## 4 Discussion
Hence, if the predominant morphology of platelets, and in some regions with inserts of short rods, is associated with high Zn\({}^{2+}\) concentrations, one can observe the formation of smaller, elongated, or rounded nanoparticles when decreasing the concentration. Our results indicate that an increased reaction time leads to larger size ZnO platelets and rods, with mean lengths varying from 157 nm (after 15 min reaction time) to 217 nm (after 60 min reaction time) for the highest precursor concentration (0.3488 mol/L). This trend of increasing the length with the increase in synthesis time was also observed for the second concentration (0.1744 mol/L) when a mean length of 140 nm was associated with the S2_15 sample and 165-166 nm for the other two (S2_30 and S2_60). For the latter, an increase in the platelet thickness, rather than in length (30 nm mean thickness for S2_60), was registered. Similar findings are presented in the literature but are limited to a 20 min reaction time [36]. When examining the effect of precursor concentration on particle size, it is evident that for the samples synthesized over 15 min, the trend is consistently decreasing, with the smallest particle lengths observed for S5_15. These results are in good agreement with the BET-specific surface area values, where a reduced reaction time (associated with a decrease in particle length) leads to larger specific surface areas for S1_15, S2_15, S3_15, S4_15, and S5_15 ZnO powders. The smallest SSA values were registered for S1_30 (14.8443 \(\pm\) 0.0467 m\({}^{2}\)/g) and S1_60 (14.6759 \(\pm\) 0.1356 m\({}^{2}\)/g), which have the biggest mean lengths. When discussing the effect of precursor concentration on the specific surface area, a strictly monotonic trend cannot be established. This inconsistency may be due to the change in morphology observed with decreasing Zn\({}^{2+}\) concentration, shifting from predominantly platelets and rod-like structures to rounded nanoparticles, which exhibit a higher tendency to agglomerate. Even though Gram-negative bacteria are considered easier to penetrate by external factors such as nanoparticles due to their thinner bacterial cell wall, our findings show that the Gram-positive _S. aureus_ strain was more sensitive to the antimicrobial action of ZnO than _E. coli_ or _C. albicans_. In this case, reaction time variation plays an important role, showing statistically significant differences between samples, with longer reaction times associated with decreased inhibition zone diameters. This effect becomes less pronounced with lower Zn\({}^{2+}\) precursor concentrations, as there are no statistically significant differences between the S3_15, S4_15, and S5_15 samples. These findings align with previous research conducted by [PERSON] et al. [36] and [PERSON] et al. [37] which also observed a similar trend in sensitivity. A potential explanation provided by [PERSON] and co-workers suggests that the peptidoglycan layer surrounding Gram-positive bacteria can facilitate the penetration of ZnO particles into the cell, enhancing their antimicrobial activity. In contrast, the cell wall components of Gram-negative bacteria, including lipopolysaccharidesaccharides, can mitigate this penetration, thereby reducing the effectiveness of ZnO particles [38]. While our study provides valuable insights, supporting the hypothesis that increased precursor concentration and reaction time promote more extensive crystal growth, as evidenced by the larger particle sizes, it is not without limitations, most of them deriving from the inconsistencies registered in the morphology of the obtained ZnO. Future research should address these limitations and better control the resulting shapes either by using stabilizing agents or by varying the polar character of the solvent used in the reaction. Among the main stabilizing agents studied in the literature are polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly(L-glutamic acid) (PGA) [39].