Red light-activable biotinylated copper(II) complex-functionalized gold nanocomposite (Biotin-Cu@AuNP) towards targeted photodynamic therapy.

We report the synthesis and characterization of red-light activable gold nanoparticle functionalized with biotinylated copper(II) complex of general molecular formula, [Cu(L)(L)]-AuNPs (Biotin-Cu@AuNP), where L = N-(3-((E)-3,5-di-tert-butyl-2-hydroxybenzylideneamino)-4-hydroxyphenyl)-5-((3aS,4S,6aR)-2-oxo-hexahydro-1H-thieno[3,4-d]imidazol-4-yl)pentanamide, L = 5-(1,2-dithiolan-3-yl)-N-(1,10-phenanthrolin-5-yl)pentanamide, which was explored for their photophysical, theoretical and photo-cytotoxic potentials. The nanoconjugate exhibits differential uptake in biotin positive and biotin negative cancer cells as well as normal cells. The nanoconjugate also shows remarkable photodynamic activity against biotin positive A549 (IC: 13 μg/mL in red light; >150 μg/mL in dark) and HaCaT (IC: 23 μg/mL in red light; >150 μg/mL in dark) cells under red light (600-720 nm, 30 Jcm) irradiation, with significantly high photo-indices (PI>15). The nanoconjugate is less toxic to HEK293T (biotin negative) and HPL1D (normal) cells. Confocal microscopy confirms preferential mitochondrial and partly cytoplasmic localization of Biotin-Cu@AuNP in A549 cells. Several photo-physical and theoretical studies reveal the red light-assisted generation of singlet oxygen (O) (Ф (O) =0.68) as a reactive oxygen species (ROS) which results in remarkable oxidative stress and mitochondrial membrane damage, leading to caspase 3/7-dependent apoptosis of A549 cells. Overall, the nanocomposite (Biotin-Cu@AuNP) exhibiting red light-assisted targeted photodynamic activity has emerged as the ideal next generation PDT agents.