Adsorption and desorption of tyrosine kinase inhibitor erlotinib on gold nanoparticles. 
We investigated interfacial behaviors of erlotinib (EL) on gold nanoparticles (AuNPs) by means of Raman spectroscopy.  The adsorption reactions and structures of EL on AuNP surfaces were examined by UV-Vis absorption spectroscopy and surface-enhanced Raman scattering (SERS).  Density functional theory calculations were performed to estimate the energetic stabilities of the drug-AuNP composites.  Among the binding units in EL, the acetylenic C≡C group was calculated to be the most strongly binding on the AuNP cluster atoms, consistent with the SERS spectra.  The concentration-dependent SERS spectra indicated that ∼10(-5) M of EL exhibited the highest SERS signals.  The attached EL appeared to desorb more efficiently with 2mM glutathione than with cell culture media.  The lack of a strong SERS signal of EL in the dark-field microscopy images of AuNP-EL complexes suggested almost complete desorption of EL inside cells.