Plasmonic cell nanocoating: a new concept for rapid microbial screening

Nanocoating of single microbial cells with gold nanostructures can confer optical, electrical, thermal, and mechanical properties to microorganisms, thus enabling new avenues for their control, study, application, and detection. Cell nanocoating is often performed using layer-by-layer (LbL) deposition. LbL is time-consuming and relies on nonspecific electrostatic interactions, which limit potential applications for microbial diagnostics. Here, we show that, by taking advantage of surface molecules densely present in the microbial outer layers, cell nanocoating with gold nanoparticles can be achieved within seconds using surface molecules, including disulfide- bond-containing (Dsbc) proteins and chitin. A simple activation of these markers and their subsequent interaction with gold nanoparticles allow specific microbial screening and quantification of bacteria and fungi within 5 and 30 min, respectively. The use of plasmonics and fluorescence as transduction methods offers a limit of detection below 35 cfu mL^–1 for E. coli bacteria and 1500 cfu mL^–1 for M. circinelloides fungi using a hand-held fluorescent reader.