Shen-Ming Chen

Preparation and characterization of PtAu hybrid film modified electrodes and their use in simultaneous determination of dopamine, ascorbic acid and uric acid

A novel biosensor was fabricated by electrochemical deposition of platinum and gold nanoparticles (nanoAu) with l-Cysteine on glassy carbon electrode. It was found that the nanoAu particle size distribution range was (50-80 nm), and the platinum particle size range was (200-300 nm). The hybrid film could be produced on gold and transparent indium tin oxide electrodes for different kind of studies such as electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) and electrochemical studies. The PtAu hybrid film was applied to the electro catalytic oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) at pH 4.0 using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The modified electrode was quite effective not only to detect DA, AA and UA individually but also in simultaneous determination of these species in a mixture. The overlapping anodic peaks of DA, AA and UA were resolved into three well-defined voltammetric peaks in CV and DPV. The catalytic peak currents obtained from CV and DPV increased linearly with concentration. The relative standard deviation (% R.S.D., n=10) for AA, DA and UA were less than 2.0% and DA, AA and UA can be determined in the ranges of 0.103-1.65, 0.024-0.384 and 0.021-0.336 mM, respectively. In addition, the modified electrode also shows good sensitivity, and stability. Satisfactory results were achieved for the determination of DA, AA and UA in dopamine injection solution, vitamin C tablets and human urine samples.

A simple electrochemical approach to fabricate a glucose biosensor based on graphene–glucose oxidase biocomposite

We report a simple electrochemical approach for the immobilization of glucose oxidase (GOx) on reduced graphene oxide (RGO). The immobilization of GOx was achieved in a single step without any cross linking agents or modifiers. A simple solution phase approach was used to prepare exfoliated graphene oxide (GO), followed by electrochemical reduction to get RGO-GOx biocomposite. The direct electrochemistry of GOx was revealed at the RGO-GOx modified glassy carbon electrode (GCE). The electrocatalytic and electroanalytical applications of the proposed film were studied by cyclic voltammetry (CV) and amperometry. It is notable that the glucose determination has been achieved in mediator-free conditions. RGO-GOx film showed very good stability, reproducibility and high selectivity. The developed biosensor exhibits excellent catalytic activity towards glucose over a wide linear range of 0.1-27mM with a sensitivity of 1.85μAmM(-1)cm(-2). The facile and easy electrochemical approach used for the preparation of RGO-GOx may open up new horizons in the production of cost-effective biosensors and biofuel cells.

Direct electrochemistry of glucose oxidase at electrochemically reduced graphene oxide-multiwalled carbon nanotubes hybrid material modified electrode for glucose biosensor.

Direct electrochemistry of glucose oxidase (GOx) at an electrochemically reduced graphene oxide-multiwalled carbon nanotubes hybrid (ERGO-MWCNT) modified glassy carbon electrode (GCE) has been reported. The π-π stacking interaction operating between the MWCNT and graphene oxide (GO) has been revealed by UV-Vis absorption spectroscopy. GOx was well immobilized onto the ERGO-MWCNT hybrid film, as a result direct electrochemistry of GOx has been achieved. Compared with pristine MWCNT, 2.1 fold higher peak current and very low peak to peak separation (ΔE(p)) of 26 mV were observed at the hybrid film, demonstrating faster electron transfer between GOx and the modified electrode surface. Moreover, the modified film exhibited high electrocatalytic activity towards glucose via reductive detection of oxygen consumption and in the presence of mediator. The proposed biosensor exhibits low detection limit of 4.7 μM with wide linear range of 0.01-6.5mM and acquires excellent storage and operational stabilities. The accurate glucose determination in human blood serum and good recoveries achieved in spiked urine samples revealed their great potential in the practical applications.

The electrochemical properties of dopamine, epinephrine, norepinephrine, and their electrocatalytic reactions on cobalt(II) hexacyanoferrate films

Abstract The electrochemical properties of epinephrine, dopamine, and norepinephrine in aqueous solutions with various pH values have been investigated. The second redox couple of epinephrine shows an obvious reversible redox, with the formal potentials being pH dependent in the range 3≤pH≤13. The electrochemical properties of dopamine, epinephrine, and norepinephrine were pH dependent, and they exhibited different cyclic voltammograms. Cobalt(II) hexacyanoferrate films were electrocatalytically oxidation active for dopamine, epinephrine, and norepinephrine in aqueous solutions, with the electrocatalytic oxidation current developing through the Co(II)CNFe(III) film. Cobalt(II) hexacyanoferrate also shows reversible electrocatalytic properties. Such films electrocatalytically reduce those oxidation products of dopamine, epinephrine, and norepinephrine that are produced from the electrocatalytic oxidation of these compounds by a cobalt(II) hexacyanoferrate film. Cobalt(II) hexacyanoferrate modified films are also electrocatalytically oxidation active for dopamine, epinephrine, and norepinephrine, and their electrochemical properties were investigated using the rotating ring-disk electrode method.

Performing enzyme-free H2O2 biosensor and simultaneous determination for AA, DA, and UA by MWCNT–PEDOT film

An enzyme-free hydrogen peroxide (H2O2) biosensor based on MWCNT-PEDOT film modified electrode has been successfully performed on glassy carbon electrode (GCE) and indium tin oxide (ITO) electrode. At an applied potential of -0.5V vs. Ag/AgCl, the MWCNT-PEDOT electrode exhibited linearly dependence on H2O2 concentration in the range of 0.1-9.8 mM. It can be observed two significantly linear sections. One shows sensitivity of 943 μM mM(-1) cm(-2) with signal/noise of 6; and the other one shows sensitivity of 174 μM mM(-1) cm(-2) with signal/noise of 4 in pH 7 PBS. It also presented excellent stability at room temperature, with a variation of response current less than 5% over 30 days. Moreover, the sensor was characterized by cyclic voltammetry (CV), scanning electronic microscopy (SEM), atomic force microscopy (AFM), and different pulse voltammetry (DPV). This sensor also can simultaneously detect AA, DA, and UA and can be utilized to develop multifunctional biosensors.

Nanostructured Zinc Oxide Particles in Chemically Modified Electrodes for Biosensor Applications

Abstract Zinc oxide (ZnO) has received considerable attention because of its unique optical, semiconducting, piezoelectric, and magnetic properties. ZnO nanostructures exhibit interesting properties including high catalytic efficiency and strong adsorption ability. Recently, the interest has been focused toward the application of ZnO in biosensing because of its high isoelectric point (9.5), biocompatibility, and fast electron transfer kinetics. Such features advocate the use of this exciting material as a biomimic membrane to immobilize and modify biomolecules. This review highlights the potential use of ZnO in modified electrodes and biosensing.

Electroanalytical determination of acetaminophen using nano-TiO2/polymer coated electrode in the presence of dopamine

We report a new method for selective determination of acetaminophen (AP) in physiological condition. A new hybrid film modified electrode was fabricated using inorganic semiconducting nano-TiO(2) particles and redox active polymer. Redox polymer, poly(acid yellow 9) (PAY) was electrochemically deposited onto nano-TiO(2) coated glassy carbon (GC) electrode. Surface characterizations of modified electrode were investigated by using atomic force microscope and scanning electron microscope. The PAY/nano-TiO(2)/GC hybrid electrode shows stable redox response in the pH range 1-12 and exhibited excellent electrocatalytic activities towards AP in 0.1M phosphate buffer solution (pH 7.0). Consequently, a simple and sensitive electroanalytical method was developed for the determination of AP. The oxidation peak current was proportional to the concentration of acetaminophen from 1.2 x 10(-5) to 1.20 x 10(-4)M and the detection limit was found to be 2.0 x 10(-6)M (S/N=3). Possible interferences were tested and evaluated that it could be possible to selective detection of AP in the presences of dopamine, nicotinamide adenine dinucleotide (NADH), ascorbic acid and uric acid. The proposed method was used to detect acetaminophen in commercial drugs and the obtained results are satisfactory.

Preparation, characterization, and electrocatalytic oxidation properties of iron, cobalt, nickel, and indium hexacyanoferrate

Abstract Using consecutive cyclic voltammetry, iron(II), cobalt(II), nickel(II), and indium(III) hexacyanoferrate films have been prepared, and their electrocatalytic properties in electrolytes containing various cations have been determined. Cyclic voltammograms recorded the electrochemical formation of nickel(II) hexacyanoferrate films using 13 cations: Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , H + , NH 4 + , tetraethylammonium cation, and Al 3+ . The electrochemical formation of the iron(II), indium(III), and cobalt(II) hexacyanoferrate films from different cation solutions with the same concentration showed different cyclic voltammograms. The deposition growth of the cobalt(II) and nickel(II) hexacyanoferrates in aqueous Ca(NO 3 ) 2 and Ba(NO 3 ) 2 solutions immersed in various aqueous cation solutions were consistent with the EQCM and spectroscopic data. The electrocatalytic oxidation of SO 3 2− and S 2 O 3 2− by various metal hexacyanoferrate film catalysts in electrolytes of various cations showed some selectivity towards several cations and also showed varying redox potentials.

Nanomaterials - Acetylcholinesterase Enzyme Matrices for Organophosphorus Pesticides Electrochemical Sensors: A Review

Acetylcholinesterase (AChE) is an important cholinesterase enzyme present in the synaptic clefts of living organisms. It maintains the levels of the neurotransmitter acetylcholine by catalyzing the hydrolysis reaction of acetylcholine to thiocholine. This catalytic activity of AChE is drastically inhibited by trace amounts of organophosphorus (OP) pesticides present in the environment. As a result, effective monitoring of OP pesticides in the environment is very desirable and has been done successfully in recent years with the use of nanomaterial-based AChE sensors. In such sensors, the enzyme AChE has been immobilized onto nanomaterials like multiwalled carbon nanotubes, gold nanoparticles, zirconia nanoparticles, cadmium sulphide nano particles or quantum dots. These nanomaterial matrices promote significant enhancements of OP pesticide determinations, with the thiocholine oxidation occurring at much lower oxidation potentials. Moreover, nanomaterial-based AChE sensors with rapid response, increased operational and long storage stability are extremely well suited for OP pesticide determination over a wide concentration range. In this review, the unique advantages of using nanomaterials as AChE immobilization matrices are discussed. Further, detection limits, sensitivities and correlation coefficients obtained using various electroanalytical techniques have also been compared with chromatographic techniques.

The electrocatalytic properties of biological molecules using polymerized luminol film-modified electrodes

Polymerization of luminol performed in strongly acidic aqueous solution can produce thin electrochemically active films of one redox couple. The film can be produced on glassy carbon, platinum, gold and transparent semiconductor tin(IV) oxide electrodes. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study in situ growth of the polyluminol film. The modified film is electrocatalytically active for NADH oxidation in acidic and neutral aqueous solutions, and the electrocatalytic oxidation current develops from the anodic peak of the redox couple. The direct electrocatalytic oxidation of epinephrine, dopamine, ascorbic acid, and l-cysteine by the polyluminol film in acidic and neutral aqueous solutions also shows electrocatalytic oxidation activity. The electrocatalytic oxidation properties of dopamine, ascorbic acid, and epinephrine by polyluminol film in the presence of mixtures of the three compounds or of only one compound are also discussed. The results show a selective measurement of dopamine and ascorbic acid. The polymer films were more stable in acidic solutions, their formal potentials being pH-dependent with a slope of −58 mV pH−1.