Polydopamine (PDA) has emerged as a versatile biomaterial with unique properties that make it highly suitable for various biomedical applications. This thesis focuses on investigating the potential of PDA nanoparticles (PDA NPs) in antioxidant therapy and near-infrared (NIR) responsive biomedical applications. Specifically, PDA NPs were investigated as a potential therapeutic agent for mitochondrial diseases such as mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS), and progressive external ophthalmoplegia (PEO), as well as in the treatment of hepatocellular carcinoma (HCC). Mitochondrial diseases, specifically, are a class of rare genetic diseases characterized by dysfunctional mitochondria, where mutations in mitochondrial DNA (mtDNA) have been observed.