A versatile microfluidic chip for millisecond time-scale kinetic studies by electrospray mass spectrometry

Area of Science:

• Analytical Chemistry
• Chemical Kinetics
• Biophysical Chemistry

Background:

• Measuring fast reaction kinetics (millisecond timescale) in solution is challenging.
• Existing methods may have limitations in speed, dead volume, or reproducibility.
• Microfluidic devices offer potential for precise control and rapid mixing.

Purpose of the Study:

• To introduce a novel electrospray-coupled microfluidic reactor.
• To enable the measurement of millisecond time-scale, solution-phase kinetics.
• To develop a theoretical framework for analyzing kinetic data from laminar flow.

Main Methods:

• Fabrication of a two-channel microfluidic device using laser ablation in polymethyl methacrylate (PMMA).
• Laser cutting of the device outlet to a sharp tip for low dead volume 'on chip' electrospray.
• Characterization of device performance using a cytochrome c unfolding reaction.

Main Results:

• The microfluidic reactor successfully measured unfolding processes with rates exceeding 30 s(-1).
• A 'native-like' intermediate was observed, maximally populated at 180 ms post-initiation.
• The device fabrication proved to be fast, straightforward, and highly reproducible.

Conclusions:

• The developed electrospray-coupled microfluidic reactor is effective for studying millisecond-scale kinetics.
• The device supports rapid prototyping and large-scale reproduction for kinetic studies.
• A new theoretical framework aids in extracting reliable kinetic rates from square-channel laminar flow data.