We present a novel surface adsorption mechanism that leads to densely packed nanoparticle-monolayer coatings on most surfaces, including glass, semiconductors, and several polymers, without the need for specific functionalization of the surfaces.  The nanoparticles (~ 5 nm) display electrostatic charges (“+” or “-“) from end-functionalized thiol capping agents.  The nanoparticle-monolayer forms due to the presence of both positive and negative particles in solution, and its density is possible to control by changing the solution pH and the relative ratio of positive to negative particles in solution.  Detailed modeling of the particle-particle and particle-surface interactions provides a new insight into assembly processes at this length scale.  Since the assembly depends largely on the charges of the nanoparticles, this method allows a level of abstraction when designing nanoparticles monolayers by defining only the number of charged particles, independent from the materials used.  Mixed monolayers of gold, silver, platinum and palladium nanoparticles with various compositions are demonstrated.  Initial studies of the monolayers reveal novel plasmonic effects, as well as an application for the creation of antibacterial surfaces.  The antibacterial properties of monolayers of silver nanoparticles have been demonstrated on glass, and a number of medically relevant polymers.