Anomalous resonance in a nanomechanical biosensor
- Amit K. Gupta*,†,
- Pradeep R. Nair*,†,
- Demir Akin*,†,‡,
- Michael R. Ladisch‡,
- Steve Broyles§,
- Muhammad A. Alam*,†, and
- Rashid Bashir*,†,‡,¶
- *Birck Nanotechnology Center,
- †School of Electrical and Computer Engineering,
- ‡Weldon School of Biomedical Engineering, and
- §Department of Biochemistry, Purdue University, West Lafayette, IN 47907
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Edited by L. B. Freund, Brown University, Providence, RI, and approved July 20, 2006 (received for review March 13, 2006)
Abstract
The decrease in resonant frequency (−Δωr) 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 (sensitivity ≈ −0.5ωr/mC, where mC is the mass of the cantilever), 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.
Footnotes
- ¶To whom correspondence should be addressed. E-mail: bashir{at}purdue.edu
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Author contributions: A.K.G., D.A., M.R.L., S.B., M.A.A., and R.B. designed research; A.K.G., P.R.N., and D.A. performed research; A.K.G., P.R.N., D.A., M.A.A., and R.B. analyzed data; and A.K.G., P.R.N., M.A.A., and R.B. wrote the paper.
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Conflict of interest statement: No conflicts declared.
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This paper was submitted directly (Track II) to the PNAS office.
- Abbreviation:
- CPD,
- critical point drying.
- © 2006 by The National Academy of Sciences of the USA
