Using roughened glass slides patterned with gold electrodes, the researchers created microchannels to sort, trap, and identify bacteria. The technique uses surface enhanced Raman spectroscopy. This type of spectroscopy, says Chang, "is based on the measurement of scattered light from the vibration energy levels of chemical bonds following excitation in a craggy metal surface, which enhances the vibration energy." Different components like proteins or other chemical components on the surface of bacteria become attached to the craggy gold zone; when excited, these components cause representative peaks at different wavelengths, creating spectral "fingerprints."
Although some species of bacteria could show very similar signatures because the components on their surfaces are almost the same, says Chang, bacteria from different genera are distinguishable using the technique.
"In the future, different species of fungi could also be sorted based on their different electrical or physical properties by optimizing conditions such as the flow rate, applied voltage, and frequency," he says. "This portable device could be used for preliminary screening for the pathogenic targets in bacteria-infected blood, urethral irritation, and of raw milk and for food monitoring."