Dynamic-mode cantilever biosensors are an attractive technology for biological sensing. However, researchers are constantly seeking ways to increase their sensitivity, especially in liquids, in order to rapidly detect biological particles in dilute samples. Here, we investigate a novel gap method for increasing their sensitivity. We design cantilevers with a micron-sized gap between their free end and a supporting structure that constrains the motion of individual particles deposited across the gap. When individual particles are deposited across the gap, they form a bridge between the free end of the cantilever and the supporting structure and generate fundamental resonant frequency shifts that are two orders of magnitude higher than when they are deposited on conventional cantilevers. Through experiments and simulation in air, we show that cantilevers based on the gap method rely on stiffness-change instead of mass-change, and that they are significantly more sensitive than conventional cantilevers.
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