Research On Physical Forces In Linear Assembly Of Metal Nanoparticles

Noble metal self-assembled nanostructures have singular unique plasmonic optical properties,which have broad applications in the fields of biological detection and medical treatment.As demonstrated in previous studies,how to balance the multiple interparticle forces involved in the self-assembly process plays a key role to determine the assembled structures as well as the corresponding properties.Investigating and regulating physical forces at nanoscale together with manipulating assembled structures and corresponding optical properties has become one of the most interesting and active research areas in nanotechnology.In this dissertation,we preliminary explored several physical forces involved the formation of linear self-assembly process of gold nanorods.Meanwhile,we attempted to manipulate the self-assembled structures and the plasmonic chiroptical responses of gold nanorods by using optical forces.(1)By using cysteine molecules functionalized gold nanorods as building blocks,we studied the physical forces during the formation of typical end-to-end and side-by-side self-assembly of gold nanorods.We investigated the cysteine molecules mediated zwitterionic electrostatic and hydrogen bonding interactions by measuring the plasmonic resonance absorption,circular dichroism and surface-enhanced Raman spectra of gold nanorods assemblies in both neutral and acidic solutions.Results have shown that plasmons circular dichroism can selectively recognize zwitterionic electrostatic and hydrogen bonding interactions.On the other hand,these plasmonic chiroptical actives of linear assembled gold nanorods can further be used to in-suit detect different chiral interactions of biomolecules at nanoscale interfaces in solution phase.(2)We also studied the electrostatic forces and van der Waals forces during the side-by-side assembly process of gold nanorods.By measuring the dynamic plasmon resonance absorption and circular dichroism spectra during the assembly process,we investigated the effects of different physical forces on the chiral assembled structures and the corresponding chiroptical properties.For electrostatic force mediated side-by-side assembly of gold nanorods,we regulated the Zeta potential values of discrete gold nanorods and the addition of oppositely charged stabilizations to adjust the electrostatic repulsion forces between gold nanorods,enabling to manipulate the kinetics of the assembly process.Furthermore,Logistic function was used to theoretically fit the kinetics of gold nanorods assembly process.We attempted to establish the relationship between the simulation parameters and the assembly rates.(3)We introduced the chiral optical force into the electrostatic force mediated side-by-side assembly process of gold nanorods,and explored the optical force manipulated plasmonic optical properties of chiral assembled gold nanorods.Results have shown that left/right polarized light perturbation can selectively amplify/decrease the plasmonic circular dichroism responses of chiral enantiomers,whereas the linearly polarized light perturbed plasmonic optical activity can be ignored.We believe that the above findings will provide new insights into the development of tunable surface plasmonic chiroptical functional materials and optical devices.