Junli Hong

Amperometric detection of dopamine in human serumby electrochemical sensor based on gold nanoparticles doped molecularly imprinted polymers

In this work, a highly sensitive and selective biomimetic electrochemical sensor for the amperometric detection of trace dopamine (DA) in human serums was achieved by gold nanoparticles (AuNPs) doped molecularly imprinted polymers (MIPs). Functionalized AuNPs (F-AuNPs), a novel functional monomer bearing aniline moieties on the surface of the AuNPs, were prepared via a direct synthesis method and then used to fabricate the conductive MIPs film on the modified electrode by electropolymerization method in the presence of DA and p-aminobenzenethiol (p-ATP). The obtained electrochemical sensor based on the conductive film of AuNPs doped MIPs (AuNPs@MIPs) could effectively minimize the interferences caused by ascorbic acid (AA) and uric acid (UA). The linear range for amperometric detection of DA was from 0.02 μmol L(-1) to 0.54 μmol L(-1) with the detection limit of 7.8 nmol L(-1) (S/N=3). Furthermore, the AuNPs@MIPs modified electrode (AuNPs@MIES) was successfully employed to detect trace DA in different human serums.

Magnetic molecularly imprinted nanoparticles based on dendritic-grafting modification for determination of estrogens in plasma samples

In order to resolve the low imprinting efficiency of surface molecularly imprinted polymers (MIPs), a dendritic-grafting method introducing more functional groups was proposed to modify the SiO(2)-coated magnetic nanoparticles (SiO(2)-coated MNPs). And then magnetic MIPs (MMIPs) were obtained using 17-ethyl estradiol (EE2) as a pseudo template with dendronized SiO(2)-coated MNPs as the supporter, aiming to avoid residual template leakage and to increase the imprinting efficiency. The resulting MMIPs showed high adsorption capacity, quick binding kinetics and good selectivity for trace estrogens. Meanwhile, MMIPs were used as magnetic dispersive solid-phase extraction (MDSPE) materials coupled with HPLC-UV for the detection of trace estrogens. The amounts of three estrogens which were detected from the plasma samples of pregnant women were 5.28, 5.31 and 4.17 ng mL(-1), and the average recoveries were 87.8%, 93.1% and 90.6% for the spiked samples with RSDs in the range of 1.4-6.3%, respectively. All these results reveal that MMIPs as MDSPE materials has good applicability to selective extraction and separation of trace estrogens from complex samples.

Selective separation and enrichment of glibenclamide in health foods using surface molecularly imprinted polymers prepared via dendritic grafting of magnetic nanoparticles

In this paper, the novel surface molecularly imprinted polymers based on dendritic-grafting magnetic nanoparticles were developed to enrich and separate glibenclamide in health foods. The density functional theory method was used to give theoretical directions to the synthesis of molecularly imprinted polymers. The polymers were prepared by using magnetic nanoparticles as supporting materials, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the cross-linker. The characteristics of magnetic nanoparticles and polymers were measured by transmission electron microscope and SEM, respectively. The enriching ability of molecularly imprinted polymers was measured by Freundlich Isotherm. The molecularly imprinted polymers were used as dispersive SPE materials to enrich, separate, and detect glibenclamide in health foods by HPLC. The average recoveries of glibenclamide in spiked health foods were 81.46-93.53% with the RSD < 4.07%.

Vanillin-molecularly targeted extraction of stir bar based on magnetic field induced self-assembly of multifunctional Fe3O4@Polyaniline nanoparticles for detection of vanilla-flavor enhancers in infant milk powders

A molecularly imprinted stir bar was constructed based on Fe3O4@Polyaniline nanoparticles with magnetic field-induced self-assembly process. The monomer, methacrylic acid, was pre-assembled into the pre-polymers with vanillin as template by the formation of hydrogen bonds. After that, the magnetic complexes were generated by the hydrogen bonding, the hydrophobic and π-π interaction between the pre-polymers and Fe3O4@Polyaniline. The complexes were adsorbed on the surface of magnetic stir bar under the magnetic induction, and the coating of vanillin-molecularly imprinted polymers was generated by the one-step copolymerization basing on the cross linking of ethylene glycol dimethacrylate. The molecular imprinting stir bar showed superior selectivity and fast binding kinetics for vanillin, and was used for the enrichment of vanilla-flavor enhancers (vanillin, ethyl maltol and methyl vanillin) in infant milk powders. The results measured by HPLC-UV exhibited good linear ranges of 0.01-100, 0.02-100 and 0.03-100μgmL(-1) with the limit of detection of 2.5-10.0ngmL(-1), and the recoveries were 94.7-98.9%, 82.1-96.7% and 84.5-93.2% with RSD<7.2% for the three enhancers, respectively.

RGO LBL modified biomimetic electrochemical sensor for detection of Sildenafil in herbal sexual healthproducts

In this work, a highly sensitive and selective biomimetic electrochemical sensor for Sildenafil in herbal sexual health products was prepared. Reduced graphene oxide (RGO), a novel highly conductive material was used to modify glassy carbon electrode (GCE) through layer-by-layer (LBL) self-assembly. The conductive molecularly imprinted films were constructed on the functional electrode surface using Sildenafil as template molecules, p-phenylenediamine (p-PD) as functional monomers. The obtained molecularly imprinted electrochemical sensor (MIES) was successfully used to detect Sildenafil in herbal sexual health products. The limit of detection (LOD) was 6.2 nmol L⁻¹. The recoveries for the spiked Sildenafil contents were in the range of 92.34-97.71% with the RSD < 2.31%. The selective efficiencies for Sildenafil and other structurally related analogues only slightly varied from 0.93 to 1.09.

Dumbbell-shaped stir bar coated with dendrimer-based MIPs for selective extraction and analysis of vardenafil and its analogue sildenafil in health foods

A novel dendrimer-based molecularly imprinted polymers (MIPs) coated dumbbell-shaped stir bar (DSB) was developed to enrich and analyze two kinds of phosphodiesterase type 5 (PDE-5) inhibitors in health foods (Hfs). The MIPs, with vardenafil as the template molecule and methacrylic acid (MAA) as the functional monomer, were synthesized on the surface of the dendritic-grafting DSB which was filled with magnetic core as substrate. The MIPs-DSB possessed mechanical stability, high adsorption capacity and good selectivity for vardenafil and its analogue sildenafil. A method for the determination of vardenafil and sildenafil in Hfs was established by stir bar sorptive extraction (SBSE) coupled with HPLC-UV. The contents of vardenafil and sildenafil were found to be 3.65 and 2.66 μg g−1, respectively, and the average recoveries in spiked Hfs were 86.5–91.8% with a relative standard deviation (RSD) below 5%. All results revealed that the MIPs-DSB coupled with HPLC-UV could be applied to the highly selective extraction and sensitive determination of trace analytes in a complex matrix.

Molecular imprinting‐based micro‐stir bar sorptive extraction for specific analysis of Glibenclamide in herbal dietary supplements

A novel molecularly imprinted polymers (MIPs) coated micro-stir bar (MSB) for Glibenclamide (GM) was developed. The MIPs, with GM as template molecular and methacrylic acid as functional monomer, were synthesized at the surface of the silylated MSB that was filled with magnetic core as substrate. Computational simulation was used for the optimal selection of functional monomers and porogen. The thickness of MIPs coating for MSB was about 10 μm, the adsorption and desorption time were about 40 and 20 min, respectively. The MIPs coated MSB possessed mechanical stability, high adsorption capacity, and good selectivity for GM. To achieve the optimum extraction performance, several parameters including extraction and desorption time, stirring rate, extraction and desorption solvent were investigated. A method for the determination of GM in herbal dietary supplements by MIPs coated MSB coupled with HPLC-UV was established. The results exhibited good linear ranges of 10-6250 μg L(-1) with the low limit of detection of GM (3.05 μg L(-1)) and the good recoveries (81.9-101.4%).

Selective separation and determination of the synthetic colorants in beverages by magnetic solid-phase dispersion extraction based on a Fe3O4/reduced graphene oxide nanocomposite followed by high-performance liquid chromatography with diode array detection

A facile adsorbent, a nanocomposite of Fe3 O4 and reduced graphene oxide, was fabricated for the selective separation and enrichment of synthetic aromatic azo colorants by magnetic solid-phase dispersion extraction. The nanocomposite was synthesized in a one-step reduction reaction and characterized by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction and Brunauer-Emmett-Teller analysis. The colorants in beverages were quickly adsorbed onto the surface of the nanocomposite with strong π-π interactions between colorants and reduced graphene oxide, and separated with the assistance of an external magnetic field. Moreover, the four colorants in beverages were detected at different wavelengths by high performance liquid chromatography with diode array detection. A linear dependence of peak area was obtained over 0.05-10 μg/mL with the limits of detection of 10.02, 11.90, 10.41, 15.91 ng/mL for tartrazine, allure red, amaranth, and new coccine, respectively (signal to noise = 3). The recoveries for the spiked colorants were in the range of 88.95-95.89% with the relative standard deviation less than 2.66%. The results indicated that the nanocomposite of Fe3 O4 and reduced graphene oxide could be used as an excellent selective adsorbent for aromatic compounds and has potential applications in sample pretreatment.

An analytical method for estrogens in milk powder by pseudo template imprinted polymer coated fiber coupled with HPLC

This paper reports a novel molecularly imprinted polymer (MIP) coated fiber for extraction of estrogens. A rationally designed 17-ethylestradiol (ED) that exhibits resemblance to estrogens has been synthesized and used as a pseudo template. A DFT-based computational simulation method was proposed to choose the best functional monomer. The MIP coated fiber was fabricated by using silica fiber as substrate, ED as pseudo template, 2-(trifluoromethyl) acrylic acid (TFMAA) and acrylic acid (AA) as composite functional monomers, and ethylene glycol dimethacrylate (EGDMA) as the cross-linking agent. A series of investigations indicated that the MIP coated fiber possessed excellent stability, rebinding capacity, selectivity and kinetics. An analytical method for the determination of estrogens in milk powder samples, combining molecularly imprinted solid phase micro-extraction (MISPME) with high performance liquid chromatography-ultraviolet (HPLC-UV), was developed. The limits of detection were in the range of 0.83–2.5 ng mL−1, the recoveries were 86–92%, 88–97%, 90–93% and 95–99% with RSD < 6.7% for estrone, 17β-estradiol, estriol and 17-ethynylestradiol, respectively.

Development and application of novel clonazepam molecularly imprinted coatings for stir bar sorptive extraction.

The molecularly imprinted magnetic stir bar coatings were created based on graft-functional Fe3O4 nanoparticles with magnetic field-induced self-assembly. The magnetic complex including clonazepam as template, the graft-functional Fe3O4 nanoparticles and methacrylic acid as monomers was pre-assembled through π-π interaction and hydrogen bonding, then was directionally adsorbed on the surface of magnetic stir bar under the magnetic induction. The molecularly imprinted coating with well-ordered structure was generated by one-step copolymerization based on the cross linking of ethylene glycol dimethacrylate. The molecularly imprinted coating with multiple recognition sites could be manufactured and applied in polar solvents, and showed superior selectivity and fast binding kinetics for benzodiazepines. The analytes in herbal health foods, treated by stir bar sorptive extraction, were determined by HPLC-UV. Good linearity was observed in the range of 0.01-2 μg mL(-1). The content of clonazepam in the herbal health foods was found to be 44 ng g(-1), and the average recoveries were 89.8-103.3% with a relative standard deviation (RSD) <6.5%, demonstrating the successful application in real sample analysis.