Recent Plant-Derived Bioactive Compounds for Nanoparticle Synthesis and applications: A Review

1. INTRODUCTION

Nanotechnology has developed rapidly because materials at the nanoscale exhibit unique physicochemical, optical, catalytic and biological properties. Metal and metal-oxide nanoparticles have attracted particular attention because of their high surface-area-to-volume ratio, tunable morphology and surface reactivity [1,2]. These characteristics have resulted in applications in medicine, environmental remediation, agriculture, food technology, catalysis and materials science. However, conventional physical and chemical methods for nanoparticle synthesis may require high temperatures, high energy input, organic solvents and potentially toxic reducing or stabilizing agents. These limitations have encouraged researchers to develop environmentally compatible synthesis strategies. Green synthesis using biological materials has therefore become an important alternative. Among biological sources, plants are especially attractive because they are readily available and contain a large diversity of metabolites capable of reducing metal ions and stabilizing the resulting nanoparticles. Plant extracts can function as natural reducing, capping and stabilizing systems, thereby reducing the requirement for additional synthetic chemicals [3]. Recent reviews have reported successful plant-mediated synthesis of Ag, Au and Cu nanoparticles as well as ZnO, MgO, Co₃O₄ and TiO₂ nanoparticles [4]. The chemical composition of the plant extract is particularly important in determining nanoparticle formation. Phenolic compounds, flavonoids, alkaloids, terpenoids, proteins, sugars and other biomolecules can participate in metal-ion reduction and surface stabilization. These compounds can also influence nucleation, particle growth, aggregation and surface functionality. Consequently, differences in plant species, plant part and extraction method can result in nanoparticles with substantially different sizes, shapes and biological properties. Recent research has increasingly focused on the relationship between plant phytochemicals, nanoparticle physicochemical characteristics and biological activity. A recent review of plant-mediated metal oxide nanoparticles reported that phenolics, flavonoids, alkaloids, terpenoids and proteins act as important reducing, capping and stabilizing agents, while parameters such as pH, temperature and extract concentration influence nanoparticle size, morphology and surface properties. Another recent review emphasized the importance of biological metabolites in controlling reduction, nucleation, growth and stabilization and linked these processes to antimicrobial behavior. The biological properties of plant-mediated nanoparticles are also receiving increasing attention. Antimicrobial activity is particularly important because nanoparticles can act against microorganisms through several mechanisms, including membrane disruption, reactive oxygen species generation and interference with DNA and protein synthesis [5] Antioxidant activity is another important property, particularly where plant phytochemicals remain associated with the nanoparticle surface. Recent reviews have highlighted the potential of plant-derived nanoparticles in antimicrobial therapy, wound healing, drug delivery and other biomedical applications. Recent experimental research further demonstrates this trend. Carissa spinarum leaf extract has been used for the green synthesis of Ag nanoparticles, followed by evaluation of their antioxidant and antimicrobial properties [6]. CuO NPs synthesized using Rumex nepalensis Spreng., offering insights into their potential applications in antimicrobial and antioxidant fields [7] an efficient and greener approach for the synthesis of copper oxide nano-particles using Rivina humilis whole plant extract [8].Similarly, Dillenia indica flower extract has been employed for the synthesis of Ag nanopartices, with subsequent evaluation of their structural characteristics, antibacterial activity and antioxidant potential [9]. More recently, Morus rubra leaf extract was investigated for the phytosynthesis of selenium nanoparticles and evaluation of their antioxidant, antimicrobial and anticancer properties [10]. Therefore, plant-mediated nanoparticle synthesis is evolving from a simple green alternative to chemical synthesis into a multidisciplinary approach involving phytochemistry, nanomaterials science, microbiology and biotechnology. This review focuses on the role of plant-derived bioactive compounds in nanoparticle synthesis and summarizes recent advances in their applications of plant-mediated nanoparticles.

2. Plant Bioactive Compounds Involved in Nanoparticle Synthesis

Plants contain numerous secondary metabolites that can participate in nanoparticle synthesis. Phenolic compounds and flavonoids are particularly important because their hydroxyl and other functional groups can facilitate electron-transfer reactions [11]. Phenolic acids such as gallic acid, caffeic acid, chlorogenic acid and ferulic acid can contribute to metal-ion reduction, while flavonoids such as quercetin, kaempferol, rutin and catechins can participate in both reduction and surface stabilization. Terpenoids, alkaloids, tannins, proteins, polysaccharides and sugars may also contribute to nanoparticle formation [12]. The relative contribution of these compounds depends on the plant species and extraction conditions. Because plant extracts contain multiple compounds, nanoparticle formation is generally considered a complex synergistic process rather than the action of a single reducing molecule. Flavonoids are of particular interest because a recent systematic review identified their important role in green synthesis of antimicrobial nanoparticles. Flavonoids can function as reducing and stabilizing molecules while also contributing biological activity to the resulting nanomaterials. This provides an important connection between phytochemistry and nanoparticle functionality [13].

3. Mechanism of Plant-Mediated Nanoparticle Synthesis

Plant-mediated nanoparticle synthesis can generally be described through the stages of reduction, nucleation, growth and stabilization. During the initial stage, phytochemicals present in the plant extract interact with metal ions and facilitate their reduction. The reduced species subsequently undergo nucleation and particle growth [14] Biomolecules present in the extract can adsorb onto the newly formed nanoparticle surfaces and restrict uncontrolled aggregation. The overall process can be represented in fig.1.

Figure:1. Mechanism of Plant-Mediated Nanoparticle Synthesis

The exact mechanism depends on the nature of the metal precursor and plant extract. For silver and gold nanoparticles, reduction of metal ions to elemental metal is generally involved [15]. In metal oxide systems such as ZnO and CuO, the plant metabolites participate in precursor conversion and stabilization followed by formation of the oxide phase.Synthesis parameters strongly influence the resulting nanoparticles. Changes in pH, temperature, extract concentration, precursor concentration and reaction time can modify the reduction rate and nucleation process and therefore influence particle size and morphology. Standardization of these parameters is consequently essential for reproducible synthesis.

4. Recent Plant-Mediated Nanoparticle synthesis and applications

Recent studies demonstrate the growing diversity of plants and nanoparticle systems investigated using green synthesis.

5. Characterization of Plant-Mediated Nanoparticles

Characterization is essential for confirming nanoparticle formation and understanding their physicochemical properties. UV–visible spectroscopy is commonly used to monitor nanoparticle formation and optical characteristics. FTIR spectroscopy provides information regarding functional groups associated with plant-derived molecules on nanoparticle surfaces. X-ray diffraction is used to determine crystalline structure and crystallinity, while SEM and TEM provide information about morphology and particle size. Energy-dispersive X-ray spectroscopy can confirm elemental composition, whereas dynamic light scattering provides hydrodynamic size and polydispersity. Zeta-potential measurements are useful for evaluating surface charge and colloidal stability [31]. Recent reviews emphasize that comprehensive characterization is essential for establishing relationships between synthesis conditions, nanoparticle properties and biological performance.

6. CONCLUSION

Plant-mediated nanoparticle synthesis has emerged as an environmentally friendly, cost-effective, and promising approach for producing biologically active nanomaterials. Plant extracts contain diverse phytochemicals, including phenolics, flavonoids, tannins, terpenoids, alkaloids, proteins, sugars, and organic acids, which participate in metal-ion reduction, nucleation, growth, capping, and stabilization of nanoparticles. Thus, plant extracts can act as natural reducing, capping, and stabilizing agents, reducing the dependence on hazardous chemicals used in conventional synthesis. The physicochemical characteristics of plant-mediated nanoparticles are influenced by the plant species, plant part, extraction method, phytochemical composition, metal precursor, pH, temperature, reaction time, and extract concentration. Optimization of these parameters is essential for controlling particle size, morphology, crystallinity, surface chemistry, and stability. Techniques such as UV–Visible spectroscopy, FTIR, XRD, SEM, TEM, EDX, and zeta-potential analysis are important for confirming nanoparticle formation and evaluating their properties. Plant-mediated nanoparticles demonstrate considerable antioxidant, antibacterial, antifungal, anticancer, anti-inflammatory, and photocatalytic activities. Their biological effects may result from both nanoparticle-specific properties and phytochemicals present on their surfaces. plant-mediated nanoparticle synthesis represents an important integration of green chemistry, nanotechnology, and phytochemistry, with significant potential for sustainable biomedical, environmental, agricultural, and industrial applications.

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