Shuqing Gu

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.

Mild and novel electrochemical preparation of β-cyclodextrin/graphene nanocomposite film for super-sensitive sensing of quercetin

A mild and novel preparation tactics based on electrochemical techniques for the fabrication of electro-deposited graphene (E-GR) and polymerized β-cyclodextrin (P-βCD) nanocomposite film were developed. The structure and morphology of GR-based nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Simultaneously, the electrochemical properties of this nanocomposite were characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Based on the synergistic effect of E-GR and P-βCD, a super-sensitive electrochemical sensor for quercetin was successfully fabricated. Under optimum conditions, the determination range for quercetin was from 0.005 to 20 µM with a low detection limit of 0.001 µM (S/N=3). Moreover, this sensor also displays excellent sensitivity, fine reproducibility and stability. To further study the practical applicability of the proposed sensor, the determination of real samples was carried out with satisfactory results.

A droplet-based microfluidic electrochemical sensor using platinum-black microelectrode and its application in high sensitive glucose sensing.

We describe a droplet-based microfluidic electrochemical sensor using platinum-black (Pt-black) microelectrode. Pt-black microelectrode was generated by electrodeposition of Pt nanoparticles on bare Pt microelectrode. Scanning electron microscope (SEM) image displays a flower-like microstructure of Pt nanoparticels. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) indicate that the Pt-black efficiently decreased the charge transfer resistance and improved the electrocatalytic activity towards oxidation of hydrogen peroxide (H2O2). Compared with bare Pt microelectrode, the current response on Pt-black microelectrode increased 10.2 folds. The effect of applied potential and electrodeposition time has been investigated in detail. The proposed sensor was validated by performing enzyme activity assay in flowing droplets. For demonstration, glucose oxidase (GOx) is chosen as the model enzyme, which catalyzes the oxidation of β-D-glucose to the product H2O2. The enzyme activity of GOx was evaluated by measuring the electrochemical current responding to various glucose concentrations. And the results indicate that this microfluidic sensor holds great potential in fabricating novel glucose sensors with linear response up to 43.5mM. The analytical applications of the droplet-based microfluidic sensor were tested by using human blood serum samples. Reproducibility, interferences, and long-term stability of the modified electrode were also investigated. The present approach shows the feasibility and great potentials in constructing highly sensitive and low-consumption sensors in the field of droplet microfluidics.

A novel nonenzymatic sensor based on LaNi0.6Co0.4O3 modified electrode for hydrogen peroxide and glucose.

In this paper, LaNi(0.6)Co(0.4)O(3) (LNC) nanoparticles were synthesized by the sol-gel method, and the structure and morphology of LNC nanoparticles were characterized by X-ray diffraction spectrum, scanning electron microscopy and transmitting electron microscopy. And then, LNC was used to modify carbon paste electrode (CPE) without any adhesive to fabricate hydrogen peroxide and glucose sensor, and the results demonstrated that LNC exhibited strong electrocatalytical activity by cyclic voltammetry and amperometry. In H(2)O(2) determination, linear response was obtained in the concentration range of 10 nM-100 μM with a detection limit of 1.0 nM. In glucose determination, there was the linear region of 0.05-200 μM with a detection limit of 8.0 nM. Compared with other reports, the proposed sensor also displayed high sensitivity toward H(2)O(2) (1812.84 μA mM(-1)cm(-2)) and glucose (643.0 μA mM(-1)cm(-2)). Moreover, this prepared sensor was applied to detect glucose in blood serum and hydrogen peroxide in toothpaste samples with satisfied results, indicating its possibility in practical application.

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.

Synthesis of Mn-doped CdTe quantum dots and their application as a fluorescence probe for ascorbic acid determination

A novel and highly sensitive fluorescence probe has been developed for determination of ascorbic acid (AA) based on the distinct fluorescence quenching of Mn-doped CdTe fluorescence emission in the presence of AA. Mn-doped CdTe quantum dots were prepared by using inorganic salts as precursors and L-cysteine as the stabilizer in an aqueous system. Their optical properties were characterized by ultraviolet-visible spectrometry, spectrofluorometry, structural features by X-ray diffraction spectrometry, transmission electron microscopy, Fourier transform infrared spectrometry, and exact composition by energy dispersive spectrometry, respectively. Under the optimum conditions, the response is linearly proportional to the concentration of AA in the range of 0.4 to 10 nM with an extremely low detection limit of about 0.081 nM. The newly developed method was successfully applied for the determination of AA in pharmaceutical tablets with good recoveries.

Application of L-cysteine capped core–shell CdTe/ZnS nanoparticles as a fluorescence probe for cephalexin

In this paper, a novel method was developed for rapid and quantitative determination of cephalexin on the basis of the fluorescence quenching of L-cysteine capped core–shell CdTe/ZnS nanoparticles (NPs). The functionalized CdTe/ZnS NPs were successfully synthesized in aqueous solution. L-Cysteine capped CdTe/ZnS NPs were characterized by the means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Experimental results displayed that the fluorescence intensity of CdTe/ZnS NPs reduced in the presence of cephalexin due to interaction between L-cysteine capped CdTe/ZnS NPs and cephalexin, with the emission wavelength at about 665 nm. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of cephalexin ranging from 3.4 × 10−6 to 1.0 × 10−4 M with a detection limit of 0.83 × 10−6 M. The L-cysteine capped CdTe/ZnS NPs fluorescence probe showed an obvious and good response to cephalexin, and the result was also satisfactory when it was applied to analyzing cephalexin in a real sample.

Simultaneous detection of roxithromycin and dopamine using a sensor platform based on poly(sulfosalicylic acid) and its application in human serum studies

A novel poly-sulfosalicylic acid-modified glassy carbon electrode (PSA/GCE) was developed for the detection of roxithromycin (RM) and its simultaneous determination with dopamine (DA). The morphologies and interface properties of the PSA film were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Fourier transform infrared (FTIR) spectra indicated that PSA was successfully modified on the electrode. The electro-catalytic oxidation of RM on the PSA/GCE was investigated, individually and simultaneously, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) under optimum conditions. The proposed method exhibited a wide linear dynamic range from 2 × 10−8 to 1 × 10−5 M with a low detection limit (S/N = 3) of 6.67 × 10−9 M for roxithromycin. The modified electrode showed good stability, reproducibility and high selectivity, and demonstrated its feasibility for analytical purposes and human serum samples.