Acoustic standing wave based microsystem for low-concentration oil detection and separation

Detection and quantification of extremely small amount of oil on site and at low cost has broad applications in environmental monitoring, both in oil spills as well as in routine marine/costal ecosystem monitoring. For example, dispersed oil, generated through the use of chemical dispersants in oil spills to break up oil slick into small droplets so that they can be rapidly diluted in 3D space are the greatest concern and poses the most challenges in detection. Fluorometry is the current standard method, however is bulky and expensive, limiting its wide deployment in the field. Here we demonstrate for the first time the development of an acoustic standing wave based microfluidic platform capable of processing large amount of liquid samples from which dispersed oil can be concentrated and separated to a detectable level by acoustophoretic force. The microfluidic platform consists of a recirculation channel structure into which dispersed oil droplets can be continuously separated from the main sample flow stream. A piezoelectric transducer attached at the bottom of the silicon-glass microfluidic channel creates the acoustic standing wave that exerts acoustophoretic force to oil droplets. An optical detector measures the presence of concentrated oil droplets by their distinct fluorescent signatures.