For covalent conjugation of Cyt C and Zn Porph, a fresh EDC/NHS mix solution was made by adding EDC (19.17 mg, 100 µmol) and NHS (23 mg, 200 µmol) in MES buffer (pH 5). A total of 100µL of EDC/NHS mix was added to the 1 mL solution of AuNP-PEG and was left stirring for 1 hour. The solution was then centrifuged at 13,400 rpm for 30 minutes to form a pellet of the AuNP with activated PEG-COOH. To this pellet Cyt C (1 mL, 200 µM) and Zn Porph (1 mL, 200 µM) were added under constant stirring (in AuNP-PEG-Cyt C only Cyt C was added, and in AuNP-PEG-Zn Porph only Zn Porph was added). The solution was stirred for 24 hours followed by three cycles of centrifugation at 13,400 rpm to remove any unbound Cyt C and Zn Porph. The obtained pellet was resuspended in 1 mL of water to yield a monodispersed sample of AuNP-PEG-Cyt C/Zn Porph.