New designs of paper based analytical devices (PADs) for completing replication analysis of a sample within a single...

Paper-based analytical devices (PADs) with four new designs could be fabricated using commercially available home-based scan-and-cut printer. They serve for miniaturised platforms for chemical analysis. Replication analysis of a sample together with the calibration (using the analyte standards at different concentrations) can be completed in a single run, by utilising smartphone as the detector. Some new approaches for choosing detection zones were suggested. The four proposed PAD designs here were used as models in microliter scale operation to demonstrate the well-known chemistries of colorimetric determinations of iron, phosphate, and hardness using 1,10-phenanthroline and simple aqueous guava leaf extract; molybdate, and EBT-EDTA complexometric titration, respectively, through calibrations: where Blue (B) value = 88.2log [Fe³⁺] - 80.8, R² = 0.989; B value = 1.75 [Fe³⁺] + 0.198, R² = 0.999; Grey scale (I) value = 1.77 [Fe³⁺] - 1.22, R² = 0.997; Red (R) value = 16.1log [PO₄^3-] + 8.95, R² = 0.999; Hue (H) value = 43.3log [Ca²⁺] + 233, R² = 0.994, respectively. For the hardness, using one of the PAD designs, true titration was also possible. Applications of the proposed devices and procedures were demonstrated for real world samples with validation. Additionally, kinetic study of the molybdenum blue for phosphate was demonstrated using one of the PADs.