Microelectromechanical disk resonators for direct detection of liquid-phase analytes

• Piezoelectric rotational-mode disk MEMS resonators are capable of direct real-time detection of biomolecular adsorption events in liquid media with very high sensitivities.
• Molecular mass sensitivities as high as 65 Hz cm2/ng are shown for such resonators when operating in liquid media.
• ∼2× difference in measured frequency shifts for one order of magnitude change in concentration of functionalizing HS-ssDNA solution is measured.
• Such sensors are capable of directly and specifically measuring concentration of thiol-terminated DNA molecules in liquid media.

This paper presents preliminary measurement results for real-time detection of biomolecules using rotational-mode MEMS resonant structures and capability of such to directly and specifically measure concentration of thiol-terminated DNA molecules in liquid. Thin film piezoelectric disk resonators with quality factors (Q) as high as ∼100 in aqueous solutions have been fabricated and utilized as direct biomolecular detectors that can address the problem of low Q for MEMS resonators when in direct contact with liquid. To adsorb thiol-terminated molecules, a gold layer is deposited on the top resonator surface. A gradual frequency shift of ∼10 kHz (3800 ppm) was recorded in real-time while forming monolayers of mercaptohexanol in aqueous solution, demonstrating the potential of such structures as highly sensitive biosensors. Over and above detection of target single-stranded-DNA (ssDNA) sequences using the disk resonators (with mass sensitivities as high as 19.3 ppm cm2/ng (65 Hz cm2/ng) in aqueous solution), the response of such devices has been characterized using different concentrations of thiol-terminated DNA molecules. For one order of magnitude change in concentration of functionalizing thiol-terminated-ssDNA solution, ∼2X difference in measured frequency shifts of the disk resonators was observed.