Rapid and Sensitive Escherichia coli Detection: Integration of SERS and Acoustofluidics in a Lysis-Free Microfluidic Platform

Bacterial infections, such as sepsis, require prompt and precise identification of the causative bacteria for appropriate antibiotics treatment. Traditional methods such as culturing take 2–5 days, while newer techniques such as reverse transcription-polymerase chain reaction and mass spectrometry are hindered by blood impurities. Consequently, this study developed a surface-enhanced Raman scattering (SERS)-based acoustofluidic technique for rapid bacterial detection without culturing or lysing. Target bacteria are first tagged with SERS nanotags in a microtube. The solution with tagged bacteria and unbound SERS nanotags is passed through a silicon microfluidic channel. A piezoelectric transducer generates acoustic waves within the channel, concentrating larger tagged bacteria in the center and pushing smaller unbound nanotags toward the channel walls. A laser beam is focused at the center of the channel, and the Raman signals of bacteria passing through the focal volume are measured for quantitative analysis. As a proof of concept, this study detected various concentrations of Escherichia coli at a limit of detection of 1.75 × 105 CFU/mL within 1 h. This method offers significant clinical potential, enabling rapid and accurate bacterial identification without genetic material extraction, cultivation, or lysis.