Nitrite Colorimetric Detection in Saliva using Optimal Mixing

Microfluidic analytical/diagnostic tools, especially microfluidic paper-based analytical devices ( PADs) have attracted considerable attention due to their numerous advantages including their low operational costs, small analyte consumption, and limited required skills for use, and easy disposal/recycling. μPADs have been successful in detection of various diseases with no external deriving units. The aim of this study is to develop a micromixer for colorimetric detection of nitrite in saliva using Griess reaction and widening the limit of detection (LOD) by mixing improvement. Micromixers were fabricated using laser cut after a simple design. Five different geometries were examined and compared including straight, curved, zigzag, square wave and hexagonal, by numerical simulation and experimental tests for mixing part in micromixer. Simulations were performed in ANSYS CFX with homogeneous two-phase flow model in a porous media. As the result inclined hexagonal micromixer showed the best performance (in comparison with the straight one) exhibiting 44.24% of improvement which leads to a detection range and LOD of and , respectively. Considering the significant impact of micromixers in microfluidics, the quality of mixing and therefore the accuracy of the devices was improved by simple geometrical modifications.