Low-cost photolithographic fabrication of nanowires and microfilters for advanced bioassay devices
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Doan, Nhi; Qiang, Liangliang; Li, Zhe; Vaddiraju, Santhisagar; Bishop, Gregory; Rusling, James; Papadimitrakopoulos, Fotios (2015). Low-cost photolithographic fabrication of nanowires and microfilters for advanced bioassay devices. Sensors 15 (3), 6091-6104
Integrated microfluidic devices with nanosized array electrodes and microfiltration capabilities can greatly increase sensitivity and enhance automation in immunoassay devices. In this contribution, we utilize the edge-patterning method of thin aluminum (Al) films in order to form nano- to micron-sized gaps. Evaporation of high work-function metals (i.e., Au, Ag, etc.) on these gaps, followed by Al lift-off, enables the formation of electrical uniform nanowires from low-cost, plastic-based, photomasks. By replacing Al with chromium (Cr), the formation of high resolution, custom-made photomasks that are ideal for low-cost fabrication of a plurality of array devices were realized. To demonstrate the feasibility of such Cr photomasks, SU-8 micro-pillar masters were formed and replicated into PDMS to produce micron-sized filters with 3-4 mu m gaps and an aspect ratio of 3. These microfilters were capable of retaining 6 mu m beads within a localized site, while allowing solvent flow. The combination of nanowire arrays and micro-pillar filtration opens new perspectives for rapid R&D screening of various microfluidic-based immunoassay geometries, where analyte pre-concentration and highly sensitive, electrochemical detection can be readily co-localized.