In Situ Grown Gold Nanoparticles Enable Plasmonic Staining of Bacteria for High-Performance On-Site Microbial Analysis in Drinking Water

On-site analysis of bacteria is important, but high-practicality methods are challenging due to their limited sensitivity and weak anti-interference. Herein, nitrocellulose (NC) membranes with hydrophilic characteristics and porous structures are utilized to filter those small coexisting substances in samples and selectively enrich target bacteria at the NC surfaces. To visualize bacteria with enhanced stability and sensitivity, the in situ growth of plasmonic Au nanocrystals on bacteria is implemented via the incubation of the bacterium-loaded NC membranes in Au reaction solutions. The bacteria are remarkably stained by the plasmonic Au nanocrystals, exhibiting responsive color changes for quantitative analysis. First, bacteria are visualized by in situ grown Au nanocrystals. In comparison with the presynthetic Au nanocrystals, those chemicals in Au reaction solutions are more stable, which ensures comparable stability and reproductivity. Second, the bacterium responses are amplified via plasmonic chemical reactions. Those Au nanocrystals are considered not only visual probes but also signal amplifiers. Overall, the protocol of Au-stained bacteria on NC membranes facilitates the on-site microbial analysis with characteristics of high simplicity, speediness, sensitivity, stability, and anti-interference, largely contributing to the progress of nanotechnologies from fundamental research to practical applications.