Zinc oxide particles made with onion-peel extract were associated with reduced viability in human A549 lung adenocarcinoma cells, the study reports. The cells also showed staining patterns associated with apoptosis, a form of cell death, a shift in cell-cycle distribution, higher reactive oxygen species (ROS) signal and stronger nuclear p53 localization. Because the work used an established cell line, it is an early laboratory finding, not evidence that the preparation works as a cancer treatment.
The material behind the test
The preparation was called O3. To make it, the researchers added 3 mL of onion-peel extract to 0.2 M zinc sulfate, followed by 1 M NaOH. They heated the mixture at 40°C for 2 hours, washed it four times with 50% ethanol and dried it for 8 hours at 80°C.
Characterization tests described O3 as wurtzite-phase zinc oxide with a hexagonal crystal structure and rod-shaped particles averaging about 400 nm in length and 140 nm in width. The material had an absorption peak at 345 nm.
A separate measurement of the particles in liquid gave a hydrodynamic size of 955 nm and a zeta potential of −10.5 mV. The authors attributed the large apparent size to agglomeration, meaning the particles were clumping together in the dispersion.
A concentration estimate near the upper edge
For the cell assays, the methods list O3 at 100, 150, 200 and 250 μg/mL for 24- and 48-hour exposures, with untreated cells as controls. Biological experiments were performed in triplicate and repeated three times, and the analysis used one-way ANOVA with Dunnett post hoc testing at p < 0.05.
Viability fell in a dose-dependent pattern, with the reduction more evident after 48 hours. The reported IC50—the study’s estimate of the concentration associated with a halfway reduction in viability—was 192.63 μg/mL. The results describe 200 μg/mL as the highest reported tested concentration, although the methods also list 250 μg/mL; that mismatch limits how precisely the estimate can be read.
What the cells showed
At 192.63 μg/mL for 48 hours, crystal violet images showed fewer cells, with more rounded, shrunken and poorly adherent cells. At the same IC50 dose, AO/PI imaging showed early apoptosis, secondary necrosis and chromatin condensation.
The cell-cycle profile also shifted toward G1, an early phase of the cycle. G1 accounted for 66.7% of untreated cells and 79.2% after O3 exposure; the S-phase share was 11.4% versus 9.5%, and G2 was 17.9% versus 7.3%.
The study tracked reactive oxygen species, or ROS, through DHE fluorescence. The signal was higher in cells treated with cisplatin, onion extract and O3 than in controls, while chemically synthesized zinc oxide showed no noticeable increase.
Immunofluorescence imaging—the method used to show where a protein sits in a cell—found strong nuclear p53 localization with O3 and cisplatin. Onion extract alone produced a weaker increase, while chemically synthesized zinc oxide was minimal, similar to the control.
What the findings leave open
The authors interpret the combined findings as consistent with an apoptosis-related, ROS-associated and p53-related effect, including a possible shift at the G1 checkpoint. The experiment did not directly manipulate ROS or p53, however, so it cannot establish that either signal caused the observed viability, staining or cell-cycle changes.
Nor can the study answer whether O3 would spare normal lung cells or be effective and safe in people or animals: it tested established A549 cells only. The IC50 estimate needs testing across a reconciled, broader concentration range, while the proposed ROS and p53 pathways would require direct experiments before conclusions about treatment can be drawn.
Paper data and sources
Original title: Green synthesis of zinc oxide nanoparticles using waste Allium cepa (onion) peel extract and their ROS-mediated cytotoxic activity against A549 lung cancer cells
Authors: Nayak R, Kajol, Rawat K et al.
Journal/Repository: Frontiers in chemistry
Status: Peer-reviewed
First online: 2026-08-19
DOI: Not available
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