Abstract: The present invention describes optical discs on which polymer molecules can be analyzed. There is a method for determining a plurality of characteristics of a target molecule, the target molecule being localized on an optical substrate comprising pits and lands, comprising the steps of: (i) carrying out a series of reactions to interrogate different defined characteristics of the target molecule, wherein each of the reactions occurs in a distinct pit; (ii) treating the optical substrate to modify either those pits where a reaction has occurred, or alternatively, those pits where a reaction has not occurred, to alter the reflective characteristics of the pits; and (iii) measuring reflectivity within the pits, to thereby determine different characteristics of the target.