Figure 2.

Experiment to track the temperature shift of picoliter droplets undergoing a chemical reaction by measuring shifts in the spectral reflectivity of TLC reporter particles. (a) Light from a halogen lamp is directed to a microfluidic chip using beamsplitter BS1 and focused onto the outlet channel using a 20× dark-field objective. Scattered light from the sample returns through BS1 and is directed either to the input slit S1 of a spectrograph using mirror M2 or to a camera using flip mirror M1. (b) Detailed schematic top view of the chip’s outlet channel. Aqueous droplets pinch off in a fluoropolymer oil sheath flow and move down the outlet channel at a rate of 70–80 mm/s. Scattered light is collected from a field of view of 200 × 100 µm. By translating the chip along the × direction and detecting the TLC color as in (a), snapshots of the temperature throughout the ongoing reaction are acquired. The color shift is exaggerated for clarity.