  There remains a need for techniques to monitor thermal processes at high
spatiotemporal resolution, with myriad potential applications in chemistry,
biology, and engineering. Measurement of temperature from nanoscale molecular
phenomena are particularly promising due to their general compatibility with
biological systems. Among these phenomena, fluorescence polarization anisotropy
is particularly attractive due to its high sensitivity to thermal and
photophysical information, and its general utility with a wide spectrum of
fluorophores. In this work, we propose that the measurement of the intrinsic
fluorescence polarization anisotropy of tryptophan can be used to measure
label-free temperature at the nanoscale in a variety of tryptophan-containing
proteins. We present a theoretical model of the temperature sensitivity of
fluorescence polarization in free tryptophan and tryptophan-containing
proteins, empirically explore these properties, and discuss the potential
development of proteins as thermal memory sensors.
