Nucleic acids and their analogs as nanomaterials for biosensor development

Nucleic acids are natural biopolymers that store the genetic information of organisms. This makes the detection and characterization of DNA and RNA a relevant task in biotechnology, with applications ranging from medicine to environmental control. During the last decades, a large effort has been focused on the development of biosensors, among them those devoted to the detection of nucleic acids in natural samples and those that include nucleic acids as nanosized capture probes for different biomolecules. DNA microarray technology has been successfully used in biotechnological applications including genotyping and gene expression studies. Nevertheless, the performance of DNA microarrays has a limitation imposed by the need of a previous fluorescent labeling of the target molecule to be analyzed. This encouraged the use of alternative detection methods, such as optical and electrochemical ones, and recently others based on surface characterization techniques. New trends in nanotechnology point towards new tools for manipulating molecules and macromolecules that could be developed as high performance biosensors. This interdisciplinary approach towards the integration of novel biosensors can benefit from the capability of certain polymers to form self-assembled monolayers (SAMs) on different surfaces. Thiol-modified DNA can form SAMs on gold surfaces with reduced efficiency, and the biological activity of the probe is decreased upon adsorption. Therefore, thiolated DNA has a very limited use in biosensor development. These constraints have been successfully by-passed using uncharged, artificial analogs of natural nucleic acids, such as peptide nucleic acids (PNAs), as molecular probes. This contribution reviews the state of the art in the use of nucleic acids and their analogs as biosensor nanomaterials, and summarizes the novel approach towards the development of biosensors based on SAMs of PNAs. Finally, we present the current trends in this promising aspect of nano biotechnology.