Plants and Microbes Emerge as Green Factories for Making Nanoparticles

Nanoparticles have quietly become one of the most transformative tools in modern science, powering everything from cancer therapies to water purifiers. Yet the way most of them are made has long been an environmental liability. Conventional synthesis routes rely on toxic reducing agents such as sodium borohydride, energy-intensive furnaces, and organic solvents that leave behind hazardous by-products. A comprehensive review published in Discover Green Chemistry by Shoaeb Mohammad Syed and colleagues at Dayanand College of Pharmacy in Latur, India, argues that a quieter revolution is underway: the use of plants, bacteria, fungi, yeast, and algae as living nanofactories that can assemble metal and metal oxide nanoparticles under mild, aqueous, and remarkably gentle conditions.

The core chemistry is elegant in its simplicity. Plant extracts are rich in phytochemicals—polyphenols, flavonoids, tannins, terpenoids, alkaloids, and proteins—that perform a dual role. First, they donate electrons to dissolved metal ions, reducing silver nitrate or chloroauric acid into neutral atoms that nucleate into nanoscale clusters. Second, the same biomolecules adsorb onto the growing particle surfaces, acting as capping agents that prevent aggregation and confer colloidal stability. The review emphasizes that this dual functionality means a single leaf extract can replace both the reducing agent and the stabilizer that would otherwise require two separate synthetic chemicals. Screening studies cited in the review show that many medicinal plants, not just a handful of exotic species, can reliably produce stable silver nanoparticles, with extracts such as Aloysia citrodora demonstrating reproducible synthesis and measurable biological activity.

Microorganisms take an alternative route to the same destination. Bacteria such as Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa, along with fungi like Aspergillus niger, use reductase enzymes and cell-wall proteins and polysaccharides to convert metal salts into nanoparticles either inside the cell or, more usefully for industry, in the surrounding culture medium. Extracellular synthesis is preferred because it simplifies downstream purification and scales more easily. The review notes that culture conditions—growth medium composition, incubation temperature, pH, and precursor concentration—exert strong control over particle size, shape, and surface functionality, giving microbial systems an edge in uniformity for therapeutic and antimicrobial applications. Algae add a further dimension: their extraordinary capacity to hyperaccumulate heavy metal ions, combined with a biochemical arsenal of carbohydrates, pigments, vitamins, and bioactive compounds, positions microalgae as particularly promising and cost-effective nano-factories, a field the authors describe as phyco-nanotechnology.

What determines the final properties of a green-synthesized nanoparticle? The review is emphatic that the answer lies in the reaction parameters. Extract composition, pH, temperature, metal ion concentration, and incubation time all shape particle size, morphology, and stability. Extracts rich in biopolymers tend to yield particles with superior colloidal stability and functional performance in biomedical settings. A striking mechanistic insight highlighted by the authors is the formation of a biomolecular corona: surface-bound proteins, polyphenols, and carbohydrates adsorb onto the nanoparticle and dynamically define its biological identity. This corona, rather than the pristine metal core, governs cellular uptake, biodistribution, toxicity, and overall bioactivity—meaning that understanding corona formation is critical for predicting how green-synthesized silver nanoparticles will behave in vivo.

Characterization is where the field shows both its rigor and its weaknesses. The standard toolkit includes UV–visible spectroscopy, which tracks surface plasmon resonance to confirm nanoparticle formation and monitor size evolution; X-ray diffraction, which reveals crystal lattice structure; Fourier-transform infrared spectroscopy, which identifies the amine, carbonyl, and thiol functional groups responsible for capping; and scanning and transmission electron microscopy, which resolve particle morphology down to the nanometer scale. Energy-dispersive spectroscopy confirms elemental composition. But the review delivers a pointed critique: many studies rely on a single analytical technique, report averaged values without adequate statistical treatment, and rarely correlate synthesis parameters with structural characteristics and functional performance. This inconsistency makes cross-study comparison difficult and obscures batch-to-batch variability, undermining the reproducibility that clinical and industrial translation demands.

The applications surveyed are strikingly broad. In medicine, green-synthesized silver nanoparticles exhibit broad-spectrum antimicrobial effects against bacterial and fungal pathogens, with documented success in wound healing and infection treatment, though activity varies considerably with particle size, surface chemistry, and biological source. Gold nanoparticles, prized for their unique optical absorption and biocompatibility, serve as drug and gene delivery vehicles and as agents in photothermal cancer therapy, where they convert light into localized heat that kills tumor cells. Iron oxide nanoparticles are being explored as contrast agents for magnetic resonance imaging, while selenium-based particles show antioxidant and anti-inflammatory activity in dermatological disease models, with studies measuring cytokine modulation offering stronger evidence of disease-modifying effects than purely phenotypic observations.

Beyond the clinic, the review highlights environmental and agricultural frontiers. Green-synthesized nanoparticles demonstrate strong adsorption and photocatalytic degradation of pollutants in water and soil, including dye decolorization and antibiotic breakdown. In agriculture, nanofertilizers promise improved nutrient use efficiency and reduced fertilizer runoff, while nanopesticides—such as neem-derived formulations—offer targeted pest control with lower chemical loads on soil and water. Antimicrobial nanoparticles are also finding roles in food packaging and textiles. Yet the authors temper this enthusiasm with caution: nanoparticle recovery, environmental persistence, soil accumulation, effects on non-target organisms, and long-term consequences for crop ecosystems remain insufficiently studied, and results often conflict across different crops, soil types, and concentrations.

The review also examines phytotoxicity with unusual nuance, since the same nanoparticles promoted as agricultural enhancers can harm plants under the wrong conditions. Particles smaller than roughly 20 nanometers penetrate root tissues more easily, and their high surface-to-volume ratio drives reactivity, oxidative stress, and membrane damage. Shape matters too: high-aspect-ratio particles interact differently with cell surfaces than spheres, altering adhesion, uptake, and ion release. Dose-response relationships are clear—low to moderate concentrations may even stimulate growth, while higher doses overwhelm plant defenses, generating reactive oxygen species, chlorosis, and biomass loss. Crucially, these effects are combinatorial rather than additive: a particle that is harmless or beneficial in one species can be lethal in another, depending on cuticle thickness, root anatomy, antioxidant capacity, and metal detoxification machinery.

The honest accounting of limitations may be the review’s most valuable contribution. Biological sources are inherently variable—plant extract chemistry shifts with species, growth conditions, season, and extraction method, producing inconsistent particle size, shape, and yield. Precise control of pH, temperature, and concentration is harder than in chemical synthesis, threatening batch-to-batch consistency. The biomolecules responsible for reduction and stabilization are often incompletely identified, complicating mechanistic understanding, and purification from complex biological matrices can alter surface properties. Scaling up remains constrained by contamination risks in microbial systems and the challenge of maintaining nanoparticle stability over time. The authors argue that standardized protocols, full-scale characterization, systematic toxicological profiling, and regulatory readiness must be integrated into future development frameworks before green nanotechnology can move reliably from laboratory benches to clinics and factories.

Looking forward, the review sketches a roadmap that pairs optimism with rigor. Deeper mechanistic insight—aided by omics technologies and computational modelling—should enable more predictable and scalable synthesis, while good manufacturing practice-compliant production of biogenic nanoparticles could accelerate their adoption in drug delivery, diagnostics, biosensing, and targeted therapeutics. Their photocatalytic prowess points toward sustainable environmental cleanup at industrial scale. The central message is that green synthesis is no longer a niche curiosity but a genuine contender to replace hazardous conventional methods, provided the field embraces the standardization, comparative study design, and safety validation that separate promising laboratory results from real-world impact. If it does, the humble leaf, bacterium, and alga may become the preferred chemical plants of the nanotechnology age.

Subject of Research: Green synthesis of metal and metal oxide nanoparticles using plant extracts and microorganisms

Article Title: A comprehensive review of green synthesis methods and applications of nanoparticles derived from plant extracts and microorganisms

Article References: Syed, S. M., Kulkarni, S., Patil, M., & Satpute, K. (2026). A comprehensive review of green synthesis methods and applications of nanoparticles derived from plant extracts and microorganisms. Discover Green Chemistry, 1(1), Article 6. https://doi.org/10.1007/s44509-026-00006-2

Image Credits: AI Generated

DOI: 10.1007/s44509-026-00006-2

Keywords: green synthesis, nanoparticles, plant extracts, microorganisms, silver nanoparticles, gold nanoparticles, algae, biomolecular corona, photocatalysis, nanofertilizers, antimicrobial, environmental remediation