A microfiber sensor for high-sensitivity detection of trace phosphate ions in tap water and serum samples

Phosphate ions are essential for biological and environmental processes; however, their excessive accumulation in water bodies can lead to eutrophication, and their entry into the human body through the food chain can cause metabolic disorders and other health issues. Therefore, developing a rapid, sensitive, and precise detection method is crucial for controlling drinking water pollution and monitoring human health. To address this critical issue, this paper proposes a single mode-tapered multimode-single mode (STMS) fiber sensor for trace phosphate ion detection. Experimental results show that the proposed fiber sensor exhibits good spectral stability, with a specific detection time for phosphate ions of less than 10 min. In tap water sample testing, the STMS microfiber sensor exhibits a low limit of detection (LoD) of 0.25 pM and good selectivity, with minimal cross-reactivity to common anions in water, including cl^-, SO₄^2-, CO₃^2-, and NO₃^-. Furthermore, results for the detection of phosphate ion in serum samples also demonstrated a low LoD of 0.6 pM, which is far below the normal physiological phosphate concentration range in adult serum or plasma (0.81 to 1.45 mmol/L) as defined by the National Institutes of Health. These findings suggest that the propo-sed microfiber sensor has potential for drinking water monitoring and clinical diagnostics.