I want to use nanoparticles to interact with different solutions in a microfluidic channel. The nanoparticles will be placed in the channel and the solution will be pumped through the channel. I want to avoid the nanoparticles to be washed away with the solution. I know that the nanoparticles can be made magnetic and hold them in place using a magnet. I would like to know if anyone has used/came across a different technique to hold the nanoparticles in one place. Thank you.