Renewable reagentless hydrogen peroxide sensor based on direct electron transfer of horseradish peroxidase immobilized on colloidal gold-modified electrode

Hemoglobin/colloidal silver nanoparticles immobilized in titania sol–gel film on glassy carbon electrode: Direct electrochemistry and electrocatalysis

By vapor deposition method, both hemoglobin (Hb) and colloidal silver nanoparticles (CSNs) were entrapped in a titania sol-gel matrix on the surface of a glassy carbon electrode (GCE). CSNs could greatly enhance the electron transfer reactivity of Hb and its catalytic ability toward nitrite. Direct fast electron transfer between Hb and the GCE was achieved, and a pair of well-defined, quasi-reversible redox peaks was observed. The anodic and cathodic peak potentials are located at -0.298 V and -0.364 V (vs. Ag/AgCl), respectively. The dependence of the formal potential on solution pH indicated that the direct electron transfer reaction of Hb was a one-electron transfer coupled with a one-proton transfer reaction process. Meanwhile, the catalytic ability of Hb toward the reduction of NO2- was also studied. Accordingly, a NO2- biosensor was prepared, with a linear range from 0.2 mM to 6.0 mM and a detection limit of 34.0 microM. The apparent Michaelis-Menten constant was calculated to be 7.48 mM. Moreover, the biosensor had good long-term stability.

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.

Self-assembling gold nanoparticles on thiol-functionalized poly(styrene-co-acrylic acid) nanospheres for fabrication of a mediatorless biosensor

A novel strategy to construct a sensitive mediatorless sensor of H2O2 was described. At first, a cleaned gold electrode was immersed in thiol-functionalized poly(styrene-co-acrylic acid) (St-co-AA) nanosphere latex prepared by emulsifier-free emulsion polymerization St with AA and function with dithioglycol to assemble the nanospheres, then gold nanoparticles were chemisorbed onto the thiol groups and formed monolayers on the surface of poly(St-co-AA) nanospheres. Finally, horseradish peroxidase (HRP) was immobilized on the surface of the gold nanoparticles. The sensor displayed an excellent electrocatalytical response to reduction of H2O2 without the aid of an electron mediator. The biosensor showed a linear range of 8.0 micromol L(-1)-7.0 mmol L(-1) with a detection limit of 4.0 micromol L(-1). The biosensor retained more than 97.8% of its original activity after 60 days' storage. Moreover, the studied biosensor exhibited good current reproducibility and good fabrication reproducibility.

Amperometric biosensor for hydrogen peroxide based on ferrocene-bovine serum albumin and multiwall carbon nanotube modified ormosil composite

A novel amperometric biosensor for hydrogen peroxide (H(2)O(2)) was developed by entrapping horseradish peroxidase (HRP) in a new ormosil composite doped with ferrocene monocarboxylic acid-bovine serum albumin conjugate and multiwall carbon nanotubes (MWNTs). The ormosil was prepared using 3-(aminopropyl)triethoxysilane and 2-(3,4 epoxycyclohexyl)-ethyltrimethoxy silane as monomers. The encapsulated conjugate showed excellent electrochemistry and acted as an electron transfer mediator. The presence of MWNTs improved the conductivity of the composite film. This matrix showed a biocompatible microenvironment for retaining the native activity of the entrapped HRP and a very low mass transport barrier to the substrate, which provided a fast amperometric response to H(2)O(2). The proposed H(2)O(2) biosensor exhibited a linear range of 0.02-4.0 mM with a detection limit of 5.0 microM (S/N = 3) and a K(M)(app) value of 2.0 mM. It could be used for flow injection analysis of hydrogen peroxide with a liner range from 0.02 to 4.5 mM, sensitivity of 0.042 microA/mM and analytical time of 20 s per sample. This biosensor possessed good analytical performance and storage stability.

Colloidal gold nanoparticle modified carbon paste interface for studies of tumor cell adhesion and viability

A non-toxic biomimetic interface for immobilization of living cells and electrochemical exogenous effect study of cell viability was constructed by mixing colloidal gold nanoparticles in carbon paste. A new approach to study the effects of anti-tumor drug and other exogenous factors on cell viability was proposed. The nanoparticles were efficient for preserving the activity of immobilized living cells and preventing their leakage from the electrode surface. The immobilized living AsPC-1 cells (pancreatic adenocarcinoma cells derived from ascites) exhibited an irreversible voltammetric response related to the oxidation of guanine. The presence of guanine was verified by liquid chromatography-mass spectrometry. The contents of guanine in cytoplasm of each AsPC-1 and normal pancreatic cell were detected to be 370 and 22amol, respectively. The cytotoxic effect of adriamycin resulted in a decrease in peak current of guanine. The optimal exogenous factors that affected cell viability, including pH, temperature and salt concentration of electrolyte, were just consistent with cell growth conditions in culture. This simple and rapid method could be applied for the electrochemical investigation of exogenous effect and characterization of the viability of living cells.

Direct electrochemistry and electrocatalytic activity of catalase incorporated onto multiwall carbon nanotubes-modified glassy carbon electrode

The direct voltammetry and electrocatalytic properties of catalase, which was adsorbed on the surface of multiwall carbon nanotubes (MWCNTs), was investigated. A pair of well-defined and nearly reversible cyclic voltammetry peaks for Fe(III)/Fe(II) redox couple of catalase adsorbed on the surface of MWCNTs at approximately -0.05 V versus reference electrode in pH 6.5 buffer solution, indicating the direct electron transfer between catalase and electrode. The surface coverage of catalase immobilized on MWCNTs glassy carbon electrode was approximately 2.4x10(-10) molcm-2. The transfer coefficient (alpha) was calculated to be 0.4, and the heterogeneous electron transfer rate constant was 80 s-1 in pH 7, indicating great facilitation of the electron transfer between catalase and MWCNTs adsorbed on the electrode surface. The formal potential of catalase Fe(III)/Fe(II) couple in MWCNTs film had a linear relationship with pH values between 2 and 11 with a slope of 58 mV/pH, showing that the electron transfer is accompanied by single proton transportation. Catalase adsorbed on MWCNTs exhibits a remarkable electrocatalytic activity toward the reduction of oxygen and hydrogen peroxide. The value for calculated Michaelis-Menten constant (1.70 mM) was high, indicating the potential applicability of the films as a new type of reagentless biosensor based on the direct electrochemistry of the catalase enzyme.

Enzyme nanoparticles-based electronic biosensor

A simple and effective method to prepare an enzyme electronic biosensor by immobilizing enzyme nanoparticles directly onto the gold electrode surface is described; prepared horseradish peroxidase nanoparticles have been successfully used to develop reagentless electronic biosensors for H2O2 detection without promoters and mediators and offer great potential to develop enzyme-based electronic biosensors.

Third-generation biosensors based on the direct electron transfer of proteins

Recent progress in third-generation electrochemical biosensors based on the direct electron transfer of proteins is reviewed. The development of three generations of electrochemical biosensors is also simply addressed. Special attention is paid to protein-film voltammetry, which is a powerful way to obtain the direct electron transfer of proteins. Research activities on various kinds of biosensors are discussed according to the proteins (enzymes) used in the specific work.

Electrochemical and chemiluminescent immunosensors for tumor markers

The determination of serum tumor markers plays an important role in clinical diagnoses for the patients with certain tumor-associated disease. Although many commercial kits have been applied in clinical immunoassays, conventional methods always have some disadvantages, resulting in the need of other new, efficient, and easily automated methods. Immunosensors, considered as a major development in immunochemical field, have attracted considerable attention. With the aim of rapid screening, many immunosensors that are small, semi-automated and portable are being developed. This brief review focuses on the current research of immunosensors for tumor markers based on the electrochemical and chemiluminescent detection with emphasis on recent advances, challenges, and trends. The works on series of novel immunosensors developed for the determination of tumor markers in our group in the last few years are also introduced.

Sensitive determination of heroin based on electrogenerated chemiluminescence of tris(2,2′-bipyridyl)ruthenium(ii) immobilized in zeolite Y modified carbon paste electrode

A novel method for rapid, inexpensive, sensitive and selective determination of heroin was proposed by flow injection electrogenerated chemiluminescence (ECL). Zeolite Y sieves were used for the preparation of a ECL sensor by immobilizing tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) in their supercages, which was achieved through the ion exchange properties of the sieves. The electrochemical and ECL behaviors of Ru(bpy)3(2+) immobilized in zeolite Y modified carbon paste electrode was investigated. The immobilized Ru(bpy)3(2+) displayed a pair of surface-controlled redox peaks with an electron transfer rate constant of 1.2 +/- 0.1 s(-1) in 0.1 mol dm(-3) pH 6.3 phosphate buffer. The modified electrode showed an electrocatalytic response to the oxidation of heroin, producing a sensitized ECL signal. The ECL sensor showed a linear response to flow injection of heroin in the range of 2.0-80 micromol dm(-3) with a detection limit of 1.1 micromol dm(-3). This method for heroin determination possessed good sensitivity and reproducibility with a coefficient of variation of 1.99% (n = 15) at 50.0 micromol dm(-3). The ECL sensor showed good selectivity and long-term stability. Its surface could be renewed quickly and reproducibly by a simple polish step.

A comparison of different strategies for the construction of amperometric enzyme biosensors using gold nanoparticle-modified electrodes

A comparison of the analytical performances of several enzyme biosensor designs, based on the use of different tailored gold nanoparticle-modified electrode surfaces, is discussed. Glucose oxidase (GOx) and the redox mediator tetrathiafulvalene were coimmobilized in all cases by crosslinking with glutaraldehyde. The biosensor designs tested were based on the use of (i) colloidal gold (Au(coll)) bound on cysteamine (Cyst) monolayers self-assembled on a gold disk electrode (AuE) and (ii) glassy carbon electrodes (GCEs) modified with electrodeposited gold nanoparticles (nAu). The results obtained with these designs were compared with those provided by a GOx/Cyst-AuE and a GOx/MPA-AuE. In the second case (ii), configurations based on direct immobilization of GOx on nAu (GOx/nAu-GCE) or on Cyst or MPA self-assembled monolayers (SAMs) previously bound on gold nanoparticles (GOx/Cyst-nAu-GCE or GOx/MPA-nAu-GCE, respectively) were compared. The analytical characteristics of glucose calibration plots and the kinetic parameters of the enzyme reaction were compared for all of the biosensors tested. The GOx/Au(coll)-Cyst-AuE design showed a sensitivity for glucose determination higher than that achieved with GOx/Cyst-AuE and GOx/Au(coll)-Cyst/Cyst-AuE and similar to that achieved with GOx/MPA-AuE. Moreover, the useful lifetime of one single GOx/Au(coll)-Cyst-AuE was 28 days, remarkably longer than that of the other GOx biosensor designs.

A new film for the fabrication of an unmediated H2O2 biosensor

A novel and stable film made from polyethylene glycol (PEG) on pyrolytic graphite (PG) electrode was presented in this paper for incorporating horseradish peroxidase (HRP) to study the direct electrochemistry of the enzyme. In PEG film, HRP showed a thin-layer electrochemistry behavior. The apparent standard potential (E degrees ') was -0.379 V versus SCE at pH 7.2. Moreover, the PEG-HRP modified electrode exhibited excellent electrocatalytical response to the reduction of H2O2 with a calibration range between 2.0 x 10(-6) and 6.0 x 10(-4) M and a good linear relation from 2.0 x 10(-6) to 1.0 x 10(-4) M, on which an unmediated H2O2 biosensor was based. The detection limit of 6.7 x 10(-7) M was estimated when the signal-to-noise ratio was 3. The relative standard deviation (R.S.D.) was 4.7% for six successive determinations at a concentration of 4.0 x 10(-5) M. The apparent Michaelis-Menten constant (Km app) of the sensor was found to be 1.38 mM. Epinephrine, dopamine, and ascorbic acid did not interfere with the sensitive determination of H2O2.

Direct electrochemistry and electrocatalysis of myoglobin immobilized on a hexagonal mesoporous silica matrix

The direct electrochemistry of myoglobin (Mb) immobilized on a hexagonal mesoporous silica (HMS)-modified glassy carbon electrode was described. The interaction between Mb and HMS was investigated by using Fourier transfer infrared spectroscopy, nitrogen adsorption isotherm, and cyclic voltammetry. Two couples of redox peaks corresponding to Fe(III) to Fe(II) conversion of the Mb intercalated in the mesopores and adsorbed on the surface of the HMS were observed with the formal potentials of -0.167 and -0.029V in 0.1M, pH 7.0, phosphate buffer solution, respectively. The electrode reaction showed a surface-controlled process with one proton transfer. The immobilized Mb displayed good electrocatalytic responses to the reduction of both hydrogen peroxide (H(2)O(2)) and nitrite (NO(2)(-)), which were used to develop novel sensors for H(2)O(2) and NO(2)(-). The apparent Michaelis-Menten constants of the immobilized Mb for H(2)O(2) and NO(2)(-) were 0.065 and 0.72mM, respectively, showing good affinity. Under optimal conditions, the sensors could be used for the determinations of H(2)O(2) ranging from 4.0 to 124microM and NO(2)(-) ranging from 8.0 to 216microM. The detection limits were 6.2x10(-8) and 8.0x10(-7)M at 3 sigma, respectively. The HMS provided a novel matrix for protein immobilization and the construction of biosensors via the direct electron transfer of immobilized protein.

Reagentless glucose biosensor based on direct electron transfer of glucose oxidase immobilized on colloidal gold modified carbon paste electrode

The direct electrochemistry of glucose oxidase (GOD) adsorbed on a colloidal gold modified carbon paste electrode was investigated. The adsorbed GOD displayed a pair of redox peaks with a formal potential of -(449+/-1) mV in 0.1 M pH 5.0 phosphate buffer solution. The response showed a surface-controlled electrode process with an electron transfer rate constant of (38.9+/-5.3)/s determined in the scan rate range from 10 to 100 mV/s. GOD adsorbed on gold colloid nanoparticles maintained its bioactivity and stability. The immobilized GOD could electrocatalyze the reduction of dissolved oxygen and resulted in a great increase of the reduction peak current. Upon the addition of glucose, the reduction peak current decreased, which could be used for glucose detection with a high sensitivity (8.4 microA/mM), a linear range from 0.04 to 0.28 mM and a detection limit of 0.01 mM at a signal-to-noise ratio of 3sigma. The sensor could exclude the interference of commonly coexisted uric and ascorbic acid.

Direct voltammetry and electrochemical catalysis with horseradish peroxidase in polyacrylamide hydrogel films

This paper reports the direct voltammetry of horseradish peroxidase (HRP) incorporated in amphiphilic polyacrylamide (PAM) films modified on pyrolytic graphite (PG) electrodes. Cyclic voltammetry of HRP-PAM films showed a pair of well-defined, nearly reversible peaks at approximately -0.33 V vs. SCE in pH 7.0 buffers, characteristic of HRP heme Fe(III)/Fe(II) redox couple. The PAM films in solution contained large amounts of water and formed a hydrogel, and provided a favorable microenvironment for HRP and facilitated its direct electron transfer with underlying PG electrodes. The apparent heterogeneous electron transfer rate constant (k(s)) and formal potential (E*') were estimated by fitting the data of square wave voltammetry (SWV) with the non-linear regression analysis. UV-vis absorption spectra demonstrated that HRP in PAM films retained its secondary structure similar to its native state. The embedded HRP in PAM films showed the electrocatalytic activity to various substrates such as nitrite, oxygen and hydrogen peroxide. The possible mechanism of catalytic reaction of H(2)O(2) with HRP-PAM films was proposed.

Electrochemical biosensors for environmental monitoring

Highly sensitive electrochemical biosensors offer precision, sensitivity, rapidity, and ease of operation for on-site environmental analysis. An electrochemical biosensor is an analytical device in which a specific biological recognition element (bioreceptor) is integrated within or intimately associated with an electrode (transducer) that converts the recognition event to a measurable electrical signal for the purpose of detecting a target compound (analyte) in solution. The signal generated allows both qualitative and quantitative measurements of an analyte in real time. In most cases, a miniaturized electrochemical cell contains a low volume of analyte, which is vital when dealing with hazardous materials and makes such devices ideal for environmental monitoring. This approach not only provides the means for on-site analysis but also removes the time delay and sample alteration that can occur during transport to a centralized laboratory. We first address the basic principles of electroanalytical measurement and the merger of electrochemistry and biology into a biosensing system, and then we discuss various environmental monitoring strategies involving this technology.