Role of synthetic antifreeze agents in catalyzing ice nucleation

Nature endows antifreeze (glyco)proteins (AF(G)Ps) with the excellent capability of inhibiting ice crystal growth. Recent years have also witnessed the emergence of many potent AF(G)P mimics such as poly (vinyl alcohol) (PVA). As researchers are revealing the molecular mechanisms of inhibiting ice crystal growth by AF(G)Ps and their synthetic substitutes, there remains no agreement about their effect on ice nucleation. In this study, we report the observation of ice nucleation catalyzed by PVA of different polymerization degrees using a freeze-on-a-chip platform which allows the monitoring of freezing and melting events over hundreds of monodisperse, picoliter-sized aqueous droplets. Aqueous droplets made of 1 mg/ml PVA solution exhibit a median freezing temperature of around -36 °C, two degrees higher than the observed homogeneous nucleation temperature of water. The findings in our study bring useful insights into the different roles of synthetic antifreeze agents in controlling ice formation.