Surface acoustic wave based analytical system for the detection of liquid detergents

A novel analytical sensing system has been designed for the characterization and discrimination of different detergents in water. This micro-sensor system could play a key role in the development of more efficient and environmentally-friendly washing machines by enabling the measurement of residual detergents. The sensing system comprises a dual shear-horizontal surface acoustic wave (SH-SAW) resonator sensor housed within a poly-dimethylsiloxane (PDMS) microfluidic chamber. Free and electrically shorted SAW designs were used to analyze synthetic samples of liquid detergents with varying concentrations. Two anionic surfactants, namely sodium dodecylbenzene sulfonate and sodium laureth sulphate, and one non-ionic surfactant, polyoxyethylene (9.5) t-octylphenol have been studied. Dilution tests have been performed in order to determine the sensitivity or detection limit of this liquid sensing system and have been found to be ca. 10 ppm. The SAW based sensor system correctly classified all three detergents through the use of the transient signal response. Because the sensor operates without the need for a selective chemical or biological coating, it should be both robust and reliable. We believe that such technology could be used to make environmentally-friendly and greener washing machines by minimizing the use of detergents and hot water.