Low-cost stopped-flow and freeze-quench device for double mixing.

Experiments based on fast reagent mixing and observation of reaction progress are considered a powerful tool for investigating the kinetics of chemical and enzymatic reactions. Various spectroscopic methods are used in monitoring the reaction progress, which require different sample preparation methods. Stopped-flow is the most widespread method, where the reaction in the liquid phase is observed by optical absorption spectroscopy. Albeit less popular, the freeze-quench method is also used, in which the reaction is rapidly stopped by freezing the sample at a given time point after the reaction onset. The frozen droplets of the sample are collected and measured at low temperatures in the solid state. Currently, many commercial solutions are available for freeze-quench or stopped-flow experiments, but despite the high price of the devices, most of these do not allow combining both these methods in a single experiment. This study presents a relatively simple solution that combines both these methods, thus making a complete study of chemical or enzymatic reactions possible. Besides, the presented solution enables sequential double mixing of reagents, which is generally problematic and cannot be done using commercial instruments.