# Biosynthesis of Zinc Oxide Nanoparticles Using Seaweed: Exploring Their Therapeutic Potentials
## 1 Introduction  
The creation of multifunctional nanomaterials is now a widespread trend due to their distinctive features, which may be reached by reducing particle size and increasing surface area [1]. ZnO nanoparticle applications (ZnO-NPs) are greatly expanded in this new technological era, including antimicrobial, anticancer, and antioxidant uses, among others [2]. As an n-type semiconductor, ZnO has a variety of appealing qualities, including being non-toxic, having a large band gap, giving strong chemical stability at an ambient temperature and having a high binding energy. ZnO can be manufactured in the nanometer range using traditional methods on a large scale via a variety of chemical and mechanical procedures [3]. Several limits are apparent when using these traditional methodologies, notwithstanding their applicability in the business sector. For instance, the chemical synthesis of ZnO nanoparticles involves the use of poisonous and dangerous compounds as reductants and stabilizers, whilst other processes may demand high temperatures, which consume significant energy [4]. The public becomes more aware of environmental pollution as a result, and interest in the one-pot green synthesis method increases. The preference for synthesizing ZnO nanoparticles has emerged as a result of the benefits of green approaches, such as their simplicity and inexpensive operating costs. Many naturally occurring, renewable resources, including yeast, bacteria, seaweed, and plant extract, are used for the environmentally friendly manufacture of ZnO nanoparticles in place of hazardous chemicals. These natural materials, known as \"bioresources\", are exceptionally rich in bioactive components such as amino acids, carbohydrates, and polyphenic compounds, which can act as reducing agents and prevent the creation of ZnO nanoparticles [5]. Compared to hazardous chemicals, biological substances are less toxic because they are natural and biodegradable [6]. Consequently, this green synthesis method will be considered a viable substitute for the commercial and industrial manufacture of ZnO nanoparticles in the future. With regard to their high content of biomolecules such as sugars and proteins, seaweed (marine macroalgae) is an excellent choice for use as a bioresource in the effective green production of ZnO nanoparticles [7]. Seaweed nanoparticles are relatively stable in solutions, harmless to the environment, and largely safe in a variety of fields. By virtue of the presence of lipids, proteins, and polysaccharides with different functional groups on the surfaces of their cell walls, seaweed has a substantial metal-binding capacity [8]. According to published research by ref. [9], green synthesis utilizing alga extract as a bio-reducant successfully generated ZnO nanoparticles with rod-like shapes. The research found that interaction between the zinc precursor and the possibly bioactive compounds found in the green seaweed compounds, including amine, carbonyl, and nitro groups, led to the formation of ZnO nanoparticles. It was unexpected that the seaweed-mediated ZnO nanoparticles outperformed the chemically generated ZnO nanoparticles in terms of antibacterial activity. Furthermore, ref. [10] used ZnO nanoparticles generated from _Spiurlina_ sp. (Cyanobacteria) on an ultrafiltration membrane to remove drugs. The results showed that green-produced ZnO nanoparticles improved membrane performance by increasing hydrophilicity and antifouling features. According to numerous research studies [11; 12; 13], green seaweed-derived ZnO-NPs can be utilized to inhibit the growth of bacteria and fungi that are resistant to antibiotics. According to [14], _Ulva lactuca_ (Chlorophyta) extract was used to biosynthesize zinc oxide nanoparticles. As materials for antioxidant defense against free radicals generated during metabolism, ZnO-NPs are also essential, according to ref. [15].