Zinc-Catalyzed Asymmetric Cascade Michael/Acyl Transfer Reaction between α-Hydroxy Aryl Ketones and Enynones.

We described herein a neoteric enantioselective cascade Michael/acyl transfer reaction of enynones and α-hydroxy aryl ketones catalyzed by dinuclear zinc cooperative catalysis. A series of structurally diverse chiral 1,5-dicarbonyl compounds were synthesized in good yields with excellent stereoselectivities. This strategy features broad substrate scope, high atom economy, as well as enynones as efficient electrophilic acyl transfer reagents in asymmetric cascade reactions for the first time.

Dinuclear zinc-catalyzed asymmetric Friedel-Crafts alkylation/cyclization of 3-aminophenols with α,α-dicyanoolefins.

An enantioselective Friedel-Crafts alkylation/cyclization tandem reaction of 3-aminophenols with α,α-dicyanoolefins has been performed successfully using a chiral dinuclear zinc catalyst, leading to a range of chiral 2-amino-4H-chromenes (up to 98% yield and >99% ee). To the best of our knowledge, this is the first asymmetric example of the dinuclear zinc-catalysed functionalization of aromatic C(sp2)-H bonds.

Advantages of time-resolved fluorescent nanobeads compared with fluorescent submicrospheres, quantum dots, and colloidal gold as label in lateral flow assays for detection of ractopamine.

Label selection is a critical factor for improving the sensitivity of lateral flow assay. Time-resolved fluorescent nanobeads, fluorescent submicrospheres, quantum dots, and colloidal gold-based lateral flow assay (TRFN-LFA, FM-LFA, QD-LFA, and CG-LFA) were first systematically compared for the quantitative detection of ractopamine in swine urine based on competitive format. The limits of detection (LOD) of TRFN-LFA, FM-LFA, QD-LFA, and CG-LFA were 7.2, 14.7, 23.6, and 40.1pg/mL in swine urine samples, respectively. The sensitivity of TRFN-LFA was highest. In the quantitative determination of ractopamine (RAC) in swine urine samples, TRFN-LFA exhibited a wide linear range of 5pg/mL to 2500pg/mL with a reliable coefficient of correlation (R2=0.9803). Relatively narrow linear ranges of 10-500pg/mL (FM-LFA) and 25-2500pg/mL (QD-LFA and CG-LFA) were acquired. Approximately 0.005µg of anti-RAC poly antibody (pAb) was used in each TRFN-LFA test strip, whereas 0.02, 0.054, and 0.15µg of pAb were used in each of the FM-LFA, QD-LFA, and CG-LFA test strips, respectively. In addition, TRFN-LFA required the least RAC-BSA antigens and exhibited the shortest detection time compared with the other lateral flow assays. Analysis of the RAC in swine urine samples showed that the result of TRFN-LFA was consistent with that of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and a commercial enzyme-linked immunosorbent assay (ELISA) kit.

DNA-based hybridization chain reaction and biotin-streptavidin signal amplification for sensitive detection of Escherichia coli O157:H7 through ELISA.

This study reported on a novel sandwich enzyme linked immunosorbent assay (ELISA) for the sensitive determination of Escherichia coli O157:H7 (E. coli O157:H7) by using DNA-based hybridization chain reaction (HCR) and biotin-streptavidin signal amplification. The anti-E. coli O157:H7 polyclonal antibody (pAb) was immobilized in the ELISA wells. The anti-E. coli O157:H7 monoclonal antibody (mAb) and initiator strand (DNA1) were labeled on gold nanoparticle (AuNP) to form a mAb-AuNP-DNA1 complex. In the presence of the target E. coli O157:H7, the sandwiched immunocomplex, which is pAb-E. coli O157:H7-mAb-AuNP-DNA1, could be formed. Two types of biotinylated hairpin were subsequently added in the ELISA well. A nicked double-stranded DNA (dsDNA) that contained abundant biotins was formed after HCR. Detection was performed after adding horseradish peroxidase-streptavidin and substrate/chromogen solution. Under optimal conditions, E. coli O157:H7 could be detected in the range of 5×10(2) CFU/mL to 1×10(7) CFU/mL; the limit of detection was 1.08×10(2) CFU/mL in pure culture. The LOD of the novel ELISA was 185 times lower than that of traditional ELISA. The proposed method is considerably specific and can be applied in the detection of whole milk samples inoculated with E. coli O157:H7. The coefficient of variation of in pure culture and in whole milk was 0.99-5.88% and 0.76-5.38%, respectively. This method offers a promising application in the detection of low concentrations of food-borne pathogens.