Abstract: The invention provides a chip comprising a substrate with at least one surface and a layer of particles having a non-metallic core and a coating made of a metal or a metal alloy, characterized in that each non-metallic core, on average, forms a metal-surrounded contact point with at least one other non-metallic core and/or the substrate surface. The invention also provides a method for preparing a chip, comprising the steps of, adsorbing non-metallic particles on said surface of the substrate, and, subsequently, adsorbing colloids of a metal on said non-metallic particles to provide the shell made of a metal or a metal alloy, and a chip which is obtainable by said method. The chip can be employed in optical devices for the detection of analytes.