CONFORMATIONAL STUDY OF CITRATES ADSORBED ON GOLD NANOPARTICLES USING FOURIER TRANSFORM INFRARED SPECTROSCOPY

We investigated the structure of citrates adsorbed on Au nanoparticles ( AuNPs ) synthesized by the Frens method by Fourier transformed infrared spectroscopy (FTIR). We found that physisorbed citrates are stable enough to stay on the surface of AuNPs during purification. The FT-IR spectra of citrates on AuNPs are quite uniquely different from bulk citrates, suggesting the formation of coordination bond between carboxylate group and gold. The shifts of carboxylate vibration modes on AuNPs are larger than that on flat Au substrates, as expected from the stronger dipole field on AuNPs compared with that on flat substrates.