The central insight of the review is that everything hinges on excited-state dynamics. When a carbon dot absorbs a photon, an electron is promoted from the ground singlet state to an excited singlet level, then rapidly relaxes to the lowest excited singlet state. From there, three competing pathways determine the fate of the energy: radiative fluorescence, non-radiative relaxation that releases heat, or intersystem crossing into the triplet manifold, which enables the production of reactive oxygen species. The relative rates of these processes, described by the rate constants for fluorescence, non-radiative decay, and intersystem crossing, dictate whether a given carbon dot behaves as an imaging agent, a photothermal heater, or a photosensitizer.

Photothermal therapy relies on the second pathway. Carbon dots that channel absorbed energy, particularly in the near-infrared window between 700 and 1100 nanometres where tissue penetration is deepest, dissipate it as localized heat through vibrational relaxation and phonon generation. Reported photothermal conversion efficiencies for carbon dots typically range from 20 to 50 percent, below the values above 60 percent achievable with gold nanorods, but the review argues that carbon dots compensate with biodegradability, lower cytotoxicity, scalable synthesis, and superior water dispersibility. Hybrid materials such as carbon dot reduced-graphene-oxide composites have pushed efficiencies beyond 45 percent through plasmonic coupling and improved charge transfer.

Photodynamic activity follows a different logic. Here the triplet state is the key intermediate, because its long lifetime provides the temporal window for energy or electron transfer to molecular oxygen. In the Type II pathway, energy transfers directly from the excited triplet carbon dot to ground-state oxygen, generating singlet oxygen, the cytotoxic species central to conventional photodynamic therapy. In the Type I pathway, electrons or hydrogen atoms are transferred instead, producing superoxide and hydroxyl radicals. The review stresses that Type I chemistry is more tolerant of the hypoxic conditions found in solid tumours, although it is not fully oxygen-independent, since superoxide formation still requires molecular oxygen as the terminal electron acceptor.

The engineering levers that tip these competing pathways are remarkably accessible. Nitrogen doping introduces electron-rich active sites that enhance fluorescence and catalytic activity, while sulfur and phosphorus doping alters surface charge and extends light absorption. Heavier atoms such as iodine, selenium, and manganese strengthen spin-orbit coupling through the heavy-atom effect, accelerating intersystem crossing and boosting singlet oxygen yields that pristine carbon dots cannot achieve alone. Donor-acceptor structures built through surface functionalization narrow the singlet-triplet energy gap, and polymer passivation with polyethylene glycol or polyethylenimine improves water solubility, biocompatibility, and drug-conjugation chemistry. PEI-functionalized dots, rich in amine groups, have proven particularly effective in antimicrobial photodynamic therapy.

Crucially, the review emphasizes that photothermal and photodynamic outputs compete for the same excited-state population. Excessively rapid non-radiative decay increases heat release but shortens the excited-state lifetime and suppresses reactive oxygen generation, while highly emissive systems lose energy as fluorescence before either heat or triplet formation becomes efficient. Rational design therefore demands a careful kinetic balance, especially for multifunctional dots expected to deliver both heat and oxidative damage under a single excitation wavelength. Nitrogen and sulfur co-doped dots that absorb in the near-infrared while simultaneously forming reactive oxygen species exemplify this dual-modal strategy.

The application landscape is strikingly broad. In oncology, nitrogen-doped carbon dots prepared from folic acid precursors have targeted folate receptor-overexpressing cancer cells and driven complete tumour regression under 808-nanometre laser irradiation in animal models. Heat from photothermal therapy can trigger immunogenic cell death, releasing tumour antigens that, combined with immune checkpoint inhibitors, amplify systemic anti-tumour immunity in the emerging field of photoimmunotherapy. Against antibiotic-resistant bacteria, nitrogen-doped dots under 808-nanometre irradiation have reduced viability of E. coli and Staphylococcus aureus by more than 99.9 percent within minutes, with heat helping reactive oxygen species penetrate biofilms.

Environmental and agricultural uses extend the same photochemistry in different directions. Carbon dots generate singlet oxygen, hydroxyl radicals, and superoxide under visible or near-infrared light to degrade persistent pollutants such as synthetic dyes, antibiotics, and endocrine disruptors; sulfur- and nitrogen-loaded dots completely broke down tetracycline and chloramphenicol within thirty minutes under simulated sunlight. Paper-based sensors built from carbon dots detect mercury at levels as low as 0.1 micrograms through visible fluorescence quenching, and smartphone-assisted fluorescence readers now enable low-cost field measurements. In crop protection, sunlight-activated dots produce reactive oxygen species that disrupt the membranes of phytopathogens such as Xanthomonas, Pseudomonas, and Botrytis cinerea, offering a pesticide-free alternative derived from agricultural waste like citrus peels and rice husks.

The review is candid about the barriers standing between laboratory promise and real-world impact. Batch-to-batch variability arising from precursor composition, reaction temperature, purification methods, and the inherent chemical inconsistency of biomass feedstocks produces apparently similar materials with markedly different properties. Inconsistent performance metrics, unreliable reactive oxygen species assays prone to false positives from probe adsorption and inner-filter effects, shallow optical penetration, incomplete mechanistic understanding, and limited long-term safety data all hinder translation. No carbon-dot phototherapy platform has yet received regulatory approval, and ecotoxicity studies show that zebrafish embryos exposed to high concentrations can suffer hatching retardation and developmental anomalies.

The path forward, the review argues, runs through standardized synthesis and reporting protocols, intrinsically near-infrared-II-active carbon dots in the 1000 to 1700 nanometre window, scalable good-manufacturing-practice production, comprehensive chronic toxicology, and field-scale validation of agricultural applications. Artificial intelligence and machine learning are expected to accelerate the search for optimal precursor and doping combinations by predicting structure-property relationships from large datasets. If those pieces come together, carbon dots could anchor a genuinely integrated platform spanning diagnosis, therapy, and environmental stewardship, a prospect few single material classes can credibly claim.

Subject of Research: Structure-property relationships and excited-state photophysics of carbon dots for photothermal and photodynamic applications

Article Title: Structure property relationships and excited state photophysics of carbon dots for photothermal and photodynamic applications

Article References: Anku, W. W. (2026). Structure property relationships and excited state photophysics of carbon dots for photothermal and photodynamic applications. Discover Chemistry, 3(1), Article 476. https://doi.org/10.1007/s44371-026-00928-7

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00928-7

Keywords: carbon dots, photothermal therapy, photodynamic therapy, reactive oxygen species, intersystem crossing, nanomaterials, heteroatom doping, singlet oxygen, photocatalysis, biomedicine, environmental remediation, agriculture

The physical foundation rests on two nonlinear effects that emerge whenever acoustic waves interact with suspended matter. The first is the acoustic radiation force, which arises from momentum transfer between scattered waves and particles. When a sound wave encounters a microscopic object, part of its energy is scattered, and this exchange of momentum pushes the particle in predictable directions. The second mechanism is acoustic streaming, a steady fluid flow generated by the viscous dissipation of acoustic energy. While an ideal fluid would simply oscillate back and forth with the passing wave and return to rest, real fluids with viscosity break this time-reversal symmetry, producing net flows that can be harnessed for mixing, pumping, and propulsion. Together, these two forces form what the review describes as a shared physical language underlying every acoustic manipulation system, whether it is levitating a droplet in mid-air or propelling a bacterium-sized robot through a blood vessel.

The choice of acoustic device architecture fundamentally shapes what a system can do. Bulk acoustic waves, typically generated by piezoelectric transducers vibrating at frequencies below 10 megahertz, penetrate deeply into tissue and are well suited for large-scale manipulation. Surface acoustic waves, created by interdigital transducers on piezoelectric substrates such as lithium niobate, operate at higher frequencies and offer much finer spatial resolution but shallower penetration. Between these extremes, gigahertz resonators push spatial resolution to submicron levels, while phased arrays of dozens or hundreds of independently addressable elements can dynamically sculpt complex three-dimensional acoustic fields in real time. Acoustic metasurfaces and holographic lenses offer a passive alternative, encoding intricate wavefront patterns into engineered structures that shape sound without bulky electronics. Each architecture occupies a distinct position in the trade-off space between penetration depth, spatial resolution, power requirements, and system complexity.

Perhaps the most striking demonstration of acoustic control is levitation, in which radiation forces counteract gravity to suspend objects in mid-air without any container. Single-axis levitators can hold droplets steady for nanoparticle self-assembly experiments, eliminating the coffee-ring artifacts that plague conventional drying. More sophisticated multiaxis systems and phased-array platforms can transport elongated objects along arbitrary three-dimensional paths, and holographic acoustic tweezers have even been integrated with visual displays and haptic feedback to create levitating volumetric interfaces. The review notes that the principal bottleneck lies in the trade-off between trapping stiffness and workspace size: adding more transducer elements improves spatial control but dramatically increases cost and complexity, while most current systems can still manipulate only one or a few objects at a time.

In liquid environments, acoustic manipulation reaches its greatest practical maturity. Acoustic tweezers based on standing surface acoustic waves can trap, translate, and rotate individual cells with remarkable precision, and recent joint subarray systems have achieved full six-degree-of-freedom control of single cells by independently activating different transducer frequencies. Separation technologies exploit the fact that radiation forces scale with particle volume while streaming drag scales with particle radius, creating a natural size-dependent sorting mechanism. Tilted-angle standing surface acoustic wave devices have demonstrated separation efficiencies exceeding 95 percent for cells and microparticles, and acoustofluidic systems have been developed to remove donor-specific antibodies from blood in transplantation settings. At the nanoscale, oscillating microbubble arrays have achieved rapid, high-purity isolation of exosomes from whole blood in approximately three minutes, a capability with direct implications for liquid biopsy and cancer diagnostics.

Beyond sorting and trapping, acoustic fields can organize biological matter into functional architectures. Standing wave fields generate periodic lattices that pattern cells into ordered arrays, while Faraday wave platforms exploit low-frequency interfacial oscillations to assemble heterogeneous cell populations into spatially defined structures. Acoustic holography overcomes the inherent periodicity of standing waves by encoding arbitrary three-dimensional wavefront patterns into engineered plates or programmable metasurfaces, enabling the fabrication of complex tissue constructs. Researchers have used these approaches to build aligned muscle tissue within collagen hydrogels, construct hepatic lobule models that recapitulate key liver functions in vitro, and form vascular networks within hydrogels by combining surface and bulk acoustic waves. The review emphasizes that maintaining pattern fidelity at high throughput remains a major challenge, as does developing predictive models for the competition between radiation forces and interparticle Bjerknes forces in dense assemblies.

The most forward-looking section of the review concerns acoustically driven microswimmers, tiny robots that convert acoustic energy into autonomous locomotion. At the microscale, where viscous forces utterly dominate over inertia, the scallop theorem dictates that simple reciprocal motions cannot produce net propulsion. Effective swimmers must therefore break symmetry, either through geometric or density asymmetry, through acoustic cavitation generated by oscillating bubbles, or through sharp-edge oscillations inspired by the flagella of bacteria and sperm. Bubble-based swimmers are particularly powerful because resonantly oscillating gas pockets generate intense localized microstreaming that can overcome the drag of high-viscosity biological fluids, and their intrinsic acoustic impedance mismatch with surrounding tissue makes them visible to standard ultrasound imaging, enabling real-time tracking in vivo.

Recent in vivo demonstrations illustrate how quickly this field is maturing. Biodegradable hydrogel microrobots with eccentric dual-orifice cavities have been navigated by magnetic fields and tracked by ultrasound in mouse bladders bearing orthotopic tumors, combining propulsion, imaging, and drug delivery in a single platform. Acoustic microbubble swarms have been steered through branched cerebral vessels in living mice using transducer arrays mounted on the skull, representing the first evidence of robust upstream motion and wall adhesion in the brain vasculature. Model-based reinforcement learning frameworks have been introduced to enable closed-loop navigation of ultrasound-driven microrobots, with success rates approaching 90 percent in simulated-to-real transfer experiments. These advances mark a transition from task-specific laboratory demonstrations toward adaptive, intelligent swarm systems capable of operating in the complex, dynamic environments of living organisms.

Despite the remarkable progress, the review is candid about the obstacles separating laboratory demonstrations from clinical reality. The acoustic diffraction limit imposes a fundamental bound on spatial resolution that prevents subcellular targeting, and higher frequencies that improve resolution also increase attenuation and reduce penetration depth. Acoustic biocompatibility is strongly parameter-dependent: excessive exposure can induce thermal damage, streaming-induced shear stress, and cavitation that compromise cell viability and membrane integrity. Sonogenetics, which uses ultrasound to activate genetically engineered mechanosensitive ion channels, requires exceptionally precise pressure control because the therapeutic window between effective neuromodulation and adverse biological responses is narrow. In the vasculature, blood flow can exceed acoustic trapping forces by orders of magnitude, and tissue heterogeneity distorts acoustic fields in ways that are difficult to predict.

The path forward, the authors argue, requires coordinated advances across physics, materials science, biology, and engineering. Near-term priorities include standardized acoustic exposure protocols, cell-type-specific safety databases, and chip-scale integration with closed-loop control in physiologically relevant models. Mid-term goals encompass real-time three-dimensional imaging for navigation, validation in large-animal models, and the development of biodegradable or retrievable microswimmers supported by regulatory-grade safety assessments. Long-term, the field aims toward fully implantable or ingestible acoustic microsystems with artificial-intelligence-driven adaptive control for targeted therapy. Whether acoustic manipulation evolves from a specialized laboratory technique into a transformative clinical and industrial platform will depend on sustained interdisciplinary collaboration and on solving the persistent engineering challenges of manufacturing reproducibility, dosage control, and standardized performance benchmarking that currently separate proof-of-concept from practice.

Subject of Research: Micro- and nanoscale acoustic manipulation of particles and acoustically driven microswimmers

Article Title: Micro/Nanoscale Acoustic Manipulation: From Particle Control to Autonomous Microswimmers

Article References: Chu, J., Zhang, L., Wang, X., Li, W., & Liu, Y. (2026). Micro/Nanoscale Acoustic Manipulation: From Particle Control to Autonomous Microswimmers. Advanced Science, 13(55), Article e77557. https://doi.org/10.1002/advs.77557

Image Credits: AI Generated

DOI: 10.1002/advs.77557

Keywords: acoustic manipulation, acoustofluidics, acoustic radiation force, acoustic streaming, microswimmers, microrobots, acoustic tweezers, surface acoustic waves, bulk acoustic waves, acoustic levitation, drug delivery, biomedicine

Natural deep eutectic solvents occupy a curious place in chemistry. They arise when certain natural compounds, typically a hydrogen bond donor and a hydrogen bond acceptor such as an amino acid, a sugar, an organic acid or choline chloride, are mixed in specific ratios. The resulting mixture behaves in a striking way: instead of crystallizing as its individual components would, it melts or remains liquid at temperatures far lower than either ingredient alone, forming a stable eutectic liquid. The concept gained prominence in 2011, when researchers proposed in Plant Physiology that such mixtures might be the missing link in understanding cellular metabolism, since cells are crowded with exactly these kinds of small molecules. By 2013, Dai and colleagues had framed NADES as a new potential medium for green technology, and the field has expanded steadily since.

What makes NADES attractive to pharmaceutical scientists is the combination of properties they bring to the table. They are largely non-toxic, biodegradable and inexpensive to produce, often from food-grade or metabolite-grade starting materials. They can be synthesized sustainably by several methods, and their characteristics can be tuned, for example by adjusting water content, which alters viscosity and other physicochemical parameters. Studies have shown that adding water tailors NADES properties to facilitate applications, and that these solvents even modulate the thermal behavior of water, which has led to their exploration as non-toxic cryoprotective agents. Crucially for drug delivery, NADES excel at dissolving poorly water-soluble molecules, a chronic bottleneck, since a large fraction of active pharmaceutical ingredients and phytochemicals exhibit solubility so low that oral absorption becomes unreliable.

The review’s central argument is that pairing NADES with nanocarriers multiplies these advantages. Conventional drug delivery systems face a familiar litany of shortcomings: lack of targeted delivery, fluctuation in drug release, possible side effects, frequent dosing requirements, environmental hazards and high costs. Nanocarrier-based delivery already offers substantial rewards over conventional systems, but the carriers themselves often rely on solvents and excipients that raise toxicity or environmental concerns. The authors highlight, for instance, pro-inflammatory concerns that have been raised with lipid nanoparticles, the platform behind mRNA vaccines, and safety questions surrounding these systems for nucleic acid delivery. NADES-integrated nanocarriers, by contrast, promise low toxicity, biodegradability, cost-effectiveness and tunability, while enhancing the therapeutic efficacy of bioactive drugs.

The technical landscape covered in the review is broad. Solid lipid nanoparticles and nanostructured lipid carriers, established platforms for improving bioavailability and enabling targeted therapy, have been combined with NADES to encapsulate compounds such as curcumin, a notoriously insoluble but biologically active polyphenol. One 2024 study reported enhanced curcumin delivery and stability through NADES-based niosomes, vesicular carriers assembled from non-ionic surfactants. Another line of work integrated natural deep eutectic solvents into nanostructured lipid carriers with an explicitly industrial outlook, and a 2025 study used green nanostructured lipid carriers and NADES to solubilize extracts from Brazilian Cerrado byproducts, boosting antioxidant potential and simultaneously valorizing agricultural waste. Thermosensitive niosomes have even been designed from eutectic mixtures of natural fatty acids, adding stimulus-responsive behavior to the toolkit.

Polymeric systems feature prominently as well. Researchers have synthesized biodegradable poly(2-hydroxyethyl methacrylate) using NADES for sustainable cancer drug delivery, and fabricated green poly(vinyl alcohol) nanofibers with NADES for fast-dissolving drug delivery. Doxorubicin, a mainstay chemotherapy agent, has been loaded onto functional graphene nanocarriers using ternary deep eutectic solvent systems. A targeted solid-liquid polymer carrier supported by NADES has been explored for breast cancer therapy. Beyond polymers, the review describes NADES-based surfactant-free microemulsions that solubilize and extract curcumin from turmeric, and eutectogels, gel networks formed within deep eutectic solvents, that have been engineered for colon-targeted delivery of mesalazine, an anti-inflammatory drug used in inflammatory bowel disease. Smart supramolecular eutectogels have been designed for pH- and thermo-responsive transdermal delivery of anticancer curcumin, illustrating how the platform can incorporate environmental triggers.

The application domains extend well beyond cancer. In wound care, a curcumin emulgel enriched with a camphor-menthol-based deep eutectic solvent demonstrated wound healing efficacy, and NADES-based chitosan hydrogels have been developed for enhanced photoimmunomodulation treatment of various wounds. Nano-electrospun membranes combining NADES with Platostoma palustre polysaccharides and polyvinyl alcohol showed transdermal properties and bioactivity. In dermatology, a deep eutectic solvent-assisted kaempferol hydrogel emerged as a promising therapeutic approach for psoriasis-like skin inflammation. Ocular medicine has joined in too: green-sourced polyphenols delivered through a sustainable NADES-based approach have been proposed for dry eye disease treatment. Cosmeceutical applications include the green extraction of Rosa canina and Prunus spinosa by NADES followed by encapsulation in chitosan nanoparticles, and deep eutectic solvent nanoparticles have been used to enhance intradermal delivery of hyaluronic acid for anti-aging and moisturizing effects.

The mechanisms underlying these systems are as varied as the formulations. NADES can act as solubilizing media within the carrier, as structural components of the carrier itself, or as permeation enhancers that interact with biological membranes. Research into how NADES interact with artificial and natural membranes supports their role in facilitating transport across the skin and mucosal barriers. Choline chloride-malic acid NADES containing hydrophobic drugs has been studied for solubility and permeability behavior in digestive tract models, informing oral delivery design. Methotrexate solubilization and transdermal delivery have been enhanced in microemulsions with NADES screened by computational COSMO-RS methods, showing how molecular simulation can guide solvent selection. Pharmacokinetic evidence is accumulating as well: rutin dissolved in a proline-glycine NADES showed improved bioavailability after oral administration in rats, and deep eutectic solvents altered the pharmacokinetics of salvianolic acid B in rats, with acute toxicity testing performed alongside. Notably, NADES have also been shown to protect RNA from thermal degradation, and a ready-to-use lipid nanoparticle technology for nucleic acid delivery based on deep eutectic solvents has been developed, hinting at relevance for gene therapy and mRNA medicine.

Safety data, while still maturing, are encouraging. Cytotoxicity profiling of choline chloride-based NADES has been carried out, and toxicity studies of a betaine-glycerol NADES in rats have been published. A noncytotoxic, hemocompatible ion gel was prepared by self-polymerization of 2-hydroxyethyl methacrylate in a green deep eutectic solvent, and hydrogel formulations containing lidocaine have incorporated NADES to advantage. Buccal xanthan gum-hyaluronic acid eutectogels with dual anti-inflammatory and antimicrobial properties have been reported, relevant given the well-documented organ damage and gastrointestinal risks associated with long-term nonsteroidal anti-inflammatory drug use. Alginate hydrogels incorporating essential oils loaded in chitosan nanoparticles extend the platform to biomedical applications such as antimicrobial wound management.

The review is candid about the obstacles standing between laboratory promise and clinical reality. Viscosity, limited recyclability and safety data, long-term stability and scalability remain key issues for large-scale industrial application. High viscosity complicates handling, mixing and manufacturing; the recyclability of these solvents at industrial scale is not yet established; and comprehensive long-term safety and stability profiles are still being assembled. Regulatory pathways for such novel combination products also require clarification, a theme echoed in broader discussions of nanopharmaceutical quality-by-design frameworks and post-marketing surveillance. The authors frame their work as identifying these challenges, research gaps and opportunities for translating NADES-based nanocarrier technologies from laboratory scale to clinical and industrial application, and as a theoretical foundation for broader use in pharmaceutical and biomedical fields. If those gaps close, the vision is compelling: drug carriers built from the same molecular vocabulary that cells themselves use, delivering difficult medicines more safely, more sustainably and more effectively.

Subject of Research: Natural deep eutectic solvent-based nanocarriers for sustainable drug delivery

Article Title: Engineering green nanocarriers using natural deep eutectic solvents: a sustainable platform for modern drug delivery

Article References: Patil, N. B., & Gopinath, S. C. B. (2026). Engineering green nanocarriers using natural deep eutectic solvents: a sustainable platform for modern drug delivery. Journal of Nanoparticle Research, 28(9), Article 233. https://doi.org/10.1007/s11051-026-06749-0

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06749-0

Keywords: natural deep eutectic solvents, NADES, nanocarriers, drug delivery, green chemistry, lipid nanoparticles, niosomes, eutectogels, curcumin, biomedicine, pharmaceuticals, sustainability

Secondary metabolites occupy a curious place in biology. Unlike primary metabolites such as sugars, amino acids, and nucleotides, which are essential for growth and reproduction, secondary metabolites are optional extras from the organism’s point of view. Yet they are anything but optional for the ecosystems around them. Alkaloids deter herbivores, flavonoids shield leaves from ultraviolet radiation, tannins inhibit microbial attacks, and terpenoids perfume flowers to attract pollinators. What has captured the attention of nanotechnologists is that many of these compounds carry functional chemical groups—hydroxyl, carbonyl, and carboxyl moieties among them—that are ideally suited to mediating the transformation of metal salts into nanoscale particles suspended in water.

The core chemistry is conceptually simple. When an extract rich in phenolic acids or flavonoids is mixed with, say, a silver nitrate solution, the electron-donating capacity of the metabolites reduces silver ions to metallic silver atoms. These atoms then nucleate and grow into clusters, a process classically described by the LaMer model of monodisperse hydrosol formation, first articulated in 1950. Crucially, the same metabolites that drive the reduction also adsorb onto the surfaces of the growing particles, forming a stabilizing shell that prevents the clusters from clumping together into bulk precipitate. This dual role—reductant and capping agent in one molecule—is what makes plant and microbial extracts so attractive as single-pot synthesis media.

The review catalogs the major phytochemical players in detail. Flavonoids such as hesperidin, naringin, and diosmin have been shown to generate silver nanoparticles with demonstrable antibacterial effects. Tannins, the astringent polyphenols abundant in many woody plants, can reduce gold salts to produce nanoparticles that have been coated onto cotton textiles for the catalytic degradation of Congo red dye. Terpenoids have been credited with mediating a range of metal and metal oxide syntheses with biomedical relevance. Saponins, alkaloids, and phenolic acids round out the roster, each contributing characteristic functional groups that influence how quickly ions are reduced and how the resulting particles are shaped and stabilized.

Perhaps the most consequential point the authors emphasize is that the identity and concentration of the metabolites directly govern the physical properties of the nanoparticles that emerge. Particle size, morphology, surface charge, and colloidal stability all depend on which molecules are present and in what proportions. Because different plant species, and even different tissues within the same plant, harbor distinct metabolic profiles, the choice of extract becomes a design variable. A leaf extract rich in one class of polyphenol may yield small, spherical silver particles, while a seed extract dominated by tannins may produce larger, anisotropic structures. This tunability, the review suggests, is both an opportunity and a challenge: it offers enormous flexibility but demands careful standardization of extracts if reproducible, scalable production is the goal.

The advantages over conventional synthesis routes are laid out clearly. Physical methods such as laser ablation and sputtering, and chemical methods relying on borohydrides, hydrazine, or organic solvents, typically demand high energy inputs, generate toxic byproducts, or leave hazardous residues on particle surfaces. Green synthesis with secondary metabolites operates at or near ambient conditions, uses water as the preferred solvent, and produces particles whose organic coating is often biocompatible by default. That last point matters enormously for biomedical applications, where residual chemical surfactants can compromise cell viability and trigger inflammatory responses. The review notes that reduced toxicity, lower energy requirements, and cost-effectiveness are the recurring advantages cited across the literature it surveys.

On the application side, the breadth is striking. Biologically synthesized metal and metal oxide nanoparticles have demonstrated antimicrobial activity against bacterial and fungal pathogens, antioxidant capacity relevant to oxidative-stress disorders, and anticancer and anti-inflammatory effects documented across numerous cell and preclinical studies. Silver nanoparticles made with potato steroidal alkaloids have been deployed against phytopathogenic fungi, while zinc oxide nanoparticles biosynthesized through microbial routes show antimicrobial promise. In environmental remediation, iron-based nanoparticles produced with plant extracts serve as adsorbents for water treatment, and silver nanoparticles paired with nano-fibrillated cellulose from citrus peel waste have been used to remove cadmium and chromium from contaminated water. Catalytic degradation of industrial dyes, colorimetric detection of metal ions, and biosensing round out the environmental and analytical applications.

Agriculture emerges as a particularly promising frontier. The review highlights the role of metal and metal oxide nanoparticles in crop stress management, including the mitigation of heavy metal toxicity in plants, as well as nanosensing of biotic threats. Nanoparticles are being explored as components of fertilizers and pesticides, as delivery vehicles in precision farming, and as tools in plant biotechnology, including the emerging use of nanoparticles to advance CRISPR-Cas genetic engineering of plants. The biocompatibility and colloidal stability conferred by metabolite capping layers make these particles plausible candidates for agricultural formulations that must survive field conditions without harming soil microbiota. The authors also point to biomedical devices and food technology as sectors where green-synthesized particles could find roles, from antimicrobial fabrics to food preservation systems.

The review does not shy away from the field’s limitations. Reproducibility remains a persistent concern, since natural extracts vary with season, geography, plant age, and extraction protocol. The precise molecular mechanisms by which particular metabolites reduce particular metal ions are still being worked out, and scaling laboratory successes to industrial production volumes poses engineering challenges that green chemistry has not yet fully solved. Studies of fungal production of copper oxide nanoparticles, for example, have taken a physiological and metabolic approach to identify which secondary metabolites are actually responsible, underscoring how much fundamental biochemistry remains to be mapped. Toxicological questions about the nanoparticles themselves, particularly in food applications, also demand continued scrutiny.

What the review ultimately makes the case for is a convergence of two traditionally separate domains: natural products chemistry and materials science. The authors argue that deliberately leveraging plant- and microbe-derived metabolites offers a sustainable path to scalable nanoparticle production capable of meeting global needs in medicine, agriculture, and environmental management. As demand for nanomaterials grows across sectors, the prospect of manufacturing them with molecules that organisms already produce—rather than with petrochemical reagents and energy-hungry reactors—represents exactly the kind of cross-disciplinary innovation that green chemistry advocates have long promised. The next step, the review implies, is moving from elegant laboratory demonstrations to standardized, mechanistically understood, industrially viable processes, a transition that will require chemists, biologists, and engineers to speak the same molecular language.

Subject of Research: Green synthesis of metal and metal oxide nanoparticles using plant and microbial secondary metabolites

Article Title: Significance of secondary metabolites for synthesis of metal and metal oxide nanoparticles and their applications

Article References: Nazneen, S., Azra, B. H., Keerthi, M. M., Ashraf, A. M., Rajasekar, G., Rasool, A., & Anand, A. (2026). Significance of secondary metabolites for synthesis of metal and metal oxide nanoparticles and their applications. The Science of Nature, 113(5), Article 120. https://doi.org/10.1007/s00114-026-02168-2

Image Credits: AI Generated

DOI: 10.1007/s00114-026-02168-2

Keywords: secondary metabolites, green synthesis, nanoparticles, metal oxide nanoparticles, phytochemicals, flavonoids, tannins, antimicrobial, environmental remediation, biomedicine, agriculture, sustainable nanotechnology