Direct patterning using protein-based water lithography

We report a facile micro-patterning method on protein substrates using the high-precision inkjet printing technology. Water - either pure or functionally doped - is used as the “exposure” source and water-dissolvable silk fibroin as the resist. Micropatterns of ~ 16 μm (including both planar and greyscale ones) are successfully demonstrated and the resolution can be further improved by using a smaller nozzle size (therefore smaller droplets) and optimized printing conditions. The printing parameters are comprehensively investigated to improve the lithographic performances. With a subsequent lift-off or ion beam etching process, metallic patterns can be fabricated on a variety of substrates including planar and even curved surfaces. The direct fabrication of microlens arrays with adjustable focal lengths are demonstrated, underscoring the utility of applying this approach as an environmental friendly, low-cost, high yield and flexible alternative to fabricate functional patterns for biomedical, optical and photonic applications.