(601u) On-Demand Immobilization of C. elegans Based on Photothermal Phase Transition of Pluronics

Caenorhabditis elegans (C. elegans) is a great multicellular model organism for biological studies including genetics, neuroscience, and developmental biology. Immobilization of this transparent and actively-moving nematode is an essential step for high-resolution imaging and analysis. Typically, C. elegans is immobilized by anesthetizing or gluing on an agar pad, but these methods are laborious and low-throughput as well as not compatible with physiological processes. Here we report development of a novel worm immobilization technique based on optical control of sol-gel transition of the thermo-sensitive Pluronic block copolymer. Since the Pluronic gel becomes stiff enough to prevent even minute movement only with small increase in temperature, the worms could be fully immobilized under normal physiological conditions (~ 26°C). In addition, the critical temperature for the gelation can be easily adjusted by changing the concentration of the solution. Here we applied a photoabsorbing layer to make the optical-to-thermal energy transfer as efficient as possible, leading to a simple, versatile, and biocompatible immobilization of C. elegans by light exposure. With a white light from a halogen lamp, the temperature of the Pluronic gel approaches to a steady state within 1 min and ΔT ~ 5°C, which is enough to induce gelation, leading to complete immobilization of the worms. This novel worm immobilization technology also allows us on-demand selective immobilization of a specific worm on a conventional microscopy integrated with a liquid crystal display. Using this technology, we could successfully observe the development of D motor neurons in C. elegans. In addition, we applied this immobilization technology for transgenesis of C. elegans via microinjection of DNA. We expect this technology to open a new avenue for long-term live imaging of these small animals for monitoring the development of in vivo cellular networks as well as for development of an automated microinjection system.