چكيده به لاتين
Paper-based microfluidics as a growing research field has created a suitable platform for using papers use in a variety of applications and because of its unique characteristics, has been of great concern to the researchers in the past two decades. One of the most fundamental applications of paper-based microfluidics is the clinical diagnosis. Paper-based microfluidics with the ability to make it easier and less costly, and no need to external stimulus forces, has succeeded in detecting many diseases. Nitrite is also one of the cases where its abnormal presence in saliva can be a sign of disease. Therefore, the detection of nitrite in saliva with the help of paper-based microfluidics can enable all people with any level of financial ability to use easily. Also, the use of saliva instead of blood due to non-invasive properties increases the efficiency and application of the µpad.
The ability of different fluids mixing is one of the benefits of microfluidics, which is required in many chemical and biological reactions. So mixing improvement can directly affect the speed and accuracy of the reactions. The purpose of this thesis is to find a micromixer that can be used with optimal mixing in the colorimetric nitrite detection in the saliva using the Griess reaction. As a result, the device's limit of detection will improve. First, 5 different geometries, straight, curved, zigzag, square wave and hexagonal are designed for the micromixer mixing section. In order to have a proper view, the simulation was carried out in the ANSYS CFX software with a homogeneous multiphase flow model in porous media. Then, along with the numerical solution, micromixers, which were prepared with a simple and low-cost laser cut, were tested by Griess reaction. Finally, the hexagonal micromixer with 38.99 and 44.24% improving than the straight micromixer in experiment and simulation, respectively, had the best mixing efficiency. The mixing index has been defined based on the concentration deviation so that the deviation from a certain amount is less, the mixing operation is performed more successfully. In following, using hexagonal micromixer under optimum conditions the limit of detection of 5.7 µmolL^(-1) has been obtained in the linear detection range of 5-1000 µmolL^(-1). In this range, the color intensity is evaluated linearly in terms of logarithmic nitrite concentration, which allows the consumers of this µpad to quantitatively determine the concentration of the nitrite based on the color intensity of the detection area of the µpad in a wide range.
