Water temporarily becomes supercooled below 0 °C. However, once a seed crystal forms, ice crystals start growing quickly. During cryopreservation of food, medical products, and cells, cryoprotectants are added to prevent rapid crystal growth.
 To improve cryopreservation technology, it is essential to understand how cryoprotectants prevent ice growth. Thus, we studied this process in rapidly frozen aqueous solution of glucose using spin-contrast-variation (SCV) small-angle neutron scattering (SANS), which relies on how neutrons scatter based on proton spins (Fig. 1). With the conventional SANS (Fig. 2a), we did not even know what the scatterer was before the structural analysis. In contrast, the scattering curves in SCV-SANS (Fig. 2b) changed with the spin direction, with the gentle slope in the figure indicating the scattering from nano-ice crystals and the steep slope from amorphous ice. In addition, nano-ice crystals in frozen aqueous solution of glucose are plate-like, and their thickness of 2–3 nm is almost the same size as the critical diameter for ice crystal formation in supercooled water.
 This suggests that glucose molecules bind to specific faces of the nano-ice crystals to prevent the crystal growth in that direction. Using theoretical calculations, we aim to understand how cryoprotectants like glucose preferentially bind to nano-ice crystals.

This work was performed in collaboration with Comprehensive Research Organization for Science and Society (CROSS) and Hiroshima University as part of proposals Nos. 2020P0202, 2021P0502, 2022P0502, and 2020P0203 at the J-PARC MLF, and supported by JSPS KAKENHI Grant Number JP21H03741.