Peihong Deng

Electrochemical determination of bisphenol A in plastic bottled drinking water and canned beverages using a molecularly imprinted chitosan–graphene composite film modified electrode

Herein, a novel electrochemical sensor based on an acetylene black paste electrode modified with molecularly imprinted chitosan-graphene composite film for sensitive and selective detection of bisphenol A (BPA) has been developed. Several important parameters controlling the performance of the sensor were investigated and optimised. The imprinted sensor offers a fast response and sensitive BPA quantification. Under the optimal conditions, a linear range from 8.0 nM to 1.0 μM and 1.0 to 20 μM for the detection of BPA was observed with the detection limit of 6.0 nM (S/N=3). Meanwhile, the fabricated sensor showed excellent specific recognition to template molecule among the structural similarities and coexistence substances. Furthermore, this imprinted electrochemical sensor was successfully employed to detect BPA in plastic bottled drinking water and canned beverages.

Electrochemical behavior and voltammetric determination of vanillin based on an acetylene black paste electrode modified with graphene-polyvinylpyrrolidone composite film.

The graphene-polyvinylpyrrolidone composite film modified acetylene black paste electrode (GR-PVP/ABPE) was fabricated and used to determine vanillin. In 0.1M H3PO4 solution, the oxidation peak current of vanillin increased significantly at GR-PVP/ABPE compared with bare ABPE, PVP/ABPE and GR/ABPE. The oxidation mechanism was discussed. The experimental conditions that exert influence on the voltammetric determination of vanillin, such as supporting electrolytes, pH values, accumulation potential and accumulation time, were optimized. Besides, the interference, repeatability, reproducibility and stability measurements were also evaluated. Under the optimal experimental conditions, the oxidation peak current was proportional to vanillin concentration in the range of 0.02-2.0 μM, 2.0-40 μM and 40-100 μM. The detection limit was 10nM. This sensor was used successfully for vanillin determination in various food samples.

Acetylene black paste electrode modified with graphene as the voltammetric sensor for selective determination of tryptophan in the presence of high concentrations of tyrosine

A reliable sensor was fabricated by modifying an acetylene black paste electrode with graphene (denoted as GR/ABPE) for sensitive and selective determination of tryptophan (Trp). Due to the high sorption ability, large surface area and numerous active sites, the GR/ABPE showed a strong enhancement effect on the oxidation of Trp, and greatly increased the peak current. The parameters affecting the Trp determination were investigated. In 1.0 M H2SO4 the voltammetric responses of Trp and tyrosine (Tyr) were well separated into two distinct peaks with peak potential difference (ΔE(pa)) of 115 mV. Under the optimized conditions, in the presence of 0.1 mM Tyr, the oxidation peak current of Trp was proportional to its concentration in the range between 0.1 μM and 0.1 mM, with the limit of detection of 60 nM (S/N=3). The GR/ABPE was applied to the direct detection of Trp in pharmaceutical and biological samples with satisfactory results. This work provides a simple and easy approach to selective detection of Trp in the presence of Tyr.

Ag/N-doped reduced graphene oxide incorporated with molecularly imprinted polymer: An advanced electrochemical sensing platform for salbutamol determination

In this work, the metallic silver and non-metallic nitrogen co-doped reduced graphene oxide (Ag-N-RGO) was first synthesized by a simple and cost-effective strategy, and then a molecularly imprinted polymer (MIP) was formed in situ at the surface of the prepared composite via electropolymerization of o-phenylenediamine in the presence of salbutamol as the template molecule. The electrochemical characterizations demonstrate that the bifunctional graphene-based composite shows improved catalytic performance than that of pristine graphene doped with one-component or none. The MIP sensor based on Ag-N-RGO owns high porous surface structure, resulting in the increased current response and enhanced recognition capacity than that of non-imprinted sensor. The outstanding performance of the developed sensor derives from the combined advantages of Ag-N-RGO with effective catalytic property and MIP with excellent selectivity. Under the optimal conditions, the electrochemical response of the developed sensor is linearly proportional to the concentration of salbutamol in the range of 0.03-20.00µmolL-1 with a low detection limit of 7 nmol L-1. The designed sensor has exhibited the multiple advantages such as low cost, simple manufacture, convenient use, excellent selectivity and good reproducibility. Finally, the proposed method has been extended for the determinations of salbutamol in human urine and pork samples, and the satisfactory recoveries between 98.9-105.3% are achieved.

Simultaneous determination of ascorbic acid and rutin in pharmaceutical preparations with electrochemical method based on multi-walled carbon nanotubes-chitosan composite film modified electrode.

In this paper, the simultaneous voltammetric determination of ascorbic acid (AA) and rutin (Ru) has been achieved at an acetylene black paste electrode modified with multi-walled carbon nanotubes-chitosan composite film (denoted as MWCNTs-CHIT/ABPE). Compared with bare electrode, the peak currents of AA and Ru at MWCNTs-CHIT/ABPE increased greatly and the anodic peak potential difference (ΔE(pa)) between AA and Ru are up to 342mV, which is undoubtedly attributed to the unique characteristics of AB and MWCNTs such as excellent electric conductivity, high surface area and strong adsorptive abilities, resulting in higher accumulation efficiency to AA and Ru. The influences of some experimental conditions on the oxidation of AA and Ru were tested and the calibration plot was examined. Under the optimized condition, a good linearity was obtained in the concentration range of 1μM-0.4mM for AA in the presence of 10μM Ru and 20nM-10μM for Ru in the presence of 1mM AA. The detection limits (S/N=3) of AA and Ru are 0.8μM and 10nM, respectively. The proposed method was successfully applied to the simultaneous determination of AA and Ru in pharmaceutical samples with reliable recovery.

Facile synthesis of 3D porous nitrogen-doped graphene as an efficient electrocatalyst for adenine sensing

In this work, a simple, low-cost and eco-friendly strategy for fabricating the three-dimensional porous nitrogen-doped graphene (3D-N-GN) is demonstrated by combining the hydrothermal assembly and freeze-drying process without using any framework support. The desired features for 3D-N-GN, such as rich macroporosity, nitrogen-doping structure and high active surface area have been confirmed by scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical techniques, respectively. In comparison with two-dimensional graphene (2D-GN) and nitrogen-doped graphene (2D-N-GN), 3D-N-GN makes a more negative shift in the oxidation peak potential of adenine together with a remarkable increase in the oxidation peak current, highlighting the importance of the nitrogen-doping and 3D construction of the graphene-based support for improving the electrocatalytic performance. It also indicates that 3D-N-GN can be used as an efficient electrocatalyst for adenine sensing. Furthermore, the sensing conditions are optimized and the resulting sensor displays excellent analytical performance in the detection of adenine at low concentrations ranging from 0.02 to 1.20 μM, with a detection limit of 8 nM. Finally, this proposed method not only exhibits preferable reproducibility, stability and adequate sensitivity, but also demonstrates good efficiency in the detection of adenine in biological fluids.

Preparation of 2D molecularly imprinted materials based on mesoporous silicas via click reaction

The two-dimensional (2D) molecular imprinting approach has attracted extensive research interest in recent years due to its potential advantages such as simple construction, fast template removal and rapid mass transfer. In this study, a new 2D imprinting approach based on the combination of mesoporous silica materials and molecular imprinting technology is reported. 2D molecularly imprinted materials (MIMs) for cholesterol were prepared by using cholesterol as the template, azide modified β-cyclodextrin (azide-β-CD) as the functional monomer and alkynyl-modified SBA-15 (alkyne-SBA-15) as the skeleton. In this method, azide-β-CD molecules were first assembled around the templates by formation of template-monomer complexes, and thus the mutual positions of azide-β-CD molecules were fixed. Then, azide-β-CD molecules were anchored to the walls of the nano-pores of SBA-15 via click chemistry. After removal of the template molecules, the resulting cavities, i.e., recognition sites were formed in the nano-pores of mesoporous silicas. The synthesized MIM was characterized by FT-IR, X-ray diffraction (XRD), elemental analysis (EA), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and so on. Binding kinetic experiments demonstrated that the 2D imprinting approach can improve site accessibility for the template effectively. The 2D MIM exhibited binding affinity and specificity for the template, as revealed by equilibrium binding experiments. When using MIM as a stationary phase for HPLC, baseline separation of cholesterol from other compounds can be achieved. In addition, the use of 2D imprinting significantly reduced the peak broadening and tailing.

Sensitive determination of bisphenol A in plastic products by derivative voltammetry using an acetylene black paste electrode coated with salicylaldehyde-modified chitosan

A sensitive and reliable electrochemical method was developed for determination of bisphenol A (BPA) in plastic products using an acetylene black paste electrode coated with salicylaldehyde-modified chitosan (denoted as S-CHIT/ABPE). In the second-order derivative linear sweep voltammetry technique, BPA yielded a very sensitive and well-defined oxidation peak at 842 mV in 0.2 mol L−1 HCl solution. Owing to its unique structure and extraordinary properties, S-CHIT/ABPE showed higher accumulation efficiency toward BPA compared with bare ABPE, and significantly enhanced the oxidation peak current of BPA. Under the optimum conditions, the oxidation peak current was proportional to the concentration of BPA over the range of 4.0 × 10−8 mol L−1 ∼ 1.0 × 10−5 mol L−1. The detection limit (S/N = 3) was 2.0 × 10−8 mol L−1. The fabricated S-CHIT/ABPE not only exhibited strong adsorption capacity toward BPA, but also provided remarkable stable and quantitatively reproducible analytical performance. Additionally, this newly-developed method possesses some obvious advantages including high sensitivity, extreme simplicity, rapid response and low cost.

Fluorescent molecularly imprinted polymers based on 1,8-naphthalimide derivatives for efficiently recognition of cholic acid

Fluorescent molecularly imprinted polymers (MIPs) have attracted increasing attentions in recent years due to their high selectivity and sensitivity for target molecules. In this study, two cholic acid imprinted fluorescent polymers, i.e., MIP1 and MIP2, were prepared using 4-dimethylamino-N-allylnaphthalimide (F1) and 4-piperazinyl-N-allylnaphthalimide (F2) as the fluorescent functional monomers, respectively. The fluorescence intensity of MIP1 decreased linearly with the increase of the template concentration in the range of 1.50-120.0 μM, while the fluorescence intensity of MIP2 increased linearly with the increase of the template concentration in the range of 0.40-110.0 μM. The detection limits of MIP1 and MIP2 for cholic acid were 0.42 and 0.083 μM, respectively. The mechanisms of the fluorescence responsive of the imprinted polymers were discussed. The results of fluorescence measurement and binding experiments demonstrated that both imprinted polymers have high recognition abilities and binding affinities for the template. The imprinted polymers have been successfully applied to the determination of cholic acid in human serums. The present study indicated that 1,8-naphthalimide can be used as a modular building block for design and construction of various fluorogenic molecularly imprinted materials for practical sensing and separation.

Fluorescent boronic acid terminated polymer grafted silica particles synthesized via click chemistry for affinity separation of saccharides

Boronic acids are important for effective separation of biological active cis-diols. For the purpose of constructing a new type of saccharide-sensitive material which can not only provide convenient separation but also improve the access of boronic acid to guest molecules, the fluorogenic boronic acid terminated, thermo-sensitive polymers (BA-polyNIPAm) were grafted to an alkyne modified silica gel through the exploitation of click chemistry. The BA-polyNIPAm grafted silica gel (BA-polyNIPAm-SG) was characterized by FT-IR, fluorescence spectra, fluorescence microscopy, elemental analysis (EA), thermal gravimetric analysis (TGA), scanning electron microscope (SEM) and so on. BA-polyNIPAm-SG displayed affinity binding ability for saccharides under physiological pH value and allowed saccharides to be conveniently separated from solution. The maximum binding capacities for fructose and glucose are 83.2 μmol/g and 70.4 μmol/g polymer, respectively. The intensity of fluorescence emission of BA-polyNIPAm-SG increased with the increasing of fructose concentration. The present study provides a new kind of composite material which contains moveable and flexible grippers for recognizing and binding guest molecules.