Molecular folding induced nanogold aggregation

Ca2+-induced folding of bisacridinedione scaffold on gold nanoparticle and dual spectral responses. Bisacridinedione-functionalized gold nanoparticles (bisADD-GNPs) were prepared and characterized. BisADD is a flexible acyclic moiety and a specific Ca2+ sensor. Signaling of the binding events is achieved by the cation-induced folding of the bisADD-GNPs and the resultant fluorescence enhancement and visual color change are attributed to the suppression of photoinduced electron transfer (PET) through space and nano-Au aggregation. The selective binding of Ca2+ is clear from steady state fluorescence and TEM techniques.