a method for assembling a micro - fluidic device better preserves the integrity of a filter in a filter layer and simplifies the bonding of the filter layer to the channel layers on each side of the filter layer . the method includes aligning a polymer layer having a plurality of filter elements and a plurality of fluid passages arranged between the filter elements between two substrates of a micro - fluidic device , and bonding the polymer layer between the two substrates to seal an area between the filter elements and the fluid passages to enable fluid flow through the filter elements to be segregated from fluid flow through the fluid passages .