multiwall carbon nanotubes (CNTs) in CS film (CNTs/CS). The properties of Au-PtNPs/CNTs/CS were characterized by scan electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectra (EIS). Primary study indicated that Au-PtNPs/CNTs had a better synergistic electrocatalytic effect on the reduction of hydrogen peroxide than did AuNPs/CNTs or PtNPs/CNTs at a low applied potential window. With GOx as a model enzyme, a new glucose biosensor was fabricated. The biosensor exhibited excellent performances for glucose at a low applied potential (0.1V) with a high sensitivity (8.53 microA mM(-1)), a low detection limit (0.2 microM), a wide linear range (0.001-7.0 mM), a fast response time (<5s), and good reproducibility, stability, and selectivity. In addition, the biosensor was applied in the determination of glucose in human blood and urine samples, and satisfied results were obtained.

A Disposable Multianalyte Electrochemical Immunosensor Array for Automated Simultaneous Determination of Tumor Markers

Background: Automated and convenient multianalyte detection with high throughput is increasingly needed in clinical diagnosis. We developed a disposable 4-by-2 array for programmed simultaneous amperometric immunoassay of 4 tumor markers.

Methods: We used a screen-printed technique, 1-step immobilization method, and flow injection technique. We immobilized carcinoembryonic antigen, α-fetoprotein, β-human choriogonadotropin, and carcinoma antigen 125 as model analytes in a redox mediator–grafted, biopolymer-modified, screen-printed carbon electrode array to capture corresponding horseradish peroxidase-labeled antibodies in competitive immunoreactions. The simultaneous multianalyte immunoassay was automatically carried out to amperometrically monitor the mediator-catalyzed enzymatic response to hydrogen peroxide, which decreased in proportion to the concentrations of analytes in samples.

Results: The multianalyte immunosensor array had a throughput of 60 samples/h and allowed simultaneous detection of carcinoembryonic antigen, α-fetoprotein, β-human choriogonadotropin, and carcinoma antigen 125 in clinical serum samples with concentrations up to 188 μg/L, 250 μg/L, 266 IU/L, and 334 kIU/L, respectively. The detection limits (limits of the blank, mean of blank plus 3 SD) were 1.1 μg/L, 1.7 μg/L, 1.2 IU/L, and 1.7 kIU/L. The inter- and intraassay imprecision (CVs) of the immunosensor arrays were &lt;7.8% and &lt;9.0%, respectively. The immunosensor arrays were stable for 28 days.

Conclusions: This newly constructed immunosensor array provides a simple, automated, simultaneous multianalyte immunoassay with high throughput, short analytical time, and sufficiently low detection limits for clinical application. This method offers the capability of miniaturizing the multianalyte detection device.

Synthesis and electrochemical applications of gold nanoparticles

This review covers recent advances in synthesis and electrochemical applications of gold nanoparticles (AuNPs). Described approaches include the synthesis of AuNPs via designing and choosing new protecting ligands; and applications in electrochemistry of AuNPs including AuNPs-based bioelectrochemical sensors, such as direct electrochemistry of redox-proteins, genosensors and immunosensors, and AuNPs as enhancing platform for electrocatalysis and electrochemical sensors.

Room temperature ionic liquid doped DNA network immobilized horseradish peroxidase biosensor for amperometric determination of hydrogen peroxide

A novel electrochemical H(2)O(2) biosensor was constructed by embedding horseradish peroxide (HRP) in a 1-butyl-3-methylimidazolium tetrafluoroborate doped DNA network casting on a gold electrode. The HRP entrapped in the composite system displayed good electrocatalytic response to the reduction of H(2)O(2). The composite system could provide both a biocompatible microenvironment for enzymes to keep their good bioactivity and an effective pathway of electron transfer between the redox center of enzymes, H(2)O(2) and the electrode surface. Voltammetric and time-based amperometric techniques were applied to characterize the properties of the biosensor. The effects of pH and potential on the amperometric response to H(2)O(2) were studied. The biosensor can achieve 95% of the steady-state current within 2 s response to H(2)O(2). The detection limit of the biosensor was 3.5 microM, and linear range was from 0.01 to 7.4 mM. Moreover, the biosensor exhibited good sensitivity and stability. The film can also be readily used as an immobilization matrix to entrap other enzymes to prepare other similar biosensors.

A simple method to fabricate a chitosan-gold nanoparticles film and its application in glucose biosensor

A novel film of chitosan-gold nanoparticles is fabricated by a direct and facile electrochemical deposition method and its application in glucose biosensor is investigated. HAuCl(4) solution is mixed with chitosan and electrochemically reduced to gold nanoparticles, which can be stabilized by chitosan and electrodeposited onto glassy carbon electrode surfaces along with the electrodeposition of chitosan. Then a model enzyme, glucose oxidase (GOD) is immobilized onto the resulting film to construct a glucose biosensor through self-assembly. The resulting modified electrode surfaces are characterized with both AFM and cyclic voltammetry. Effects of chitosan and HAuCl(4) concentration in the mixture together with the deposition time and the applied voltage on the amperometric response of the biosensor are also investigated. The linear range of the glucose biosensor is from 5.0 x 10(-5) approximately 1.30 x 10(-3) M with a Michaelis-Menten constant of 3.5 mM and a detection limit of about 13 microM.

Chitosan: a soft interconnect for hierarchical assembly of nano-scale components

Traditional microfabrication has tremendous capabilities for imparting order to hard materials (e.g., silicon wafers) over a range of length scales. However, conventional microfabrication does not provide the means to assemble pre-formed nano-scale components into higher-ordered structures. We believe the aminopolysaccharide chitosan possesses a unique set of properties that enable it to serve as a length-scale interconnect for the hierarchical assembly of nano-scale components into macro-scale systems. The primary amines (atomic length scale) of the glucosamine repeating units (molecular length scale) provide sites to connect pre-formed or self-assembled nano-scale components to the polysaccharide backbone (macromolecular length scale). Connections to the backbone can be formed by exploiting the electrostatic, nucleophilic, or metal-binding capabilities of the glucosamine residues. Chitosan's film-forming properties provide the means for assembly at micron-to-centimetre lengths (supramolecular length scales). In addition to interconnecting length scales, chitosan's capabilities may also be uniquely-suited as a soft component-hard device interconnect. In particular, chitosan's film formation can be induced under mild aqueous conditions in response to localized electrical signals that can be imposed from microfabricated surfaces. This capability allows chitosan to assemble soft nano-scale components (e.g., proteins, vesicles, and virus particles) at specific electrode addresses on chips and in microfluidic devices. Thus, we envision the potential that chitosan may emerge as an integral material for soft matter (bio)fabrication.

Design and development of a highly stable hydrogen peroxide biosensor on screen printed carbon electrode based on horseradish peroxidase bound with gold nanoparticles in the matrix of chitosan

The design and development of a screen printed carbon electrode (SPCE) on a polyvinyl chloride substrate as a disposable sensor is described. Six configurations were designed on silk screen frames. The SPCEs were printed with four inks: silver ink as the conducting track, carbon ink as the working and counter electrodes, silver/silver chloride ink as the reference electrode and insulating ink as the insulator layer. Selection of the best configuration was done by comparing slopes from the calibration plots generated by the cyclic voltammograms at 10, 20 and 30 mM K(3)Fe(CN)(6) for each configuration. The electrodes with similar configurations gave similar slopes. The 5th configuration was the best electrode that gave the highest slope. Modifying the best SPCE configuration for use as a biosensor, horseradish peroxidase (HRP) was selected as a biomaterial bound with gold nanoparticles (AuNP) in the matrix of chitosan (HRP/AuNP/CHIT). Biosensors of HRP/SPCE, HRP/CHIT/SPCE and HRP/AuNP/CHIT/SPCE were used in the amperometric detection of H(2)O(2) in a solution of 0.1M citrate buffer, pH 6.5, by applying a potential of -0.4V at the working electrode. All the biosensors showed an immediate response to H(2)O(2). The effect of HRP/AuNP incorporated with CHIT (HRP/AuNP/CHIT/SPCE) yielded the highest performance. The amperometric response of HRP/AuNP/CHIT/SPCE retained over 95% of the initial current of the 1st day up to 30 days of storage at 4 degrees C. The biosensor showed a linear range of 0.01-11.3mM H(2)O(2), with a detection limit of 0.65 microM H(2)O(2) (S/N=3). The low detection limit, long storage life and wide linear range of this biosensor make it advantageous in many applications, including bioreactors and biosensors.

Determination of carbaryl pesticide using amperometric acetylcholinesterase sensor formed by electrochemically deposited chitosan

A sensitive, fast and cheap sensor for quantitative determination of carbaryl pesticide using amperometric acetylcholinesterase (AChE) sensor based on electrochemically deposited chitosan was reported. From a mildly acidic chitosan solution, a chitosan film is electrochemically deposited on Au electrode surface via a negative voltage bias, leading to a stable AChE sensor. The characteristics of the deposited layer were observed to be dependent upon the deposition time, pH, and the chitosan concentration. Fourier-transform infrared spectra proved that the immobilized enzyme could preserve their native structure due to the excellent biocompatibility and non-toxicity of chitosan. Under the optimal experimental conditions, the carbaryl inhibition on AChE-CHIT/Au was proportional to its concentration in two ranges, from 0.005 to 0.1 microg/ml and 0.5 to 5 microg/ml, with the correlation coefficients of 0.9966 and 0.9982, respectively. The detection limit was 0.003 microg/ml taken as the concentration equivalent to a 10% decrease in signal. The determination of carbaryl in garlic samples obtained from export of farm base showed acceptable accuracy. The developed sensor exhibited good fabrication reproducibility and acceptable stability, which provided a new promising tool for pesticide analysis.

Biopolymer-based materials: the nanoscale components and their hierarchical assembly

Protein and nucleic acid biopolymers are well appreciated for their high-performance capabilities for molecular recognition, catalysis and information storage. Increasingly, these biopolymers are being examined for materials applications. Less tractable are polysaccharides and polymers of phenols, which, despite being nature's most abundant macromolecules, remain largely ignored for advanced materials applications. In our opinion, it seems certain that biology will contribute two major capabilities for materials biofabrication - the means to generate biopolymeric components with nanoscale precision, and the mechanisms for the hierarchical assembly of nanocomponents. These capabilities will enable unprecedented control of materials structure and provide exciting opportunities at the convergence of molecular biology and macromolecular science.

Mechano-transduction of DNA hybridization and dopamine oxidation through electrodeposited chitosan network

While microcantilevers offer exciting opportunities for mechano-detection, they often suffer from limitations in either sensitivity or selectivity. To address these limitations, we electrodeposited a chitosan film onto a cantilever surface and mechano-transduced detection events through the chitosan network. Our first demonstration was the detection of nucleic acid hybridization. In this instance, we electrodeposited the chitosan film onto the cantilever, biofunctionalized the film with oligonucleotide probe, and detected target DNA hybridization by cantilever bending in solution (static mode) or resonant frequency shifts in air (dynamic mode). In both detection modes, we observed a two-order of magnitude increase in sensitivity compared to values reported in literature for DNA immobilized on self-assembled monolayers. In our second demonstration, we coupled electrochemical and mechanical modes to selectively detect the neurotransmitter dopamine. A chitosan-coated cantilever was biased to electrochemically oxidize dopamine solution. Dopamine's oxidation products react with the chitosan film and create a tensile stress of approximately 1.7 MPa, causing substantial cantilever bending. A control experiment was performed with ascorbic acid solution. It was shown that the electrochemical oxidation of ascorbic acid does not lead to reactions with chitosan and does not change cantilever bending. These results suggest that chitosan can confer increased sensitivity and selectivity to microcantilever sensors.

Amperometric phenol biosensor based on laponite clay–chitosan nanocomposite matrix

A novel strategy to fabricate an amperometric biosensor for phenol determination based on chitosan/laponite nanocomposite matrix was described. The composite film was used to immobilize PPO on the surface of a glassy carbon electrode. Chitosan was utilized to improve the analytical performance of the pure clay-modified bioelectrode. The biosensor exhibited a series of properties: good affinity to its substrate (the apparent Michaelis-Menten constant for the sensor was found to be 0.16 mM), high sensitivity (674 mA M(-1)cm(-2) for catechol) and remarkable long-term stability in storage (it retains 88% of the original activity after 60 days). In addition, optimization of the biosensor construction as well as effects of experimental variables such as pH, operating potential and temperature on the amperometric response of the sensor were discussed.

Protein assembly onto patterned microfabricated devices through enzymatic activation of fusion pro-tag

We report a versatile approach for covalent surface-assembly of proteins onto selected electrode patterns of pre-fabricated devices. Our approach is based on electro-assembly of the aminopolysaccharide chitosan scaffold as a stable thin film onto patterned conductive surfaces of the device, which is followed by covalent assembly of the target protein onto the scaffold surface upon enzymatic activation of the protein's "pro-tag." For our demonstration, the model target protein is green fluorescent protein (GFP) genetically fused with a pentatyrosine pro-tag at its C-terminus, which assembles onto both two-dimensional chips and within fully packaged microfluidic devices in situ and under flow. Our surface-assembly approach enables spatial selectivity and orientational control under mild experimental conditions. We believe that our integrated approach harnessing genetic manipulation, in situ enzymatic activation, and electro-assembly makes it advantageous for a wide variety of bioMEMS and biosensing applications that require facile "biofunctionalization" of microfabricated devices.

The effect of the layer structure on the activity of immobilized enzymes in ultrathin films

The molecular engineering capability of the layer-by-layer (LbL) method for fabricating thin films has been exploited in order to immobilize glucose oxidase (GOD) in films with alternating layers of chitosan. Chitosan was proven a good scaffolding material, as GOD molecules preserved their catalytic activity towards glucose oxidation. Using electrochemical measurements, we showed that chitosan/GOD LbL films can be used to detect glucose with a limit of detection of 0.2 mmol l-1 and an activity of 40.5 microA mmol-1 L microg-1, which is highly sensitive when compared to other sensors in previous reports in the literature. The highest sensitivity of the LbL film was achieved when only the top layer contained GOD, thus indicating that GOD in inner layers did not contribute to glucose oxidation, probably because it hampers analyte diffusion and electron transport through the deposited layers. This may be explained by the dense packing of GOD molecules in the LbL films with chitosan, as inferred from estimates of the amount of GOD adsorbed per layer using a quartz crystal microbalance.

Glucose biosensor based on the layer-by-layer self-assembling of glucose oxidase and chitosan derivatives on a thiolated gold surface

The work proposed here deals with the design and characterization of biorecognition layers for the amperometric glucose determination based on the self-assembling of new chitosan derivatives, Nafion and glucose oxidase onto thiolated gold electrodes. The supramolecular multistructure is obtained by deposition of a layer of chitosan derivative (quaternized or hydrophobic) onto the gold surface modified with the sodium salt of 3-mercapto-1-propansulfonic acid, followed by the deposition of a layer of Nafion (as anti-interference barrier) and by the alternate deposition of the chitosan derivative and glucose oxidase (as biocatalytic layer). The influence of the deposition time and concentration of polyelectrolytes, organization and number of layers, and nature of the chitosan derivative on the sensitivity and selectivity of the bioelectrode is examined and optimized in order to obtain a rational design of the biosensor. The system is studied electrochemically from the oxidation at 0.700 V of the hydrogen peroxide enzymatically generated using gold as substrate, and spectrophotometrically from the protein absorption at 277 nm using quartz as substrate. The selected biosensor containing five quaternized chitosan/glucose oxidase bilayers exhibits very good analytical performance with a sensitive ((4.9+/-0.2) x 10(2) nA mM(-1)) and highly selective response (0% interference for maximum physiological levels of ascorbic acid and uric acid), demonstrating that the alternate electrostatic adsorption of conveniently selected polyelectrolytes allows noticeable improvements in the selectivity and sensitivity of a biosensor.

A disposable electrochemical immunosensor for flow injection immunoassay of carcinoembryonic antigen

A new simple immunoassay method for carcinoembryonic antigen (CEA) detection using a disposable immunosensor coupled with a flow injection system was developed. The immunosensor was prepared by coating CEA/colloid Au/chitosan membrane at a screen-printed carbon electrode (SPCE). Using a competitive immunoassay format, the immunosensor inserted in the flow system with an injection of sample and horseradish peroxidase (HRP)-labeled CEA antibody was used to trap the labeled antibody at room temperature for 35 min. The current response obtained from the labeled HRP to thionine-H(2)O(2) system decreased proportionally to the CEA concentration in the range of 0.50-25 ng/ml with a correlation coefficient of 0.9981 and a detection limit of 0.22 ng/ml (S/N=3). The immunoassay system could automatically control the incubation, washing and current measurement steps with good stability and acceptable accuracy. Thus, the proposed method proved its potential use in clinical immunoassay of CEA.

Glucose oxidase/colloidal gold nanoparticles immobilized in Nafion film on glassy carbon electrode: Direct electron transfer and electrocatalysis

The direct electron transfer of glucose oxidase (GOD) was achieved based on the immobilization of GOD/colloidal gold nanoparticles on a glassy carbon electrode by a Nafion film. The immobilized GOD displayed a pair of well-defined and nearly reversible redox peaks with a formal potential (Eo ') of -0.434 V in 0.1 M pH 7.0 phosphate buffer solution and the response showed a surface-controlled electrode process. The dependence of Eo ' on solution pH indicated that the direct electron transfer reaction of GOD was a two-electron-transfer coupled with a two-proton-transfer reaction process. The experimental results also demonstrated that the immobilized GOD retained its electrocatalytic activity for the oxidation of glucose. So the resulting modified electrode can be used as a biosensor for detecting glucose.

Electrochemically deposited nanocomposite of chitosan and carbon nanotubes for biosensor application

A simple and controllable electrodeposition method for the formation of a chitosan-carbon nanotube nanocomposite film on an electrode surface was proposed and further used for the construction of an electrochemical biosensor.

Covalent attachment of glucose oxidase to an Au electrode modified with gold nanoparticles for use as glucose biosensor

A feasible method to fabricate glucose biosensor was developed by covalent attachment of glucose oxidase (GOx) to a gold nanoparticle monolayer modified Au electrode. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of ferrocyanide followed and confirmed the assemble process of biosensor, and indicated that the gold nanoparticles in the biosensing interface efficiently improved the electron transfer between analyte and electrode surface. CV performed in the presence of excess glucose and artificial redox mediator, ferrocenemethanol, allowed to quantify the surface concentration of electrically wired enzyme (Gamma(E)(0)) on the basis of kinetic models reported in literature. The Gamma(E)(0) on proposed electrode was high to 4.1 x 10(-12) mol.cm(-2), which was more than four times of that on electrode direct immobilization of enzyme by cystamine without intermediate layer of gold nanoparticles and 2.4 times of a saturated monolayer of GOx on electrode surface. The analytical performance of this biosensor was investigated by amperometry. The sensor provided a linear response to glucose over the concentration range of 2.0 x 10(-5)-5.7 x 10(-3) M with a sensitivity of 8.8 microA.mM(-1).cm(-2) and a detection limit of 8.2 microM. The apparent Michaelis-Menten constant (K(m)(app)) for the sensor was found to be 4.3 mM. In addition, the sensor has good reproducibility, and can remain stable over 30 days.