Study On Fabrication Of Microfluidic Paper-based Analytical Devices And Manipulation Of Microfluidic Flow In Paper-based Channels Using A Hand-held Corona Treater

Microfluidic paper-based analytical device (μPADs) is a burgeoning microfluidic technique. Compared to conventional microfluidic chips often made of glass and polymer substrates, μPADs fabricate hydrophilic-hydrophobic microstructures on paper substrates. Thus, μPADs possess attractive features such as low-cost, easy-to-fabricate, easy-to-use and portable and holds great potentials for applications in clinical diagnosis, food quality control as well as environmental monitoring. However, research on μPADs is still at an early stage, significant research efforts including fabrication of μPADs and fluids manipulation in μPADs will be needed to nurture μPADs into a more matured analytical platform. This work aims to establish a simple and quick method for fabricating microfluidic paper-based analytical device and controlling the movement of fluids in paper-based channels using a hand-held corona treater. The thesis is composed of two chapters:In chapter1, both the fabrication techniques and applications of microfluidic paper-based analytical devices are reviewed. Firstly, various fabrication techniques reported in the literature have been introduced, including UV photolithography, wax printing, plasma treatment, ink printing, ink jet etching, plotting, screen printing, flexography printing and laser treatment. Each technique has its advantages and disadvantages. Secondly, applications of microfluidic paper-based analytical devices in clinical diagnosis, food quality control as well as environmental monitoring are also reviewed. Thirdly, a brief introduction to the application of corona treater with tip-formed electrode in the fabrication of microchip was made.In chapter2, a novel and facile method for fabricating microfluidic paper-based analytical devices and manipulating capillary-driven flow in paper-based channels using a hand-held corona treater was established. First, filter paper was hydrophobized by coupling octadecyltrichlorosilane (OTS) to paper fibers. Then, with the help of a plastic mask, the hydrophobic paper was exposed to corona emanated from the Spring Tip electrode. Thus OTS in selective regions was degraded and hydrophilic patterns were formed. The effect of corona treatment time to paper’s hydrophilic property was investigated. Results showed that water contact angle decreased to0°and hydrophilic depth increased to its peak value (about50μm) with increase of corona treatment time. X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform-infrared (ATR-FT-IR) spectroscopy were employed to understand the mechanism of hydrophobic-hydrophilic conversion of the paper caused by corona-treatment. The hydrophilic property remained the same as its initial status after storage for1month under a dry ambient. Colorimetric assay of nitrite in saliva sample was demonstrated with the developed μPADs and the results agreed well with that determined by ion chromatography. Manipulating capillary-driven flow in paper-based channels was also realized through on-site pattern.