Tiny Virus Shells Become Molecular Solar Factories for Artificial Photosynthesis
Deep in the laboratory of the University of South Bohemia, a team of scientists has done something that would have sounded like science fiction just a decade ago: they took a virus that infects bacteria, hollowed it out, stuffed it with a photosynthetic protein and an electron-carrying partner, and turned the whole assembly into a working solar-powered nanoreactor. The result, published this week on arXiv, is a modular molecular toolkit that could rewrite how we think about artificial photosynthesis — and eventually, how we produce fuels, chemicals, and medicines using nothing but sunlight.
“We’re essentially building a molecular factory inside a virus shell,” says David Kaftan, the project leader. “The virus provides the walls. The photosynthetic proteins provide the engine. And the whole thing self-assembles in a test tube.”
The study, led by a collaboration between Czech and Canadian researchers, takes a bacteriophage known as P22 — a virus that normally attacks Salmonella bacteria — and repurposes its protein shell as a nanoscale containment vessel. At roughly 50 nanometers in diameter, the P22 capsid is large enough to hold macromolecular complexes but small enough to impose a crucial physical constraint: the photosynthetic components can’t drift away from each other.
That proximity turns out to be the secret sauce.
The Problem with Artificial Photosynthesis
Natural photosynthesis is arguably the most important chemical process on Earth. Plants, algae, and photosynthetic bacteria use sunlight to split water and fix carbon dioxide with an efficiency that, while seemingly modest in aggregate, has powered the entire biosphere for billions of years. Scientists have long dreamed of building artificial versions — biohybrid devices that combine biological photosystems with synthetic components to produce hydrogen, methanol, or other storable fuels directly from sunlight.
But there’s a catch. Natural photosynthesis works inside chloroplasts, where proteins are packed at extraordinarily high densities in membrane-bound compartments. When researchers extract those proteins and try to use them in artificial systems, the performance plummets. The components drift apart in solution. Electrons that should be transferred efficiently between the photosystem and the next protein in the chain get lost to side reactions. The system leaks.
“The spatial organization is everything,” explains David Bina, a co-author on the study. “In nature, the electron transfer chain is a carefully choreographed relay race. If you take the runners out of the stadium and put them in an open field, they can’t hand off the baton efficiently.”
A Virus as a Stadium
The P22 bacteriophage solved this problem billions of years ago. Its protein capsid — the shell that protects its genetic material — is a remarkably stable, self-assembling structure. Researchers have known for years that you can remove the viral DNA and use the empty capsid as a nanoscale container. But loading it with functional photosynthetic machinery was another matter entirely.
The team developed a clever conjugation strategy. They took a scaffolding protein from the P22 virus — a protein that normally helps the capsid assemble around viral DNA — and genetically fused it to two distinct cargo molecules: the photosynthetic reaction center from the purple bacterium Cereibacter sphaeroides, and cytochrome c, a small electron-carrier protein. When the scaffolding proteins were mixed together in solution, they self-assembled into complete virus shells, dragging the photosynthetic cargo along for the ride.
The result was a population of 50-nanometer spheres, each packed with roughly 30 copies of the photosynthetic reaction center and an equal number of cytochrome c molecules. The capsid shell itself is porous, allowing small molecules — electron donors, acceptors, and mediators — to diffuse freely in and out while retaining the large protein complexes inside.
Light, Meet Electron
To test whether the system actually worked, the researchers hit the nanoreactors with light and measured what happened. Using optical spectroscopy, they tracked the flow of electrons through the system.
Here’s where the confinement effect becomes visible. When the same photosynthetic reaction centers and cytochrome c molecules were mixed freely in solution, the light-driven electron transfer was sluggish. But when they were packed inside the P22 capsid, the transfer rate accelerated dramatically.
| Configuration | Relative Electron Transfer Rate | Cargo Loading (copies per capsid) | Stability (days at 4°C) |
|---|---|---|---|
| Free in solution (no capsid) | 1.0× (baseline) | N/A | < 1 |
| Encapsulated in P22 (co-loading) | 3.4× | ~30 RC + ~30 Cyt c | > 14 |
| Encapsulated (RC only, no Cyt c) | 1.2× | ~30 RC only | > 14 |
| Mixed capsids (RC in one, Cyt c in another) | 1.8× | ~30 each (separate) | > 14 |
Table: Experimental results showing the effect of confinement on light-driven electron transfer in the P22 nanocontainer system. RC = photosynthetic reaction center from C. sphaeroides; Cyt c = cytochrome c. Data adapted from Kaftan et al., arXiv:2606.27238 (2026).
The data tell a clear story. Co-encapsulation of both the reaction center and cytochrome c inside the same virus shell produced a 3.4-fold improvement in electron transfer rate over the free-solution baseline — more than triple the performance. Strikingly, even just confining the reaction center alone gave a modest improvement (1.2×), suggesting that the capsid environment itself has some stabilizing effect. But the real magic came from bringing both partners together in close quarters.
How It Works: The Flow of Energy Inside a Virus
The nanoreactor design follows a simple but elegant architecture:
LIGHT (photons)
|
v
+---------------------+
| P22 Capsid Shell | (porous, ~50 nm diameter)
| (self-assembled |
| from 420 coat |
| proteins) |
| |
| +---------------+ |
| | Photosynthetic | | ~30 copies
| | Reaction | | *Cereibacter*
e⁻ ---->| | Center (RC) | | *sphaeroides*
| +-------+-------+ |
| | e⁻ |
| v |
| +---------------+ |
| | Cytochrome c | | ~30 copies
| | (Cyt c) | | electron carrier
| +-------+-------+ |
| | |
+----------|----------+
| e⁻
v
+---------------------+
| External mediator |
| (e.g., quinones) |
+---------------------+
|
v
Sustainable chemical
production (H₂, fuels)
*Figure 1: Architecture of the P22-based photosynthetic nanoreactor. Light excites the photosynthetic reaction center (RC), which drives electron transfer to cytochrome c (Cyt c) confined inside the virus capsid. Small mediator molecules diffuse through the porous shell to carry electrons to external chemical reactions.
Beyond Proof of Concept
What makes this work particularly compelling isn’t just the performance numbers — it’s the modularity. The researchers designed the system so that any protein of interest can be fused to the P22 scaffolding protein. Want to swap in a different photosystem that absorbs more red light? It can be done. Want to add a hydrogenase enzyme to produce hydrogen gas directly? The platform supports it.
“The modular toolkit concept is what we’re most excited about,” says Kaftan. “You can think of it as a Lego system for photosynthesis. The virus shell is the baseplate. The photosystem is one block. The redox partner is another. You can mix and match depending on what you want to produce.”
The P22 capsid itself has additional advantages. It’s remarkably robust — the assembled shells remain stable for over two weeks at 4°C, compared to unencapsulated complexes that degrade within a day. The porous shell protects the delicate photosynthetic proteins from aggregation and denaturation while remaining permeable to the small molecules needed for sustained catalysis.
The Road to Practical Devices
There are, of course, caveats. The current system is a proof of concept, not a production device. The electron transfer rates, while improved by confinement, are still orders of magnitude below what would be needed for commercial fuel production. The nanoreactors operate in solution, meaning they’d need to be integrated into some kind of electrode or membrane configuration for practical use. And scaling up from a test tube to industrial volumes is a nontrivial engineering challenge.
But the trajectory is encouraging. Other groups have explored virus-based scaffolds for energy applications — the tobacco mosaic virus has been used to template nanowires for lithium-ion batteries, and the M13 bacteriophage has been deployed in dye-sensitized solar cells. What sets this P22 system apart is that it uses the virus shell not as a template or a scaffold, but as a genuine reaction vessel — a container that actively improves the chemistry happening inside it.
For the field of artificial photosynthesis, this represents a genuinely new approach. Most efforts to build biohybrid devices have focused on wiring photosynthetic proteins directly to electrodes or embedding them in synthetic polymers. The virus approach offers something different: a biologically derived container that evolution has already optimized for self-assembly, stability, and molecular permeability.
“Evolution had 3 billion years to figure out how to build this capsid,” Bina notes. “We’re just borrowing its homework.”
A Platform, Not Just a Paper
Looking ahead, the team plans to explore several extensions of the platform. One obvious direction is to incorporate additional components of the natural electron transport chain — such as the cytochrome bc₁ complex or a terminal oxidase — to create a more complete photosynthetic pathway inside the capsid. Another is to introduce enzymes that use the exported electrons to drive carbon fixation or hydrogen evolution.
If those experiments succeed, the implications go well beyond academic curiosity. A scalable, self-assembling nanoreactor that converts sunlight into chemical energy could transform how we produce everything from pharmaceutical precursors to carbon-neutral fuels. It would be the closest thing yet to an artificial leaf — one built not from silicon and platinum, but from viruses and proteins.
“We’re still at the very beginning,” Kaftan says. “But for the first time, we have a platform that lets us ask the question: what happens if we build photosynthesis the way nature does — by putting everything in the right place?”
The answer, based on this work, is that everything works better when it’s inside a virus.
📄 Source: Kaftan, D., Bina, D., Wolf, G.M., Baroch, M., Kodel, J., Dian, J., Dycka, F., & Beatty, J.T. “Modular molecular toolkit for photochemical energy conversion in a self-assembling nanocontainer.” arXiv:2606.27238v1, June 2026. Department of Chemistry, University of South Bohemia; Institute of Parasitology, Biology Centre CAS; Charles University; Czech Academy of Sciences; University of British Columbia.