Microfluidic encapsulated nanoelectromechanical resonators

Resonant nanoelectromechanical systems have been demonstrated as sensitive mass detectors with subattogram and even single molecule sensitivity [Ilic, Nano Lett. 5, 925 (2005); Ilic, J. Appl. Phys. 95, 3694 (2004)]. Measurements of sub-ng/ml protein concentrations and DNA hybridization using deflection based microelectromechanical system (MEMS) devices have also been shown [Wu, Nat. Biotechnol. 19, 856 (2001); Fritz, Science 288, 316 (2000)]. Sample delivery is generally difficult in such cases requiring the entire device chip to be submersed into an analyte containing mixture. Additionally, in the case of MEMS resonators, high vacuum is required to remove viscous damping to improve sensitivity. In this work, the authors present a method where arrays of nanoelectromechanical devices are encapsulated in individually accessible, parallel microfluidic channels. The microchannels were used for delivery of liquids and nitrogen (for drying). The channels were pumped down to pressures where viscous damping effects are negligible. Due to the small volume of the channels, achieving the necessary vacuum took less than 1 min; the cycle time for measurement was therefore vastly reduced. The methods for encapsulation described herein are not limited to nanomechanical resonators and could have applications with other types of nanoelectromechanical systems.