A Sub-nL Chip Calorimeter and Its Application to the Measurement of the Photothermal Transduction Efficiency of Plasmonic Nanoparticles

Here, we introduce a microchip for differential measurements of aqueous samples in twin calorimetric arms with a sub-nL enclosed space. Each arm features a fluidic microchannel located in close proximity to a thin-film resistance thermometer and heater patterned on a low-stress SiN membrane held over a Si cavity with suspension beams. The chip exhibits a rapid response with a thermal time constant of less than 10 ms in atmosphere and a residual thermal conductance below
$6{\mu }\text{W}{\cdot }\text{K}^{-1 }$
, one of the lowest reported and accounts for the excellent sensitivity registered in vacuum up to 11
$\text{V}{\cdot }\text{W}^{-1 }$
. These values are in good agreement with those ones predicted by modeling using finite element method, lumped-capacitance analysis, and calorimeter electrothermal circuit simulation together with the measurement system. Long suspension beams in each arm ensure uniform temperature maintained across its membrane as revealed by the fluorescence-based melting curve analysis. We share the specific heat capacity values of water, glycerin, and mineral oil accurately measured by the chip. Lastly, we demonstrate the chip calorimeter utility on the measurement of the photothermal transduction efficiency of plasmonic nanoparticles, which makes our study further unique in expanding the applications of chip calorimeters. [2021-0044]