Real-World Implementation of Particle-Based Microfluidics: On-Spot Test for Iron and Copper Ions in Water

Water is an essential part of everyday life, and similarly, numerous industries depend on it. Regular water analysis is needed for both home use and in more specific fields, e.g., in agriculture, to ensure necessary quality. For an inexpensive and more convenient alternative to laboratory analysis, reliable and easy-to-use on-spot analysis devices are required. In this study, a novel particle-based microfluidic test for the quantitative analysis of iron and copper ions was developed. This is the first time that particle-based microfluidics has been demonstrated in a self-contained test to analyze real-world samples. The working range for both analytes was from 0.05 to 5 ppm with detection limits of 38 ppb for copper and 10 ppb for iron. This was achieved through a novel approach with sequentially placed immobile colorimetric reagents that can concentrate the analytes from the sample. In addition to the excellent suitability of monitoring drinking water, the applicability of the test to samples containing chelating agents was demonstrated. Different tap water samples and nutrient solutions from a hydroponic farm were used to successfully cross-validate tests' performance with accredited laboratory methods. To the authors' knowledge, such on-spot tests for complex samples containing strong chelating agents have not been successfully demonstrated before. Overall, the tests required under a minute of hands-on time, and no expertise is needed to perform the analysis. An ordinary portable flatbed scanner was used for quantification, allowing the entire analysis to be performed on the spot.