The development of an optical DNA hybridization biosensor based on ruthenium electrochemiluminescence (ECL) was designed to detect DNA hybridization, using the detection of specific DNA sequences, which are indicative for antibiotic resistant strains of Mycobacterium tuberculosis as a model. The development of the sensor involved the characterization and optimization of the individual elements of the biosensor. Using this approach it was possible to ensure that the complete biosensor system was optimized to its maximum sensitivity for the electrochemiluminescent optical signal, which is produced during the DNA hybridization event. The transduction element used in this work is a solid-state silicon PIN photodiode. The miniaturization of the optical element to 5 mm(2) and smaller has made it possible to integrate the optical element internally as part of the biosensor scheme. Ruthenium ECL is a chemiluminescent reaction that is initiated by electrical stimulation. Photolithographic techniques were used to deposit and pattern gold electrodes directly onto the surface of the PIN photodiodes for the initiation of the ECL reaction. The gold electrodes also act as a biological support layer for DNA immobilization via thiol -gold linkage chemistry. The characterization and optimization of the individual components of this biosensor have allowed us to fabricate a miniaturized and integrated system that is compatible with a flow-through system.