A Diamond Heater‐Thermometer Microsensor for Measuring Localized Thermal Conductivity: A Case Study in Gelatin Hydrogel

Abstract Understanding the microscopic thermal effects of the hydrogel is important for its application in diverse fields, including thermal‐related studies in tissue engineering and thermal management for flexible electronic devices. In recent decades, localized thermal properties, such as thermal conductivity, have often been overlooked due to technical limitations. To tackle this, the study proposes a new hybrid diamond microsensor that is capable of simultaneous temperature control and readout in a decoupled manner. Specifically, the sensor consists of a silicon pillar (heater) at ≈10 microns in length, topped by a micron‐sized diamond particle that contains silicon‐vacancy (SiV) centers (thermometer) with 1.29 temperature measurement sensitivity. Combining this innovative, scalable sensor with a newly established simulation model that can transform heating‐laser‐induced temperature change into thermal conductivity, an all‐optical decoupled method is introduced with ≈0.05 W m⁻¹ K⁻¹ precision, which can reduce laser crosstalk. For the first time, the thermal conductivity change of hydrogels during the gelation process is tracked and the existence of variation is demonstrated. The study introduces a rapid, undisturbed technique for measuring microscale thermal conductivity, potentially serving as a valuable tool for cellular thermometry, and highlights the idea that decoupling can reduce crosstalk from different lasers, which is helpful for quantum sensing.