In this study, peroxidase-mimicking core–shell Au@Pt nanoparticles (Au@Pt NPs) were synthesized, and both Hg2+ and Ag+ were found to intensively inhibit the catalytic activity of the Au@Pt NPs. The interactions between the two metal ions and Au@Pt NPs were analyzed through characterization by TEM, DLS, EPR and XPS, etc. Based on the inhibition of both Hg2+ and Ag+ toward the catalytic activity of the Au@Pt NPs and the shielding of sodium dodecyl sulfate (SDS) toward interfering metal ions, a highly sensitive and selective colorimetric assay for Hg2+ and Ag+ was developed. In addition, L-cysteine can be used to mask Hg2+ in the presence of Ag+; therefore, a specific detection of Ag+ ions can be accomplished by this Au@Pt NP-based assay. The limits of detection (LODs) for Hg2+ and Ag+ are 3.5 nM and 2.0 nM, respectively. The linear ranges for detecting Hg2+ and Ag+ are from 10 nM to 200 nM and from 5.0 nM to 100 nM, respectively. Moreover, the colorimetric assay is highly selective toward Hg2+ and Ag+ over other common metal ions. This work demonstrates that the optimization of metal nanoparticle preparation and surface modification play very important roles in developing metal ion sensing based on metal NP enzyme mimics. In addition, the metallic nanozyme based colorimetric method here demonstrates advantages in practical applications as it is low-cost, simple, and highly sensitive and selective, although it needs a two-step reaction.

A resistance effect between retrograded starch and iodine and its potential use for evaluating retrogradation properties of rice starch were investigated in this study. Our results showed that the resistance effect obviously occurred during the interaction of retrograded starch and iodine ions. The extent of the resistance was selected as a parameter to explore the kinetics of starch recrystallisation, indicating that the recrystallisation data obtained were suited to the Avrami equation (all correlation coefficients R > 0.99). Furthermore, the resistance was suitably employed to clarify some properties of starch retrogradation, including the rate constant (0.11 d−1 ⩽ k ⩽ 0.17 d−1) and the Avrami exponent (1.18 ⩽ n ⩽ 1.29). These results suggest that the resistance extent is able to provide potential data for measuring the degree of starch retrogradation.

The objective of this study was to develop a new method to measure the degree of amylose retrogradation in rice starch using size-exclusion high performance liquid chromatography (SE-HPLC). This developed method is based on the change in molecule size related to the retention time of amylose. Results showed that SE-HPLC was able to provide accurate data to evaluate the amylose retrogradation by comparing with other well-established methods. The principle of the measurement was further studied in molecular level by molecular dynamic (MD) simulation. It indicated that amylose molecules were transformed from disordering configuration to ordering one due to the increase in Van der Waals (Vdw) and hydrogen forces, and decrease in bonded interaction during the short-term storage.

Biotinylated denatured bovine serum albumin (Bt-dBSA)-coated cadmium telluride (CdTe) quantum dot (QD) conjugates were prepared and used to develop the multiplexed fluoroimmunoassay for the simultaneous determination of five chemical residues. An immune complex was formed using avidin as the bridge to link the Bt-dBSA-QDs with the antibodies. Primarily, individual quantitative determinations of five representative chemical residues were carried out based on the different emission properties of the QDs. Five antibodies were then conjugated with the corresponding QDs to establish the indirect competition fluorescent-linked immunosorbent assay (ic-FLISA) for the simultaneous detection of five chemicals in one well of a microplate. The linear range for dexamethason (DEX) was from 0.33 μg/kg to 10 μg/kg, 0.28 μg/kg to 10 μg/kg for gentamicin (GM), 0.16 μg/kg to 25 μg/kg for clonazepam (CZP), 0.17 μg/kg to 10 μg/kg for medroxyprogesterone acetate (MPA) and 0.32 μg/kg to 25 μg/kg for ceftiofur (CEF), respectively. The limit of detection (LOD) for the simultaneous determination of DEX, GM, CZP, MPA and CEF were as low as 0.13 μg/kg, 0.16 μg/kg, 0.07 μg/kg, 0.06 μg/kg and 0.14 μg/kg, respectively. This detection method was used to analyze samples of pork muscle and the recoveries ranged from 61.3% to 80.3% for DEX and from 74.0% to 87.2% for MPA. Further more, good correlation between the novel ic-FLISA and traditional ELISA was demonstrated during the determination of DEX and MPA residues in real samples. The QD-based protocol described here is less time consuming than the classical method and it may be sufficiently flexible to be used in other systems for the simultaneous multicolor detection of the drugs.

A new heterologous ELISA method for detecting acetylgestagen multi-residues in animal fat was developed. An antibody generated has high cross-reactivity with relative progestogens (up to 50%) and no cross-reactivity with other steroids (<0.1%) in homologous ELISA. Three heterologous immunoassay were developed and one of them improved not only sensitivity but also the class-selectivity compared with the homologous assay against these progestogens. The IC50 for four acetylgestagens, chlormadinone acetate (CMA), 17α-hydroxyprogesterone acetate (HPA), megestrol acetate (MEGA) and medroxyprogesterone acetate (MPA) were, 4.5, 2.5, 2.9 and 1.8 μg/L, respectively. The cross-reactivity for CMA, HPA and MEGA were 40%, 72% and 62% when they were compared with MPA. Progestogens recoveries from spiked swine fat averaged between 61% and 78%. Results obtained from LC/MS/MS method showed the heterologous ELISA method developed was reliable and suitable for rapid screening the four progestogens residues in fat tissues.

The inclusion complex of astaxanthin (ASX) with hydroxypropyl-β-cyclodextrin (HP-β-CD) was prepared. Infrared spectroscopy (IR) proved the formation of the inclusion complex. The water solubility of the inclusion complex was >1.0 mg/ml, which is much better than that of ASX. The solid state thermal behaviour of the inclusion complex was investigated by thermogravimetric/differential thermal analysis (TG/DTA). The starting decomposition temperature of ASX was enhanced to about 290 °C. The stability of the inclusion complex in solution was also tested. Forming of the inclusion complex greatly enhanced the stability of ASX against light and oxygen. Furthermore, the release of ASX from the inclusion complex was controlled.