Stable paper-based colorimetric sensor for selective detection of phosphate ion in aqueous phase

Phosphorus is one of the vital nutrients for sustenance; however, its excess concentration can cause adverse impacts on the ecosystem. Numerous sensors have been developed and deployed to monitor phosphate ions (Pi) in the environment in the past decade. However, their high cost, non-portability, and lengthy and complex fabrication processes are detrimental to their widespread use. Accordingly, the objective of the study was to develop a low-cost, convenient paper-based colorimetric sensor with brilliant green (BG) as the probe. The use of triarylmethane dye as a colouring reagent allows naked eye-visible detection of Pi in the range of 13.6–0.27 mg L−1 with the limit of detection as 0.07 mg L−1. Moreover, the proposed sensor resolves the challenges of traditional methods like the formation of insoluble complexes, the requirement of surfactants, poor reagents storability, dependence on time and temperature. The sensitivity and selectivity of BG toward Pi was verified in the aqueous phase. Later, the paper-based sensor (W-BG) was developed via dip coating as a portable detection tool. The storability, stability, and applicability of the developed strips were tested and validated using FT-IR, UV-DRS, and XRD. Additionally, the performance of the strips was compared with a microfluid paper-based device to ensure the feasibility and versatility of the strips. The sensing mechanism is deduced as the formation of the phosphomolybdate complex, which was responsible for the delocalization of the lone pair of electrons on BG, thus rendering a distinct endpoint. The selectivity and sensitivity of the sensor were maintained in real water and wastewater samples. Overall, with affordable cost (0.08 $) and portability, W-BG can be considered as a smart and environmentally friendly water quality monitoring tool.