Piezoelectric immunosensor for Francisella tularensis detection using immunoglobulin M in a limiting dilution

Francisella tularensis is a pathogenic bacterium causing the serious disease tularemia and is potentially considered as a bioweapon agent. The piezoelectric immunosensor for F. tularensis (Ft) assay was developed using the quartz crystal microbalance (QCM) with covalently immobilized Ft antigen. Samples containing the bacterium were preincubated with a highly diluted anti-Ft IgM, and the mixture was injected to the flow cell containing the immunosensor. IgM alone as well as Ft cells alone were not giving any response, and therefore, it is assumed that the sensor responded to the IgM(x)-Ft(y) complex formed during the preincubation step. The effects of pH, time of preincubation, and IgM concentration were tested. This rapid method allowed us to detect 5 (.) 10(6) Ft cells/mL. RSD of measurements was near 1%. The total time of one analysis was 35 min, and one sensor was used for more than 30 times without losing sensitivity.