End-to-end and side-by-side assemblies of gold nanorods induced by dithiol poly(ethylene glycol)

The assemblies of gold nanorods (Au NRs) exhibit unique properties distinct from the isolated Au NR. We report an effective and simple method for the end-to-end (E-E) and side-by-side (S-S) assemblies of Au NRs with a molecularly defined nanogap (1-2 nm) only in the presence of dithiol poly(ethylene glycol) (HS-PEG-SH). The assembled methods need neither the pH value adjustments nor the addition of other organic solvent. With increasing amount of dithiol molecules, assembled modes of Au NRs experience an interesting procedure, changing from E-E to S-S orientation. The experimental results indicate that when the concentration of HS-PEG-SH is less than 0.25 mu M, electrostatic repulsion of positive-charged CTA(+) is stronger than the affinity of the Au-S binding, resulting in the E-E oriented assembly. Otherwise, the S-S oriented mode is predominated. The current assembled method will be potentially useful for the optoelectronics and biomedical engineering. (C) 2014 AIP Publishing LLC.