Accumulation of Antifreeze Proteins on Ice Is Determined by Adsorption.

Antifreeze proteins (AFPs) facilitate the survival of diverse organisms in frigid environments by adsorbing to ice crystals and suppressing their growth. The rate of AFP accumulation on ice is determined by an interplay between AFP diffusion from the bulk solution to the ice-water interface and the subsequent adsorption of AFPs to the interface. To interrogate the relative importance of these two processes, here, we combine nonequilibrium fluorescence experiments with a reaction-diffusion model. We find that as diverse AFPs accumulate on ice, their concentration in the aqueous solution does not develop a gradient but remains equal to its bulk concentration throughout our experiments. These findings lead us to conclude that AFP accumulation on ice crystals, which are smaller than 100 µm in radius, is not limited by the diffusion of AFPs, but by the kinetics of AFP adsorption. Our results imply that mass transport limitations do not hinder AFPs from performing their biological function.

A Microfluidic Approach for the Study of Ice and Clathrate Hydrate Crystallization.

An accurate mechanistic description of water crystallization is challenging and requires a few key elements: superb temperature control to allow the formation of single microscopic crystals and a suitable microscopy system coupled to the cold stage. The method described herein adds another important feature that includes exchanging solutions around ice and clathrate hydrate crystals. The described system comprises a combination of unique and home-developed instruments, including microfluidics, high-resolution cold stages, and fluorescence microscopy. The cold stage was designed for microfluidic devices and allows for the formation of micron-sized ice/hydrate crystals inside microfluidic channels and the exchange of solutions around them. The temperature resolution and stability of the cold stage is one millikelvin, which is crucial for controlling the growth of these small crystals. This diverse system is used to study the different processes of ice and hydrate crystallization and the mechanism by which the growth of these crystals is inhibited. The protocol describes how to prepare microfluidic devices, how to grow and control microscopic crystals in the microfluidic channels, and how the utilization of the flow of liquids around ice/hydrate crystals affords new insights into the crystallization of water.