Abstract
We describe here a modification of properties of colloidal gold nanorods (NRs) resulting from the chemical treatment used to carry out their transfer into isopropanol (IPA) solution. The NRs acquire a tendency to attach one to another by their ends (end-to-end assembly). We focus on the investigation of the change in position and shape of the longitudinal surface plasmon (l-SPR) band after self-assembly. The experimental results are supported by a theoretical calculation, which rationalizes the dramatic change in optical properties when the NRs are positioned end-to-end at short distances. The detailed spectroscopic characterization performed at the consecutive stages of transfer of the NRs from water into IPA solution revealed the features of the interaction between the polymers used as ligands and their contribution to the final stage, when the NRs were dispersed in IPA solution. The efficient method of aligning the NRs detailed here may facilitate applications of the self-assembled NRs as building blocks for optical materials and biological sensing.Graphical
Highlights
Plasmonic nanoparticles made of noble metals are promising as materials since they possess unique properties due to the presence of localized surfaceR
Piela (&) Department of Physical and Quantum Chemistry, Wrocław University of Technology, Wybrzez_e Wyspianskiego 27, 50-370 Wroclaw, Poland e-mail: katarzyna.piela@pwr.edu.pl final stage, when the NRs were dispersed in IPA solution
The additional layers surrounding a gold nanorod screen the electron oscillation in the metal, decreasing the plasmon energy (Prodan et al 2002).When NRs are dispersed in IPA, a significant change is seen in the intensity, location, and half width of the longitudinal surface plasmon band, namely, a red shift of around 100 nm, and the band becomes approximately twice broader
Summary
NRs@CTAB, NRs@PSS, NRs@PAH, and NRs@PVP solutions were added dropwise on diamond crystal, evacuated, and ATR spectra were measured in the same range and with the same spectral resolution. Refractive index of a layer surrounding the NRs was calculated as a weighted average based on the relative content of the mixture of polymers and surfactants: 45 % PVP (n = 1.4215), 15 % PSS (n = 1.3718), 20 % PAH (n = 1.382), and 20 % CTAB (n = 1.449) (based on the ATR spectrum).
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