Improved size-tunable synthesis and SERS properties of Au nanostars
- 840 Downloads
Multibranched Au nanoparticles with sharp tips (commonly called nanostars, NSTs) have attracted significant attention as bright scattering labels, photothermal transducers, nanocarriers, and surface-enhanced Raman scattering (SERS) tags. However, for surfactant-free synthesized NSTs, the existing data on the size tuning and the relation between the size of NSTs and their SERS efficiency still remain limited. Here, we address these questions by synthesizing and comparing SERS for surfactant-free NSTs of different sizes and plasmon resonance (PR) wavelengths. The NSTs were fabricated by seeded growth through a two-step surfactant-free approach in which quasispherical seeds were overgrown via reduction of added Au by ascorbic acid in the presence of Ag ions. By varying the seed size from 3 to 35 nm, we tuned the final NST size from 45 to 150 nm while retaining the star-like morphology with sharp tips and ensuring PR tunability from 630 to 900 nm. The NST size and PR limits can be expanded from 40 to 200 nm and from 600 to 930 nm, respectively, by simultaneous variation in the seed size and concentration. The SERS efficiency of the fabricated NSTs was examined by Raman measurements of 1,4-aminothiophenol (ATP) adsorbed on the surface of colloidal NST particles. Although the homogenous analytical enhancement factor (AEF) did not depend essentially on the NST size and varied from 4 × 106 to 107, the enhancing properties of single-particle NST tags were strongly size-dependent. Specifically, the AEF for 150-nm NST35-ATP complexes was 30 and 100 times greater than that for 70-nm NST15-ATP and 45-nm NST3-ATP complexes, respectively. These properties make the NST–ATP complex a prospective platform for SERS imaging.
KeywordsAu nanostars Surfactant-free synthesis Plasmon resonance Extinction spectra SERS
The work by BN and NK was supported by grant No. 14-13-01167 from the Russian Scientific Foundation. The work on NST synthesis by EP and VK was supported by grants from the Russian Foundation for Basic Research (no. 13-02-12413), the Government of the Russian Federation (no. 14.Z50.31.0004), and a scholarship from the President of the Russian Federation CП-3575.2013.4. We thank D.N. Tychinin (IBPPM RAS) for his help in preparation of the manuscript.
- Van De Broek B, Grandjean D, Trekker J, Ye J, Verstreken K, Maes G, Borghs G, Nikitenko S, Lagae L, Bartic C, Temst K, Van Bael MJ (2011b) Temperature determination of resonantly excited plasmonic branched gold nanoparticles by X-ray absorption spectroscopy. Small 7:2498–2506Google Scholar