Picoliter-Volume Isothermal Titration Calorimetry Using Parylene Chip Calorimeter Integrated with on-Demand Droplet Microfluidics

Abstract

Isothermal titration calorimetry (ITC) is a gold-standard technique for directly quantifying biomolecular interactions, but its broader applicability is limited by large sample consumption and low throughput. To address these challenges, considerable efforts are made to develop chip calorimeter systems. Here, a high-sensitivity chip calorimeter integrated with on-demand droplet microfluidics is presented, capable of performing ITC with picoliter-volume samples. The device combines vanadium pentoxide thermistors, vacuum-insulated parylene microfluidics, and multilayer Polydimethylsiloxane microfluidics to achieve precise thermal measurement and fluidic control. On-demand generation and merging of titrant and titrand droplets enable accurate control of molar ratios for droplet-based titration. The chip calorimeter achieves a temperature resolution of 14.9 µK and a power resolution of 2.31 nW. The platform is validated by measuring the binding interaction between 18-crown-6 and barium chloride, with extracted thermodynamic parameters in good agreement with conventional ITC. This work advances miniaturized ITC technology by providing a scalable and efficient platform for quantitative biochemical analysis, particularly in sample-limited and high-throughput applications.