Total Internal Reflection Transient Absorption Microscopy: An Online Detection Method for Microfluidics

Abstract

Microreactors have garnered widespread attention for their tunability and precise control of synthetic parameters to efficiently produce target species. Despite associated advances, a lack of online detection and optimization methods has stalled the progression of microfluidic reactors. Here we employ and characterize a total internal reflection transient absorption microscopy (TIRTAM) instrument to image excited state dynamics on a continuous flow device. The experiments presented demonstrate the capability to discriminate between different chromophores as well as in differentiating the effects of local chemical environments that a chromophore experiences. This work presents the first such online transient absorption measurements and provides a new direction for the advancement and optimization of chemical reactions in microfluidic devices.

Leaving the Limits of Linearity for Light Microscopy

“…As the flow rate in the channel is changed, the IR-144 diffuses to a greater extent across the channel, which is extracted via the TIRTAM signal cross sections shown in the bottom plot. In addition to showing mixing, this study also captured TIRTAM’s ability to generate contrast from both differences in solvation environment and molecular structure . When imaging a microreactor, the theme of traversing timescales is captured, as the mapping of the chemical kinetics at different spatial locations throughout the device can be bridged to the transient absorption, molecular timescale that is being recorded.…”

“…(B) Graph of intensity vs channel position at the three different flow rates of 0.05 mL/min (red), 0.01 mL/min (blue), and 2.7 μL/min (black). Error bars show the standard deviation from three measurements . Reprinted in part with permission from ref .…”

“…Error bars show the standard deviation from three measurements . Reprinted in part with permission from ref . Copyright 2020 American Chemical Society.…”

“…58 Our group has also recently demonstrated the capability to collect TAM images using a total internal reflection (TIR) excitation geometry. 59 This instrument alleviates restrictions on the sample and simplifies the use of a standard microscope base for signal collection. These advantages were exploited to image chromophore diffusion as a function of flow rate in a microfluidic device.…”

“…In addition to showing mixing, this study also captured TIRTAM's ability to generate contrast from both differences in solvation environment and molecular structure. 59 When imaging a microreactor, the theme of traversing timescales is captured, as the mapping of the chemical kinetics at different spatial locations throughout the device can be bridged to the transient absorption, molecular timescale that is being recorded. In linking these time regimes, the ability to greatly augment the specificity and efficiency for microreactors becomes attainable, as new doors are opened to probe transient absorption dynamics along any timescale in a chemical reaction.…”