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 (∼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 γ-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. One-pot green synthesis of gold nanoparticles of desired shapes is developed by using FDA approved and economic GRAS materials. The gold nanoparticles exhibit radio-sensitization in A549 cells with star shaped nanoparticles showing maximum efficacy.