Controllable Fabrication of Multifunctional Micro-thermocouples for Temperature Detection inside Single Suspended Droplets

Microdroplets have recently emerged as an exciting technological platform for wide applications. In this work, we developed a controllable fabrication approach to novel tungsten-platinum micro-thermocouples that function not only as a sensitive temperature sensor but also as a flexible suspender for individual microdroplet studies. The controllable fabrication hinges on the formation of tungsten tip apex nodes to make junctions with platinum, which was achieved through a unique combinational strategy, involving gradient coating with a complete insulating layer and subsequent targeted removal by tip electroporation. Benefiting from its coaxial structure, microspherical contact node end, hydrophobic surface, and thermoelectric performance, the as-fabricated micro-thermocouple was successfully employed for the microdroplet suspension and in situ temperature detection throughout the droplet evaporation cycle. It was observed that the temperature inside the suspended microdroplets was lower than that of the external environment, and there existed temperature discontinuity during droplet evaporation. By integrating the capabilities of temperature monitoring and droplet manipulation into a single micro-thermocouple, this work demonstrates its versatility and promising applications in expanded sensing for single microdroplets and other microsystems.