Materials and Methods. The ligands/indicators used in this experiment include tetrakis(4-carboxyphenyl)porphyrin (TCPP), amine of (3-aminopropyl)triethoxysilane (-NH2), toluene (MePh), sodium iodide (NaI), potassium iodide (KI) and (C6H4(NH2)2) 1,2-phenylenediamine (12P). Copper (Cu 2+ ), iron (Fe 3+ ), nickel (Ni 2+ ), chromium (Cr 2+ ), mercury (Hg 2+ ), and lead (Pb 2+ ) ions were prepared from their metal salt in aqueous solution purchased from Sigma-Aldrich. Whatman ® qualitative filter paper Grades 1 and 4, and commercial candles were used to create µPADs hydrophobic barriers using a wax stamping method and a metal stamp. A calibration reference of Munsell colorchecker 24 charts, and MATLAB Image Processing Tools were employed to execute the color calibration algorithm.
Choice of Paper. The performance of Whatman ® qualitative filter paper, Grades 1 and 4 were studied. Their performance was examined in terms of: (a) volume of indicators, (b) reaction colour quality between the indicator and the HMIs, and (c) the microfluidic channel resolution. 5 out of 6 uniform Cu 2+ complexes colour reproduced using Grade 1 with a binding time twice as fast as Grade 4 paper and 50% smaller wax diffusion rings observed at 2 seconds stamping time. Section 6 in the Supporting Information explains the characteristic of the paper in detail.
Choice of Paper. The performance of Whatman ® qualitative filter paper, Grades 1 and 4 were studied. Their performance was examined in terms of: (a) volume of indicators, (b) reaction colour quality between the indicator and the HMIs, and (c) the microfluidic channel resolution. 5 out of 6 uniform Cu 2+ complexes colour reproduced using Grade 1 with a binding time twice as fast as Grade 4 paper and 50% smaller wax diffusion rings observed at 2 seconds stamping time. Section 6 in the Supporting Information explains the characteristic of the paper in detail.