Short-term optical stability of CTAB-gold nanorods (CTAB-GNRs) dispersed in different biologically relevant media. CTAB-GNRs, optical density 0.5 at 800 nm, were centrifuged once and resuspended in same volume of (A) deionized or DI water, (B), phosphate-buffered saline (PBS) (C) serum-free medium, and (D) serum-containing medium. Absorbance spectra were monitored from 400 nm to 999 nm for up to 48 h in respective media.