Ice-binding proteins (IBPs) produced by psychrophilic organisms to adapt for the survival of psychrophiles in subzero conditions have received illustrious interest as a cryopreservation agent required for cells and tissues to completely recover after freezing/thawing. Depressing water-freezing point and avoiding ice-crystal growth affect their activities which are closely related to the presence of ice crystal well-matched binding moiety. The interaction of IBPs with ice and water is critical in enhancing their freeze avoidance against cell or tissue damage. Metal–organic frameworks (MOFs) with a controllable lattice at the molecular level and a size at the nanometer scale can offer periodically ordered ice-binding sites by modifying organic linkers and controlling microcurvature at the ice surface. Herein, zirconium (Zr)-based MOF-801 nanoparticles (NPs) with good biocompatibility were used as a cryoprotectant that is well dispersed and colloidal-stable in an aqueous solution. The MOF NP size was precisely controlled, and 10, 35, 100, and 250 nm NPs were prepared. The specific IBPs-mimicking pendants (valine and threonine) were simply introduced into the MOF NP-surface through the acrylate-based functionalization to endow with hydrophilic and hydrophobic dualities. When small-sized MOF-801 NPs were attached to ice, they confined ice growth in high curvature between the adsorption sites because of the decreased radius of the convex area of the growth region, leading to highly enhanced ice recrystallization inhibition (IRI). Surface-functionalized MOF NPs could increase the number of anchored clathrate water molecules with hydrophilic/hydrophobic balance of the ice-binding moiety, effectively inhibiting ice growth. The MOF-801 NPs were biocompatible with various cell lines regardless of concentration or NP surface-functionalization, whereas the smaller-sized surface-functionalized NPs showed a good cell recovery rate after freezing/thawing by induction of IRI. This study provides a strategy for the fabrication of low-cost, high-volume antifreeze nanoagents that can extend useful applications to organ transplantation, cord blood storage, and vaccines/drugs.

Antifreeze proteins (AFPs) that enable polar organisms to survive subzero temperatures are structurally bound to a specific ice surface, regulating crystal formation and growth. To design emerging cryopreservatives that mimic AFPs, it is necessary to understand how the binding intervals corresponding to a particular ice crystal plane and how the amphiphilic nature of AFPs affect the growth of ice crystals. Herein, we report peptide nanoscaffolds containing a glycyl−histidyl−lysine (GHK) tripeptide capable of tethering with gold nanoparticles (Au NPs) that can readily monitor ice recrystallization inhibition (IRI) activity. Representative ice-binding amino acids were introduced into the main scaffold of N-fluorenylmethyloxycarbonyl-diphenylalanine, which forms robust, self-assembled fibrillar nanoaggregates with enhanced colloidal stability due to π−π stacking. This resulted in an enhanced IRI effect. The IRI activity was differentiated depending on the amphiphilicity of the outermost ice-binding pendant of peptide fibrils. This could be confirmed through a colorimetric assay based on the dispersion of Au NPs in peptide fibrils. The adsorbing process to the ice-binding surface could be directly visualized through enhanced scattering caused by Au NPs confined in peptide nanofibrils. The designed peptide supramolecular nanotracker provides a facile strategy to screen antifreeze performance by allowing visualization of how ice growth is prevented. The selected biocompatible peptide nanoagents could further mimic the properties of native AFP through more sophisticated structural controls at the molecular and nanoscale levels and have the potential to be used as cryopreservatives for cord blood, oocytes, sperm, stem cells, tissues, and organs as well as optical labeling nanoprobes for IRI.