Immobilization of the nematode Caenorhabditis elegans with addressable light-induced heat knockdown (ALINK)

Caenorhabditis (C.) elegans is a model animal used in genetics, neuroscience, and developmental biology. Researchers often immobilize squirming worms to obtain high-quality images for analysis. However, current methods usually require physical contact or anesthetics. This can cause injuries to worm bodies or neuron disturbances. This study presents an alternative technique, called addressable light-induced heat knockdown (ALINK), to effectively immobilize worms by using light-induced sublethal heat. A microchip composed of an indium-tin-oxide (ITO) glass plate and an ITO glass plate coated with a photoconductive layer (a-Si:H) was produced. Worms to be immobilized were immersed in a liquid medium and sandwiched between the two plates. When the worms were irradiated with a focused laser beam in the presence of electric fields (referred to as an optoelectric treatment), the optoelectric effect heated the liquid medium. The neural functions of the worms shut down temporarily when a critical temperature (>31 °C) was reached. Their neural functions resumed after the heat source was removed. A temperature above 37 °C killed all worms. Using short-wavelength light reduced the worms' recovery time. An equivalent circuit was modeled to predict the operating modes, and an optoelectric treatment with a high-concentration medium enhanced rapid heating. A safe operating range (20 Vpp (peak-to-peak voltage), 100 kHz to 10 MHz, 31 to 37 °C) to induce heat knockdown (KD) was also investigated. The results show that the heat KD was well controlled, autonomous, and reversible. This technique can be used for worm immobilization.