Anomalous resonance in a nanomechanical biosensor

Amit K. Gupta, Birck Nanotechnology Center, School of Electrical and Computer Engineering, Purdue University
Pradeep R. Nair, Birck Nanotechnology Center, School of Electrical and Computer Engineering, Purdue University
Demir Akin, Birck Nanotechnology Center, School of Electrical and Compuer Engineering, and Weldon School of Biomedical Engineering, Purdue University
Michael R. Ladisch, Weldon School of Biomedical Engineering, Purdue University
Steve Broyles, Department of Biochemistry, Purdue University
Muhammad A. Alam, Birck Nanotechnology Center, School of Electrical and Computer Engineering, Purdue University
Rashid Bashir, Birck Nanotechnology Center and Bindley Bioscience Center, Purdue University

Abstract

The decrease in resonant frequency of a classical cantilever provides a sensitive measure of the mass of entities attached on its surface. This elementary phenomenon has been the basis of a new class of bio-nanomechanical devices as sensing components of integrated microsystems that can perform rapid, sensitive, and selective detection of biological and biochemical entities. Based on classical analysis, there is a widespread perception that smaller sensors are more sensitive, and this notion has motivated scaling of biosensors to nanoscale dimensions. In this work, we show that the response of a nanomechanical biosensor is far more complex than previously anticipated. Indeed, in contrast to classical microscale sensors, the resonant frequencies of the nanosensor may actually decrease or increase after attachment of protein molecules. /We demonstrate theoretically and experimentally that the direction of the frequency change arises from a size-specific modification of diffusion and attachment kinetics of biomolecules on the cantilevers. this work may have broad impact on microscale and nanoscale biosensor design, especially when predicting the characteristics of bio-nanoelectromechanical sensors functionalized with biological capture molecules.