A QCM immunosensor for Salmonella detection with simultaneous measurements of resonant frequency and motional resistance

A quartz crystal microbalance (QCM) immunosensor was described for the detection of Salmonella Typhimurium with simultaneous measurements of the resonant frequency and motional resistance. The immunosensor was fabricated using protein A for the antibody immobilization. High-frequency impedance analysis indicated that the changes in resonant frequency and motional resistance (ΔF and ΔR) of the QCM were significant while the changes in static capacitance, motional capacitance, and motional inductance were insignificant. In the direct detection of S. Typhimurium in chicken meat sample, ΔF and ΔR were proportional to the cell concentration in the range of 105-108 and 106-108 cells/ml, respectively. Using anti-Salmonella-magnetic beads as a separator/concentrator for sample pretreatment as well as a marker for signal amplification, the detection limit was lowered to 102 cells/ml based on the ΔR measurement; however, ΔF was not related to the cell concentration. No interference was observed from E. coli K12 or the sample matrix.