Far field metal-enhanced luminescence nanothermometry

Near-infrared (NIR) imaging and related sensing technologies must operate under biologically constrained conditions of low excitation power and strong tissue scattering, making efficient light extraction crucial. Here, we show that a simple architecture of Ag2S-based nanoparticles deposited on metallic reflective surfaces markedly amplifies the photoluminescence (PL) signal through a mirror-induced optical feedback effect. This passive amplification enhances the signal-to-noise ratio (SNR) and allows detection through cm-thick tissue-mimicking media under low excitation power and short integration times. Furthermore, the increased SNR enables the temperature-dependent PL contrast to be quantified more reliably over the working temperature range, without modifying the intrinsic photophysical response of the emitters. Integrating nanothermometers with metals as passive optical amplifiers thus provides a scalable route toward high-performance, bio-integrated photonic platforms for NIR imaging and thermometry, under realistic, tissue-relevant conditions.