Ultrasensitive Biomems Sensors Based on Microcantilevers Patterned with Environmentally Responsive Hydrogels

An innovative platform was developed for ultrasensitive microsensors based on microcantilevers patterned with crosslinked copolymeric hydrogels. A novel UV free-radical photolithography process was utilized to precisely align and pattern environmentally responsive hydrogels onto silicon microcantilevers, after microcantilevers were fabricated and released. Specifically, a crosslinked poly(methacrylic acid) network containing high amounts of poly(ethylene glycol) dimethacrylate was prepared and investigated. Hydrogels were patterned onto the silicon microcantilevers utilizing a mask aligner to allow for precise positioning. The silicon surface was modified with -methacryloxypropyl trimethoxysilane to gain covalent adhesion between the polymer and the silicon. The hydrogels sensed and responded to changes in environmental pH resulting in a variation in surface stress that deflected the microcantilever. The bending response of patterned cantilevers with a change in environmental pH was observed, showing the possibility to construct MEMS/BioMEMS sensors based on microcantilevers patterned with environmentally responsive hydrogels. An extraordinary maximum sensitivity of 1 nm/5×10^–5pH was observed, demonstrating the ultrasensitivity of this microsensor platform.