Xiaogang Hu

Molecularly imprinted polymer coated solid-phase microextraction fiber prepared by surface reversible addition-fragmentation chain transfer polymerization for monitoring of Sudan dyes in chilli tomato sauce and chilli pepper samples.

Surface reversible addition-fragmentation chain transfer (RAFT) polymerization method was firstly applied to the preparation of molecularly imprinted polymer (MIP) coated silicon solid-phase microextraction (SPME) fibers. With Sudan I as template, an ultra-thin MIP coating with about 0.55-μm thickness was obtained with homogeneous structure and controlled composition, due to the controllable radical growing and chain propagation in surface RAFT polymerization. The MIP-coated fibers were found with enhanced selectivity coefficients (3.0-6.5) to Sudan I-IV dyes in contrast with those reported in our previous work. Furthermore, the ultra-thin thickness of MIP coating was helpful to the effective elution of template and fast adsorption/desorption kinetics, so only about 18 min was needed for MIP-coated SPME operation. The detection limits of 21-55 ng L(-1) were achieved for four Sudan dyes, when MIP-coated SPME was coupled with liquid chromatography (LC) and mass spectrometry (MS) detection. The MIP-coated SPME-LC-MS/MS method was tested for the monitoring of ultra trace Sudan dyes in spiked chilli tomato sauce and chilli pepper samples, and high enrichment effect, remarkable matrix peaks-removing capability, and consequent high sensitivities were achieved to four Sudan dyes.

Molecularly imprinted polymer coated solid-phase microextraction fibers for determination of Sudan I–IV dyes in hot chili powder and poultry feed samples

In this research, a novel strategy was developed to prepare molecularly imprinted polymer (MIP) coated solid-phase microextraction fibers on a large scale with Sudan I as template and stainless steel fibers as substrate. More than 20 fibers could be obtained in one glass tube, and the efficiency and coating repeatability were enhanced remarkably in contrast with the yield of only one fiber in our previous works. The obtained MIP-coated stainless steel fibers were characterized by homogeneous and highly cross-linked coating, good chemical and thermal stabilities, high extraction capacities, and specific selectivities to Sudan I-IV dyes. Based on the systemic optimization of extraction conditions, a simple and cost-effective method based on the coupling of MIP-coated SPME with high-performance liquid chromatography was developed for the fast and selective determination of trace Sudan I-IV dyes in hot chili powder and poultry feed samples. The limits of detection of Sudan I-IV dyes were within 2.5-4.6 ng g(-1), and the spiked recoveries were in the range of 86.3-96.3% for hot chili powder sample and 84.6-97.4% for poultry feed sample.

Molecularly imprinted polymer coated on stainless steel fiber for solid-phase microextraction of chloroacetanilide herbicides in soybean and corn.

A molecularly imprinted polymer (MIP) with metolachlor as template was firstly coated on stainless steel fiber through chemical bonding strategy to solve the fragility problem of silica fiber substrate for solid-phase microextraction. The surface pretreatment of stainless steel fiber and the polymerization conditions were investigated systematically to enhance the preparation feasibility and MIP coating performance, and then a porous and highly cross-linked MIP coating with 14.8-microm thickness was obtained with over 200 times re-usability which was supported by non-fragile stainless steel fiber adoption. The MIP coating possessed specific selectivities to metolachlor, its metabolites and other chloroacetanilide herbicides with the factors of 1.1-4.6. Good extraction capacities of metolachlor, propisochlor and butachlor were found with MIP coating under quick adsorption and desorption kinetics, and the detection limits of 3.0, 9.6 and 38 microg L(-1) were achieved, respectively. Moreover, the MIP-coated stainless steel fiber was evaluated for trace metolachlor, propisochlor and butachlor extraction in the spiked soybean and corn samples, and the enrichment factors of 54-60, 27-31 and 15-20 were obtained, respectively.

Novel liquid–liquid–solid microextraction method with molecularly imprinted polymer-coated stainless steel fiber for aqueous sample pretreatment

A novel liquid-liquid-solid microextraction (LLSME) method was developed to overcome the well-known water-compatibility problem of molecularly imprinted polymers (MIPs). The enrichment factors with MIP-LLSME method were within 70-210 for trace chloroacetanilide herbicides under optimized extraction conditions. The method was characterized by simplicity, low solvent-consumption and high selectivity, and it was suitable for the one-step pretreatment of various aqueous samples such as river water and farm water.

Synthesis and application of intercellular Ca2+-sensitive fluorescent probe based on quantum dots.

A novel Ca(2+)-sensitive fluorescent probe was synthesized and characterized with a coupled method that coupled di[2-(N,N-dicarboxylmethyl)amino]ethyl ether (EGTA) to the surface of mercaptoethylamine-modified CdTe quantum dots (CdTe/MA-EGTA QDs). The application of this probe to detect intercellular Ca(2+) change in the leaf cells of Arabidopsis thaliana was studied. Results from transmission electron micrographs showed that the particle size of CdTe/MA-EGTA was about 3-4 nm; the fluorescent spectrum indicated that the excitation spectral ranged from 350 to 490 nm with a narrow and symmetric emission spectral peak at 565 nm when excited by 400 nm, and capillary electrophoresis demonstrated that CdTe/MA-EGTA was obtained by a coupling reaction. When the detected conditions were set as an excitation wavelength of 514 nm and detection wavelength of 561-604 nm, the increase of Ca(2+) in A. thaliana leaf cells and the rapidly quenching effect of fluorescence signal induced by exogenous treatment of jasmonate acid (JA) could be measured using laser scanning confocal microscopy. The quenching rate of traditional Ca(2+)-sensitive fluorescent probe Fluo-3 reached about 80% within a minute when exciting at 488 nm, which was much faster than the novel fluorescent probe CdTe/MA-EGTA. CdTe/MA-EGTA, however, was better at resisting photo bleaching and was more suitable for long-term tracking and monitoring than Fluo-3.

In situ detection of salicylic acid binding sites in plant tissues

The determination of hormone-binding sites in plants is essential in understanding the mechanisms behind hormone function. Salicylic acid (SA) is an important plant hormone that regulates responses to biotic and abiotic stresses. In order to label SA-binding sites in plant tissues, a quantum dots (QDs) probe functionalized with a SA moiety was successfully synthesized by coupling CdSe QDs capped with 3-mercaptopropionic acid (MPA) to 4-amino-2-hydroxybenzoic acid (PAS), using 1-ethyl-3-(3-dimethyllaminopropyl) carbodiimide (EDC) as the coupling agent. The probe was then characterized by dynamic light scattering and transmission electron microscopy, as well as UV/vis and fluorescence spectrophotometry. The results confirmed the successful conjugation of PAS to CdSe QDs and revealed that the conjugates maintained the properties of the original QDs, with small core diameters and adequate dispersal in solution. The PAS-CdSe QDs were used to detect SA-binding sites in mung bean and Arabidopsis thaliana seedlings in vitro and in vivo. The PAS-CdSe QDs were effectively transported into plant tissues and specifically bound to SA receptors in vivo. In addition, the effects of the PAS-CdSe QDs on cytosolic Ca(2+) levels in the tips of A. thaliana seedlings were investigated. Both SA and PAS-CdSe QDs had similar effects on the trend in cytosolic-free Ca(2+) concentrations, suggesting that the PAS-CdSe QDs maintained the bioactivity of SA. To summarize, PAS-CdSe QDs have high potential as a fluorescent probe for the in vitro/in vivo labeling and imaging of SA receptors in plants.

Encapsulating quantum dots with amino functionalized mesoporous hollow silica microspheres for the sensitive analysis of formaldehyde in seafood

We developed a hybrid fluorescent material using amino functional mesoporous hollow silica microspheres (MHSM) encapsulated with CdTe quantum dots (QDs). The amino group plays a key role in immobilizing both QDs and formaldehyde in the inner mesoporous hole of MHSM. The present QDs-MHSM shows good fluorescence property and excellent photostability after ultrasonic irradiation in water for several times or stewing for more than 30 days. Its fluorescence intensity is quenched rapidly in the presence of formaldehyde but not by interference with commonly organic solvents. Under the optimal experimental conditions, such as the response time and pH of the solution, a sensitive fluorescence method was developed for the analysis of formaldehyde in seafood based on fluorescence quenching of QDs-MHSM. The linear response range of formaldehyde (R2 = 0.9997) ranged from 0.2 to 15.5 mg L−1 and the detection limit (S/N = 3) was as low as 0.07 mg L−1. The recovery was 99.5% with a relative standard deviation less than 5.0%, which was consistent with that obtained by the China National Standard colorimetric method, suggesting the potential application of this sensitive and simple method in food quality monitoring or other relative fields.