New Hybrid Nanocomposite Films for Optical Diagnostics and Optical Temperature Sensing: Synergy Among α‐Synuclein, Gold and Upconverting Nanoparticles

ABSTRACT The propensity of the unstructured protein α‐synuclein to undergo a conformational transition to fibrillar aggregates was harnessed to prepare an upconverting organic–inorganic hybrid film composed of Au nanoparticles (NPs) and Yb 3+ , Er 3+ ‐activated CaF 2 NPs, with α‐synuclein serving as a structural linker. The 2D nanomaterial appears as a quasi‐monolayer film, composed of distributed AuNPs and tightly packed CaF 2 :Yb,Er NPs. The film shows excellent upconversion emission arising from the Er 3+ ions following excitation of the Yb 3+ ions under 980 nm laser radiation. Optical thermometry investigations were conducted in various media (air, H 2 O, and D 2 O) to assess the performance of the film as an optical nanothermometer. The thermometric calibration curves obtained within the physiological temperature range (25–60°C) support its potential application in 2D optical nanothermometry. By evaluating the energy gap between the two thermalized levels and calibrating the upconversion at one temperature, the nanocomposite film was found to perform reliably as a primary thermometer. Furthermore, image‐based optical thermometry has demonstrated that upconversion emission can be successfully employed for local temperature estimation, thereby enabling image‐based 2D optical thermometry with micrometer‐scale spatial resolution.