In-situ stability test: Two types of in-situ electrochemical experiments were performed: chronoamperometry and continuous cyclic voltammetry. Chronoamperometry was carried out by holding the potential at 0.7 V vs Pt wire at pH7 for 1 hour. The 0.7 V applied against Pt wire is approximately 0.8 V vs Ag|AgCl (3 M KCl). This value was normalized by measuring the shift of 0.1 M ferricyanide in acetonitrile/water (10/90, v/v) in the three-electrode set-up using Pt wire or Ag|AgCl (3 M KCl) as the reference electrode. (see SI Figure ). Continuous cyclic voltammetry measurements were applied to study the electrochemical stability for Fc12-Br/dMO. The potential was swept between 0.0 V and 0.7 V vs Pt wire at 0.1 V s -1 for 1 hour.