Researchers develop an optical fiber made from gel derived from seaweed

An optical fiber made from agar has been produced at the University of Campinas (UNICAMP) in the state of São Paulo, Brazil. This device is edible, biocompatible and biodegradable. It can be used in vivo for imaging of body structure, localized light delivery in phototherapy or optogenetics (eg, Stimulating neurons with light to study neuronal circuits in a living brain), and localized drug delivery.

Another possible application is the detection of microorganisms in specific organs, in which case the probe would be completely absorbed by the body after performing its function.

The research project, which was supported by the São Paulo Research Foundation, FAPESP, was led by Eric Fujiwara, professor at the School of Mechanical Engineering at UNICAMP, and Cristiano Cordeiro, professor at the Gleb Wataghin Institute of Physics at UNICAMP, in collaboration with Hiromasa Oku, Professor at Gunma University in Japan.

An article about the study is published in Scientific reports.

Agar, also called agar-agar, is a natural gelatin obtained from seaweed. Its composition consists of a mixture of two polysaccharides, agarose and agaropectin. “Our optical fiber is an agar cylinder with an external diameter of 2.5 millimeters [mm] and a regular internal arrangement of six 0.5mm cylindrical air holes around a solid core. Light is limited due to the difference between the refractive indices of the agar core and the vents, “Fujiwara said.

“To produce the fiber, we pour food grade agar into a mold with six internal rods placed along the main axis,” he continued. “The gel is distributed only to fill the available space. After cooling, the rods are removed to form air holes, and the solidified waveguide is released from the mold. The refractive index and fiber geometry can be adapted varying the composition of the solution agar and the design of molds, respectively “.

The researchers tested the fiber in different media, from air and water to ethanol and acetone, concluding that it is context sensitive. “The fact that the gel undergoes structural changes in response to variations in temperature, humidity and pH makes the fiber suitable for optical detection,” said Fujiwara.

Another promising application is its simultaneous use as an optical sensor and a growth medium for microorganisms. “In this case, the waveguide can be designed as a disposable sample unit that contains the necessary nutrients. The cells immobilized in the device would be optically detected and the signal would be analyzed using a camera or spectrometer,” he said.