Siping Tang

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.

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.

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.

Fluorogenic molecularly imprinted polymers with double recognition abilities synthesized via click chemistry

This paper reports a new strategy for the preparation of molecularly imprinted polymer (MIP) based composite materials with double recognition abilities through the exploitation of click chemistry. Combining the inherent molecular recognition ability of MIPs and the affinity binding ability of boronic acid ligands for saccharides, a boronic acid-attached MIP with double recognition abilities was prepared. An alkyne modified 2,4-dichlorophenoxyacetic acid (2,4-D) imprinted polymer was first synthesized using a two-stage precipitation polymerization. An azide-contained boronic acid was then linked to the clickable 2,4-D imprinted polymers through copper-catalyzed azide-alkyne cycloaddition (CuAAC). The boronic acid-attached MIPs displayed recognition ability for 2,4-D and affinity binding ability for saccharides at physiological pH. The intensity of fluorescence emission of the boronic acid-attached MIPs was found to increase when increasing amounts of a cis-diol compound (i.e., fructose) were added.

Modification of mesoporous silica with molecular imprinting technology: A facile strategy for achieving rapid and specific adsorption

In order to improve the diffusion kinetics of molecularly imprinted materials (MIMs), applying imprinting technology to mesoporous materials is a promising strategy. In the present study, an imprinting approach based on the combination of mesoporous silica materials and molecular imprinting technology is reported. Molecularly imprinted material (MIM) for 2,4-dichlorophenoxyacetic acid (2,4-D) was prepared by using 2,4-D as the template molecule, alkyne-modified β-cyclodextrin and propargyl amine as the combinatorial functional monomers and SBA-15 as the supporter. The functional monomers were anchored to the azide-modified SBA-15 by azide-alkyne Click reaction. The synthesized MIM was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), thermal gravimetric analysis (TGA), low-angle X-ray diffraction (XRD) and N2 adsorption-desorption analysis. The interactions between template and functional monomers were studied by proton NMR analysis and UV-vis experiments. The results of the equilibrium binding experiments and selective tests showed that the prepared MIM has binding affinity and specificity for a group of analytes which have similar size and shape to those of template. Binding kinetic experiments demonstrated that the present imprinting approach can effectively enhance the mass transfer rate. The solid phase extraction of 2,4-D using MIM as the adsorbent was investigated. The extraction conditions for the processes of loading, washing and eluting were optimized. The recoveries of the molecularly imprinted solid phase extraction (MISPE) column for 2,4-D were 76.3-88.9% with relative standard deviations (RSD) of 3.48-7.64%.