Study of “blind point” and mass sensitivity of a magnetostrictive biosensor with asymmetric mass loading

Abstract

The existence of “blind point” lowers the mass sensitivity and reliability of magnetostrictive particle (MSP) based biosensors. In addition, asymmetric distribution of mass loading (e.g. bacteria) will cause the shift of “blind point” and change of mass sensitivity of an MSP based biosensor. In this work, a modal analysis method was introduced and conducted to derive the governing vibration equation for an MSP biosensor with asymmetric mass loading. The effects of asymmetric mass loading on the “blind point” shift and mass sensitivity were unveiled by solving the governing vibration equation. It was found that the plot of “blind point” shift showed an “M” shape with the valley located at a/l ∼ 0.5 and two peaks located at a/l ∼ 0.25 and a/l ∼ 0.75. In addition, the theoretical results showed that the resonance frequency shift (Δf) depends on the value of a/l (i.e. both the attached mass and mass distribution) and their relationship is nonlinear. Based on the definition of mass sensitivity (Sm), the values of Sm were derived for the selected values of a/l. The results showed that Sm decreased initially with increasing a/l, reaching the minimum, and then increased until a/l = 1. That is, the maximum mass sensitivity is obtained when a/l equals to a critical value Xc (0 < Xc < l). Based on the result, an optimal mass loading distribution design criterion for developing a more sensitive MSP based biosensor was proposed.