Frozen zebrafish embryos thaw better with lasered gold nanorods

Zebrafish are widely used as model organisms for developmental biology research. But after being frozen and thawed, zebra­fish embryos rarely survive, meaning they can’t be stored for later experiments or shared with other labs. Now, researchers report that propylene glycol, a biocompatible antifreeze, when combined with gold nanorods can improve the embryos’ viability when they are thawed (ACS Nano 2017, DOI: 10.1021/acsnano.7b02216). John C. Bischof of the University of Minnesota, Twin Cities, and colleagues injected the antifreeze-nanorod combination into zebrafish embryos and then froze them in liquid nitrogen. After a few minutes, the team thawed the embryos with a millisecond laser pulse. The nanorods absorbed the light energy and warmed the embryos quickly and evenly, limiting damage to cell membranes from needlelike ice crystals and damage to sensitive proteins. One hour later, 31% of the embryos were viable and developed normally over the next 24 hours. In contrast, embryos warmed conventionally using a water bath did not survive thawing because they were heated unevenly or not quickly enough.With further refinement, the researchers believe the technique could also serve as a tool to conserve endangered species that have large, hard-to-freeze embryos. The work is “very creative,” says Mehmet Toner of Harvard Medical School. “Zebrafish are a very important molecular biology tool, and the embryos are extremely difficult to cryopreserve, but this technique could make it cost-effective and practical for many laboratories.”