The researchers, led by Surendirakumar Kannaiah and Suguna Paramasivam, collected the fruit pedicel waste, known locally as sundakai kambu, from household kitchens in Pudukkottai, Tamil Nadu. After washing, shade-drying, and grinding the material into a coarse powder, they boiled ten grams of the powder in one hundred milliliters of distilled water at 65 degrees Celsius for one hour. The resulting pale-yellow extract was filtered and then added to a one millimolar solution of silver nitrate, the precursor salt supplying silver ions. Within twenty-four hours of incubation in the dark at room temperature, the mixture shifted in color from pale yellow to orange brown, a visible signature that silver ions had been reduced to metallic silver nanoparticles. The team designated the resulting material ST@AgNPs, reflecting the role of the Solanum torvum extract in their creation.

The chemistry behind this transformation lies in the phytochemical richness of the turkey berry plant. Solanum torvum, a wild relative of the eggplant consumed as a vegetable across Africa and Asia and used extensively in traditional medicine, contains abundant alkaloids, flavonoids, saponins, tannins, and glycosides. In green nanoparticle synthesis, these biomolecules perform two simultaneous jobs: they donate electrons to convert silver ions into neutral silver atoms that nucleate into particles, and they adsorb onto the growing particle surfaces as capping and stabilizing agents that prevent uncontrolled clumping. Fourier-transform infrared spectroscopy of the synthesized particles revealed absorption bands characteristic of O-H and C-H stretching vibrations, amide I bands from proteins, and phenolic and aromatic functional groups, confirming that a cocktail of plant metabolites coats each nanoparticle and governs its formation.

Optical characterization confirmed the success of the synthesis. Ultraviolet-visible spectroscopy showed a distinct surface plasmon resonance peak at 418 nanometers, within the expected 390 to 450 nanometer window for silver nanoparticles and absent from the starting materials. Surface plasmon resonance arises from the collective oscillation of conduction electrons excited by incoming light, and its position and shape report on particle size, distribution, and stability. The researchers also mapped how synthesis conditions affect yield. At acidic pH values of five and six, no meaningful absorption peak appeared because particles agglomerate rather than nucleate, while neutral pH proved optimal. Temperature profiling showed that 35 degrees Celsius encouraged particle formation while preserving the integrity of the heat-sensitive biomolecules, whereas temperatures above 55 degrees Celsius degraded the extract and lowered yields. Time-course measurements revealed that absorbance increased steadily with incubation, reaching a maximum reduction of silver ions around 72 hours.

Structural analysis painted a consistent picture of crystalline, roughly spherical particles. X-ray diffraction produced sharp reflections at 2-theta values of 38.72, 44.16, 63.12, 77.60, and 82.74 degrees, indexed to the (111), (200), (220), (311), and (222) planes of face-centered cubic metallic silver, matching the standard reference pattern for elemental silver. Applying the Debye-Scherrer equation to the diffraction peaks yielded a crystallite size of approximately 22.8 nanometers for the dominant (111) plane. Field-emission scanning electron microscopy showed spherical particles, some with irregular shapes, ranging from roughly 100 to 200 nanometers with mild agglomeration attributable to capillary forces during drying. Energy-dispersive X-ray analysis confirmed elemental silver as the dominant component at 42.46 percent, with an absorption signal near 3 kiloelectronvolts characteristic of metallic silver nanocrystals, alongside contributions from carbon, oxygen, chlorine, and sulfur residues of the plant capping layer.

Transmission electron microscopy resolved individual particles as isotropic spheres with some elliptical and aggregated forms, and the size distribution histogram derived from the images gave an average particle diameter of about 108 nanometers. Selected-area electron diffraction produced concentric rings of elemental silver, confirming high crystallinity. Dynamic light scattering and zeta potential measurements added a critical stability insight: the particles carried a surface charge of negative 16.2 millivolts. This negative charge, attributed to the bioorganic capping layer inherited from the plant extract, generates electrostatic repulsion between particles and keeps the colloid from settling or fusing. The authors note that the hydrodynamic size in this study is larger than the 20 to 27 nanometer particles previously reported from Solanum torvum fruit and root extracts, a difference likely reflecting the distinct phytochemical profile of pedicel tissue compared with other plant organs.

The biological performance of the nanoparticles was tested against four human pathogenic bacteria: the Gram-positive Staphylococcus aureus and Staphylococcus haemolyticus, and the Gram-negative Klebsiella pneumoniae and Pseudomonas aeruginosa. In agar well diffusion assays, activity rose with dose. At the highest concentration of 100 micrograms per milliliter, the nanoparticles produced inhibition zones of 18 millimeters against Staphylococcus aureus, 16 millimeters against Klebsiella pneumoniae, 15 millimeters against Pseudomonas aeruginosa, and 8 millimeters against Staphylococcus haemolyticus, with a clearly dose-dependent effect when compared against the standard antibiotic ampicillin. Broth dilution assays quantified the minimum inhibitory concentrations, yielding IC50 values of 68.54 micrograms per milliliter for Staphylococcus aureus, 53.12 for Klebsiella pneumoniae, 72.78 for Pseudomonas aeruginosa, and 81.40 for Staphylococcus haemolyticus, along with marked reduction of bacterial colony formation on agar plates even at the lowest tested doses.

The mechanism of this antibacterial action operates on several fronts. Silver nanoparticles bind to the negatively charged bacterial cell surface, disrupting membrane integrity and interfering with permeability, osmoregulation, electron transport, and respiration. Particles that penetrate the cell interact with DNA, proteins, and other phosphorus- and sulfur-containing biomolecules, triggering cellular dysfunction and death. In addition, the particles release silver ions that amplify the bactericidal effect in a size- and concentration-dependent manner. Because antibiotic resistance continues to erode the effectiveness of conventional drugs, metal nanoparticles are increasingly viewed as a promising platform for new antimicrobial coatings, wound dressings, food preservation systems, and antiseptic formulations, and the low minimum inhibitory concentrations observed here support that trajectory.

Perhaps the most striking result came from the cancer experiments. Using the MTT viability assay on A549 human lung adenocarcinoma cells, the team found that ST@AgNPs suppressed cell proliferation in a dose-dependent manner with an IC50 value of 38.2 plus or minus 0.8 micrograms per milliliter. For comparison, the clinical chemotherapy drug doxorubicin, used as the positive control, showed an IC50 of 24.3 plus or minus 1.05 micrograms per milliliter. While the plant-derived nanoparticles did not outperform the commercial drug, the authors emphasize that achieving potent cytotoxicity with a material synthesized from discarded kitchen waste, without toxic chemical reagents, represents a meaningful step toward affordable bioactive therapeutics. The team cautions that further clinical studies are needed before any therapeutic application, but the convergence of waste valorization, green chemistry, and demonstrated antibacterial and anticancer activity makes ST@AgNPs a compelling example of how nanotechnology can convert environmental liabilities into biomedical assets and advance a more circular bioeconomy.

Subject of Research: Green synthesis of antibacterial and anticancer silver nanoparticles from Solanum torvum fruit pedicel waste

Article Title: Antibacterial and cytotoxic effect of green synthesized silver nanoparticles using Solanum torvum fruit pedicel waste extract

Article References: Kannaiah, S., Paramasivam, S., Sanasam, B., Sekar, N., Nongthombam, K. S., Palanivel, K., & Pandiyan, J. (2026). Antibacterial and cytotoxic effect of green synthesized silver nanoparticles using Solanum torvum fruit pedicel waste extract. Discover Biotechnology, 3(1), Article 2. https://doi.org/10.1007/s44340-026-00049-y

Image Credits: AI Generated

DOI: 10.1007/s44340-026-00049-y

Keywords: silver nanoparticles, green synthesis, Solanum torvum, food waste valorization, antibacterial activity, A549 lung cancer cells, MTT assay, phytochemicals, zeta potential, nanobiotechnology, Turkey berry, sustainable nanomaterials