a, An illustration of a self-assembling microfluidic device with PDMS inlets/outlets attached to a Si substrate and with PDMS channels integrated with a differentially crosslinked SU-8 film. b,c, A brightfield image of a 3.5 cm long multilayer SU-8/PDMS microfluidic device containing a single channel, (b) as patterned on a Si substrate, and (c) after self-assembly. d, A brightfield image of a self-assembled microfluidic device with dual channels. e,f, Fluorescence images showing the flow of (e) fluorescein (green), and (f) fluorescein (green)/rhodamine B (red) through single and dual channel devices, respectively. Scale bars are 500 μm (1 mm for b).