Cell Nanocoating for Rapid Microbial Screening

Abstract

Microbial contamination is a global challenge facing not only the food and pharmaceutical industries but also water safety and clinical hygiene control. Traditional microbial identification methods suffer from costly and time-consuming processes. Rapid microbial screening assays overcome these limitations, however, very few rapid microbial screening assays are available on the market. Rapid microbial screening refers to the detection of the total microbial load in samples without specifying the strains or species. The primary goal of this study is to develop a rapid microbial screening assay that yields accurate and quantifiable results in less than 30 min. Nanocoating of single microbial cells with gold nanostructures can confer optical, electrical, thermal and mechanical properties to the outer layers of microorganisms, thus enabling new avenues for their control, study, application and detection. Cell nanocoating is often performed using layer-by-layer (LbL) deposition of functional materials. LbL is time-consuming and relies on nonspecific electrostatic interactions, which can be unstable in adverse sample environments and limit its potential applications for microbial diagnostics. This thesis shows that by taking advantage of surface molecules densely present in the outer membrane layers, cell nanocoating with gold nanoparticles can be achieved within seconds. The objective of this thesis is to develop a rapid microbial detection system by coating the densely populated surface molecules on the outer layer of microbes with gold nanoparticles. These surface molecules include disulfide bond-containing (Dsbc) proteins and chitin, which can be activated with a simple one step process. This activation leads to subsequent interactions with gold nanoparticles that allow for specific microbial screening and quantification of bacteria and fungi within 5 and 30 min respectively. The transduction methods such as plasmonics and fluorescence offers a limit of detection below 35 cfu.mL-1 for bacteria and 1500 cfu.mL-1 for fungi using a portable reader.