A poly(St-co-EGDMA)@poly(4-vinylpyridine-co-EGDMA) composite polymer was synthesised by precipitation reversible addition–fragmentation chain transfer (RAFT) polymerization. The polymer was investigated as a sorbent for extraction of synthetic food dyes: ponceau 4R, tartrazine, sunset yellow, brilliant blue and erythrosine from soft drinks. The morphology and composition of the polymer were characterized and confirmed respectively by scanning electron microscopy and Fourier-transform infrared spectroscopy. The pH dependence experiment revealed that the adsorption of food dyes by the polymer was pH dependent and the maximum adsorption was achieved at pH 3. Adsorption between the polymer and the dyes was mainly due to electrostatic interaction. Under the optimized pH conditions, the polymer was saturated with the dye solutions at a concentration of about 200 μg mL−1 and exhibited a maximum adsorption capacity of 9 μg mg−1. The values were higher than those for polyamide, a sorbent used in the standard method. The recovery from the real samples of the three spiked concentrations 10, 50 and 100 μg mL−1 was respectively within the ranges of 83.2–107.2%, 94.5–110.7% and 79.2–111.5%, with a SD within ±4%. The sorbent could be reused more than 10 times with a recovery higher than 80%. The small volume requirement of the sample and sorbent during the sample pre-treatment, indicated that poly(St-co-EGDMA)@poly(4-vinylpyridine-co-EGDMA) was a potential material for food dye extraction in an environment-friendly and economical manner.
Herein, a novel peptidyl probe is first synthesized by the amide reaction between glutathione-capped gold nanoclusters (GSH-AuNCs) and positive charged arginine-rich peptide (Arg 9 ), and it is called Arg 9 -GSH-AuNCs. Polyuridylic acid (polyU), as a polyanion , is firstly used to induce the aggregation-induced emission enhancement (AEE) of positive charged Arg 9 -GSH-AuNCs through electrostatic attraction . The peptide bond on the carboxyl terminal of the arginine residues can be recognized and cleaved by trypsin. Hence, polyU is hard to induce the aggregation of peptidyl probe again, and the AEE from GSH-AuNCs becomes weak. It is an ideal platform to detect trypsin and screen trypsin inhibitors . The fluorescent peptidyl probe exhibits excellent sensitivity for trypsin. A good linear range of trypsin is obtained from 1 to 50 ng·mL −1 with the limit of detection (LOD) 0.31 ng·mL −1 , which is lower than those of most reported works. Furthermore, the inhibitory effects of the extracts from foods (i.e., soybean seed flour, black soybean seed flour, mung bean seed flour, and azuki bean seed flour) on the trypsin activity have been studied. The half maximal inhibitory concentration (IC 50 ) values of extracts from soybean seed flour, black soybean seed flour, mung bean seed flour, and azuki bean seed flour are 4.5, 9.3, 11.6, 20.9 μg·mL −1 , respectively. The screening results show that these extracts from foods all have inhibitory effects on trypsin. Among them, the extract from soybean seed flour exhibits significant inhibitory effect.
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