Fabrication of pH‐Responsive Thionine‐Conjugated Gold Nanoparticles for a Mediated Drug Delivery System Against Human Breast Cancer Cells

Efficient and feasible therapeutic agent delivery into the tumor is an important task in cancer therapy. A pH‐sensitive link between trisodium citrate‐capped gold nanoparticles (AuNPs) and thionine (TH) dye steps facilitates the conjugation. pH‐responsive drug release profiles were studied under different buffer conditions. A sustained release of TH was observed at pH 5.5, corresponding to endosomal conditions. Utilizing MTT assay and fluorescence activity, the biological activity of the TH‐conjugated AuNPs was studied. The synthesis of AuNPs was confirmed by the surface plasmon resonance (SPR) band in electronic spectral studies, granular particle size analysis, average particle size distribution by transmission electron microscopy (TEM) imaging, and crystalline nature by the selected area electron diffraction (SAED) pattern. The conjugated nature of AuNPs‐TH was assessed by photophysical studies, including 1:1 stoichiometry, binding constant, number of binding sites, electrostatic interaction, ground state complex through static quenching under excitation, and thermodynamic stability at a pH of 7.4 within the studied concentration range. Free citrate‐capped AuNPs showed low toxicity and good biocompatibility in the studied concentration range. TH‐conjugated AuNPs had a strong antitumor efficacy against MCF‐7 cancer cells.