Chemical imaging of microfluidic flows using ATR-FTIR spectroscopy

TLDR

Elucidating the chemical composition of microfluidic flows is crucial for understanding and optimising reactive processes in small‑volume environments. The study reports a novel ATR–FTIR spectroscopic imaging method using an infrared focal plane array detector for microfluidic applications. The technique employs an inverted prism‑shaped ATR crystal coupled to a PDMS microfluidic mixing chip and an infrared focal plane array detector to image fluid composition. The method successfully visualises mixing of liquids with differing viscosities and H₂O/D₂O isotope exchange, enabling label‑free, spatially resolved analysis of fluid composition for diverse microfluidic processes.

Abstract

Elucidating the chemical composition of microfluidic flows is crucial in both understanding and optimising reactive processes within small-volume environments. Herein we report the implementation of a novel detection methodology based on Attenuated Total Reflection (ATR)–Fourier Transform Infra-Red (FTIR) spectroscopic imaging using an infrared focal plane array detector for microfluidic applications. The method is based on the combination of an inverted prism-shape ATR crystal with a poly(dimethylsiloxane)-based microfluidic mixing device. To demonstrate the efficacy of this approach, we report the direct measurement and imaging of the mixing of two liquids of different viscosities and the imaging and mixing of H2O and D2O with consecutive H/D isotope exchange. This chemically specific imaging approach allows direct analysis of fluid composition as a function of spatial position without the use of added labels or dyes, and can be used to study many processes in microfluidics ranging from reactions to separations.