Inertial microfluidics is an emerging field deviates from the conventional microfluidics due to its unqiueness in consideration of inertia. Dean flow and Dean instability play an important role in inertial microfluidics, with a wide application in mixing and sorting. However, most studies are limited to Dean flow on the microscale. In this thesis, the Dean flow and Dean instability is studied, discussed, and employed for practical utilization. To begin with, the fundamentals of fluid dynamics, Dean flow and Dean instability and microfluidics mixing is introduced. A novel channel geometry, the tortuous channel is investigated and proposed by COMSOL Multiphysics. A detailed experimental investigation of flow development is carried out with the flow visualization by confocal microscopy. And this is the first experimental flow visualization of the Dean instability done on the deka-micron scale. The numerical and experimental result indicates the tortuous channel is superior in creating Dean instability and enhancing mixing performance. Next, The optimization of channel geometries by the radius of curvature was investigated to promote mixing. The application of the optimized tortuous channel design xv in nanoparticle synthesis demonstrated a decrease in nanoparticle size with increasing Reynolds number and Dean number. The results provide meaningful insights for future research and development on the innovative mixing techniques and systems.