Currently, various methods for fabricating microfluidic paper-based analytical devices (μPADs) have been proposed due to their great potential applications in many fields such as clinical diagnosis, food quality control and environmental monitoring. Hereby, a novel and simple method for the fabrication of microfluidic paper-based analytical devices via plasma treatment is reported. Paper was first hydrophobized via octadecyltrichlorosilane (OTS) silanization. The OTS silanized paper was then region-selectively plasma-treated via a mask with channel network. The plasma-exposed area of the paper was turned to hydrophilic channel network due to the degradation of hydrophobic OTS molecules coupled to the paper's cellulose fibres before. Two types of hybrid polymethylmethacrylate-polydimethylsiloxane (PMMA-PDMS) masks were developed to obtain well defined hydrophilic channel with the required depth. With the elastic PDMS piece adhered to the rigid PMMA piece, it excellently solved the problem of the expansion of hydrophilic channel caused by the leakage of plasma atmosphere in the gap between the mask and paper. The effect of plasma-treating time on hydrophilicity of paper was investigated. The water contact angle (WCA) dramatically decreased from 133.9°±1.3° to 0° with the prolonging of the plasma treating time from 0 s to 30 s. Meanwhile, the depth of wettable channel could also increase to nearly the thickness (180 μm) of the paper after treated for 30 s. Attenuated total reflectance Fourier transformed infrared (ATR-FT-IR) spectrometer and X-ray photoelectron spectroscopy (XPS) were applied to characterize the surface chemistry of paper during silanization and plasma treatment, and the related mechanism was discussed. The fabricated μPAD was applied for detection of plasma glucose in whole blood. After diluted with 2% NaCl by a ratio of 1:4, plasma could be separated from blood cells due to their different mobility in the channel on paper. The separated plasma reached test readout zone and reacted with the substrates of Trinder's reaction. The analytical results observed with the μPAD-based colorimetric assays agreed well with those determined by conventional glucose meter.

Key words: microfluidic paper-based analytical devices, octadecyltrichlorosilane, plasma, whole blood, glucose