Radiation-induced failure mechanisms of GaAs-based biochips

Radiation-induced-failure of biochips, which can occur via several mechanisms, are presented. These mechanisms are: destruction of the covalent bonds at the interface between the DNA- probe and the semiconductor surface; main-chain scission of single and double strand DNA; formation of covalently linked dimers between adjacent DNA strands; and scission of base units from the backbone of the DNA molecules. For biochips that consist of thiol-derivatized DNA monolayers on arsenic-terminated GaAs [001], ionizing radiation (such as high-energy electrons and gamma rays) and UV light have the capability to rupture the anchoring covalent bonds between the DNA probes and the arsenide, namely the S-As, N-As, and O-As bonds. The effects of the ionizing radiation can also be enhanced by the fact that the absorbed radiation dose in the DNA layer is greater than in the arsenic terminated GaAs; this arises from 1) differences in stopping power, 2) the fact that the fluence of backscattered secondary electrons from the semiconductor exceeds the opposing fluence backscattered from the organic layer, and 3) energy transfer effects. These phenomena increase the radiation yield of ruptures of the DNA and its anchoring covalent bonds ultimately leading to the removal of and damage to the DNA from the arsenic terminated GaAs [001]. Ionizing radiation also induces random scissions on the backbone of the DNA molecules demolishing its biosensing capability.