Binding and Assembly of Functionalized Colloids

Any biointeraction e.g. a standard hybridization is a useful tool to assemble colloidal particles in solution or at surfaces. By use of this technique arrays of colloids are easily obtained at a substrate surface. These particle arrays deviate in their optical and electrical behavior from single isolated colloidal particles. 

In optical devices regular arrays of nano-clusters give a very sharp resonance signal due to the large number of cooperative interactions in between the particles. Whereas this effect allows precise resonance tuning the same cooperative effect limits the dynamic range of the reaction if used for direct analyte detection. E.g. DNA-covered nano-clusters 

Immobilization of short synthetic oligonucleotides to gold nanoparticles follows slightly different rules than the attachment of proteins. A gold colloid 15-20 nM in particle concentration is reacted with a 200 fold access of a thio-functionalized oligonucleotide (3.5 pM) in water. In order to allow reorientation at the surface the reaction is allowed to stand for 24 hours at room temperature. The excess of reagent is 

Whereas thiol bonds are stable at room and slightly elevated temperatures the stability at 70-100°C is low. To increase the chemical stability either multivalent thiols or silanes are applied. Both strategies clearly target at multiple attachment sites in between the oligonucleotides and the cluster. Using silane coated colloids the DNA is bound covalently to functional groups at the surface of the coated particle. 

Nature provides a complete bolbox of specific biomolecular reagents, such as ligases, endonucleases, methalyses and another DNA modifying enzymes, which allow for the processing and handling of DNA-nanocluster material with atomic precision and accuracy. 

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