Nucleic acids-based aptamers are single-stranded DNA or RNA sequences that, folding into several secondary and tertiary different structural elements, can recognize peptides, proteins, chemical organic and inorganic molecules, drugs, whole cells and viruses with high affinity and specificity. The discovery of aptamers and of the Systemic Enrichment of Ligands by EXponentially amplification (SELEX) for their selection, have led to an increasing interest for basic research and bio-medical applications. Undoubtedly, aptamers are very versatile molecular tools for developing applications in many fields as reviewed in this chapter.
