Direct, surface-scanning detection of pathogenic bacteria using a wireless biosensor

This paper investigates the accuracy of surface-scanning measurement of a wireless magnetoelastic (ME) biosensor for direct pathogen detection on solid surfaces. The model experiments were conducted on the surface of a at polyethylene (PE) plate. An ME biosensor (1 mm x 0.2 mm x 30 µm) was placed on the PE surface, and a surface-scanning detector was aligned to the sensor for wireless resonant frequency measurement. The position of the detector was accurately controlled by using a motorized three-axis translation system (i.e., controlled X, Y, and Z positions). The results showed that the resonant frequency variations of the sensor were -125 to +150 Hz for X and Y detector displacements of ± 600 µm and Z displacements of +100 to +500 µm. These resonant frequency variations were small compared to the sensor's initial resonant frequency (˂ 0.007% of 2.2 MHz initial resonant frequency) measured at the detector home position, indicating high accuracy of the measurement. In addition, the signal amplitude was, as anticipated, found to decrease exponentially with increasing detection distance (i.e., Z distance). Finally, additional experiments were conducted on the surface of cucumbers. Similar results were obtained.