Anhydrous ethanol solution

30% hydrogen peroxide (H₂O₂), potassium nitrate (KNO₃), ethanolamine, amine-PEG2-biotin, 1-ethyl-3-(3-(dimethylamino)propyl)-carbodiimide HCl (EDC), and potassium ferricyanide (Fe-(cn)₆^3–) were purchased from Thermofisher Scientific (Fairlawn, NJ, USA). Anhydrous ethanol solution, 2-(N-morpholino)ethanesulfonic acid (MES) buffer, sulfo-N-hydroxsulfosuccinimide (NHS), lipoic acid, 11-mercaptoundecanoic acid (MUA), and potassium hexacyanoferrate(II) trihydrate (Fe(CN)₆^4–) were purchased from Sigma-Aldrich (St. Louis, MO). 6-(Ferrocenyl)hexanethiol (Fc-(CH)₆SH) was purchased from Santa Cruz Biotech (Dallas, TX). Sodium hydroxide (NaOH) was purchased from JT Baker (TX, USA). All solutions were prepared in ultrapure Milli-Q water (18.2 MΩ cm, MilliPore, MA, USA). Whatman 1 chromatography paper was purchased from GE healthcare sciences (UK). Scotch Heavy Duty Shipping packing tape (3M) was purchased from Office Max. Streptavidin (SA) microparticles were purchased from Life Technologies. High purity silver paint was purchased from SPI Supplies (West Chester, PA). Au microwires (99.99% pure, 25 μm diameter) were purchased from California Fine Wire Company (Grover Beach, CA). 0.05 M pH 6.0 MES buffer was made with MES, and pH was adjusted to 6.0 with NaOH.