2019 Volume 77 Issue 11 Pages 1116-1127
The fluorescence properties, e.g., fluorescence intensity, of fluorescent sensors can change due to covalent derivatization or noncovalent complexation with a target chemical species (i.e., molecules and ions) or by variations in circumstantial physical parameters (e.g., temperature and viscosity). The internal charge transfer (ICT) character and photoinduced electron transfer (PET) efficiency can be used to tune the fluorescence switching mechanism, facilitating the development of new fluorescent sensors. In addition, the utilization of an environment-sensitive (i.e., polarity- and hydrogen bonding-sensitive) fluorophore in stimulus-responsive macromolecules to design novel fluorescent sensors has been proposed. Based on this concept, highly sensitive fluorescent polymeric thermometers and (extremely sensitive) digital fluorescent pH sensors have been developed. These thermometers are being used to measure the temperature of live cells in biological and medical studies. This concept has also allowed nanoscale proton mapping near membranes, which exemplifies the downsizing of targets for fluorescent sensing from a micrometer-scale to a nanometer-scale.