Modulating phenolic compounds synthesis and antioxidant activity in Dunaliella salina microalgae by metal oxide nanoparticles under variable salinity conditions

Abstract

The increasing use of metal oxide nanoparticles (NPs) in various applications raises concerns about their ecological impact, but also offers opportunities for targeted modulation of microalgal metabolism. This study evaluates the effects of titanium dioxide (TiO₂), zinc oxide (ZnO), and copper oxide (CuO) nanoparticles on the phenolic content and antioxidant activity of the green microalga Dunaliella salina, cultivated in mineral media under two salinity conditions (60 g/L and 120 g/L NaCl). The microalgal culture was exposed to NPs at concentrations ranging from 0.1 to 30 mg/L. Total phenolic content was quantified in aqueous extracts, while antioxidant activity was measured using the ABTS assay in ethanolic extracts. The results demonstrated that nanoparticle type, concentration, and salinity level interactively influenced the biosynthesis of phenolic compounds and the antioxidant potential of the biomass. Low NP concentrations (0.1–1 mg/L), particularly under moderate salinity (60 g/L NaCl), stimulated phenolic accumulation, with CuONPs showing the most consistent and pronounced effect. In contrast, higher concentrations of TiO₂ and ZnO, especially under high salinity (120 g/L NaCl), led to a significant decrease in phenolic levels. Antioxidant activity followed similar trends, being enhanced by low to moderate levels of CuONPs and ZnONPs, particularly under high salinity, but was suppressed at higher NP doses, likely due to excessive oxidative stress. These findings highlight the potential of controlled nanoparticle application to enhance the biosynthesis of valuable antioxidant compounds in Dunaliella salina.