Thermoresponsive gold nanoparticles with adjustable lower critical solution temperature as colorimetric sensors for temperature, pH and salt concentration

Thermoresponsive gold nanoparticles (AuNPs) with lower critical solution temperature (LCST) adjustable over a broad range were explored to be potentially used as colorimetric sensors. Upon raising the temperature above the LCST the surface plasmon resonance (SPR) peaks of the obtained thermoresponsive AuNPs red-shifted sharply in a narrow temperature range, accompanied by a color transition from transparent red to transparent purple–red until turbid red, which made them suitable to be used as sensitive colorimetric sensors for detecting environmental temperature variation. Moreover, the temperature range of sensitivity of the obtained thermoresponsive AuNPs could be tuned by modulating the molecular weight of core or degree of substitution of the thermoresponsive polymers employed. Furthermore, the solution colors of the thermoresponsive AuNPs were also sensitive to pH and NaCl concentration variation, as a result of which they could also be used as colorimetric sensors for detecting the variation of pH and salt concentration.