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Until now, there have been many reports on the regulation of inorganic metal ions on the catalytic activity of nanozymes, but few reports on the regulation of anions (such as NO2−) on enzyme activity. In this work, a copper-molybdenum doped carbon dots (Cu, Mo-CDs) with peroxidase-like (POD) activity was synthesized by simple one-step microwave digestion method. The Cu, Mo-CDs + NO2−system can promote 3,3′,5,5′-tetramethylbenzidine (TMB) oxidizing to blue oxidative product (oxTMB) due to the formation of ∙NO2free radical. While Hg2+was introduced into the system, the POD-like activity of Cu, Mo-CDs + NO2−system was inhibited due to the strong interaction and the electron transfer between Cu, Mo-CDs and Hg2+. The formation of ∙NO2and the electron transfer capability of Cu, Mo-CDs + Hg2+were confirmed through ESR spectra and FMN experiments. The bioenzyme-free colorimetric assay based on Cu, Mo-CDs nanozyme is used for detection of NO2−and Hg2+, showing lower detection limit (LOD) of 1.63 µg/L for NO2−, 0.13 µg/L for Hg2+, respectively and good recovery from 90.79 to 108.90%. The work paves a new way to design a nanozyme-based colorimetric protocol for traces NO2−and Hg2+residues in food analysis.

ObjectiveGut microbiota dysbiosis is closely linked to the pathogenesis of rheumatoid arthritis (RA). We aimed to identify potential probiotic gut microbes that can ameliorate the development of RA.DesignMicrobiota profiling in patients with RA and healthy individuals was investigated via 16S rDNA bacterial gene sequencing and shotgun metagenomics. Collagen-induced arthritic mice and TNF-α transgenic mice were used to evaluate the roles of the gut commensal Parabacteroides distasonisin RA. The effects of P. distasonis-derived microbial metabolites on the differentiation of CD4+T cells and macrophage polarisation were also investigated.ResultsThe relative abundance of P. distasonisin new-onset patients with RA and patients with RA with history of the disease was downregulated and this decrease was negatively correlated with Disease Activity Score-28 (DAS28). Oral treatment of arthritic mice with live P. distasonis(LPD) considerably ameliorated RA pathogenesis. LPD-derived lithocholic acid (LCA), deoxycholic acid (DCA), isolithocholic acid (isoLCA) and 3-oxolithocholic acid (3-oxoLCA) had similar and synergistic effects on the treatment of RA. In addition to directly inhibiting the differentiation of Th17 cells, 3-oxoLCA and isoLCA were identified as TGR5 agonists that promoted the M2 polarisation of macrophages. A specific synthetic inhibitor of bile salt hydrolase attenuated the antiarthritic effects of LPD by reducing the production of these four bile acids. The natural product ginsenoside Rg2 exhibited its anti-RA effects by promoting the growth of P. distasonis.ConclusionsP. distasonisand ginsenoside Rg2 might represent probiotic and prebiotic agents in the treatment of RA.