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

An electrospray coupled microfluidic reactor for the measurement of millisecond time-scale, solution phase kinetics is introduced. The device incorporates a simple two-channel design that is etched into polymethyl methacrylate (PMMA) by laser ablation. The outlet of the device is laser cut to a sharp tip, facilitating low dead volume 'on chip' electrospray. Fabrication is fast, straightforward and highly reproducible, supporting rapid prototyping and large-scale reproduction. Device performance is characterized using a cytochrome c unfolding reaction. Unfolding processes with rates in excess of 30 s(-1) are easily measured, including the appearance of a 'native-like' intermediate that is maximally populated 180 ms post reaction initiation. To extract reliable rates from the data, a theoretical framework for the analysis of kinetics acquired under square-channel laminar flow is introduced.