3D Nanoprinting Meets Fiber Optics: A New Optical Fiber Makes It Possible to Observe Nanoparticles Directly in Liquids

Researchers have developed an optical fiber that not only guides light, but also makes moving nanoparticles visible. This technology provides insight into the world of the tiniest particles and paves the way for new tools in bioanalytics and environmental research.

A precisely guided beam of light illuminates a tiny hollow chamber made of glass, revealing how nanoparticles move through a liquid. Researchers at Leibniz IPHT developed this new type of optical fiber, which guides light and functions as a miniature measurement chamber. This allows them to observe how tiny particles, such as gold nanoparticles, diffuse in a liquid. Complex microscopy is no longer necessary thanks to this precise, compact, and robust fiber-based technology.

A Hollow Core at the Fiber Tip

At the center of the research is a hollow-core waveguide, which is a microscopic, hollow channel that guides light. Diana Pereira, the study’s first author and a visiting researcher from Portugal, collaborated with Prof. Markus Schmidt and his team from the Fiber Photonics research department and the Sensors and System Integration technology group. Together, they developed a method for printing such a waveguide directly onto the tip of a standard optical fiber.

Using a highly precise 3D nanoprinting process, the researchers fabricated a square tube made of transparent polymer that was perfectly aligned with the fiber cross-section. “The key advantage of this approach is that everything is created in a single structure,” explains Markus Schmidt. “We integrate the laboratory module directly with the optical fiber—without lenses and without alignment. That makes the system much more stable and flexible to use.”

How Does Light Behave Inside the Hollow Channel?

Light can propagate inside the hollow core with almost no loss. Its polarization, or the direction in which the light waves oscillate, can be controlled very precisely. Since the waveguide is integrated directly into the fiber, the system remains compact and does not require optical alignment.

Most importantly, light interacts almost entirely with the medium inside the hollow channel. Nearly all of the optical energy is concentrated where the particles are suspended in the liquid. This strong interaction enables particularly sensitive measurements.

Making Nanoparticles Visible

To demonstrate the new structure’s capabilities, the researchers performed an experiment that often challenges conventional optical methods: nanoparticle tracking analysis (NTA). In this technique, the random motion of individual particles— their so-called Brownian motion— is observed to determine their size and physical properties. For the experiment, the team filled the tiny, hollow chamber at the fiber tip with a diluted solution containing gold nanoparticles. A laser beam guided through the fiber illuminated the particles inside the cavity. A microscope camera recorded the light scattered by the particles as they diffused through the chamber.

A Compact Fiber Was Used Instead of a Large Microscope

The novelty of this approach lies in its combination of nanoprinting and fiber-based integration. Traditional methods for observing nanoparticles usually require large, delicate microscopes. The team led by Markus Schmidt demonstrates that a compact optical fiber can serve the same purpose while maintaining high measurement accuracy.

At the same time, the entire device is monolithic; the light-guiding structure, measurement chamber, and optical coupling are all part of a single component.

From Bioanalytics to Quantum Technologies

Researchers see many potential applications for the new technology. In bioanalytics, for example, it could analyze proteins, viruses, and extracellular vesicles without the need for chemical labeling. In environmental science, tiny particles in water samples could be detected directly within the fiber. This concept could also be useful in quantum technologies or experiments that manipulate nanoparticles using light.

A Window into the Nanoworld

Next, the team plans to further develop the structure by extending the hollow waveguides to reduce optical losses or adding nanostructures that selectively excite specific light modes. They also plan to apply functional coatings with molecules or metals to enable chemical reactions or plasmonic effects. In this way, an optical fiber becomes more than just a light guide. It transforms into a microscopic laboratory and a new window into the world of the smallest particles.

Original Publication: https://doi.org/10.1038/s41377-025-01827-9