Antifreezing Gold Colloids

Abstract

Gold (Au) colloids are becoming ubiquitous across biomedical engineering, solar energy conversion, and nano-optics. Such universality has originated from the exotic plasmonic effect of Au colloids (i.e., localized surface plasmon resonance (LSPRs)) in conjunction with the versatile access to their synthetic routes. Herein, we introduce a previously undiscovered usage of Au colloids for advancing cryoprotectants with significant ice recrystallization inhibition (IRI). Oligopeptides inspired by the antifreeze protein (AFP) and antifreeze glycoprotein (AFGP) are attached onto the surface of well-defined Au colloids with the same sizes but different shapes. These AF(G)P-inspired Au colloids can directly adsorb onto a growing ice crystal via the synergistic interplay between hydrogen bonding and hydrophobic groups, in stark contrast to their bare Au counterparts. Dark-field optical microscopy analyses, benefiting from LSPR, allow us to individually trace the in situ movement of the antifreezing Au colloids during ice growth/recrystallization and clearly evidence their direct adsorption onto the growing ice crystal, which is consistent with theoretical predictions. With the assistance of molecular dynamics (MD) simulations, we evidently attribute the IRI of AF(G)P-inspired Au colloids to the Kelvin effect. We also exploit the IRI dependence on the Au colloidal shapes; indeed, the facet contacts between ice and Au colloids can be better than the point-like counterparts in terms of IRI. The design principles and predictive theory outlined in this work will be of broad interest not only for the fundamental exploration of the inhibition of ice growth but also for enriching the application of Au colloids.