UCLA

Resonant sensors can detect chemical and biological analytes by measuring shifts in the resonant frequency due to adsorption-induced mass changes. This work describes a sensing approach that provides the sensitivity of nanoscale devices without sacrificing capture area through the use of highly porous surface so as to increase the adsorbed mass. Three strategies for exceptional capturing area are studied to achieve high sensitivity gas sensors; (1) porous-etched silicon resonator, (2) ZIF (zeolitic imidazolate framework)-agglomerated resonator by drop casting, and (3) ZIF-coupled resonator by dielectrophoresis.

Microscale silicon resonators with nanoscale pores are developed for increased surface area. Increased mechanical stability and detection performance are also achieved by keeping parts of the resonating device nonporous and adding a receptor coating. Partially-porous silicon resonators and receptor-coated partially-porous silicon resonators are improved up to 165% and 654% in resonator sensitivity, respectively, as compared to nonporous silicon resonators.

This work also presents ZIF-agglomerated resonators whose sensitivity shows an improvement up to 78 times (780% improvement) over the silicon resonators with identical dimensions while additionally utilizing the inherently selective adsorption properties of ZIFs. ZIF nanoparticles provide previously unattainable surface area as well as the ability to tailor crystal structure for inherent selectivity. A unique fabrication technique in combination with a drop casting method is presented, enabling deposition of a wide variety of materials on released MEMS devices by providing a temporary support layer of photoresist.

Lastly, ZIF nanoparticles are coupled to resonators using dielectrophoresis (DEP) to maximize adsorption of ZIFs so as to gain further sensitivity enhancement. By utilizing an inherently sensitive and selective adsorption property of ZIFs, amplitude of frequency shift shows a sensitivity improvement up to 158 times over the silicon resonator. Also, consistent decay constant of the frequency shift provide significant chemical recognition ability of the ZIF-coupled resonant sensor.