Development of a layered dye nanoparticle-coated test strip for on-site analysis of manganese aerosol

We propose an advanced test strip for the on-site analysis of manganese aerosol fine particles in a working environment based on two important functions of particle dissolution and Mn²⁺ detection. Initially, a thin layer of several hundred nanometers composed of 2-(3,5-diBromo-2-pyridylazo)-5-diethylaminophenol (3,5-diBr-PADAP) dye nanoparticles for the color detection of Mn²⁺ was prepared on the top surface of a fine membrane filter by the filtration of 3,5-diBr-PADAP nanoparticle dispersion. Next, 3 wt% gelatin gel containing 0.05 mol L⁻¹ borax was impregnated over the entire membrane to keep the pH of 3,5-diBr-PADAP thin layer ca. 9.5. Finally, an acidic and a reductive gel layer of ca. 40 μm in thickness containing 5 wt% gelatin and 0.1 mol L⁻¹ _L-ascorbic acid was applied for coating over the 3,5-diBr-PADAP layer in order to dissolve manganese oxide particles and to produce Mn²⁺. The resulting layered test strip was applied for detecting fine manganese particles. Since manganese aerosol is not replicable, a mixture of ca. 1 μm of Mn₃O₄ particles and ca. 2.3 μm of AlOOH was applied for evaluating the test strip by being contacted with each other. The color of the test strip changed from orange to purple with an increase of the Mn₃O₄ percentage. A calibration curve by using the b^* of the L^*a^*b^* color space exponentially decreased, and it was expressed as b^* = 2.28 + 47.8exp(-4.60[Mn]) (r² = 0.977) with the 3σ detection limit of 0.02 μg cm⁻² (n = 5) and the quantification range of 0.08∼1.2 μg cm⁻². The successful determination of manganese particle was concluded that the ion transport flow of Mn²⁺ works well in the reductive gel layer, in the dye layer, and between them during the color detection. (author)