Immobilization strategies for the attachment of nucleotide probes to both microarrays and microfabricated interdigitated electrodes differ to address the specific requirements for optical and electrochemical detection, respectively. The DNA immobilization chemistry dictates how the probe molecule is presented to its complement during hybridization and thereby contributes significantly to the final detection signal. This chapter introduces the relevant immobilization strategies for DNA probes on both microarrays and microfabricated interdigitated microsensor electrode arrays. Specifically, we examine immobilization via electrostatic attraction and covalent coupling. The immobilization of DNA presents many challenges because of the need to promote efficient hybridization while minimizing or eliminating nonspecific adsorption to exposed areas of the device substrate. The immobilization strategies also present challenges because of the various materials and surface chemistries that may be involved, the flow characteristics during detection, and the need to perform hybridizations under specific buffer and temperature cycling conditions. This paper provides a rationale for the move towards low-density genosensors using electrochemical detection with focused example applications in human health care. Specifically, electrochemical impedance spectroscopy (EIS) is introduced and discussed as an advantageous method for DNA hybridization detection. The various immobilization strategies are discussed in reference to EIS detection. In conclusion, the advantages of impedance detection are addressed with critical assessments for the advancement of impedance detection for DNA hybridization.