Protocol A5 by Negahdary et al. [80]: Electrodeposition of fern-leaf-like gold nanostructures with increased surface area for aptamer immobilization Reagents Solution for electrodeposition: 0.5 M H2SO4, 20 mM HAuCl4, 0.1 M polyethylene glycol (PEG) 6000; 10 µM tris[2-carboxyethyl] phosphine; Ethyl acetate; 10 mM phosphate buffer, containing 5 mM NaCl, 2 mM KCl, 1 mM MgCl2, pH = 7.4; 1 mM mercaptohexanol (MCH); Artificial CSF: 126 mM NaCl, 2.5 mM KCl, 1.24 mM NaH2PO4, 1.2 mM MgSO4, 2 mM CaCl2, 26 mM NaHCO3, 10 mM D-glucose, pH 7.35. Method Immerse the cleaned electrode in the corresponding solution. Electrodeposition was potentiostatically performed at 0 mV for a duration of 5 min; Mix the thiolated aptamer (concentration? Amount?) with 3.6 µL of 10 µM tris[2-carboxyethyl] phosphine and vortex for 2 h; Add ethyl acetate in three portions (total volume of 100 μL), and remove the upper layer after each addition; Mix the resultant liquid with the phosphate buffer solution; Incubate the electrode in the obtained solution for 1 h at 4 °C; Rinse with deionized water; Incubate with 1 mM MCH solution for 30 min at RT; Rinse thoroughly with deionized water. For storage, incubate in 20 mM Tris-HCl buffer at 4 °C. For the bioassay, incubate with Aβ (linear range: 2 pg/mL–1.28 ng/mL, diluted in artificial CSF) for 10 min at 37 °C and rinse with deionized water. For regeneration, immerse in deionized water for 5 min at 95 °C to release bound Aβ.