Green biosynthesis of titanium dioxide quantum dots using watermelon peel waste: antimicrobial, antioxidant, and anticancer activities

In this study, watermelon peel waste was used for biosynthesis of titanium dioxide quantum dots (TiO 2 Qds) through green and ecofriendly method for the first time. The biosynthesized TiO 2 Qds were fully characterized using UV–visible, FTIR, XRD, SEM, EDX, mapping, TEM, and TGA. The characterization of TiO 2 Qds revealed that the synthesized TiO 2 Qds is a polycrystalline crystal structure with an average particle size of 7 nm. The antimicrobial results revealed that TiO 2 Qds exhibited promising antimicrobial activity against Bacillus subtilis , Escherichia coli , Cryptococcus neoformans , Candida albicans , Aspergillus niger , and A. fumigatus where minimum inhibitory concentrations (MIC s ) were 15.62, 62.5, 7.81, 7.81, 31.25, and 1.95 µg/mL, respectively. Moreover, TiO 2 Qds have a strong antioxidant activity where IC50 was 31 µg/mL using DPPH method. Furthermore, TiO 2 Qds have potential anticancer activity against MCF7 cancerous cell line where IC50 was 114 µg/mL, and inhibition percentages at 1000 and 500 µg/mL were 99 and 93%, respectively. In conclusion, the biosynthesized TiO 2 Qds using watermelon peel waste have antimicrobial, antioxidant, and anticancer activities with high biocompatibility.