Structural and optical characterization of folate-conjugated gold-nanoparticles

Gold nanoparticles (AuNPs) represent a novel nanomaterials applied in various nanotechnology fields because of their special optical properties. On the other hand, folic acid and folate can be used for selective targeting of nanoparticles towards cancer cells. Folate conjugated AuNPs can be considered as an effective nanoconjugate in the field of nanotargeted photothermal therapy of cancer. In the present work, we report our synthesis of a new nanoconjugate composed of folate, AuNP and 4-aminothiophenol (4Atp) as the linker and named Folate-4Atp-AuNP. The results of our investigations on properties of this new nanoconjugate are presented here including the effects of addition of folate and 4Atp to AuNP on its structural and optical properties. We studied the structural characteristics of Folate-4Atp-AuNP using X-ray diffraction. In addition, we determined its optical band gap energy (1.365 eV), its optical constants using Kramers-Kronig analysis and we identified its metallic face-centered cubic (fcc) lattice structure and particular crystal planes. Our findings indicate that the presence of 4Atp and folate in Folate-4Atp-AuNP had no significant effect on its optical band gap energy. However, some appreciable changes in its optical constants were observed due to the presence of 4Atp and folate in nanoconjugate. The significant changes in optical constants values are apparently as a result of the presence of some special bonds and a few particular functional groups in the nanoconjugate. (C) 2009 Elsevier B.V. All rights reserved.