Commercial nanodiamonds for precise fluorescence-based temperature sensing

Nanothermometry is crucial for understanding physical, chemical, and biological systems, which require precise temperature measurement. Fluorescent nanodiamonds containing nitrogen-vacancy (NV) color centers offer an approach to temperature sensing. In this study, we present the spectrofluorometric characteristics of the NV zero-phonon lines (575 and 637 nm), in 100 nm nanodiamonds in aqueous volume ensembles at a concentration of 0.5 mg/ml, across the temperature range of 30-45 °C. The NV⁰ and NV⁻ fluorescence intensities achieved high linear correlation values of 0.99 (I_NV⁰) and 0.94 (I_NV⁻), respectively, demonstrating their efficiency in high precision temperature assessment. Additionally, we explore NV⁰ width as temperature increases, NV populations intensity ratios, and I_NV⁰/I_NV⁻ ratios to gain insights into thermal quenching phenomena in fluorescent nanodiamonds, where upon heating, an increasing trend for I_NV⁻/(I_NV⁰+I_NV⁻) is observed, while an antisymmetric effect takes place for I_NV⁰/(I_NV⁰+I_NV⁻). These findings indicate the potential of commercial nanodiamonds for precise all-optical fluorescence-based temperature sensing.