Microplastic Detection in Water Using a Tapered Fiber Tip Sensor

Recent studies show that the average person consumes a significant amount of microplastics through daily drinking water, making microplastic consumption's potential adverse health effects a substantial focus of global research. Consequently, various microplastic detection and identification techniques (e.g., Raman Spectroscopy, Scanning Electron Microscopy) have been proposed in the literature. Although they offer fair accuracy, they require state-of-the-art lab facilities and professional staff, which limits their overall in-field applications. We propose a rapid, portable, specialist-free, and economical optical sensor for microplastic detection in drinking water to overcome these limitations. Using the heat and pull technique, we fabricate 1 to 3-micron tapered fiber tips from single-mode fibers to serve as sensing heads. The fiber tip is immersed in 1 mL solutions with polystyrene microplastic concentrations ranging from 0.01 mg/mL to 0.03 mg/mL. We connect a 1550 nm laser to the tapered fiber through a circulator and measure the reflected power as the microplastic concentrations change. The physical sensing principle is governed by two factors: (i) the effective index of the tapered fiber tip surroundings changes with varying microplastic concentrations; a higher surrounding effective index results in more losses for the tapered fiber, and (ii) the higher surface tension of water keeps microplastics close to the tapered fiber tip, increasing power loss due to scattering, thus causing the tapered fiber to experience more losses as microplastic concentration increases. We show that our sensor can achieve the detection limit of 0.01 mg/mL and sensitivity of 6 mu W/mg/ml. We anticipate that the proposed sensing modality will lead toward an accurate, portable, and easy-to-use optical sensor for in-field microplastic detection in water.