Semi-synthetic DNA-protein conjugates: novel tools in analytics and nanobiotechnology.

This article reports on the syntheses, characterization and applications of semi-synthetic conjugates composed of nucleic acids, proteins and inorganic nanoparticles. For example, self-assembled oligomeric networks consisting of streptavidin and double-stranded DNA are applicable as reagents in immunoassays, model systems for ion-switchable nanoparticle networks as well as nanometer-scaled 'soft material' standards for scanning probe microscopy. Covalent conjugates of single-stranded DNA and streptavidin are utilized as biomolecular adapters for the immobilization of biotinylated macromolecules at solid substrates via nucleic acid hybridization. This 'DNA-directed immobilization' allows for reversible and site-selective functionalization of solid substrates with metal and semiconductor nanoparticles or, vice versa, for the DNA-directed functionalization of gold nanoparticles with proteins, such as immunoglobulins and enzymes. This approach is applicable for the detection of chip-immobilized antigens. Moreover, covalent DNA-protein conjugates allow for their selective positioning along single-stranded nucleic acids, and thus for the construction of nanometre-scale assemblies composed of proteins and/or nanoclusters. Examples include the fabrication of functional biometallic nanostructures from gold nanoparticles and antibodies, applicable as diagnostic tools in bioanalytics.