Micro-patternable nanoporous polymer integrated with microstructures for molecularfiltration

Abstract

This paper proposes a facile method to fabricate nanoporous microstructures by aphoto-patternable SU-8 photoresist, to serve as a molecular filter in microfluidic systems.The fabrication process involves solvent-controlled nanoporous structure formationcombined with standard photolithography steps for microstructure fabrication. Theself-formed nanoporous morphology embedded inside the microstructure exhibits asufficient mechanical strength and eliminates complex processes or protocols forintegration/assembly of nano- and microstructures. Field emission gun scanning electronicmicroscopy (FEGSEM) images showed the fabricated nanoporous morphologies withembedded nanogaps of about 6–10 nm. Atomic force microscopy (AFM) images alsodepicted a clear difference on the degree of porosity between the solvent-controlled SU-8and the standard resist. Fluorescent dyes, namely Rhodamine-B and Rhodamine-6G, wereemployed to estimate the diffusivity of the fabricated SU-8 based nanofilter anddemonstrated that the Rhodamine based fluorescent molecules can penetrate thesenanosized filtration structures. The fabricated nanofilter was capable of providing amolecular weight cut-off range up to 70 kDa, estimated roughly for a molecule witha diameter of 6–10 nm. This simple process provides a novel way to integratethe nanofiltration capability into microstructures while maintaining a sufficientmechanical strength for molecular level filtration in lab-on-chip (LOC) systems.