Development of a Piezoimmunosensor for the Detection of Salmonella typhimurium

Piezoelectric (PZ) crystals are pieces of oscillating quartz on which there is an adsorbent that selectively interacts with the analyte. Adsorption of the analyte increases the mass of the crystal and decreases proportionally its basic frequency of oscillation, which is generally 9 or 14 MHz. The limit of detection of this technique is estimated to be about lo '* g. To date, most of the previous analytical work with piezoelectric biosensors has centered on the use of inorganic or organic coatings of gaseous environmental pollutants such as HCI, isocyanates, CO, NO,, and SO,. A review of this field is available from the literature.' In 1972, Shons et al.'first showed the use of P Z crystals for studying immunochemical reactions. Since then, the use of antibodies and antigens as specific coatings in P Z biosensors has been widespread in liquid phase analysis. In this study, antibody to Salmonella was immobilized on the surface of a quartz crystal that then selectively interacted with Salmonella typhimurium to produce a change in resonant frequency. The sensor was applied to a pure culture of Salmonella and artificially infected food samples. Needless to say, a rapid procedure for detection of Salmonella has been needed by the food industry for years. When present in foods, these bacteria are usually low in number in comparison with the total bacterial flora.3