Agar-based optical sensors for electric current measurements

Biodegradable optical waveguides are breakthrough technologies to light delivery and sensing in biomedical and environmental applications. Agar emerges as an edible, soft, low-cost, and renewable alternative to traditional biopolymers, presenting remarkable optical and mechanical characteristics. Previous works introduced agar-made optical fibers for chemical measurements based on their inherent response to humidity and surrounding concentration. Therefore, we propose, for the first time, an all-optical, biodegradable electric current sensor. As flowing charges heat the agar matrix and modulate its refractive index, we connect the optical device to a DC voltage source using pin headers and excite the agar sample with coherent light to project spatiotemporally deviating speckle fields. Experiments proceeded with spheres and no-core fibers comprising 2 wt% agar/water. Once the increasing current stimulates the speckles' motion, we acquire such images with a camera and evaluate their correlation coefficients, yielding exponential decay-like functions whose time constants provide the input amperage. Furthermore, the light granules follow the polarization of the applied voltage drop, providing visual information about the current direction. The results indicate a maximum resolution of similar to 0.4 mu A for electrical stimuli <= 100 mu A, which fulfills the requirements for bioelectrical signal assessment.

Automated summary

Biodegradable optical waveguides made of agar show great potential for light delivery and sensing in biomedical and environmental applications. We propose an all-optical, biodegradable electric current sensor utilizing agar's thermal effect and refractive index modulation. By connecting the optical device to a DC voltage source and exciting the agar sample with coherent light, we can measure the input amperage based on the motion of speckle fields.