A method of measuring Escherichia coli O157:H7 at 1 cell/mL in 1 liter sample using antibody functionalized piezoelectric-excited millimeter-sized cantilever sensor

Piezoelectric-excited millimeter-sized cantilever (PEMC) sensors immobilized with antibody specific to Escherichia coli (EC) O157:H7 is used to detect EC at 1 cell/mL in 1 mL and 1 L samples in a batch and flow mode, respectively. Two sensor designs were used. The first design (PEMC-a) has both the piezoelectric and non-piezoelectric layer anchored, while in the second design (PEMC-b) had only the piezoelectric layer anchored. PEMC-a, used in batch mode with 1 mL sample, showed limit of detection at 10 cells/mL using the second bending mode at 85.5 kHz in air. PEMC-b exhibited resonant frequencies at 186.5, 883.5, and 1778.5 kHz in air and 162.5, 800.0, and 1725.5 kHz in sample flow conditions. A one-liter sample containing 1000 EC cells was introduced at 1.5, 2.5, 3, and 17 mL/min, and the change in resonant frequency was monitored. The total frequency change observed for the mode at 800 kHz and sample flow rates of 1.5, 2.5, 3, and 17 mL/min were 2230 +/- 11, 3069 +/- 47, 4686 +/- 97, and 7188 +/- 52 Hz, respectively. Each detection experiment was confirmed by exposing the sensor to a low pH solution followed by a phosphate buffered saline (PBS) rinse, which caused the release of the attached EC. The final frequency change observed was nearly identical to the value prior to EC attachment. Kinetic analysis showed that the observed binding rate constant at 1.5, 2.5, 3 mL/min were 0.009, 0.015, and 0.021 min(-1), respectively. The significance of these results is that very low concentration of pathogens in large sample volumes can be measured in a short time period without the need for filtration or enrichment.