Selectivity of Piezoelectric-excited Millimeter-sized Cantilever (pemc) Sensors to Bacillus Anthracis Spores in the Presence of Bacillus Thuringiensis and Bacillus Cereus Spores in a Flow Cell

We report a highly sensitive, rapid and reliable method for the detection of Bacillus Anthracis spores at 300/mL using a piezoelectric-excited millimeter-sized cantilever (PEMC) sensor. Antibody specific to Bacillus anthracis (BA, Sterne strain 7702) spores was immobilized on PEMC sensors, and exposed to spores (300 to 3x10 spores/mL). The resonant frequency decreased at a rate proportional to the spore concentration and reached a steady state frequency change of 5 ± 5 (n=3), 92 ± 7 (n=3), 500 ± 10 (n=3), 1030 ± 10 (n=2), and 2696 ± 6 (n=2) Hz corresponding to 0, 3x10, 3x10, 3x10, and 3x10 spores/mL, respectively. Selectivity of the antibody functionalized sensor was determined with samples containing BA (3 x 10/mL) mixed with Bacillus thuringiensis (BT; 1.5x10/mL) in various volume ratios that yielded BA:BT ratios of 1:0, 1:0.008, 1:0.004, 1:0.002 and 0:1. The corresponding resonance frequency decreases were, 2345, 1980, 1310, 704 and 10 Hz. Sample containing 100% BT spores (1.5 x 10/mL and no BA) gave a steady state frequency decrease of 10 Hz, which is within noise level of the sensor, indicating excellent selectivity. These results show that detection of Bacillus anthracis spore at a very low concentration (300 spores/mL) and with high selectivity in presence of another Bacillus spore (BT) can be accomplished using piezoelectricexcited millimeter-sized cantilever sensors.