Sub-Diffraction Limited Wide Field Imaging and Microfabrication Based on Surface Plasmons

Abstract

Standing-wave surface plasmon resonance fluorescence (SW-SPRF) is a microscopy technique combining standing-wave total internal reflection fluorescence (SW-TIRF) microscopy and surface plasmon resonance (SPR) or surface plasmon-coupled emission (SPCE). Previous studies have shown that SW-TIRF technique can enhance lateral image resolution by more than twice utilizing standing evanescence waves. Further improvement may be generated using surface plasmons by reflecting light on the gold surface through the cover glass at a specific angle inducing collective excitation of electrons in the metal. In this study, we developed imaging and lithography method with less than 100 nm resolution by applying SW-SPRF microscopy with corrugated gold surface. We used corrugated gold surface to induce surface plasmon waves with larger wave number compared to uncorrugated one. This matching process requires proper optimization of parameters including grating constant, perturbation depth, incidence angle of the beam, and excitation wavelength. The fabrication of the corrugated gold surface was done by e-beam etching. For imaging, sub-diffraction size fluorescent particles were used to measure point spread function. For lithography, nano-patterns were produced by the exposure of interfering evanescent waves on azo dye (Congo-Red) thin films produced by spin-coating. The resultant patterns were measured with AFM. We gratefully acknowledge funding from the Singapore-MIT Alliance (SMA-2), the Singapore-MIT Alliance for Research and Technology (SMART), and the Samsung Scholarship.