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Browsing by Subject "wax printing"

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  • Peuraniemi, Tuukka (2012)
    The aim of this research was to evaluate the use of microfluidic paper-based devices (µPAD) in drug analysis. Micro total analysis systems (µTAS) channels are in the range of a few micrometers and are capable of performing all steps of a chemical analysis. The advantages of miniaturization are lower sample consumption and faster analysis time. µTASs are usually fabricated of glass, silicon or polymers and their fabrication requires cleanroom facilities and specific equipment. Paper offers an inexpensive and versatile substrate for µTASs. Paper wicks liquids and no external pumps are required. µPADs advantages over µTAS are its ease of use and inexpensive and simple fabrication. µPADs are fabricated by patterning hydrophobic barriers in hydrophilic paper. There are several fabrication methods for µPADs such as photolithography, cutting and methods based on the application of wax (etching, wax printing, wax dipping). In this research wax printing was selected as the fabrication method because it's simple, rapid and inexpensive. Wax was printed using Xerox Phaser 8560DN solid ink printer. After printing the wax was melted through the paper by heating the paper at 150 °C for 120 seconds on a hotplate. Thus the wax creates a hydrophobic barrier on the hydrophilic paper which channels the liquids flow. Owing to papers anisotropic nature the wax also spreads horizontally in the paper when heated, thus reducing the wax patterns resolution and making the pattern coarse. Wax printing is an inexpensive and simple fabrication method suitable for fabricating µPADs. Also liquids flow velocity and methods for controlling the flow rate were studied. By knowing the flow velocity, one can assure that the analytes and reagents reach the reaction site. Controlling the flow velocity enables the use of multiphase reactions or the use of multiple simultaneous reactions on the µPAD. The liquid flow velocity can be controlled by changing the hydrophilic channels width, reducing the average pore size by melting a layer of wax inside the hydrophilic channel or by changing the surface tension or viscosity of the liquid used. Colorimetric assays are the most commonly used detection methods in µPADs, but also electrochemical sensing and detection methods based on fluorescence are used. In this study direct and indirect fluorescence detection methods were studied. In the detection method based on direct fluorescence, fluorescein and coumarine derivates were studied. In indirect fluorescence amino acids fluorescamine conjugates, which were created in the paper, were studied. Level of the analytes detected in direct fluorescence detection was 10-13 mol in the range of visible light and 10-12 mol in the range of UV-light. Level of the amino acids fluorescamine conjugates detected in indirect fluorescence detection was 10-9 mol. According to our results the fluorescence based detection methods used in this study are suitable for drug analysis on µPADs.