A pulsed wave excitation system to characterize micron-scale magnetoelastic biosensors

This paper describes the design of a resonant frequency measurement system based on a pulsed wave excitation technique that can be used to resonate and measure micron-size Magnetoelastic (ME) biosensors. Current measurement techniques can only detect millimeter and above size ME biosensors. By using a specially designed, dedicated coil and low noise cascade amplifier, the system described in this paper is capable of measuring micron-size (ME) biosensors as small as 200 μm in length (200 × 40 × 15 μm). In the system, a square pulse current is applied to an excitation coil to excite the ME sensors, and a pick-up coil senses its mechanical vibration and converts it to an electrical output signal. The output signal is amplified by a signal amplification circuit and the output waveform is shown on an oscilloscope. Based on the acquired damped oscillating signal, the frequency change due to the mass change on the surface of the ME biosensor can be calculated. The impact of signal amplification on the resonant frequency, amplitude, and Q-factor of the resonant frequency peak, has been studied. The average resonant frequency of a 200 μm sensor was found to be 10.8283 ± 0.0027 MHz. As a proof-in-concept experiment, the detection system was used in combination with JRB7 phage-coated ME biosensors to detect different concentrations of Bacillus anthracis spores. A statistically significant difference for all concentrations of 5 × 102 spore/ml and higher can be reached by the system.