Separation and enrichment of trace ractopamine in biological samples by uniformly-sized molecularly imprinted polymers

In order to prepare a high capacity packing material for solid-phase extraction with specific recognition ability of trace ractopamine in biological samples, uniformly-sized, molecularly imprinted polymers （MIPs） were prepared by a multi-step swelling and polymerization method using methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, and toluene as a porogen respectively. Scanning electron microscope and specific surface area were employed to identify the characteristics of MIPs. Ultraviolet spectroscopy, Fourier transform infrared spectroscopy, Scatchard analysis and kinetic study were performed to interpret the specific recognition ability and the binding process of MIPs. The results showed that, compared with other reports, MIPs synthetized in this study showed high adsorption capacity besides specific recognition ability. The adsorption capacity of MIPs was 0.063 mmol/g at 1 mmol/L ractopamine concentra- tion with the distribution coefficient 1.70. The resulting MIPs could be used as solid-phase extraction materials for separation and enrichment of trace ractopamine in biological samples.

Selective extraction of dimethoate from cucumber samples by use of molecularly imprinted microspheres

Molecularly imprinted polymers for dimethoate recognition were synthesized by the precipitation polymerization technique using methyl methacrylate （MMA） as the functional monomer and ethylene glycol dimethacrylate （EGDMA） as the cross-linker. The morphology, adsorption and recognition properties were investigated by scanning electron microscopy （SEM）, static adsorption test, and competitive adsorption test. To obtain the best selectivity and binding performance, the synthesis and adsorption conditions of MIPs were optimized through single factor experiments. Under the optimized conditions, the resultant polymers exhibited uniform size, satisfactory binding capacity and significant selectivity. Furthermore, the imprinted polymers were successfully applied as a specific solid-phase extractants combined with high performance liquid chromatography （HPLC） for determination of dimethoate residues in the cucumber samples. The average recoveries of three spiked samples ranged from 78.5% to 87.9% with the relative standard deviations （RSDs） less than 4.4% and the limit of detection （LOD） obtained for dimethoate as low as 2.3 μg/mL.

Nanosphere molecularly imprinted polymers doped with gold nanoparticles for high selectivity molecular sensors

We report the first attempt of using molecularly imprinted polymers （MIPs） in the shape of nanoparticles that were doped with gold nanoparticles （AuNPs） for surface enhanced Raman scattering （SERS）-based sensing of molecular spedes. Specifically, AuNPs doped molecularly imprinted nano-spheres （AuNPs@nanoMIPs） were synthesized by one-pot precipitation polymerization using Sudan IV as the template for the SERS sensing. The AuNPs@nanoMIPs were characterized by various modes of scanning transmission electron microscopy （STEM） that showed the exact location of the AuNPs inside the MIP particles. The effects of Au concentration and solution stirring on the shape and the polydispersity of the particles were studied. Significant enhancement of the Raman signals was observed only when the MIP particles were doped with the AuNPs. The SERS signal improved significantly with increase in the Au concentration inside the AuNPs@nanoMIPs. Selectivity measurements of the Sudan IV imprinted AuNPs@nanoMIPs carried out with different Sudan derivatives showed high selectivity of the AuNPs-doped MIP particles.