In situ detection of Bacillus anthracis spores using fully submersible, self-exciting, self-sensing PMN-PT/Sn piezoelectric microcantilevers

Abstract

In this study, we have demonstrated in situ, all-electrical detection of Bacillus anthracis (BA) spores using lead magnesium niobate–lead titanate/tin (PMN-PT/Sn) piezoelectric microcantilever sensors (PEMS) fabricated from PMN-PT freestanding films and electrically insulated with methyltrimethoxysilane (MTMS) coatings on the tin surface. Antibody specific to BA spore surface antigen was immobilized on the platinum electrode of the PMN-PT layer. In phosphate-buffered saline (PBS) solution, the PMN-PT/Sn PEMS exhibited quality (Q) values ranging from 50 to 75. The detection was carried out in a closed-loop flow cell with a liquid volume of 0.8 ml and a flow rate of 1 ml min⁻¹. It was shown that one sensor, “PEMS-A” (500 µm long, 800 µm wide, with a 22 µm thick PMN-PT layer, a 20 µm thick tin layer and a 1 ± 0.5 × 10⁻¹² g Hz⁻¹ mass detection sensitivity) exhibited resonance frequency shifts of 2100 ± 200, 1100 ± 100 and 700 ± 100 Hz at concentrations of 20 000, 2000, and 200 spores ml⁻¹ or 16 000, 1600, and 160 total spores, respectively. Additionally, “PEMS-B” (350 µm long, 800 µm wide, with an 8 µm thick PMN-PT layer, a 6 µm thick tin layer and a 2 ± 1 × 10⁻¹³ g Hz⁻¹ mass detection sensitivity) exhibited resonance frequency shifts of 2400 ± 200, 1500 ± 200, 500 ± 150 and 200 ± 100 Hz at concentrations of 20 000, 2000, 100, and 45 spores ml⁻¹ or 16 000, 1600, 80, and 36 total spores, respectively.