Oxidized Quasi-Carbon Nitride Quantum Dots Inhibit Ice Growth

Antifreeze proteins (AFPs), a type of high-efficiency but expensive and often unstable biological antifreeze, have stimulated substantial interest in the search for synthetic mimics. However, only a few reported AFP mimics display thermal hysteresis, and general criteria for the design of AFP mimics remain unknown. Herein, oxidized quasi-carbon nitride quantum dots (OQCNs) are synthesized through an up-scalable bottom-up approach. They exhibit thermal-hysteresis activity, an ice-crystal shaping effect, and activity on ice-recrystallization inhibition. In the cryopreservation of sheep red blood cells, OQCNs improve cell recovery to more than twice that obtained by using a commercial cryoprotectant (hydroxyethyl starch) without the addition of any organic solvents. It is shown experimentally that OQCNs preferably bind onto the ice-crystal surface, which leads to the inhibition of ice-crystal growth due to the Kelvin effect. Further analysis reveals that the match of the distance between two neighboring tertiary N atoms on OQCNs with the repeated spacing of O atoms along the c-axis on the primary prism plane of ice lattice is critical for OQCNs to bind preferentially on ice crystals. Here, the application of graphitic carbon nitride derivatives for cryopreservation is reported for the first time.