Green synthesis, characterization and anticancer activity of luminescent gold nanoparticles capped with apo-α-lactalbumin

A green synthesis was developed in order to prepare protein coated gold nanoparticles using a metal free, alpha-helical protein, i.e., apo-alpha-LA, that acts as both the reducing as well as stabilizing agent to result in Au-0 nanoparticles from Au3+ which are luminescent and hence can be used for biological imaging, including of cells. The nanoparticles, apo-alpha-LA-AuNPs, thus synthesized were characterized by multiple techniques, such as, analytical, spectral, microscopy and light scattering, in order to support the presence of NPs in terms of their size and shape, involvement of Au-0 and the protein encapsulation and its structural changes upon coating. The 10-16 nm sized apo-alpha-LA-AuNPs were shown to be non-toxic to healthy cells as studied using normal mouse fibroblast cells (L929). Having found that these NPs are biocompatible and possess structurally altered apo-alpha-LA protein, the luminescent apo-alpha-LA-AuNPs were demonstrated to have cytotoxicity towards cancer cells as studied by cell viability tests as well as fluorescence microscopy. While these NPs kill similar to 75% of MCF-7 cells, at the same concentration these are capable of killing only similar to 30% of HeLa cells, thus exhibiting cell dependency. The present study clearly demonstrates the advantage of the luminescent apo-alpha-LA-AuNPs in their attack of cancer cells in general and selective killing of breast cancer cells in particular. Thus coating AuNPs with the protein apo-alpha-LA enhanced their anticancer activity several fold.