Fluorescent sensing platform based on green luminescence carbon dots and AuNPs for clenbuterol detection in pork liver.

In this paper, water-soluble green fluorescent carbon dots (G-CDs) were prepared using p-phenylenediamine and glutathione (GSH) as the precursors. The G-CDs exhibit excellent optical properties, and the maximum emission wavelength is located at 522 nm (under 410 nm excitation), which greatly overlaps with the absorption spectrum of AuNPs. Consequently, an effective "off-on" fluorescent sensing platform involved in G-CDs and AuNPs for detection of clenbuterol (CLB) was constructed. The fluorescence of G-CDs was strongly quenched by AuNPs due to the inner filter effect (IFE). As CLB was introduced, the quenched fluorescence intensity was recovered due to the specific interaction between the AuNPs and CLB. The recovered fluorescence intensity is linear to CLB concentration in the range of 13-270 ng mL-1 with a low detection limit of 3.75 ng mL-1. The prepared sensor has been successfully applied for CLB detection in pork liver and could be utilized in food analysis.

[Preparation of metal chelate affinity chromatographic medium and its application in the purification of 6 x histidine-tagged protein].

Using Sepharose CL-6B as support, 3-Chloro-1, 2-epoxypropane as activated agent, carboxymethylated aspartate (CM-Asp) as chelating ligand, A chelate affinity chromatographic medium based on Co2+, named Co-CM-Asp-Sepharose, was prepared and used to purify 6 x His-tagged fusion proteins. The amount of Co-CM-Asp-Sepharose reacted with 200 microL of lysate, the incubation time, wash condition and the imidazole concentration in the elution buffer were optimized. The purification results using Co-CM-Asp-Sepharose and Ni-NTA-Agarose (product of Qiagen) were compared. The CD155D1 fusion protein was also purified from 5mL of lysate and the amount of protein was determined by Bradford method. The results show that 60 microL of Co-CM-Asp-Sepharose (50% suspension) was suitable for the protein purification from 200 microL of lysate, the optimal incubation time of medium and lysate was 30 min, the optimal imidazole concentration in the eluting buffer was 200 mmol/L, and 200 microg of fusion protein was obtained. In a big scale experiment, 4.6 mg of fusion protein was obtained from 5 mL of lysate using 1.5 mL of Co-CM-Asp-Sepharose (50% suspension). Compared with Ni-NTA-Agarose, the Co-CM-Asp-Sepharose medium exhibits higher selectivity and the protein possesses higher purity.

[Spectroscopy studies on the interaction of bis(p-nitrophenyl) esters and beta-cyclodextrin].

The bis(p-nitrophenyl) esters of succinic acid, adipic acid and sebacic acid have been synthesized, respectively, by employing 1,3-dicyclohexylcarbodiimide (DCC) as a dehydration agent. The composition and structure of the esters have been characterized by elemental analysis, FTIR, 1H NMR and DSC. Furthermore, the host-guest interactions of the esters with beta-cyclodextrin (beta-CD) have been studied systematically by using fluorescence quenching, fluorescence spectroscopy and UV-Vis spectroscopy measurements. It was demonstrated that the chain of the esters was longer, the interactions was weaker between the esters and the beta-CD. Both p-nitrophenyl groups in bis(p-nitrophenyl) esters of succinic acid can enter the inner cavity of beta-CD. In contrast, only one of the groups in bis(p-nitrophenyl) esters of adipic acid can enter the cavity. For bis(p-nitrophenyl) esters of sebacic acid, however, both groups can not enter the cavity of the beta-CD. The difference in the host-guest interactions of the three esters with beta-CD has been attributed to the difference in the conformations adopted by the esters. Based upon these observations, it is proposed that the esters with short linker may be more suitable for construction of new networks, which are based upon, in concept, host-guest interactions.