Spa 400

Transmission electron microscope (TEM) images of the fabricated membranes were observed using a JEM-2100F electron microscope (JEOL Ltd., Tokyo, Japan). Field Emission Scanning Electron Microscope (FE-SEM) images were observed using JSF-7500F electron microscope (JEOL Ltd.). Atomic force microscopy (AFM) images were observed using a SPA-400 (Hitachi High-Tech Science, Tokyo, Japan). The AFM observation was performed with an OMCL-AC160TS-C3 cantilever (OLYMPUS, Tokyo, Japan) in dynamic force mode. The crystal structures of the fabricated membranes were measured by powder X-ray diffraction (XRD) (Ultima IV Protectus, Rigaku Corp., Tokyo, Japan) using monochromatized Cu Kα radiation (at 40 kV and 40 mA). The ζ-potential of the sample surfaces was measured using an electrokinetic analyzer (SurPASS™ 3; Anton Paar, Graz, Austria) in 1 mmol/L of KCl aqueous solution. The surface chemical state of the membrane was analyzed using XPS (JPS-9200, JEOL Ltd.). Raman spectroscopy was recorded using a 532 nm laser (NRS-7100, JASCO, Tokyo, Japan). The samples for Raman spectroscopy were prepared by dropping each colloidal solution on a glass plate and drying.

The morphology was characterized by using the atomic force microscope (AFM, SPA-400, Hitachi, Tokyo, Japan), field-emission scanning electron microscopy (FESEM, JSM-7410F, JEOL, Akishima, Japan), and field-emission transmission electron microscopy (FETEM, JEM-2100F, JEOL, Akishima, Japan). The crystal phase was characterized by using the X-ray diffraction (XRD) (D8 Discover X-ray diffractometer with Cu Kα radiation (Bruker, Karlsruhe, Germany)). Electrochemical measurements were performed by using a three-electrode system composed of as-prepared Ni-Co-P NSs working electrode, a platinum wire counter electrode, and an Ag/AgCl (3 M KCl) reference electrode by an electrochemical analyser (Autolab, model PGSTAT30, Eco Chemie, Utrecht, The Netherlands). All electrochemical measurements were conducted in 0.1 M phosphate-buffered saline (PBS) as the supporting electrolyte in the absence and presence of DA at ambient temperature. Cyclic voltammetry (CV) curves and differential pulse voltammetry (DPV) curves were performed between 0~0.8 V.

Samples of insulin amyloid fibrils were diluted 250 times with 25 mM HCl, and 10 µl aliquots of which were deposited onto a freshly cleaved dry mica surface. The solution was adsorbed for 1 min and then the mica surface was washed with 100 µl of water. The solution was blotted off by blotting paper and the mica plate was air-dried. AFM images were obtained by using an SPA-400 and a nano navi (Hitachi High-Tech Science, Tokyo, Japan). The scanning tip was an OMCL-AC160TS-C3 micro cantilever (Olympus Corporation, Tokyo, Japan; spring constant = 21–37 N/m, resonance frequency = 270–340 kHz), and the scan rate was 1.0 Hz.

The surface morphology of ITO, ITO/PbPc, ITO/ZnPc, ITO/PbPc/C₆₀, and ITO/ZnPc/C₆₀ was ex situ measured at RT in a 2 × 2 mm² area by atomic force microscopy (AFM: SPA400, Hitachi High-Tech Science) with a dynamic force mode, using an aluminum-coated silicon cantilever (SI-DF20, frequency: 110–130 kHz). To estimate the effective interface area (S_D/A shown in Fig. 6) of the MPc/C₆₀ (M = Pb, Zn) bilayer heterojunction, we calculated the vertical and horizontal curve lengths using the line segment between two adjacent points (512 points recorded in 2 mm) for each. In addition, to estimate the error due to the linear approximation for the line segment, we smoothed the segment at five adjacent points using the Savitzky-Golay filter^{37 (link)} and then estimated those curve lengths more precisely in terms of cubic polynomial spline interpolation. Since a comparison between the two results showed the error to be slightly 1.5%, the S_D/A values for PbPc/C₆₀ and ZnPc/C₆₀ obtained using the linear approximation are shown in Fig. 6. Assuming that the bilayer films were formed uniformly in the active area of 1 × 1 mm², the interface-area ratio of unevenness to flat obtained in the 2 × 2 mm² area can be used for the present OSC with an active area of 1 × 1 mm².