To verify the ability of CuO NPs to improve seed germination, four replicates of 25 and 100 seeds of tomato and lettuce were used in each treatment, respectively. First, seeds were disinfested in 1% sodium hypochlorite solution for 10 min, rinsed thoroughly with distilled water, and superficially dried with paper. Next, seeds were immersed in different concentrations of CuO NPs for 5 h in the dark: 25 mg/L, 50 mg/L, and 100 mg/L . Distilled water was used as a control (0 mg/L). After imbibition, seeds were transferred to Germitest roll papers moistened with distilled water and stored in a cultivation room at 25 ºC and 12h photoperiod. Seeds were evaluated daily until no seed germinated for three consecutive days. Seeds were considered as germinated when they presented 2 mm of radicle protrusion. At the end of the test, germination rate (%) and vigor, based on the germination speed index (GSI) were analyzed. GSI was calculated as the sum of the ratio between the number of germinated seeds per day and the respective day of observation: GSI = G1/N1 + G2/N2 + G3/N3 +•••+ Gn/Nn, where G1, G2, G3,..., Gn = number of germinated seeds on the day of observation, and N1, N2, N3,..., Nn = the number of days elapsed from sowing . At the end of the germination test, 15 seedlings from each of the four replicates were used to measure seedling growth. These measurements were made 10 days after sowing for lettuce seeds and 15 days for tomato seeds. Seedlings were randomly taken from the replicates without looking to avoid seedling selection . For seedling dry weight, the four samples were dried in an oven at 60 ºC for 48 h. Physiological data were subjected to homoscedasticity (Bartlett test) and normality (Shapiro-Wilk test) assessments. One-way ANOVA was performed, and the means were compared by Tukey's test (p ≤ 0.05). Data was expressed as the mean ± SD of the replicates. Statistical analysis was performed in R core team (2024).