A disposable paper-based sensor for phosphate detection using SERS technology

Phosphate is an essential nutrient in aquatic systems, however elevated phosphate discharge are a primary driver of eutrophication which in turn causes notable deterioration of water quality. Therefore, there is a critical need for simple, rapid, and low-cost methods suitable for on-site phosphate monitoring.In this work, a disposable paper-based surface-enhanced Raman spectroscopy (SERS) sensor was developed for sensitive detection of phosphate. The sensing strategy is based on an AgNPs-R6G system. Specifically, under acidic conditions,phosphate reacts with ammonium molybdate to generate phosphomolybdic acid, which subsequently interacts with rhodamine 6G (R6G).This process reduces the surface adsorption of free R6G on silver nanoparticles, resulting in the suppressed SERS signal intensity. The resulting signal decrease correlates quantitatively with phosphate concentration, enabling indirect quantitative detection of phosphate quantification. The paper-based sensor was fabricated on Whatman No. 1 filter paper where Alkyl ketene dimer (AKD) was employed to construct a hydrophobic isolation zone and a hydrophilic detection zone, thereby facilitating localized sample loading and stable SERS measurement. The proposed sensor exhibited a linear response to phosphate over the concentration range of 10^-7 M to 10^-2 M, with a detection limit of 6.5 × 10^-8 M. The assay consumed only 50 μL of reagent per test and can be completed through a simple three-step operation. Owing to its low cost, disposability, facile fabrication, and satisfactory analytical performance, fabrication, and satisfactory analytical performance, this paper-based SERS platform represents a promising potential for rapid on-site phosphate detection in water-quality assessment.