Retracted Green Nanoparticle Study Falls Amid Overlapping Figures and Spectral Irregularities

A 2023 paper that described an elegant, environmentally friendly way to make zinc oxide and aluminum oxide nanoparticles using tea and oregano leaf extracts has been retracted by the editors of PLOS One, closing the chapter on a study that once promised a greener route to pharmaceutical quality control. The retraction notice, published on October 12, 2026, cites deep concerns about the integrity of key figures in the article, including images that appear to overlap with figures in unrelated papers and spectroscopic traces showing signs of manipulation. The decision underscores a growing tension in modern materials chemistry: green synthesis is one of the field’s most appealing narratives, but the data behind some of its most cited successes are increasingly coming under forensic scrutiny.

The original study, authored by Nawal A. Alarfaj, Hessa A. Alabdulmonem, Wafa A. Al-Onazi, Amal M. Al-Mohaimeed, and Maha F. El-Tohamy at King Saud University, reported a biogenic synthesis protocol in which aqueous extracts of Camellia sinensis, the plant behind green tea, and Origanum vulgare, commonly known as oregano, served as both reducing and stabilizing agents. The authors claimed that phytochemicals in these extracts could convert metal salt precursors into zinc oxide and aluminum oxide nanoparticles without the harsh chemicals and high energy inputs typical of conventional sol-gel or hydrothermal routes. The resulting nanoparticles were then proposed as spectroscopic probes for quantifying two widely prescribed fluoroquinolone antibiotics, ofloxacin and ciprofloxacin, in commercial pharmaceutical formulations.

Technically, the approach fit squarely within the green chemistry paradigm that has swept through nanoscience over the past decade. Plant extracts contain a rich cocktail of polyphenols, flavonoids, terpenoids, and organic acids capable of donating electrons to metal ions, nucleating oxide particles, and capping their surfaces to control size and prevent aggregation. Zinc oxide nanoparticles, with their wide band gap and strong UV absorption, and aluminum oxide nanoparticles, prized for chemical stability, were presented as ideal platforms for UV-visible spectrophotometric estimation of the antibiotics. The promise was a low-cost, sustainable analytical method that laboratories in resource-limited settings could adopt for routine drug quality assessment, an attractive proposition for regulators monitoring generic formulations across global markets.

That promise collapsed under editorial review. According to the retraction notice, concerns were raised after publication regarding results presented in Figures 1 and 5 of the paper. The problems were specific and serious. Figure 1c, which purportedly showed characterization data from the PLOS One study, appeared to overlap with Figure 2b from a separate 2021 paper published in the journal Pharmaceutics on a nutmeg oil, polyurethane, and zinc oxide bionanocomposite. More strikingly, Figure 5a from the retracted article appeared identical to Figure 3a in that same Pharmaceutics paper and to Figure 2a in a third study, a 2020 PLOS One paper on magnesium oxide nanoparticles synthesized from Saussurea costus biomass that had itself already been retracted. Figure 5c, meanwhile, appeared to overlap with Figure 3a from a 2021 paper on a Plectranthus cylindraceus oil, titanium dioxide, and polyethylene glycol bionanocomposite.

The overlapping panels are the kind of red flag that image forensics specialists describe as nearly impossible to explain innocently. When the same micrograph or data plot appears in papers describing different materials, different synthesis routes, and different applications, at least some of the figures cannot represent the experiments they claim to depict. The retraction notice also documented repetitive elements in the backgrounds of Figures 5b, 5c, and 5d, a hallmark of digital splicing in which portions of one image are copied and pasted to fabricate additional panels. In microscopy and spectroscopy, background texture carries information about the sample and instrument; duplicated background regions indicate that the visual evidence was assembled rather than acquired.

The spectroscopic data fared no better under scrutiny. The editors found that in Figures 1c and 1d, some of the wavenumber markers did not match the corresponding positions on the x-axis, a discrepancy that strikes at the heart of how infrared spectra are interpreted. In vibrational spectroscopy, the position of an absorption band in wavenumbers is the primary evidence for identifying functional groups; if the axis calibration and the labeled markers disagree, the chemical assignments built on those bands become meaningless. The notice further reported areas of discontinuity in the spectral trace in Figure 1d, suggesting the spectrum had been edited or stitched together rather than recorded in a single continuous measurement.

Given the opportunity to respond, the corresponding author supplied underlying data for Figures 1 and 5. The editors assessed that material and concluded it did not resolve the concerns. In light of unresolved questions about the validity and integrity of the reported results, the PLOS One Editors retracted the article. The retraction notice also records the authors’ engagement with the process: MFET, the initials corresponding to Maha F. El-Tohamy, did not respond to the final editorial decision, while NAA, HAA, WAAO, and AMAM either did not respond directly or could not be reached. The notice does not attribute responsibility to any individual author, but the pattern of non-response leaves the scientific record without any author-endorsed correction.

The case is not an isolated incident. Two of the papers whose figures overlapped with the retracted study are connected through shared authors, and one of them, the 2020 magnesium oxide nanoparticle paper, was itself retracted by PLOS One in 2026, with the retraction published under DOI 10.1371/journal.pone.0351977. The web of overlapping images spanning a Pharmaceutics paper, a Bioinorganic Chemistry and Applications paper, and multiple PLOS One articles suggests that the same figure material circulated across what were presented as independent studies of different nanocomposite systems. For the journals involved, untangling such networks has become a substantial editorial burden, and for readers, it raises uncomfortable questions about how many similar cases remain undetected.

For the broader nanoscience community, the retraction lands on a subfield already wrestling with credibility problems. Biogenic synthesis papers have proliferated at a remarkable rate, driven by the appeal of sustainable chemistry and the relative accessibility of the experimental techniques. Characterization typically rests on a handful of standard measurements, including UV-visible spectra, X-ray diffraction patterns, electron micrographs, and infrared spectra, and it is precisely these outputs that are easiest to duplicate, reuse, or alter. The retracted study’s central analytical claim, that its nanoparticles enabled spectroscopic estimation of ofloxacin and ciprofloxacin in commercial formulations, depended entirely on the authenticity of those measurements. With the figures discredited, no reliable evidence remains that the reported synthesis or the analytical method ever performed as described.

The practical consequences extend beyond the authors involved. Researchers who cited the paper as a precedent for plant-mediated zinc oxide or aluminum oxide synthesis must now treat it as void, and any analytical protocols derived from it are unsupported. More broadly, the episode illustrates why journals increasingly deploy automated image-integrity screening and why readers should regard spectacularly convenient results in high-volume subfields with measured skepticism. Green synthesis of metal oxide nanoparticles remains a legitimate and potentially valuable research direction, with genuine applications in catalysis, antimicrobial materials, and drug sensing. But the retraction of this study is a reminder that sustainability claims in the scientific literature are only as trustworthy as the raw data behind them, and that when the spectra and micrographs fail basic consistency checks, even the most appealing green chemistry story must be struck from the record.

Subject of Research: Retraction of a study on biogenic synthesis of ZnO and Al2O3 nanoparticles for spectroscopic estimation of fluoroquinolone antibiotics

Article Title: Retraction: Biogenic synthesis of ZnO and Al 2 O 3 nanoparticles using Camellia sinensis and Origanum vulgare L. leaves extract for spectroscopic estimation of ofloxacin and ciprofloxacin in commercial formulations

Article References: The PLOS One Editors (2026). Retraction: Biogenic synthesis of ZnO and Al2O3 nanoparticles using Camellia sinensis and Origanum vulgare L. leaves extract for spectroscopic estimation of ofloxacin and ciprofloxacin in commercial formulations. PLOS One, 21(10), e0360347. https://doi.org/10.1371/journal.pone.0360347

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0360347

Keywords: PLOS One, retraction, green synthesis, zinc oxide nanoparticles, aluminum oxide nanoparticles, Camellia sinensis, Origanum vulgare, ofloxacin, ciprofloxacin, image integrity, spectroscopy, research misconduct