This morning in Stockholm, the Nobel Assembly at the Karolinska Institute awarded the 2026 Prize in Physiology or Medicine to Karl Deisseroth, Peter Hegemann, and Georg Nagel for their discoveries concerning light-gated ion channels and optogenetics. Few laboratory methods of the past two decades have changed how neuroscientists work as thoroughly as this one. Fewer still began with something as modest as a single-celled green alga.
The alga, Chlamydomonas, swims toward light using proteins called channelrhodopsins. Each one cradles a small molecule derived from vitamin A, and when a photon of blue light strikes it, the molecule bends into a new shape and opens a pore that lets charged atoms flow across the cell membrane. Hegemann and Nagel worked out how these proteins behave, and in 2005 Deisseroth and his colleagues at Stanford placed the gene for one of them into mammalian neurons and showed that brief flashes of light could make those cells fire on command.
Because the gene can be delivered to particular kinds of cells and no others, researchers could suddenly switch specific circuits in a living brain on or off and watch what the animal did next. Questions that had long been matters of correlation became matters of cause.
It is tempting to ask whether this discovery bears on our line of research, where the real connection runs through a different family of light-sensitive proteins that the optogenetics community also adopted. Many of the field's later tools are built from flavoproteins, which use a relative of vitamin B2 to absorb blue light. When these proteins are illuminated, an electron can hop from one part of the molecule to another and leave behind two unpaired electrons whose spins stay linked.
This arrangement is called a radical pair, and its fate depends on how the two spins are oriented relative to each other. Remarkably, a weak magnetic field can tip that balance. A flavoprotein called cryptochrome is the leading explanation for how migratory birds such as the European robin perceive the Earth's magnetic field.
Over the past two years these two worlds have converged. Scientists in California and at Oxford took a light-sensing domain long used as an optogenetic building block and evolved it in the laboratory into a fluorescent protein whose glow brightens and dims near a magnet. The protein, called MagLOV, can report magnetic resonance from inside living bacteria at room temperature, and related behavior has since turned up in yellow and red fluorescent proteins and even inside a living worm.
What optogenetics offers this emerging field is the opportunity to use it as another tool to study optical/spin biophotonics. Deisseroth's generation built the methods for delivering genes to precise cell types, for threading light into deep tissue through hair-thin fibers, and for collecting faint fluorescence from an animal as it behaves. Each of those methods can carry a magnetically sensitive protein as readily as a light-gated channel, which means the toolkit honored today can now be turned toward reading the spin chemistry of a cell.
The proteins that first let scientists turn neurons on with a flash of light may yet help them observe one of the subtlest processes in biology, the brief and delicate coupling of two electron spins inside a living cell which is the goal of the GATE Program.
