Real-time bio-sensing using micro-channel encapsulated thermal-piezoresistive rotational mode disk resonators

This work presents a label-free bio-molecular detection technique based on real-time monitoring of the resonant frequency of micromechanical rotational mode disk resonators in a solution. Due to their extremely high mass sensitivities, adsorption of thin films or even molecular monolayers on the surface of such devices results in a measurable frequency shift. In this work, in order to insulate the electrical connections from the solution, protect the device against contaminants, and minimize the sample size requirements, MEMS resonators were encapsulated in PDMS-based micro-fluidic channels. To demonstrate the molecular detection capability, the strong non-covalent binding of Avidin with its ligand, biotin was utilized. Biotin chained with PLL-PEG was used to functionalize the silicon dioxide surface of the resonators. The positively charged PLL backbone sticks to the negatively charged silicon dioxide surface of the resonators and the PEG side chains stretch away from the surface. A frequency shift of 3400ppm after PLL-PEG-BIOTIN adsorption and 4000ppm after Avidin adsorption was observed. Similar procedures can be used to further attach biotinylated DNA strands or other proteins for real time label-free detection of a variety of bio-molecules.