The use of polymers is finding a permanent place in sensor development as their chemical and physical properties can be tailored over a wide range of characteristics.^1–3  Great progress has been made in the last 20 years in polymeric sensors, especially for systems that make use of stimuli-responsive polymers that respond sharply with a solution-phase transition to environmental parameter changes such as temperature, pH value, or UV–vis light, or respond to chemical changes.³  The unique properties and easy accessibility of polymeric sensors enable their development as important alternative sensoric materials in areas such as biology, diagnostics, and chemical analysis.^1,3–5 

For temperature-sensing purposes, the temperature-induced solution-phase transition of a polymer can be translated into a sensory signal by incorporated solvatochromic dyes^6,7  that specifically change their optical or emissive properties in response to changes in the local environment (Figure 7.1). Such a polymer sensor system is composed of two key parts: (1) a thermoresponsive polymer that undergoes a phase transition due to the environmental temperature, in particular, polymers with a lower critical solution temperature (LCST) are used, i.e., the polymer is dissolved at lower temperatures and precipitates upon heating;⁸  and (2) the chromophore can be a fluorescent or visible solvatochromic dye that generates an output signal that can be quantitatively detected. In aqueous solution, the chromophore changes its absorbance or emission behaviour upon variation of the microenvironment from exposure to water in the soluble polymer state to the less polar collapsed polymer globules. For visible solvatochromic dyes, the change of signal could be either variation of absorption intensity or maximum absorption wavelength. In terms of fluorescent dyes, more information can be provided because numerous parameters like fluorescence decay times, fluorescence intensity, quenching efficiency, energy transfer and fluorescence polarization can be determined.