Microstructured fiber measures the size of nanoparticles

Researchers at the Leibniz Institute of Photonics Technology (Leibniz IPHT) have developed a new glass fiber design that enables extraordinarily long observations of large numbers of independent, freely moving nanoparticles in a liquid. This allows the size distribution of nano-objects in a sample to be determined with even higher precision. The scientists thus lay the foundation for even better research on environmental and bioanalytical issues in the future.

Mixtures of tiny particles are found in almost every aspect of everyday life, whether it’s for water analysis, vaccine production, or the study of biological samples, and consist of a variety of different small objects in liquid media.

Accurately identifying the individual components of such a fine mixture of particles in a liquid (dispersion) defies science, especially in terms of the breadth of size distributions and the existence of various types of particles that differ little in size. A new microstructured glass fiber (single antiresonance element fiber) developed at Leibniz IPHT offers the potential to significantly increase the measurement accuracy of nano-object size characterization.

New optical fiber for high precision analysis

Thanks to the special fiber optics made at the Jena institute, nano-objects with a diameter of less than 20 nanometers in aqueous solution can be confined, individually tracked, and precisely sized. This allows researchers to precisely analyze the size distributions of nanoparticles in mixtures. For this purpose, the glass fiber has a thin-walled micro-channel with a diameter of 17 micrometers and therefore transmits light.

To examine a sample, the particle fluid is brought into contact with the hollow-core fiber that fills with the fluid sample as a result of capillary force. The coupled light is directed through the integrated fluid channel of the fiber. The glass wall, only 756 nanometers thick, allows intense and uniform illumination of the sample to be examined and the nano-objects it contains.

The light scattered by individual nanoparticles allows their position to be tracked, thus enabling extremely precise microscopic observations. “With our new fiber optic method, individual nanoscale objects can be tracked over long periods of time. In this way, we can determine their size extremely accurately and reliably, so we can characterize the individual components in a mixture,” explains Mona Nissen, Leibniz IPHT’ PhD student in the Department of Fiber Photonics.

Using the new optical fiber, the researchers were able to demonstrate high-precision characterization in experimental studies with small size difference particle mixtures made up of polystyrene nanospheres with average diameters of 100 and 125 nanometers. The scientists were able to precisely measure the size distribution and identify individual components both in monodisperse particle mixtures with nano-objects of one type and size class, and in multi-dispersion particle compositions with objects of different properties and sizes.

Nanoscale applications

The presented fiber optic approach offers the potential to be used in nanotechnological applications in the field of environment and bioanalysis, as well as in chemistry and medicine for size control of nanoparticles. Researchers see application scenarios, for example, in examining water for microplastic residues, analyzing patient samples such as urine, monitoring synthesis products in the chemical sciences, or in drug development.

The findings were published in the journal Small.