Analytical Sciences

Abstract − Analytical Sciences, 34(5), 605 (2018).

Alternative Patterning Methods for Paper-based Analytical Devices Using Nail Polish as a Hydrophobic Reagent
Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand
A rapid, easy, and cost effective fabrication method for paper-based analytical devices (PADs) is described. This newly developed method is based on the use of nail polish as an alternative hydrophobic reagent, and the nail polish was resistant to basic and organic solvents. Three approaches for fabrication of paper-based analytical devices (PADs) were investigated, namely writing, stamping, and spraying. The writing approach was carried out by drawing the hydrophobic area of a pre-designed pattern on filter paper with a simple lab-made pen filled with nail polish as the hydrophobic agent. The stamping and spraying approaches required the use of a designed mask, which was made by laser cutting of the magnet rubber sheet. With laser cutting, two types of templates were made, i.e., positive and negative counterparts. The positive counterpart was the inside pattern and the negative counterpart was the outside pattern of the magnet sheets. For the stamping approach, the negative counterpart of the magnet rubber mask was attached onto a simple rubber stamper that was then stamped onto filter paper after loading with nail polish solution. With the spraying method, the positive counterpart was used to cover the hydrophilic area on the paper. Then, the nail polish solution was used with an air brush and sprayed on the paper covered with the magnet rubber mask. All approaches were cost effective and required neither extra equipment nor any pretreatment step. Among all three methods, however, the spraying method was found most suitable for mass production and provided the best resolution when compared with the other two approaches. With this approach, the actual channel widths obtained were similar to the designed widths, with the narrowest possible channel width of 650 μm. Furthermore, a nail polish-treated PAD was prepared by soaking the paper in the nail polish solution. The ability of the nail polish-treated PAD was examined for its resistance to a strong basic solution and an organic solvent (up to 30% ethanol and dichloromethane). The nail polish-treated paper also showed the potential to be used as an organic-aqueous separator.