Injectable nanoparticles make blind mouse retinas respond to light without genetic modification

Researchers have developed injectable nanoparticles that can make a blind retina respond to light again — no surgery, no genetic modification, no mutation-specific therapy required. In mice with advanced retinitis pigmentosa, the particles settled near surviving nerve cells in the retina and, when illuminated, triggered measurable electrical activity in the visual cortex and observable changes in behavior. The findings, published in Nature Biomedical Engineering, mark the most concrete result yet from a seven-year research project at Aarhus University.

The nanoparticles are hollow spheres made from graphitic carbon nitride, a semiconductor sensitive to visible light, and measure roughly 300 nanometres across — about 300 times smaller than the width of a human hair. In their design, the particles take cues from chloroplasts, the organelles responsible for capturing sunlight in plants. When light hits the particles, they generate local photoelectrochemical and photothermal effects that influence signaling in adjacent living cells.

The central problem they are designed to solve is a cruel feature of retinitis pigmentosa: the disease gradually destroys the eye's light-sensing photoreceptors, but other retinal neurons — including the retinal ganglion cells that relay visual information toward the brain — often survive. Existing approaches to recruit those surviving cells each carry significant drawbacks. Gene therapies work only for specific known mutations. Optogenetics requires genetically editing the surviving neurons using viral delivery. Electronic retinal implants require invasive surgery and hardware. The nanoparticle approach aims to sidestep all three constraints.

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.— Henri Leinonen, retina specialist and co-author

To conduct the experiments, the researchers injected the nanoparticles directly into the eyes of mice whose retinitis pigmentosa had reached an advanced stage. Once inside, the particles settled on the retinal surface, positioning themselves near the retinal ganglion cells. Shining light into the treated eyes produced measurable activity in the visual cortex along with observable behavioral reactions to light. The researchers also tested the particles in isolated retinal tissue from pigs, where LED light activated ganglion cells in the presence of the nanoparticles — providing a cross-species confirmation of the effect.

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.— Menglin Chen, Associate Professor, Department of Biological and Chemical Engineering, Aarhus University

The study also demonstrated the technology's range across biological scales. Using a precisely focused laser, researchers activated individual nanoparticles inside single cells and triggered signals that propagated to neighboring cells. In cardiac muscle cells, ordinary LED light was used to influence the cells' rhythm and make them beat more synchronously — an indication that the platform is not limited to retinal applications.

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.— Menglin Chen, Associate Professor, Department of Biological and Chemical Engineering, Aarhus University

The work traces back to 2019, when Chen secured a DKK 4.2 million Semper Ardens Accelerate grant from the Carlsberg Foundation to launch what was then called OptoMed at Aarhus University. The initial focus was on nanofibers and their potential to stimulate brain and heart cells; the team later shifted to hollow nanoparticles. Researchers from the University of Chicago, the University of Eastern Finland, Aarhus University Hospital, and the University of Copenhagen are now part of the international collaboration, according to Genetic Engineering & Biotechnology News.

The researchers are careful about what the results do and do not show. The experiments did not restore normal vision in the mice — they demonstrated that a measurable biological response to light is possible even when the photoreceptors that normally detect light have largely degenerated. Before human testing could even be considered, the team must address long-term safety, improve delivery methods, determine how long the particles stay functional within the eye, and assess whether the light-triggered responses can be amplified and precisely controlled in ways that would meaningfully aid vision restoration. The team has filed international patents for the technology and is currently investigating long-term ocular biocompatibility, according to Neuroscience News.

Why it matters — For the millions of people with retinitis pigmentosa and similar degenerative conditions, this research points toward a potential injectable treatment that could restore some light sensitivity without surgery or genetic modification — though significant safety and efficacy work remains before any human testing.

Reported by eurekalert.org, genengnews.com, neurosciencenews.com