A microimplant that can genetically modify specific nerve cells, control them with light and measure their activity simultaneously could pave the way for completely new experiments in neurobiology. In optogenetics, genes from certain species of algae are inserted into the genome of another organism – for instance a mouse – and when shone with a laser light, provide electrically charged particles in a nerve cell’s membrane that can allow neuroscientists to control the neural activity. Scientists from the University of Freiburg have built a microimplant that uses a laser to control individual nerve cells. Seen here: the polymer-based neural probe with platinum electrodes for the measurement of electrical signals, an injection channel for fluids (rectangular openings) and a waveguide for optical stimulation. Courtesy of IMTEK/University of Freiburg. The 3-in-1 tool developed by Birthe Rubehn and her colleagues makes this principle possible and practical. The device, at its tip only one-fourth of a millimeter wide and one-tenth of a millimeter thick, was constructed on the basis of polymers, special plastics whose safety for implantation into the nervous system has been proved. Initial experiments in which prototypes were implanted into mice were successful: The team was able to influence the activity of nerve cells in the brain in a controlled manner by means of laser light pulses. Unlike probes developed so far, the microimplant is capable of injecting substances necessary for genetic modification, emitting light for the stimulation of the nerve cells and measuring the effect through various electrical contacts all at once. In addition to optimizing the technique for serial production, the scientists plan to develop a second version whose injection channel dissolves over time, reducing the implant’s size even further. The implant prototype was detailed in Lab on a Chip (doi: 10.1039/C2LC40874K).