Basic Sets for Plasmonic Diagnostics in Aggregates of Capped and Uncapped Gold Nanorods

Gold nanorods (GNRs) have recently been developed for medical applications, and their silanization has been proposed for improving their photostability. In this paper, we show that self-assembled polyethylene glycol (PEG)ylated and silanized GNRs enjoy another benefit of silanization, i.e. its success in reshaping the plasmonic couplings typical of particle aggregation, for increasing shell widths. We investigated clusters of silanized gold nanorods that were capped with silica shells of different thickness. For a shell width of 12 nm, we obtained an optical extinction peak in the near infrared about two times greater than that in the green. In order to discuss the main features of the experimental spectra, we found it useful to model the aggregates with elementary clusters containing a small number of coupled GNRs. We availed of the discrete dipole approximation (DDA) for simulating the extinction coefficients of different basis sets. We reproduced the experimental spectrum for a shell width of 12 nm by modelling its reshaping with pairs of coupled particles in an end-to-end or side-by-side configuration and different aspect ratios. © 2014 Springer Science+Business Media New York.