Perchloric acid

Sodium hydroxide, sodium hydrogen carbonate, ammonium hydroxide, and perchloric acid were purchased from Junsei Chemicals (Seoul, Korea). Dansyl chloride and standard BAs were purchased from Sigma-Aldrich (St. Louis, MO, USA). High-performance liquid chromatography (HPLC)-grade ammonium acetate and acetonitrile were purchased from Merck (Damstadt, Germany). All chemicals used in this study were of analytical grade and were used as supplied.

Prior to synthesizing PANI, the PUNO NPA on polyethylene terephthalate (PET) film was prepared by a combined photo- and soft lithography technique using a Si nanohole master mold. A mixture of Norland Optical Adhesive 63 and PUA (MINS-311RM, Minuta Tech., Chungcheongbuk-do, Korea) was coated on the surface of the master mold using a spin coater (LSM250, SAWATEC, Jiangsu, China). After exposure to UV (EVG6200, EVG, DI Erich Thallner Strasse, Austria) for 1 min, the free-standing PUNO NPA film was peeled from the master mold. To provide a current collector, a thin conformal layer of gold/titanium was deposited onto the NPAs via vacuum evaporation. The PANI was synthesized on the surface of PUNO film via dilute polymerization. The PUNO film was immersed in a mixture solution of perchloric acid (60%, JUNSEI, Tokyo, Japan), APS (98%, Sigma-Aldrich, Seoul, Korea), aniline (99.5%, Sigma-Aldrich, Seoul, Korea), and deionized water. The molar concentrations of aniline monomer, perchloric acid, and APS varied in the range of 1‒1000 mM to control the PANI morphology (Figure 1). Polymerization was performed at 4 °C and the product incubated for 10 min to 60 h. The PANI/Au HNS was obtained after thoroughly washing with ethanol and deionized water several times.