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MEMS & NEMS (Publications)

Resonant Mass Sensors Containing Nanofluidics

The ability of nanomechanical resonators to sense mass in a liquid environment is compromised by a large dissipation of energy to the surrounding liquid. In order to overcome this problem, we have designed and fabricated nanoscale resonators that contain fluidic channels. The channel allows delivery of analytes to the resonator in liquid while the resonator is operated in vacuum to avoid viscous damping. We estimate that the channels will be sensitive to masses as small as an attogram based on the mechanical resonance properties of the devices presented here.

High-Q, in-plane modes of nanomechanical resonators operated in air

We have fabricated 90 nm thick mechanical resonators, studied the resonance spectrum as a function of pressure, and found that some higher order resonant modes feature quality factors on the order of 2000 at atmospheric pressure, namely two symmetric, in-plane resonant modes. Even after deposition of a relatively thick polymer layer, the quality factor of the in plane mode in air only decreased slightly, suggesting that functional sensing layers can be used with devices operated in air. These encouraging results open the door for resonant micro- and nanoelectromechanical systems to biosensor and chemical sensor applications at atmospheric pressure.

Prion Protein Detection with Nanomechanical Resonators

Arrays of micromechanical resonators were fabricated and used as biosensors for detecting prion proteins, that when over-produced cause Mad Cow Disease and similar diseases in sheep (Scrapie) and humans (Creutzfeldt-Jakob Disease). In order to improve sensitivity to very low concentrations of prions, a nanoparticle-based technique was used to essentially make the prions heavier, and easier to detect with the resonators. This research was published by Madhukar Varshney et al. in the journal Analytical Chemistry DOI:10.1021/ac702153p

High Quality Factor Nanostring Resonators

We have fabricated nanomechanical flexural resonators with room temperature quality factors as high as 207,000 at a frequency of 4.5 MHz, representing the highest quality factor yet obtained for devices with cross-sectional dimensions on the order of 100 nm. We demonstrate that the high quality factors are a result of the high tensile stress present in these doubly-clamped devices, and demonstrate an approach to within an order of magnitude of the thermoelastic limit for mechanical quality factor for devices of this scale. These devices, with the highest ever reported product of quality factor and surface-to-volume ratio, should prove useful as sensitive probes of the environments in which they are operated.

Enumeration of Single DNA Molecules Bound to a Nanomechanical Oscillator

We demonstrate that highly uniform arrays of nanomechanical resonators can be used to detect the binding of individual DNA molecules through resonant frequency shifts resulting from the added mass of bound analyte. Localized binding sites created with gold nanodots create a calibrated response with sufficient sensitivity and accuracy to count small numbers of bound molecules. The amount of nonspecifically bound material from solution, a fundamental issue in any ultra-sensitive assay, was measured to be less than the mass of one DNA molecule, allowing us to detect a single 1587 bp DNA molecule.