Photophysical aspects of molecular probes near nanostructured gold surfaces

Highly ordered, self-organized assemblies of organic molecules at surfaces of metal particles with sizes in the nanometer regime have been a subject of immense interest in recent years. Amongst the metal nanoparticles, considering the nobility of gold, organic fluoroprobes have often been attached to the surfaces of gold nanoparticles to form an extended network for potential technological applications. These organic-inorganic hybrid nanoassemblies offer an efficient route for the patterning of surfaces with functional nanometer-scale architectures utilizing several non-covalent intermolecular bonding interactions, e.g., hydrogen bonding, coordination bonding, etc. There is a growing recognition of fluorescence spectroscopy to achieve a molecular level understanding of the physical and chemical aspects of the molecule-surface interactions. The fluorophore-bound gold nanoparticles provide a convenient way to examine the mechanistic details of various deactivation pathways of the photoexcited fluoroprobes, such as energy and electron transfer to the particles as well as different types of intermolecular interactions involved in producing the bottom-up assembly of tailored nanostructures with a wide variety of structures and properties. The understanding of electronic absorption and dynamics in nanoparticulate systems is essential before assembling them into devices, which is essentially the future goal of the use of nanostructured systems. It is, therefore, important to elucidate the particle size and distance dependence on the interaction between excited molecular probes and the gold nanoparticles. The potential impact of the derived nanopatterned surfaces ranges from applications in molecular electronics to selective sensors to diagnostic devices. The greatest promise of these systems lies in the potential to tune functional aspects of the supramolecular assemblies at surfaces by manipulation of the interactions governing the derivation of supramolecular function that has merged the fundamental ideas of nanoscience with biology and medicine in the form of nanobiotechnology.