Integration of dielectrophoretic trapping on a glass suspended microchannel resonator

In recent years, systems based on micro and nanoscale resonators have shown their potential as mass sensors with unparalleled sensitivity: yoctogram mass resolution has been reached using the smallest carbon nanotube resonators, proportionally decreasing with increasing resonator mass. The measurements obtained with these devices have the additional advantage of being intrinsically time resolved, as the resonator response is, at any given time, directly linked to the mass on the resonator. These features make them well-suited for the study of biological samples and ultimately processes (the latter is done by monitoring mass changes in the system, an example use case would be measuring the concentration changes of a specific protein during a cellular reaction); however this introduces the need to work in liquid, which drastically reduces the resonator's sensitivity because of the fluid's damping. The suspended microchannel resonator (SMR) approach removes most of the viscous damping from the fluid by confining the solution under analysis \emph{inside} the resonator, which is now a microchannel that can be suspended in air or vacuum (hence the name); SMRs can be integrated in a more complex microfluidic system to finely control the samples that pass through the resonator and more of them can be arrayed to perform more complex measurements or increase throughput. In order to keep the sample within the resonator for longer measurements (necessary for example to study mass variations during cellular processes), various techniques have been documented: functionalizing the surface of the channel to promote selective chemisorption of the samples or exploiting the channel geometry to trap them or slow them down are examples. In this work we show the implementation of dielectrophoresis(DEP) as a trapping method in a glass SMR device, with a different configuration than usually seen in literature: the electrodes are fabricated on top of the device and do not contact the liquid. While many trapping techniques used with SMR devices require a complex fabrication process resulting in higher costs and a reduced range of possible designs, this device was made with a relatively fast and cost-effective process thanks to the combination of a 3D-resolved femtosecond laser direct writing process for the channels and SMR and an ion beam etching process only slightly modified from the standard ones) for the electrodes. The mechanical properties and particle detection capabilities of the device were tested first without DEP, then the trapping and sensing capabilities of the SMR device with the new DEP approach were confirmed.