Gold nanoparticles (AuNPs) exhibit size-dependent optical properties governed by localized surface plasmon resonance (LSPR) and strong X-ray absorption, making them attractive for biomedical imaging and radiosensitization. Understanding their response to ionizing radiation is therefore essential. Here, citrate-stabilized AuNPs synthesized by the Turkevich method were exposed to LINAC photon irradiation at doses from 0.1 to 100 Gy and characterized by UV– Vis spectroscopy, AFM, and TEM. UV–Vis measurements showed a non-monotonic dose dependence of LSPR intensity with a maximum at 1 Gy, while no significant peak position shift was observed. AFM and TEM analyses revealed dose- dependent changes in nanoparticle size distribution and morphology. Quantitative statistical evaluation indicated particle growth at intermediate doses followed by redistribution toward smaller characteristic sizes at higher doses. These findings demonstrate that clinically relevant irradiation induces measurable but moderate modifications in AuNP optical and structural properties without pronounced aggregation, contributing to the understanding of radiation– nanoparticle interactions.

1. M. Li, J. Wei, Y. Song, F. Chen, “Gold Nanocrystals: Optical Properties, Fine-Tuning of the Shape, and Biomedical Applications”, RSC Adv., vol. 12, pp. 23057–23073, 2022.
   https://doi.org/10.1039/D2RA04242H
2. A. Alhussan, E.P.D. Bozdoğan, D.B. Chithrani, “Combining Gold Nanoparticles with Other Radiosensitizing Agents for Unlocking the Full Potential of Cancer Radiotherapy”, Pharmaceutics, vol. 13, no. 4, 442, 2021.
   https://doi.org/10.3390/pharmaceutics13040442
3. S. Her, D.A. Jaffray, C. Allen, “Gold Nanoparticles for Applications in Cancer Radiotherapy: Mechanisms and Recent Advancements”, Advanced Drug Delivery Reviews, vol. 109, pp. 84–101, 2017.
   https://doi.org/10.1016/j.addr.2015.12.012
4. N.R.S. Sibuyi, et al., “Multifunctional Gold Nanoparticles for Improved Diagnostic and Therapeutic Applications: A Review”, Nanoscale Res Lett, vol. 16, pp. 1741-27, 2021.
   https://doi.org/10.1186/s11671-021-03632-w
5. S. Tarantino, et al., “Shape-Driven Response of Gold Nanoparticles to X-Rays”, Nanomaterials, vol. 13, pp. 2719-1-16, 2023.
   https://doi.org/10.3390/nano13192719
6. I. Tremi, et al., “A Guide for Using Transmission Electron Microscopy for Studying the Radiosensitizing Effects of Gold Nanoparticles In Vitro”, Nanomaterials, vol. 11, pp. 859-1-19, 2021.
   https://doi.org/10.3390/nano11040859
7. P. Marinov, et al., “UV-Visible Spectroscopy and Atomic Force Microscopy Analysis of Gold Nanoparticles Exposed to Varying Doses of Ionizing Radiation”, C. R. Acad. Bulg. Sci., vol. 78, no. 4, pp. 505-512, 2025.
   https://doi.org/10.7546/CRABS.2025.04.03
8. J. Turkevich, P.C. Stevenson, J. Hillier, “The Formation of Colloidal Gold”, J. Phys. Chem., vol. 57, no. 7, pp. 670–673, 1953.
   https://doi.org/10.1021/j150508a015
9. J. Kimling, et al., “Turkevich Method for Gold Nanoparticle Synthesis Revisited”, J. Phys. Chem. B, vol. 110, no. 32, pp. 15700–15707, 2006.
   https://doi.org/10.1021/jp061667w
10. A. Bharti, K.H. Chae, N. Goyal, “Real-Time Synthesis and Detection of Plasmonic Metal (Au, Ag) Nanoparticles under Monochromatic X-Ray Nano-Tomography”, Sci Rep, vol. 10, pp. 20877-1-11, 2020.
    https://doi.org/10.1038/s41598-020-77853-x
11. R.V. Lupusoru, et al., “Effect of TAT-DOX-PEG Irradiated Gold Nanoparticles Conjugates on Human Osteosarcoma Cells”, Sci Rep, vol. 10, pp. 6591-1-14, 2020.
    https://doi.org/10.1038/s41598-020-63245-8
12. P. Georgiev, et al., “Implementing Atomic Force Microscopy (AFM) for Studying Kinetics of Gold Nanoparticle’s Growth”, Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 434, pp. 154–163, 2013.
    https://doi.org/10.1016/j.colsurfa.2013.05.064
13. S. Tarantino, et al., “Revolutionizing Radiotherapy: Gold Nanoparticles with Polyphenol Coating as Novel Enhancers in Breast Cancer Cells – An In Vitro Study”, Nanoscale Res Lett, vol. 20, no. 10, 2024.
    https://doi.org/10.1186/s11671-025-04186-x
14. Y.C. Dong, et al., “Effect of Gold Nanoparticle Size on Their Properties as Contrast Agents for Computed Tomography”, Sci Rep, vol. 9, pp. 14912-1-13, 2019.
    https://doi.org/10.1038/s41467-019-12754-w

Philip Marinov, Ivo Petrov, Tsvetoslav Lazhovski, Krum Stoilov, Peter Temnishki, Silviya Simeonova, Peter Georgiev, Lyuben Mihaylov, Evelina Vassileva, Konstantin Balashev, "Optical and morphological analysis of gold nanoparticles exposed to ionizing radiation", RAD Conf. Proc., vol. 9, 2025, pp. 47 - 53; http://doi.org/10.21175/RadProc.2025.09