A new tool for precise mapping of local temperature fields in submicrometer aqueous volumes

Nanodiamond hosting temperature-sensing centers constitutes a closed thermodynamic system, with the only window of energy exchange with the environment without direct contacts of a sensor with intracellular substrates, which is in fact the property of an ideal nanosized thermometer. Here, a new design of a nanodiamond thermometer, based on a 500-nm luminescent nanodiamond embedded into the inner channel of a glass submicron pipette is reported. All-optical detection of temperature, based on spectral changes of the emission of "silicon-vacancy" centers with temperature, is used. We demonstrate the applicability of the thermometric tool to the study of temperature distribution near a local heater, placed in an aqueous medium. The calculated and experimental values of temperatures are shown to coincide within the measurement error at gradients up to 20 °C/μm. Until now, temperature measurements on the submicron scale at such high gradients have not been performed. The new thermometric tool opens up unique opportunities to answer the urgent paradigm-shifting questions of cell physiology thermodynamics.