Tunable Nanoparticle Thin-Film Reveals Distance Dependence of Auger-Mediated Radiation Enhancement in Diffuse Midline Glioma

Metallic nanoparticles (NPs) enhance radiotherapy through photoelectric absorption and Auger electron cascades, yet the effective spatial range over which these low-energy electrons induce biological damage remains poorly defined. Quantifying nanoscale energy deposition is essential for rational therapeutic design and safe clinical translation. Here, we establish a self-assembled polyelectrolyte-nanoparticle-cell architecture enabling nanometer-precision control of NP-cell separation (25–100 nm) to directly probe distance-dependent radiation enhancement. Layer-by-layer assembly produced uniform interfaces confirmed by spectroscopy, ellipsometry, electron microscopy, atomic force microscopy, and microgravimetry. Using human microglial (HMC3) and diffuse intrinsic pontine glioma (SU-DIPG-IV) cells, we quantified intracellular reactive oxygen species generation and γH2AX-marked DNA double-strand breaks following 137 Cs γ-irradiation. Cells positioned 25.9 nm from the NP layer exhibited significantly increased DNA damage relative to NP-free controls, whereas damage progressively decreased with increasing separation, yielding a 250% differential effect between 25.9 and 97.5 nm. Modality-dependent attenuation profiles were observed across γ-ray, X-ray, and electron irradiation. These findings define the effective nanoscale interaction radius governing NP-mediated Auger enhancement and establish a technique for the interrogation of light–matter interactions for therapeutic energy deposition.