Detection of Bacillus anthracis spores and a model protein using PEMC sensors in a flow cell at 1 mL/min

Piezoelectric-excited millimeter-sized cantilever (PEMC) sensors of 4 mm2 sensing area were immobilized with antibody specific to Bacillus anthracis (anti-BA) spores or bovine serum albumin (anti-BSA). Detection of pathogen (Bacillus anthracis (BA) at 300 spores/mL) and BSA (1 mg/mL) were investigated under both stagnant and flow conditions. Two flow cell designs were evaluated by characterizing flow-induced resonant frequency shifts. One of the flow cells labeled SFC-2 (hold-up volume of 0.3 mL), showed small fluctuations (±20 Hz) around a common resonant frequency response of 217 Hz in the flow rate range of 1–17 mL/min. The total resonant frequency change obtained for the binding of 300 spores/mL in 1 h was 90 ± 5 Hz (n = 2), and 162 ± 10 Hz (n = 2) under stagnant and flow conditions, respectively. Binding of antibodies, anti-BA and anti-BSA, were more rapid under flow than under stagnant conditions. The sensor was repeatedly exposed to BSA with an intermediate release step. The first and second responses to BSA were nearly identical. The total resonant frequency response to BSA was 388 ± 10 (n = 2) Hz under flow conditions. Kinetic analysis is carried out to quantify the effect of flow rate on antibody immobilization and the two types of detection experiments.