Smartphone-assisted dual-sided capillary microfluidic device for multiplex detection of heavy metals and nutrients in...

Heavy metal and nutrient contamination are growing global issues necessitating monitoring water resources. While laboratory-based platforms for detecting these contaminants are sensitive and accurate, they require centralized facilities, trained personnel, and significant costs. Microfluidic paper-based analytical devices have emerged as a low-cost alternative for on-site detection of these water contaminants; however, these platforms struggle with slow assay times, loss of analyte, and the need for precise volumetric pipetting. Moreover, these platforms often focus on detecting only one subgroup of contaminants, limiting the potential for comprehensive measurements.

We developed a capillary flow-driven, single-dip dual-sided detection system, enabling rapid, multiplex detection of heavy metals and nutrients in a single user step. The sensor enables both qualitative visual analysis and quantitative analysis via a smartphone app for real-time and on-site detection of Ni, Fe, Cu, NO₂^- and PO₄^3-. The limits of detection (LoD) and quantification (LoQ) were calculated as 1.3 and 4.4 ppm for Ni, 0.3 and 0.9 ppm for Fe, 0.2 and 0.6 ppm for Cu, 0.4 and 1.2 ppm for NO₂^-, and 0.5 and 1.6 ppm for PO₄^3-. Selectivity was achieved through masking strategies in each detection zone. The sensors were stable for >4 weeks under ambient conditions. Spike-recovery analysis was performed using river, tap, pond, and commercial drinking water, achieving recoveries between 86 and 112 % with accuracy and precision below 15 % RSD for all samples.

This multiplex sensor offers a solution to overcome the current limitations of paper-based devices, allowing for a more comprehensive analysis of multiple contaminant classes.