Surface modifications of gold nanoparticles: stabilization and recent applications in cancer therapy

Gold nanoparticles (GNPs) are noble metal nanocarriers that have been recently researched upon for pharmaceutical applications, imaging, and diagnosis. These metallic nanocarriers are easy to synthesize using chemical reduction techniques as their surface can be easily modified. Also, the properties of GNP are significantly affected by its size and shape which mandates its stabilization using suitable techniques of surface modification. Over the past decade, research has focused on surface modification of GNP and its stabilization using polymers, polysaccharides, proteins, dendrimers, and phase-stabilizers like gel phase or ionic liquid phase. The use of GNP for pharmaceutical applications requires its surface modification using biocompatible and inert surface modifiers. The stabilizers used, interact with the surface of GNP to provide either electrostatic stabilization or steric stabilization. This review extensively discusses the surface modification techniques for GNP and the related molecular level interactions involved in the same. The influence of various factors like the concentration of stabilizers used, their characteristics like chain length and thickness, pH of the surrounding media, etc., on the surface of GNP resulting in stability have been discussed in detail. Further, this review highlights the recent applications of surface-modified GNP in the management of tumor microenvironment and cancer therapy.