The creation of microfluidic chips capable of quickly detecting bacteria would improve food safety testing and environmental monitoring, and it would help doctors rapidly diagnose a variety of medical conditions.  The need for inexpensive diagnostic devices is especially severe in developing countries with few healthcare resources.  There already exist a number of assays to detect bacteria, including many based on cell growth, and researchers are now seeking to implement these techniques at the micro-scale. 

Growth-based bacterial detection involves four main steps: filtration, concentration, growth, and detection.  The filtration and concentration steps can be done off-chip, especially if one is seeking to detect a few bacteria in a large volume. Bacterial detection can be accomplished using electrical, optical, and mechanical methods.    Researchers in the laboratory of Rashid Bashir, PhD, have focused on electrical methods because this type of detection lends itself particularly well to automation.  As bacteria grow, they give off acidic metabolic byproducts, and these metabolites change the pH and the impedance of the media.  This change in impedance can be detected electronically on a microfluidic chip. 

Researchers are also seeking to create microfluidic chips capable of performing polymerase chain reaction (PCR).  Using PCR to detect organism-specific DNA is a valuable diagnostic technique that is currently available only to those with access to a well-equipped laboratory.  Making PCR portable would have tremendous consequences for healthcare practitioners in settings with few laboratory resources.  One obstacle to be overcome is the fact that the DNA produced by PCR is usually detected with fluorescent labels that are expensive and do not travel well.  Researchers in Bashir’s lab, however, are developing a new DNA-detection strategy based on the polarity of DNA.  Seeking to avoid detecting DNA from dead bacteria, these researchers are experimenting with ethidium monoazide dye, a chemical that makes the DNA of dead cells inaccessible to DNA polymerase.  Making PCR a point-of-care diagnostic would have tremendous consequences for public health around the globe.      

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