Diagnostic chip corrals bacteria with sound

When a patient develops sepsis, a potentially fatal inflammatory response to an infection, doctors race to identify what bacterial strain is to blame so they can deliver the best antibiotic. This hunt can take days. Now, Thomas Laurell of Lund University and colleagues have developed a microfluidic chip that detects bacteria from a drop of blood within a couple of hours (Anal. Chem. 2016, DOI: 10.1021/acs.analchem.6b00323). The device has three stages. In the first two, a piezoceramic transducer that vibrates like a cell phone generates standing acoustic waves along the channels. The waves focus blood cells into the center of the stream, allowing them to be directed into a waste compartment. The bacteria are too small to notice the sound waves, so they continue to the second stage, where they run into a honeycomb of polystyrene particles. Here, a force created by the sound waves causes the bacteria to stick to the particles. With the bacteria stuck, the remaining blood components wash away. Then the researchers turn off the transducer, releasing the bacteria from the particles so the cells can travel to the third stage where they are identified using a polymerase chain reaction method. The device successfully identified Escherichia coli in half of blood samples from septic patients.