In a typical deposition procedure, two spray solutions are needed. The first solution, denoted as Solution A, is an aqueous mixture containing Co 2+ , Cu 2+ , Zn 2+ , and Ag + ; while the other one, denoted as Solution B, is a KMnO4 aqueous solution. The separation of Co and KMnO4 in two different hand sprayers is the key to trigger the deposition only when the two solutions are mixed. The ratio of Co 2+ to MnO4 -was kept at 3:1 as the ideal stoichiometric ratio as shown in Eq. 3, while the other metal cations are twice the Co concentrations. We chose tempered glass screen protectors as the main substrates due to the wide use by the public for diverse smartphones.