A pH-controlled one-pot synthesis of gold nanostars by using a zwitterionic protein hydrolysate (gelatin): an enhanced radiosensitization of cancer cells

For the first time, the present study reports that gelatin, a protein hydrolysate, can be used as a stabilizing agent for the green seedless synthesis of gold (Au) nanoparticles of varying shapes (spherical, triangular and star) of identical size (similar to 60 nm). The detailed investigation revealed that the concentration of gelatin and the pH of a reaction mixture primarily dictated the shape of Au nanoparticles. The reaction mixture containing Au-salt (3 mM) and lower concentrations (0.5%) of gelatin at acidic pH (3-6) favoured the formation of anisotropic nanoparticles (star and triangular shaped). On the contrary, the reaction mixture containing similar precursors at basic pH (pH = 9) favoured the formation of isotropic spherical shaped particles. Furthermore, although ascorbic acid as a reducing agent did not play any role in shape determination, it was required for the formation of nanoparticles at lower pH. However, at higher pH, gelatin itself acted as a reducing agent and supported the formation of nanoparticles. Finally, the radio-sensitizing effect of Au nanoparticles was evaluated in human lung cancer cells (A549) in combination with varying absorbed doses (2-8 Gy) of gamma-radiation. This study indicated that the star shaped Au nanoparticles exhibited higher radio-sensitization in comparison to the spherical and triangular shaped Au nanoparticles with a dose modification factor of 0.76.