# Biosynthesis of Zinc Oxide Nanoparticles Using Seaweed: Exploring Their Therapeutic Potentials
## 4 Discussion
muticum_ extract ranged from 15.66 to 27.15 nm, with a mean particle size of 20.39 nm. The ZnO-NPs formed using the _U. intestinalis_ extract ranged from 32.16 to 48.25 nm, with a mean particle size of 42.27 nm [43]. _S. muticum_ aqueous extract is engaged in the synthesis of hexagonal ZnO-NPs with sizes ranging from 3 nm to 57 nm and an average size of 42 nm. In the study by ref. [41], a hexagonal wurtzite structure with an average size of 42.6 nm was visible in the TEM images of the biosynthesized ZnO-NPs. The morphology was composed of stacked rectangular particles without aggregation, which may be connected to the biochemical characteristics of _Ericaria cinita_ (Phaeophyceaeae). Any particle in suspension will display a zeta potential: a physical characteristic that indicates a particle's long-term stability. The zeta potential, which measures a particle's surface potential, is affected by changes at the particle's interface with the dispersing medium. The adsorption of ionic species from the aqueous dispersion medium or the dissociation of functional groups on the particle's surface can both cause these modifications [44]. Good physical and chemical stability of the colloidal solution depends on a relatively high value of the zeta potential, because large repulsive forces tend to prevent aggregation produced by inadvertent collisions of nearby nanoparticles. The zeta potential signal of highly cationic and highly anionic nanoparticles is characterized as being larger than +30 mV or less than 30 mV, respectively [45]. Based on this connection, the ZnO-NPs biosynthesized using _U. lactuca_, _S. muticum_, and _U. intestinalis_ were thought to be substantially anionic, which is crucial for biological applications. Refs [46; 47] reported that their zeta potential analysis verified the stability of nanoparticles that were biosynthesized using seaweed. Numerous researchers have reported on the antibacterial properties of biologically produced ZnO-NPs [48]. The ZnO-NPs produced in the current study using different seaweeds demonstrated potent antifungal action against two fungal strains, _Aspergillus niger_ and _Candida albicans_, as well as two multidrug-resistant bacterial strains, _K. pneumoniae_ and _E. coli_. This suggests that the results are noteworthy. This is important, since many bacterial and fungal strains have developed multidrug resistance as a result of the extensive usage of numerous synthetic antibacterial drugs. Generally, the ZnO-NPs concentrations increased in tandem with the inhibitory zone's diameter [10]. ZnO-NPs produced using seaweed have a large surface area-to-volume ratio, which may have an inhibitory effect. Alternatively, the positive charge of the ZnO-NPs may interact with the negatively charged microbial membrane, affecting intracellular protein leakage and cell membrane permeability, both of which inhibit growth [7]. Moreover, NPs inhibit cell proteins, stopping the growth of bacteria by combining with thiol (-SH) groups. Furthermore, this inhibition is most likely due to the interactions of the ZnO-NPs with the phosphorous group in DNA, which stops protein synthesis and DNA replication. In general, nanoparticles (NPs) can impact biological reactions by generating reactive oxygen species (ROS), which can damage cellular constituents such as proteins, DNA, and lipids, ultimately impeding growth [41]. Antioxidants diminish various diseases, including infections, ischemia, and infections caused by diabetes, cancer, and cardiovascular disease by converting reactive oxygen species (ROS) into non-toxic compounds, inhibiting their negative effects [49]. The DPPH scavenging method used in this work proved that ZnO-NPs have antioxidant activities because they have functional groups on their surface. The higher the sample's DPPH radical scavenging activity, which is a stable radical with a nitrogen core, the greater the sample's antioxidant activity [50]. The biosynthesized ZnO-NPs' quantitative total antioxidant capacity (TAC) was ascertained using a phosphor-molybdenum assay.