Plate acoustic wave sensor for detection of small amounts of bacterial cells in micro-litre liquid samples.

Ultrasonic acoustic waves propagating in thin piezoelectric plates with free faces are used for bacteria detection in micro-litre liquid samples deposited on one of the plate surface. The limits of the detection at normal conditions are as low as 0.04% for highly diluted rich cultural Luria-Bertani broth (LB-media) in distillate water, 0.07% for bacterial cells in distillate water, and 0.6% for bacterial cells in LB-media. For all analytes the most probable detection mechanism is the change in liquid conductivity. Because of no using any sorbent film the long-term stability of the detection is expected as very high.

The peculiarities of the Bleustein-Gulyaev wave propagation in structures containing conductive layer.

As known, anomalous resisto-acoustic effect is a fundamental property for weakly inhomogeneous piezoactive waves (Bleustein-Gulyaev, Love, and some leaky waves). It consists in that the velocity of aforementioned waves first increases, achieves its maximum, and only then decreases with increasing conductance of a layer placed at the surface of piezoelectric half-space. In this paper we continue to study the peculiarities of the effect appearance and the influence of different electrical boundary conditions on its characteristics. Conditions have been found under which the said effect appears and, respectively, disappears. The magnitude of positive change in velocity with increasing layer conductance is demonstrated to be reduced up to zero as a layer with arbitrary conductance has been moved away from the piezoelectric surface. The positive change in velocity increases when an perfectly conductive screen moves away from the "piezoelectric half-space - conductive layer" structure. The obtained results are useful for a more deep understanding the physical basis of propagation of weakly inhomogeneous piezoactive acoustic waves (Bleustein-Gulyaev, Love, and some leaky waves).