Biological Imaging and Sensing with Multiresponsive Microgels

Multiresponsive spiropyran-modified poly(N-isopropylacrylamide)-based microgels were synthesized and their response to temperature; UV, visible, and near-infrared radiation; pH; and Cu2+ was investigated. The responses were a result of the spiropyran groups undergoing a reversible isomerization/reaction from a neutral to a charged form. The isomerization process was investigated via experiment and theory. The two-photon excited fluorescence of the spiropyran-modified microgels was also characterized, and their ability to be used to image live cells was determined. Finally, optical devices (etalons) were fabricated using the spiropyranmodified microgels, and the ability of the devices to change color in response to the above-mentioned stimuli was also investigated. We found that the microgel's responsivity was retained in the etalon, which yielded color tunable devices and sensors. This investigation illustrates the versatility of pNIPAm-based microgels and microgel-based etalons and showcases the clear utility of such devices for remote actuation, color tunable optics, sensing, and remotely triggered drug delivery systems.