Aiming at the difficulty of traditional pesticide sampling, a low-cost and convenient flexible surface enhanced Raman scattering (SERS) gold core–silver shell-sponge (Au–Ag-sponge) substrate was synthesized by chemical reduction. The SERS substrate consisted of Au–AgNPs and a melamine sponge. The sponge had a rich open pore structure, which could well “capture” Au–AgNPs, generating a large number of “hot spots”. The SERS enhancement activity of the flexible substrate was characterized with rhodamine 6G (R6G) Raman probe molecules. The substrate showed good activity to 10−12 M rhodamine 6G with an enhancement factor (EF) of 7.72 × 106. Applying this substrate to the qualitative and quantitative detection of pesticide residues, the results showed that the Raman intensity was well related to the concentration of pesticide solution with the range of 0.1–10 mg L−1 of thiram and 1–10 mg L−1 of diquat. Furthermore, the substrate was analyzed by finite difference time domain (FDTD) simulation and the results were in good agreement with the experimental results. The reason for the difference in Raman signals of pesticide molecules on the same substrate was the different binding modes of Au–AgNPs on the sponge. Finally, we pointed out the advantages of flexible substrates in the field of pesticide residues, as well as future opportunities and challenges.
Rhizosphere microorganisms are crucial for the growth and health of their host plants. Dicamba is one of the representative herbicides used for the control of wheat weeds. In recent years, the usage of dicamba has escalated globally, particularly with the advent of dicamba-tolerant transgenic crops. However, the impacts of this herbicide on non-target organisms, particularly the rhizosphere microorganisms of wheat, is not yet clear. Furthermore, rhizosphere microorganisms are important for nitrogen cycling in soil-crop systems, the influence of dicamba on rhizosphere nitrogen cycling functionality needs further investigation. This study aims to elucidate the effects of dicamba on the microbial community, metabolite profiles, and nitrogen cycling-related genes in wheat rhizosphere. Our findings indicated that dicamba led to significant alterations in the diversity and co-occurrence patterns of the rhizosphere microbial community, notably reducing the abundances of phyla Verrucomicrobia, Planctomycetes, and Cyanobacteria. Additionally, dicamba markedly disturbed the rhizosphere metabolite profiles, particularly those associated with carbohydrate and amino acid metabolism. Notably, dicamba treatment resulted in an up-regulation of enzymatic genes catalyzing processes of assimilatory nitrate reduction to ammonium (ANRA)/dissimilatory nitrate reduction to ammonium (DNRA) (EC: 1.7.5.1, EC: 1.9.6.1, and EC: 1.7.1.15) and denitrification (EC: 1.7.2.1 and EC: 1.7.2.5). The observed increases in the abundances of the genera Cellulosimicrobium and Pseudomethylobacillus were critical for facilitating ANRA and DNRA. The application of dicamba altered soil organic matter content, which in turn influenced the abundances of microorganisms involved in ANRA/DNRA and denitrification, thereby affecting the nitrogen cycling functionality in the rhizosphere. This study offers valuable theoretical support for assessing the rhizosphere ecological effects of agrochemical application.
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