Development of single nanoparticle optical assays for imaging single living cell

Multi-drug resistance (MDR) has been reported in both prokaryotes and eukaryotes; the pathogenic gram-negative bacteria Pseudomonas aeruginosa can extrude a variety of structurally and functionally diverse substrates via a number of membrane transport systems leading to MDR. We have developed a novel nanoparticle assay to characterize both the membrane transport system composed of the MexAB-OprM efflux pump and the membrane permeability induced by antibiotics. Gold (Au) and silver (Ag) nanoparticles were investigated for use as probes to explore membrane transport in P. aeruginosa.;The surface plasmon absorption (color) of Au nanoparticle solutions was found to change in the presence of Tris(2, 2'-bipyridine)ruthenium(II). The color change was both size and temperature dependent. The change in surface plasmon absorption was caused by the formation of Au nanoparticle aggregates.;The surface plasmon absorption (color) of Ag nanoparticles was found to correlate with nanoparticle size and was readily observable using dark field microscopy. Ag nanoparticles were used to measure real-time transformation of cell permeability and MDR efflux dynamics of individual bacteria cells at nanometer resolution. The MDR efflux dynamics data was validated using time-course fluorescence of bulk cell populations.