We have designed a new folate-conjugated gold nanoparticle (AuNP) to selectively target the folate receptor that is overexpressed on the surface of tumoral cells. For this purpose, we made 4-aminothiophenol, as a bifunctional linker to react with HAuCl4 in the presence of sodium borohydride and it was binded to the AuNP surface through its thiol group. Then, we conjugated amino-terminated nanoparticles to folic acid with an amide-linkage formation. Finally, we evaluated the specific interaction between the folic acid and AuNP by the corresponding observed characteristic bands in the UV-vis and FTIR spectra. Transmission electron microscopic (TEM) images reveal the spherical AuNPs formation induced by the bifunctional linker. Powder X-ray diffraction (XRD) patterns confirmed the metallic face-centered cubic (FCC) lattice structure with (111), (200), (220), and (311) crystal planes. We estimated the average size of the conjugated nanoparticles to be about 48 nm by TEM and XRD. The Elemental analysis and atomic absorption showed 59 % organic molecules on the surface of AuNPs.

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