Colloidally Stable and Surfactant-Free Protein-Coated Gold Nanorods in Biological Media

In this work, we investigate the ligand exchange of cetyltrimethylammoniuni bromide (CTAB) with bovine serum albumin for gold nanorods: We demonstrate by surface-enhanced, Raman scattering measurements. that CTAB, which is used as a shape-directing agent in the particle,de synthesis, is completely removed from solution and particle surface. Thus, the protein-coated nanorods are suitable for bioapplications, where, cationic surfactants must be avoided. At the same time) the colloidal stability of the system is significantly increased, as evidenced by spectroscopic investigation of the particle longitudinal surface plasnion resonance, which is sensitive to aggregation. particles are stable at very high concentrations (c(Au) 20 ing/mL) in biological media such as phosphate buffer saline or Dulbecco's Modified Eagle's Medium and over a large pH range (2-12). Particles can even be freeze-dried (lyophilized)- and redispersed. The protocol was applied to gold nanoparticles with a large range of aspect ratios and sizes with main absorption frequencies covering the visible and the near-IR spectral range from 600 to 1100 nm. Thus, these colloiclally stable and surfactaia-free protein-coated nanoparticles ate of great interest for various Plasmorac and biomedical applications.