This work reports a benzoic group functionalized gold nanoflower as a bridge probe for both recognition of target sialic acids and assembly of poly(N-acetylneuraminic acid) modified gold nanoparticles, which leads to plasmonic coupling of two kinds of gold nanoprobes in a single-core-multi-satellite nanostructure to produce a sensitive surface-enhanced Raman scattering (SERS) signal for the imaging of sialic acids on living cells.

A zone-controllable SERS effect integrates the controlling of nano-substrate size to match the expression zone of protein-specific glycan for Raman imaging.

A micro-competition system integrated functionalized silica bubbles and Raman encoded nanoprobes to simultaneously assay multiple glycans on intact cell surfaces.

A strategy for information liberation of protein-specific glycosylation is designed via an exonuclease III-aided recycling "hybridization and cleavage" process with glycan and protein probes, which achieves homogeneous quantification of cell surface glycan. The protein probe contains matching and spacer DNA sequences and an aptamer specific to target protein. The glycan probe contains a complementary sequence modified with neighboring fluorescein and quencher, a spacer sequence, and a dibenzocyclooctyne-amine end to bind azide-tagged glycan. Upon sequential binding to their targets, the complementary sequences of two probes approach enough for their hybridization, which leads to the cleavage of hybridized glycan probe by exonuclease III and followed recycling "hybridization and cleavage" process of protein probe with other adjacent glycan probes to release the labeled fluorescein for obtaining the information on protein-specific glycosylation. This protocol has been used to in situ quantify EpCAM-specific sialic acid on MCF-7 cell surface and monitor its variation during drug treatment. This work demonstrates a powerful quantification tool for research of glycosylation.

Quinoxalines (Qx) are chemically synthesized antibacterial drugs with strong antibacterial and growth-promoting effects. Qx is heavily abused by farmers, resulting in large residues in animal-derived foods, which pose a serious threat to human health. Desoxyquinoxalines (DQx), which have the highest residue levels, have been identified as the major toxicant and have become a new generation of residue markers. In this study, we prepared monoclonal antibodies (mAb) based on a new generation metabolite (desoxymequindox, DMEQ) and establish an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) for the rapid determination of Qx residues in food. The mAb exhibited high sensitivity with half maximal inhibitory concentration (IC50) and a linear range of 2.84 µg/L and 0.8–12.8 µg/L, respectively. Additionally, the cross-reactivity (CR) of the mAb showed that it recognized multiple DQx to varying levels. The limits of detection (LOD), limits of quantification (LOQ), and recoveries for the ic-ELISA assay of pork, swine liver, swine kidney, chicken, and chicken liver were 0.48–0.58 µg/kg, 0.61–0.90 µg/kg, and 73.7–107.8%, respectively, and the coefficients of variation (CV) were less than 11%. The results of the ic-ELISA showed a good correlation with LC–MS/MS in animal-derived foods. This suggests that this analytical method can be used for the rapid screening of QX residues.