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

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 Yb3+, Er3+-activated CaF2 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 CaF2:Yb,Er NPs. The film shows excellent upconversion emission arising from the Er3+ ions following excitation of the Yb3+ ions under 980 nm laser radiation. Optical thermometry investigations were conducted in various media (air, H2O, and D2O) 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.