title: Anomalous resonance in a nanomechanical biosensor.
abstract: The decrease in resonant frequency (-Deltaomega(r)) 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 approximately -0.5omega(r)/m(C), where m(C) 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.
authors.affiliation: Birck Nanotechnology Center, School of Electrical and Computer Engineering, Weldon School of Biomedical Engineering, Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Amit K
authors.initials: AK
authors.lastname: Gupta
authors.forename: Pradeep R
authors.initials: PR
authors.lastname: Nair
authors.forename: Demir
authors.initials: D
authors.lastname: Akin
authors.forename: Michael R
authors.initials: MR
authors.lastname: Ladisch
authors.forename: Steve
authors.initials: S
authors.lastname: Broyles
authors.forename: Muhammad A
authors.initials: MA
authors.lastname: Alam
authors.forename: Rashid
authors.initials: R
authors.lastname: Bashir
mesh_terms: D000327:Adsorption; D000906:Antibodies / Q000378:metabolism; D000936:Antigen-Antibody Complex / Q000032:analysis; D055592:Biophysical Phenomena; D001703:Biophysics; D015374:Biosensing Techniques / Q000295:instrumentation* / Q000379:methods; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D004058:Diffusion; D016650:Fluorescein-5-isothiocyanate; D005456:Fluorescent Dyes; D007700:Kinetics; D019563:Mechanics; D044085:Microfluidics; D008954:Models, Biological; D008962:Models, Theoretical; D036103:Nanotechnology / Q000295:instrumentation* / Q000379:methods; D011506:Proteins / Q000378:metabolism / Q000648:ultrastructure; D012680:Sensitivity and Specificity; D014615:Vaccinia / Q000378:metabolism; D014732:Vibration
chemical_list: D000906:Antibodies; D000936:Antigen-Antibody Complex; D020099:Coated Materials, Biocompatible; D005456:Fluorescent Dyes; D011506:Proteins; D016650:Fluorescein-5-isothiocyanate