The overall objective of the proposal is to develop enabling chemical technologies to address two important problems in biology: detect in a nondestructive fashion gene expression or microRNA sequences in vivo and, secondly, study the role of multivalency and spatial organization in carbohydrate recognition. Both of these projects exploit the programmable pre-organization of peptide nucleic acid (PNA) to induce a chemical reaction in the first case or modulate a ligand-receptor interaction in the second case. For nucleic acid detection, a DNA or RNA fragment will be utilized to bring two PNA fragments bearing reactive functionalities in close proximity thereby promoting a reaction. Two types of reactions are proposed, the first one to release a fluorophore for imaging purposes and the second one to release a drug as an “intelligent” therapeutic. If affinities are programmed such that hybridization is reversible, the template can work catalytically leading to large amplifications. As a proof of concept, this method will be used to measure the transcription level of genes implicated in stem cell differentiation and detect mutations in oncogenes. For the purpose of studying multivalent carbohydrate ligand architectures, the challenge of chemical synthesis has been a limiting factor. A supramolecular approach is proposed herein where different arrangements of carbohydrates can be displayed in a well organized fashion by hybridizing PNA-tagged carbohydrates to DNA templates. This will be used not only to control the distance between multiple ligands or to create combinatorial arrangements of hetero ligands but also to access more complex architectures such as Hollyday junctions. The oligosaccharide units will be prepared using de novo organoctalytic reactions. This technology will be first applied to probe the recognition events between HIV and dendritic cells which promote HIV infection.