doi:10.1038/nindia.2012.38 Published online 19 March 2012
Researchers have designed a new kind of chip whose microchannels, with the help of magnetic nanoparticles and fluorescent quantum dots, can be used to detect waterborne pathogens. This device could be useful for screening food, water and environmental samples for multiple pathogens.
To find a cheap and fast detection technique, the researchers carved microchannels using copper wire in a polydimethylsiloxane-based platform. They then embedded the inlets and outlets of these microchannels with permanent magnets, thus dividing the channels into three zones — pre-capture, capture and detection.
They chose two waterborne pathogens — Esherichia coli and Salmonella typhimurium — known to cause gastrointestinal disorders. Next, they prepared magnetic nanoparticles tagged with anti-E. coli and anti-S. typhimurium antibodies. They also prepared green fluorescent cadmium telluride quantum dots tagged with anti-E. coli antibodies and red fluorescent quantum dots tagged with anti-S. typhimurium antibodies.
They injected the antibody-tagged magnetic nanoparticles into microchannels that were preloaded with bacterial samples and a solution of antibody-tagged quantum dots. Removing the magnets from the pre-capture zone moved antibody-tagged magnetic nanoparticles towards the capture zone, along the flow of bacterial samples. Removing the magnets from capture zone caused the antibody-tagged quantum dots to flow. In the detection zone, quantum dots, bacterial samples and magnetic nanoparticles formed a complex that fluoresced when irradiated with visible light.
The researchers captured the fluorescence with a microscope. They observed that the intensity of the fluorescence varied linearly with the number of E. coli and S. typhimurium bacteria. "This device will enable cheaper and rapid diagnosis of waterborne pathogens," says Dhananjay Bodas, one of the researchers.