Bacterial spore capture on an immunosensor surface in a BAW resonator

The immunocapture of bacterial-size 1 μm diameter biotinylated fluorescent microparticles on the glass acoustic reflector of a 3 MHz quarter wavelength standing wave resonator has been characterized here as a function of acoustic pressure amplitude, microparticle concentration and sample flow rate. An acoustic pressure amplitude of 565 kPa at a frequency of 2.82 MHz gave high capture efficiencies. The measured time to deposit particles on a reflector in a batch system was consistent with a calculated time of 35 s for acoustic radiation force to drive over 95 % of particles to the coated surface. A suspension flow rate of 0.1 ml/min was optimal in the sense that the average residence time of particles in the standing wave was sufficient to capture about 95% of particles from suspension. The enhancement of detection compared with the control (no ultrasound) situation was × 70. Capture of Bacillus subtilis var. niger spores was slightly higher than that of the model microparticles. An expression is derived for the dependence of concentration detectable on, number of microscopic fields examined, sample flow rate and assay time. The × 70 fold detection enhancement described here may be obtained with any assay system that depends on deposition of particles on a plane immunosensor.