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 100nm nanodiamonds in aqueous volume ensembles at a concentration of 0.5 mg/ml, across the temperature range of 30-45 C. The NV0 and N-V fluorescence intensities achieved high linear correlation values of 0.99 (INV0) 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 INV0/INV ratios to gain insights into thermal quenching phenomena in fluorescent nanodiamonds, where upon heating, an increasing trend for INV0/(INV0+I-NV) is observed, while an antisymmetric effect takes place for INV0/(INV0+(NV)). These findings indicate the potential of commercial nanodiamonds for precise all-optical fluorescence-based temperature sensing.