Multilayer Scanning Coil Detector for Improved Detection of Surface Pathogen Contamination

This paper presents an investigation into improved pathogen detection on food and food contact surfaces using a multilayer scanning coil detector combined with wireless magnetoelastic (ME) biosensors. In contrast to our previous studies of surface pathogen detection where a single-layer planar coil was employed, a more sensitive detector with a multi-layer coil design was investigated in this work. The two-fold roles of the coil detector are: (1) the application of an alternating magnetic field for the excitation of the ME sensor’s vibration and (2) detection of the resultant magnetic flux changes induced by the vibrating sensor. Surface pathogen detection can then be realized when the sensor comes into contact and binds specifically with the pathogen of interest, causing the sensor’s resonant frequency to decrease. For surfaces with large roughness and curvatures (e.g., leafy greens and cantaloupes), a long stand-off distance (distance between the sensor and detector) may be required. Hence, enhancement in the excitation power and sensitivity of coil detector with a multilayer design is a key to improving the system’s detection capabilities. Furthermore, smaller ME biosensors with higher mass sensitivity can also be measured with this sensitive multilayer coil detector. Several design parameters, including the number of layers, width, height, and spacing of coil turns, were studied. Coils were fabricated using standard microelectronic fabrication techniques (photolithograpy, electroplating, etching and sputtering) and tested.Both theoretical calculations and experimental data showed that the above coil geometric parameters have a significant impact on the signal amplitude and stand-off distance. Finally, with the newly fabricated multilayer coil detector, simultaneous measurement of multiple biosensors on spinach leaf surfaces was demonstrated. This multilayer scanning coil detector therefore facilitates the detection of pathogens on food and food contact surfaces.