A polysaccharide coated carrier having a coating of at least two successive layers of polysaccharide. The first polysaccharide layer spontaneously associates with a second polysaccharide layer and, optionally, the carrier. Each successive layer of polysaccharide spontaneously associates with a preceding layer. Spontaneous association occurs due to the presence of oppositely charged functional groups on each layer of polysaccharide or due to a spontaneous reaction between the functional groups the layers. The carrier may be any surface such as a tube, microtitration plate, bead, particle or the like and is suitable for use in diagnostic or therapeutic methods.