A simple method for fabrication of microfluidic paper-based analytical devices and on-device fluid control with a portable corona generator

This work presents a facile method for fabrication of microfluidic paper-based analytical devices (mu PADs) and on-device fluid control with a portable, hand-held corona generator. First, filter paper was hydrophobized by coupling octadecyltrichlorosilane (OTS) to paper cellulose. Then, the OTS-coated paper, covered with a stenciled plastic mask, was region-selectively exposed to the corona by scanning the electrode tip of the corona generator along the open parts of the mask. Thus, the corona-exposed regions of the paper surface resumed their native hydrophilicity while the masked regions remained highly hydrophobic. The effect of corona treatment time on the paper's hydrophilic property was investigated. Colorimetric assays of nitrite in saliva samples were demonstrated with the developed mPADs. A single-use 'on' valve based on wettability-switching was developed in the mPADs. Fluid control was realized via on-site corona discharge targeted at a hydrophobic barrier design as the 'on' valve.