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 spiropyran-modified 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.