Selective effect of procaine, tetracaine and dibucaine on gold nanoparticles.

An aqueous colloid dispersion of gold nanoparticles (AuNPs) was prepared by reduction of gold(III) chloride and its interaction with three local anesthetics (procaine, dibucaine or tetracaine) was investigated. Optical spectra reveal the modifications in the absorption band of nanoparticles related to their self assembly mediated by anesthetic molecules and depending on the progress in time of the aggregation process. TEM images show the features of the self assemblies formed by the association of gold nanoparticles in presence of anesthetics, and reveal marked differences in the behavior of the AuNPs against the three anesthetics. The main effect of various anesthetics can be described in terms of electrostatic forces between the negatively charged metal nanoparticles and anesthetic molecules, existing in their cationic form at the working pH. Then, the anesthetics functionalized nanoparticles trigger specific interactions to form different self assemblies through a selective combination of hydrophobic and hydrogen bonding interactions between the coated nanoparticles and anesthetics molecular species.