Toward Attogram Mass Measurements in Solution with Suspended Nanochannel Resonators

Abstract

Using suspended nanochannel resonators (SNRs), we demonstrate measurements of mass in solution with a resolution of 27 ag in a 1 kHz bandwidth, which represents a 100-fold improvement over existing suspended microchannel resonators and, to our knowledge, is the most precise mass measurement in liquid today. The SNR consists of a cantilever that is 50 µm long, 10 µm wide, and 1.3 µm thick, with an embedded nanochannel that is 2 µm wide and 700 nm tall. The SNR has a resonance frequency near 630 kHz and exhibits a quality factor of approximately 8000 when dry and when filled with water. In addition, we introduce a new method that uses centrifugal force caused by vibration of the cantilever to trap particles at the free end. This approach eliminates the intrinsic position dependent error of the SNR and also improves the mass resolution by increasing the averaging time for each particle.

Energy dissipation in microfluidic beam resonators: Dependence on mode number

“…Recently, Burg et al 15 developed a new type of cantilever sensor that embeds a microfluidic channel in its interior, with the region surrounding the cantilever evacuated-these devices are commonly called suspended microchannel resonators; 15,16 see Fig. 1.…”

“…Quality factors similar to those exhibited by conventional cantilevers in vacuum were observed. 15,16 Mass measurements in liquid with femtogram a͒ Electronic mail: jsader@unimelb.edu.au. sensitivity were demonstrated originally, 15 with a recent article reporting sensitivity in the attogram range upon miniaturization to the nanoscale.…”

“…sensitivity were demonstrated originally, 15 with a recent article reporting sensitivity in the attogram range upon miniaturization to the nanoscale. 16 Underpinning measurements using these microfluidic beam devices are their inherently high quality factors in the presence of liquid. Strikingly, it was observed 15 that the fundamental mode quality factor was unaffected when air or water was placed in the channel, with values of ϳ15 000 being achieved in both cases, for a single device.…”

“…In contrast to conventional cantilever beams immersed in liquid, the quality factor of microfluidic beam devices typically decreases with increasing mode number. 16,25 The underlying physical mechanisms giving rise to this behavior are explored. Critically, we find that the effects of fluid compressibility are enhanced with increasing mode number.…”

Ultimate and practical limits of fluid-based mass detection with suspended microchannel resonators

“…[8][9][10] Within a vacuum-based microcantilever structure they embed a microfluidic flow channel, which is subsequently used to transport and present fluid-based analytes to the active vibratory region of this micromechanical mass sensor. Here we analyze practical and fundamental limits to biological mass sensing with such SMRs, focusing on the ultimate sensitivity that is attainable with geometric scaling to nanometer dimensions.…”