One-step synthesis of biocompatible gold nanoparticles using gallic acid in the presence of poly-(N-vinyl-2-pyrrolidone)

A one-step method for the synthesis of biocompatible gold nanoparticles at room temperature by reducing HAuCl4 with gallic acid in the presence of poly-(N-vinyl-2-pyrrolidone) (PVP) is presented. The effect of the molar ratio of gallic acid to gold (R) on the size and shape of gold nanoparticles and the characteristic of gold nanoparticles was investigated by UV–vis and infrared spectroscopy, transmission electron microscopy, and X-ray diffraction. For an R value of about 0.4, the prepared gold nanoparticles were the smallest in size and the most close to spherical in shape. At other molar ratios, particle sizes increased and various polyhedra were formed. A reaction mechanism for the reduction of HAuCl4 by gallic acid is proposed. The incorporation of PVP effectively protected the surface of gold nanoparticles and improved their stability. The PVP-protected gold nanoparticles were modified with 3′- and 5′-alkanethiol-capped 12-base oligonucleotides, respectively, to form two different nucleic acid probes. The probes were successfully used to complex a 24-base complementary polynucleotide target in a tail-to-tail fashion.