NOVELTY - The coated substrate comprises a substrate (100), and a multi-layer nanoparticle coating (105) having a thickness of 500 nm, where the nanoparticle coating comprises a cationic polyelectrolyte layer (110) comprising polyacrylamide and an anionic multi-colloid layer disposed over the cationic polyelectrolyte layer. The anionic multi-colloid layer comprises anionic hydrophilic colloids (130) comprising silica nanoparticles, and anionic conductive colloids (120) comprising carbon based nanoparticles.    USE - The coated substrate is useful for polymer electrolyte membrane fuel cells.    ADVANTAGE - The coated substrate exhibits improved electrical conductivity.    DETAILED DESCRIPTION - The coated substrate comprises a substrate (100) and a multi-layer nanoparticle coating (105) having a thickness of 500 nm, where the nanoparticle coating comprises a cationic polyelectrolyte layer (110) comprising polyacrylamide, and an anionic multi-colloid layer disposed over the cationic polyelectrolyte layer. The anionic multi-colloid layer comprises anionic hydrophilic colloids (130) comprising silica nanoparticles, and anionic conductive colloids (120) comprising carbon based nanoparticles. The anionic hydrophilic colloids and the anionic conductive colloids are disposed over and coupled to the cationic polyelectrolyte layer. The anionic conductive colloids are separated from the hydrophilic colloids by repulsive forces. The hydrophilic colloids and the conductive colloids are coupled to the polyelectrolyte layer through electrostatic attraction, dipole-dipole interaction, ion-dipole interaction and/or van de Waals forces. The substrate comprises metal based material and/or organic based material, and is a surface of a polymer electrolyte membrane (PEM) fuel cell component. The conductive colloids comprise the silica nanoparticles having a thickness of 5-100 nm and a width of 5-800 nm. The hydrophilic colloids have a width of 5-100 nm. The polyelectrolyte layer has a width of 1 nm. The hydrophilic colloids and the conductive colloids define pH values below an iso-electrical point. The nanoparticle coating has a resistivity of 10-5 to 15 m Omega -cm2, an advancing contact angle of 5-45 degrees , a receding contact angle of 3-20 degrees and a thickness of 80-200 nm. A ratio of carbon in the conductive colloids to silica in the hydrophilic colloids is equal to 5:1-15:1. An INDEPENDENT CLAIM is included for a method for providing a nanocoating.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a multi-layer nanoparticle coating provided on a substrate.    Substrate (100)    Nanoparticle coating (105)    Cationic polyelectrolyte layer (110)    Anionic conductive colloids (120)    Anionic hydrophilic colloids. (130)