Paper-Based Analytical Device for Zinc Ion Quantification in Water Samples with Power-Free Analyte Concentration
Department of Applied Chemistry, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Kanagawa, Japan
Author to whom correspondence should be addressed.
Academic Editors: Frank A. Gomez and Carlos D. Garcia
Micromachines 2017, 8(4), 127; https://doi.org/10.3390/mi8040127
Received: 25 March 2017 / Revised: 11 April 2017 / Accepted: 13 April 2017 / Published: 18 April 2017
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
Insufficient sensitivity is a general issue of colorimetric paper-based analytical devices (PADs) for trace analyte detection, such as metal ions, in environmental water. This paper demonstrates the colorimetric detection of zinc ions (Zn2+) on a paper-based analytical device with an integrated analyte concentration system. Concentration of Zn2+ ions from an enlarged sample volume (1 mL) has been achieved with the aid of a colorimetric Zn2+ indicator (Zincon) electrostatically immobilized onto a filter paper substrate in combination with highly water-absorbent materials. Analyte concentration as well as sample pretreatment, including pH adjustment and interferent masking, has been elaborated. The resulting device enables colorimetric quantification of Zn2+ in environmental water samples (tap water, river water) from a single sample application. The achieved detection limit of 0.53 μM is a significant improvement over that of a commercial colorimetric Zn2+ test paper (9.7 μM), demonstrating the efficiency of the developed analyte concentration system not requiring any equipment.