Agar, or agar-agar, is a natural gelatin that is derived from red marine algae. So far, it was used as a culinary ingredient and culture media for microbiology. Recently though, researchers in São Paulo, Brazil found another use for agar. Researchers at the University of Campinas have managed to make an optical fiber out of it.
The cable is safe to eat (yummy!), and biodegradable. It can be utilized in phototherapy, in vivo body imaging, localized drug delivery, and optogenetics.
It can also be used to check for microorganism presence in specific organs. In this case, its biodegradability would prove quite useful as the device will be absorbed after its work is done.
The study published in Nature's Scientific Reports section is led by Eric Fujiwara, a mechanical engineering department professor, and Cristiano Cordeiro, a physics department professor at UNICAMP in collaboration with Hiromasa Oku, a professor at Gunma University in Japan.
The external diameter of the agar cylinder is 2.5 mm (0.098 inches) and inside the tubing are six regularly spaced 0.5 mm (0.019 inches) air holes with a solid core in their center. Fujiwara told phys.org "Light is confined owing to the difference between the refraction indices of the agar core and the airholes."
To produce the fiber, researchers poured food-grade agar in a mold with six rods (for air holes). After the gel settles in, rods are removed and the solidified waveguide is released from the mold. Fujiwara says, "The refraction index and geometry of the fiber can be adapted by varying the composition of the agar solution and mold design, respectively."
The researchers tested the fiber under different conditions, such as; water, air, ethanol, and acetone. The fiber turned out to be context-sensitive, meaning, how it behaved changed with the environment it was put in. Fujiwara said, "The fact that the gel undergoes structural changes in response to variations in temperature, humidity and pH makes the fiber suitable for optical sensing."
Researchers also noted another promising application as an optical sensor and a microorganism growth medium at the same time. Fujiwara stated "In this case, the waveguide can be designed as a disposable sample unit containing the necessary nutrients. The immobilized cells in the device would be optically sensed, and the signal would be analyzed using a camera or spectrometer."