The present invention is directed to a pre-coated substrate, such as a slide, that is useful for immobilizing a sample. The invention is further provides methods of preparing such pre-coated substrates and methods of analyzing biological samples immobilized on such pre-coated substrate. The substrate is coated with a polycationic polymeric coating material specifically selected such that that coated substrate exhibits increased stability and prolonged shelf-life. Preferred polymeric coating materials include allylic or vinylic polymers having cationic groups thereon and having no more than a small percentage of peptidic monomeric linkages, particularly polydiallyldimethylammonium (PDDA).