Hand Spray-Based Approach Two solutions were prepared for the hand spray-based approach. Solution A is mainly prepared by adding 0.04 mmol cobalt (II) acetate tetrahydrate [Co(CH3COO)2•4H2O; 98%; Alfa Aesar] in 100 mL deionized water. The addition of bactericidal metals was done by spiking Solution A first by 0.08 mmol copper (II) nitrate trihydrate (Cu(NO3)2•3H2O; 99%; Sigma-Aldrich), then by 0.08 mmol zinc (II) nitrate hexahydrate (Zn(NO3)2•6H2O; 98%; ACROS), and lastly by 0.08 mmol silver nitrate (AgNO3; 99.8%; AENCORE). Solution B was prepared by dissolving 0.013 mmol potassium permanganate (KMnO4; 99%; J.T. Baker) in 100 mL deionized water. These were contained in PET spray bottles ready for the spray coating. The tempered glass screen protector substrates were removed of its plastic cover before use, while the stainless steel (5 cm × 5 cm), rubber handrail (~5 cm × ~5 cm) and electric switch sample substrates were not subjected to specific cleaning steps. Microscope glass slide substrates were subjected to washing (with soapy water, deionized water, acetone, and isopropanol) and blow-drying prior to use. Indium tin oxide (ITO) substrates were washed (with concentrated nitric acid, water, acetone, and isopropanol), dried, and plasma-treated prior to deposition. For the spray process, Solution A was first sprayed directly onto the substrates at a 90º angle for at most five spray shots, or until the solution predominantly coats the entire surface. This was followed by spraying of Solution B in the same manner. The substrates were left undisturbed for 15 minutes. To simulate the potential, direct application on electronics, a damp Kimwipe was used to remove the liquid on the substrates, followed by wiping it dry with another sheet. For multiple coats, the same process above was repeated.