Abstract
Microcantilever sensors offer high sensitivity in the detection of adsorbed molecules based either on resonance frequency shift or changes in cantilever deflection, as both of these signals can be detected with very high resolution. Despite the high sensitivity offered by this platform, cantilevers suffer from poor selectivity due to the lack of sufficiently selective interfacial layers which can be immobilized on cantilever surfaces. This problem can be overcome by using photothermal cantilever deflection spectroscopy (PCDS), which exploits the high thermomechanical sensitivity of bi-material microcantilevers. A bi-material cantilever responds to heat generated by the nonradiative decay process when the adsorbed molecules are resonantly excited with infrared (IR) light. The variation in the cantilever deflection as a function of illuminating IR wavelength corresponds to the conventional IR absorption spectrum of the adsorbed molecules. In addition, the mass of the adsorbed molecules can be determined by measuring the resonance frequency shift of the cantilever as an orthogonal signal for the quantitative analysis. This multi-modal PCDS offers unprecedented opportunities for obtaining very high selectivity in chemical and biological sensing without using selective interfacial layers or extrinsic labels.
Highlights
Microcantilever sensors have attracted much attention due to their extremely high sensitivity [1,2]
Molecular adsorption-induced resonance frequency variation approach The resonance frequency, f, of a vibrating cantilever can be expressed as rffiffiffiffiffiffi f
In spite of recent advances in microfabricated cantilever sensors with extremely high sensitivity, most sensing applications are hampered by poor selectivity
Summary
Microcantilever sensors have attracted much attention due to their extremely high sensitivity [1,2]. In spite of recent advances in microfabricated cantilever sensors with extremely high sensitivity, most sensing applications are hampered by poor selectivity This challenge can be traced back to fundamental limitations imposed by the chemistry of the molecular interactions which forms the basis for signal generation in currently used chemical sensors. Orthogonal signals (nanomechanical IR spectra and mass variations) are measured by optical beam deflection method using a red diode laser and a position sensitive detector (PSD) These nonradiative decay processes result in heating up the bi-material cantilever, generating the deflection of the cantilever. The observed peak amplitudes of nanomechanical IR spectra are proportional to the amount of the adsorbed molecules, the impinging power of IR radiation, the absorption mode, and the thermomechanical sensitivity of the bi-material cantilever. Versatility: The same device can be used for different analytes
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