Metal nano clusters as transducers for bioaffinity interactions

Metal clusters excited by electromagnetic radiation exhibit high local field enhancement and nanoscale resonant behavior. Absorptive properties of these metal clusters bound to a surface are the basis of various new and highly promising setups to transduce biorecognitive interactions into an optical signal. Immunogold labelling and immunogold chromatography as well as SPR transduction of metal cluster binding have been successfully commercialized. Multilayered highly resonant systems have been proposed and recently realized employing a metal mirror, a polymer distance layer, a biomolecule interaction layer, and biorecognitively bound metal nano clusters. Experiments indicate a strong influence of cluster symmetry and cluster shell on the strong reflection minima induced by the resonant behavior. Modified clusters, clearly exhibit at least one additional narrow reflection minimum in the red or infrared region and therefore far away from spherical gold colloids (<520nm). Glass-type metal clusters synthesized by interruption of the thermal step of Au3+- reduction as well as metal-dielectric shell clusters synthesized by multiple shell deposition processes enables the shift to a near-mid IR resonance. It is possible to convert directly (without use of additional analysis steps) biorecognitive binding processes and catalytic activity of proteins by the application of surface enhanced clusters into a visible optical signal (color change of sensor surface). Disposable single step assays as well as multiuse-monitoring devices have been established employing e.g. lectin-sugar, antigen-antibody, protein-receptor, or DNA-DNA interactions.