An international research team has developed microscopic particles that can make blind retinas respond to light.
The particles act as tiny light receptors. Researchers inject them into the eye, where they settle close to nerve cells in the retina. When light hits the particles, it triggers electrical and chemical processes that can activate the nerve cells and prompt them to send signals towards the brain.
In experiments with blind mice, the researchers were able to detect light-induced signals in the visual cortex of the brain and observe behavioral responses to light. They also showed that the technology can activate nerve cells in retinal tissue from pigs.
The findings, published in Nature Biomedical Engineering , mark a new chapter in a research project that began at Aarhus University seven years ago with an ambitious idea: Could researchers develop a kind of microscopic “solar cell” that could be placed inside the body and use light to control cellular activity?
“When we started, our fundamental question was whether we could create a material that could act as a wireless interface between light and living cells. We can now see that the particles are able to activate nerve cells in blind retinas. That brings us closer to our long-term goal of developing a new type of retinal prosthesis,” says Menglin Chen, Associate Professor at the Department of Biological and Chemical Engineering at Aarhus University.
To understand how the technology works, we need to look at the back of the eye.
This is where the retina is located. Its light-sensitive photoreceptors normally capture light and initiate the signals that the brain uses to create vision.
In retinitis pigmentosa, these photoreceptors gradually degenerate. Other nerve cells and connections within the retina, however, can remain intact. The researchers aim to make use of these surviving cells.
The nanoparticles are made from the light-sensitive semiconductor graphitic carbon nitride and measure around 300 nanometres in diameter. They are hollow, and their structure makes them particularly effective at capturing visible light. Their design draws inspiration in part from chloroplasts, the structures plants use to harvest energy from sunlight.
When the nanoparticles are exposed to light, they trigger a series of physical and chemical processes in their immediate surroundings. These processes can influence signaling in living cells.
The researchers have investigated this effect at several biological scales. Using a precisely focused laser, they were able to activate individual nanoparticles inside cells and trigger a signal that travelled through the cell and on to neighboring cells. In cardiac muscle cells, the researchers used ordinary LED light to influence the cells’ rhythm and make them beat more synchronously.
But it is the results in the eye that bring the technology closer to a specific medical application.
The researchers injected the nanoparticles into the eyes of mice with advanced retinitis pigmentosa. The particles accumulated on the surface of the retina, close to the retinal ganglion cells that transmit information from the eye towards the brain.
When the researchers illuminated the eyes, they detected activity in the visual cortex. The mice also changed their behavior in response to the light. In isolated pig retinal tissue, the researchers additionally showed that LED light could activate ganglion cells when the nanoparticles were present.
“What is particularly interesting is that we are trying to make use of the nerve cells that still function in the retina. Instead of genetically modifying these cells, we use the nanoparticles to create a new connection between light and the nerve cells. In this way, we are trying to make a blind retina respond to light again,” says Menglin Chen.
The experiments do not mean that the researchers have restored normal vision in the mice. They show that the technology can generate a measurable biological response to light even when the photoreceptors that normally detect light have largely degenerated. The researchers still need to study long-term safety and function in much greater detail before the technology could potentially be tested as a treatment in humans.
“Once the photoreceptors are lost, the options for restoring light sensitivity are still very limited, and each approach in development carries its own constraint. Gene therapies are mutation-specific, optogenetics requires genetically modifying the surviving cells, and electronic implants require surgery. That is why it is worth testing strategies that work independently of the cause of the disease. What we show here is a light-evoked response in a degenerated retina, which is an early step rather than a finished prosthesis,” says Henri Leinonen, a retina specialist and co-author of the study.
The new study also shows how much the research project has evolved since it began.
In 2019, Menglin Chen received a DKK 4.2 million Semper Ardens Accelerate grant from the Carlsberg Foundation for an idea then known as OptoMed. The aim was to develop light-sensitive nanomaterials that could be placed inside the body and stimulate cells wirelessly and without genetically modifying them. At the time, the researchers were investigating nanofibers and their potential to stimulate brain and heart cells.
Since then, the team has continued to develop the technology and shifted its focus towards hollow nanoparticles. Along the way, the researchers have studied how the particles absorb light, how they affect cellular signaling, how well cells tolerate them, and whether the effect also works in tissue and living animals.
That progression is reflected in the new study: from activating a single nanoparticle inside a single cell, to synchronising cardiac muscle cells, and ultimately to producing light responses in blind mice.
At the same time, the technology has moved from fundamental research towards innovation. In 2024, the researchers filed an international patent application covering the technology. The application includes the use of the nanoparticles as an injectable, light-activated retinal prosthesis and for stimulating cardiac cells.
In 2025, Menglin Chen also received a Pioneer Innovator Grant from the Novo Nordisk Foundation for the project RetiNano: Biocompatible and injectable photovoltaic retinal prosthesis. The project focuses specifically on developing the technology for use in the eye.
“Seven years ago, we were working with a fundamental research idea. Today, we have preclinical results, an ongoing patent process and a concrete goal of developing the technology into a retinal prosthesis. There is still a long way to go before this could become a treatment for patients, but we have reached a point where we can begin to ask very specific questions about what it will take to move the technology forward,” says Menglin Chen.
For the researchers, the coming years will therefore not simply be about demonstrating that the nanoparticles work. They will also need to improve the delivery route, document how the material behaves in the eye over longer periods, investigate its safety in greater depth and continue developing the technology with a view to potential future clinical use.
The research is thus entering another new phase: moving from the question of whether microscopic “solar cells” can communicate with living cells at all, to whether the technology could one day be developed to help people who have lost their sight.
The research is led by Associate Professor Menglin Chen at the Department of Biological and Chemical Engineering, Aarhus University, in collaboration with Professor Bozhi Tian at the University of Chicago, Associate Professor Henri Leinonen at the University of Eastern Finland, Professor Thomas Corydon and Professor Yonglun Luo at the Department of Biomedicine, Aarhus University, Associate Professor Rasmus Schmidt Davidsen at the Department of Electrical and Computer Engineering, Aarhus University, Professor Mingdong Dong at the Department of Chemistry, Aarhus University, Professor Toke Bek at Aarhus University Hospital, and Professor Nikos Hatzakis at the University of Copenhagen.
Nature Biomedical Engineering
Biomimetic graphitic carbon nitride nanoparticles for multiscale photomodulation and therapeutic intervention