Rational design and SERS properties of side-by-side, end-to-end and end-to-side assemblies of Au nanorods

By taking advantage of the anisotropy of AuNRs, we design different bifunctional PEG molecules to selectively bind to either the end or side face and simultaneously protect other faces of individual AuNRs. In this way, we successfully achieve orientation-controllable assemblies of AuNRs into side-by-side (SS), end-to-end (EE) and end-to-side (ES) orientations based on the electrostatic interaction between carboxylic PEG and CTAB capping on AuNRs. Furthermore, we find that the different orientations of assembledmotifs in these three types of AuNRs assemblies exhibited different near field coupling between the surface plasma of the neighboring AuNRs, leading to different surface-enhanced Raman signals. Undoubtedly, the current rational design of oriented assembly can be potentially useful for directing anisotropic nanoparticles into well-defined orientations, which provides a powerful route in designing families of novel nanodevices and nanomaterials with programmable electrical and optical properties.