Using bioconjugated nanoparticles to monitor E. coli in a flow channel.

A simple and portable flow channel optical detection system combined with bioconjugated luminescent nanoparticles allows the rapid detection of single bacterial cells without sample enrichment. The optical system is designed to have single-molecule-detection capability in a microcapillary flow channel by decreasing the laser excitation probe volume to a few picoliters, which consequently results in a low background. Specific monoclonal antibodies were immobilized on nanoparticles to form nanoparticle-antibody conjugates. The bioconjugated nanoparticles bind to the target bacteria when they recognize the antigen on the bacterium surface, thus providing a bright luminescent signal for the detection of individual bacteria cells. The high sensitivity provided by the luminescent and photostable silica nanoparticles eliminates the need for further enrichment of bacteria samples and signal amplification. This flow channel detection system is convenient and allows the detection of single bacterial cells within a few minutes.