Detect of Escherichia coli O157:H7 in ground beef samples using piezoelectric excited millimeter-sized cantilever (PEMC) sensors

Piezoelectric-excited millimeter-sized cantilever (PEMC) sensors consisting of a piezoelectric and a borosilicate glass layer with a sensing area of 4 mm2 were fabricated. An antibody specific to Escherichia coli (anti-E. coli) O157:H7 was immobilized on PEMC sensors, and exposed to samples containing E. coli O157:H7 (EC) prepared in various matrices: (1) broth, broth plus raw ground beef, and broth plus sterile ground beef without inoculation of E. coli O157:H7 served as controls, (2) 100 mL of broth inoculated with 25 EC cells, (3) 100 mL of broth containing 25 g of raw ground beef and (4) 100 mL of broth with 25 g of sterile ground beef inoculated with 25 EC cells. The total resonant frequency change obtained for the broth plus EC samples were 16 ± 2 Hz (n = 2), 30 Hz (n = 1), and 54 ± 2 Hz (n = 2) corresponding to 2, 4, and 6 h growth at 37 °C, respectively. The response to the broth plus 25 g of sterile ground beef plus EC cells were 21 ± 2 Hz (n = 2), 37 Hz (n = 1), and 70 ± 2 Hz (n = 2) corresponding to 2, 4, and 6 h, respectively. In all cases, the three different control samples yielded a frequency change of 0 ± 2 Hz (n = 6). The E. coli O157:H7 concentration in each broth and beef samples was determined by both plating and by pathogen modeling program. The results indicate that the PEMC sensor detects E. coli O157:H7 reliably at 50–100 cells/mL with a 3 mL sample.