One doesn’t typically look at a peanut and see the future of laser technology. But inside a lab at Umeå University in northern Sweden, physicist Jia Wang and her collaborators have done just that—building a laser from nothing but birch leaves and peanuts.

Their invention is a breakthrough in sustainable photonics. By using common biological materials instead of synthetic compounds or toxic metals, the team has created a device that could one day be used to illuminate tissue during medical imaging or even spot a fake designer handbag.

“Our study shows that it is possible to create advanced optical technology in a simple way using only local, renewable materials,” said Wang, Associate Professor at Umeå University. The study is published in the journal Nanophotonics.

Upper: The biomaterial-based random laser when activated. Lower: The same laser seen in daylight. Credit: Zhihao Huang

Not Your Typical Laser

Lasers are typically associated with precise beams and high-tech equipment. But the one built by Wang’s team works differently. Called a random laser, it generates light by scattering photons through a disordered material, eventually producing a coherent glow without a traditional optical cavity.

In this case, the disordered material is a peanut kernel.

The laser’s gain medium—the part that actually amplifies the light—is made from carbon dots derived from birch leaves. These nanoscopic particles, created via a simple pressure-cooking method, glow a brilliant red when excited by light.

By injecting the carbon dot solution into peanut cubes, the researchers created a biomaterial-based laser system they call R-CDs@Peanut. Under excitation from a pulsed light source, the device emits a red laser beam. Despite its simplicity, the system’s performance matches that of many synthetic random lasers.

“The synthesis of the carbon dots is simple and straightforward, essentially a one-step pressure-cooking process,” Wang explained.

The peanut’s rough internal structure—a natural maze of folds, pores, and cell walls—scatters the light just enough to produce the essential feedback loops for random lasing. The resulting device is biodegradable, non-toxic, and remarkably cheap (you could say it costs peanuts… and now I’ll see myself out).

Long Wavelength

Red light, with its long wavelengths, is especially well-suited to biomedical imaging because it penetrates tissue more deeply than other colors. And because the carbon dots avoid the harsh phototoxicity and complexity of synthetic gain materials, the laser is gentle enough for living tissues.

The researchers measured emission thresholds across five different surfaces of their peanut-based laser. Surface I (closest to the injection point) required the least energy to trigger lasing: just 96.4 kilowatts per square centimeter. Despite some variation, all five surfaces demonstrated the ability to lase, with results “comparable with that [of] artificially designed laser cavities,” according to the study.

The R-CDs@Peanut device retained its fluorescence even under daylight, and the red emission showed no interference from the peanut’s own faint autofluorescence. In other words, the glow came purely from the birch-leaf carbon dots.

Microscopy revealed just how well-suited the peanut kernel is as a scaffold. Scanning electron microscope images showed a rough, disordered surface peppered with micropores. That’s ideal for bouncing light into random trajectories and creating the feedback loops necessary for lasing.

Applications

While the implications for medical diagnostics are clear, the researchers see potential in other domains, too.

“The potential of this biomaterial-based random laser extends beyond bioimaging and diagnostics,” said Wang. “Given its low cost, renewability, and safety, it could also be developed into an optical tag for authenticating high-value documents, luxury goods, and electronic devices”.

Each laser has a unique spectral “fingerprint” based on the natural microstructure of its peanut. This feature could be harnessed to create secure, difficult-to-clone optical markers for authentication technologies.

Unlike conventional lasers, the peanut-based laser emits diffuse light, which helps eliminate the speckle noise that plagues high-resolution imaging. That makes it especially promising for technologies where clarity and uniformity of light are key, such as imaging tissues, scanning skin, or analyzing cellular samples.

And unlike synthetic materials, these organic components break down easily and pose no environmental threat.

A Natural Laser

Birch leaves. Credit: Wikimedia Commons

This isn’t the first time researchers have experimented with biological materials to make lasers. Previous efforts used things like chlorophyll, abalone shells, or coral. But few combined natural gain media and natural scatterers into a single, working laser system. And none used ingredients as simple or as accessible as peanuts and birch leaves.

The concept emerged from the team’s earlier work. Two years ago, Wang’s lab showed that birch leaves could be used to make organic semiconductors for TV and smartphone displays. Now, those same leaves are lighting the way for sustainable lasers.

In recent years, carbon dots have gained traction in nanophotonics as safer, cheaper alternatives to synthetic quantum dots. The researchers observed that the carbon dots emitted a strong, deep-red light at 686 nanometers and retained this emission after embedding them in peanut tissue.

Most importantly, the entire fabrication process is refreshingly simple. Peanuts are sliced, injected with carbon dot solution, heated gently, and then cooled. There’s no need for sterile rooms, lithography, or rare earth metals. The researchers call it a “low-barrier path” toward scalable photonic devices.