Fenfen Zhang

A novel sensor based on electropolymerization of β-cyclodextrin and l-arginine on carbon paste electrode for determination of fluoroquinolones

An electrochemical sensor for fluoroquinolones (FQs) based on polymerization of β-cyclodextrin (β-CD) and L-arginine (L-arg) modified carbon paste electrode (CPE) (P-β-CD-L-arg/CPE) was built for the first time. Synergistic effect of L-arg and β-CD was used to construct this sensor for quantification of these important antibiotics. Scanning electron microscope (SEM) image shows that polymer of β-CD and L-arg has been successfully modified on electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) further indicate that polymer of β-CD and L-arg efficiently decreased the charge transfer resistance value of electrode and improved the electron transfer kinetic between analyte and electrode. Under the optimized conditions, this modified electrode was utilized to determine the concentrations of ciprofloxacin, ofloxacin, norfloxacin and gatifloxacin. The differential pulse voltammogram (DPV) exhibits the oxidation peak currents were linearly proportional to their concentration in the range of 0.05-100 μM for ciprofloxacin, 0.1-100 μM for ofloxacin, 0.1-40 μM for norfloxacin and 0.06-100 μM for gatifloxacin, respectively. This method was also successfully used to detect the concentrations of each drug in pharmaceutical formulations and human serum samples. In addition, this proposed fluoroquinolones sensor exhibited good reproducibility, long-term stability and fast current response.

Simultaneous determination of ofloxacin and gatifloxacin on cysteic acid modified electrode in the presence of sodium dodecyl benzene sulfonate.

A novel cysteic acid modified carbon paste electrode (cysteic acid/CPE) based on electrochemical oxidation of L-cysteine was developed to simultaneously determine ofloxacin and gatifloxacin in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectra (FTIR) indicated that L-cysteine was oxidated to cysteic acid. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) indicated that cysteic acid was successfully modified on electrode. The large peak separation (116 mV) between ofloxacin and gatifloxacin was obtained on cysteic acid/CPE while only one oxidation peak was found on bare electrode. And the peak currents increased 5 times compared to bare electrode. Moreover, the current could be further enhanced in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate. The differential pulse voltammograms (DPV) exhibited that the oxidation peak currents were linearly proportional to their concentrations in the range of 0.06-10 μM for ofloxacin and 0.02-200 μM for gatifloxacin, and the detection limits of ofloxacin and gatifloxacin were 0.02 μM and 0.01 μM (S/N=3), respectively. This proposed method was successfully applied to determine ofloxacin and gatifloxacin in pharmaceutical formulations and human serum samples.

Amperometric sensor based on tricobalt tetroxide nanoparticles–graphene nanocomposite film modified glassy carbon electrode for determination of tyrosine

An electrochemical sensor based on tricobalt tetroxide nanoparticles-graphene nanocomposite film modified glassy carbon electrodes (GCEs) for sensitive determination of L-tyrosine (L-Tyr) was presented here. The nanoparticles were fabricated by electro-polymerization technology. Scanning electron microscopy was implemented to characterize morphology of the nanocomposite film. The electron transfer behavior of modified electrodes was investigated in 5 mM K3[Fe(CN)6]/K4[Fe(CN)6] solution using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical response of modified electrodes toward L-Tyr was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), amperometry in detail. The results indicated that synergistic effect of Co3O4 NPs and graphene film dramatically improved the conductivity and sensitivity of the sensor. Under optimal conditions, a wide linear relationship between the responses and L-Tyr concentrations ranging from 1.0×10(-8) to 4.0×10(-5) mol L(-1) was obtained with a comparatively low detection limit of 1.0×10(-9) mol L(-1). Furthermore, the sensor also displays excellent sensitivity and high stability. To further study the practical applicability of the fabricated sensor, it was applied to detect real samples and the received results were satisfactory.

Droplet-based microfluidics for dose-response assay of enzyme inhibitors by electrochemical method.

A simple but robust droplet-based microfluidic system was developed for dose-response enzyme inhibition assay by combining concentration gradient generation method with electrochemical detection method. A slotted-vials array and a tapered tip capillary were used for reagents introduction and concentration gradient generation, and a polydimethylsiloxane (PDMS) microfluidic chip integrated with microelectrodes was used for droplet generation and electrochemical detection. Effects of oil flow rate and surfactant on electrochemical sensing were investigated. This system was validated by measuring dose-response curves of three types of acetylcholinesterase (AChE) inhibitors, including carbamate pesticide, organophosphorus pesticide, and therapeutic drugs regulating Alzheimers disease. Carbaryl, chlorpyrifos, and tacrine were used as model analytes, respectively, and their IC50 (half maximal inhibitory concentration) values were determined. A whole enzyme inhibition assay was completed in 6 min, and the total consumption of reagents was less than 5 μL. This microfluidic system is applicable to many biochemical reactions, such as drug screening and kinetic studies, as long as one of the reactants or products is electrochemically active.

Application of thioglycolic acid capped nano-ZnS as a fluorescence probe for the determination of nevirapine

A novel and sensitive method based on the quenching of the fluorescence intensity of functionalized ZnS nanoparticles (NPs) by nevirapine was proposed in this paper. ZnS NPs were synthesized by a hydrothermal method and modified with thioglycolic acid (TGA). The water-soluble modified ZnS NPs were characterized using transmission electron microscopy, X-ray diffractometry, zeta potential/particle sizing and photoluminescence spectroscopy. Under the optimum conditions, the relative fluorescence intensity (log(F0/F)) of ZnS NPs is linearly proportional to the nevirapine concentration ranging from 4.6 to 200 μM, and the limit of detection for nevirapine was found to be 0.73 μM. Moreover, the possible quenching mechanism was also investigated. The present method is convenient and suitable for practical applications.

Determination of L-tryptophane using a sensor platform based on LaCoO3 poriferous nanofibers by electrospinning

We report a sensor platform for the determination of L-tryptophane. It is based on a carbon paste electrode that was modified with LaCoO3 poriferous nanofibers that were synthesized by electrospinning and subsequent thermal treatment. The structures and morphologies of LaCoO3 poriferous nanofibers were characterized by X-ray diffraction spectrum and scanning electron microscopy. The electrochemical performance of the sensor was evaluated by cyclic voltammetry and amperometry, and the results demonstrated that it exhibits strong electrocatalytical activity towards the oxidation of L-tryptophan in 0.1 mol L−1 phosphate buffer solution (pH 3.0). The linear range of L-tyrosine was 5.0 × 10−8 to 5.0 × 10−6 mol L−1 with a low detection limit down to 1.0 × 10−8 mol L−1. Moreover, the modified electrode exhibited high selectivity, long-term stability and fast current response, demonstrating its feasibility for the analytical purpose.

Enantioselective discrimination of L-/D-phenylalanine by bovine serum albumin and gold nanoparticles modified glassy carbon electrode

A new chiral biosensor fabricated by immobilizing bovine serum albumin (BSA) on gold-nanoparticle-modified glassy carbon electrodes, which could discriminate and detect phenylalanine (Phe) enantiomers, was proposed for the first time. The enantioselectivity was characterized by using scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and square wave voltammetry. The results showed that the BSA-modified electrode could enantioselectively recognize Phe enantiomers, and larger response signals were obtained from L-Phe. The factors influencing the performance of the biosensor were investigated. The enantiomeric composition of the L-/D-Phe mixture could be determined from the calibration curves. The modified electrodes have the advantages of simple operation, rapid detection and low cost.