Smart Acoustic Sensor for the Detection of Bacteria in Milk

J.W. Gardner, M. Cole, C.G. Dowson, P. Newton, and G. Sehra (UK)


Biosensors and transducers, microtechnology and BioMEMS


A smart sensor has been designed that comprises a pair of shear horizontal (SH) surface acoustic wave (SAW) devices with one open delay line and one electrically shorted through a ground plane. The delay lines have been fabricated on a 36 Y-cut X-propagating lithium tantalate piezoelectric wafer using UV microlithography and have an operating frequency of ca. 60 MHz. The dual SH SAW sensor employs no biological layer and so the detection principle is based simply upon its response to certain physical properties of the analyte, such as conductivity, permittivity, and visco-elastic coupling. An investigation has been carried out to see whether the sensor can detect the presence of bacteria in dairy milk. It was observed that the smart sensor was sensitive to concentrations of S. aureus and S. uberis in milk down to the level of ca. 100 cfu/ml. This type of acoustic biosensor could potentially offer a simple, low-cost and robust (repeatable) way to assay bacterial loads in complex liquids.

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