Bismuth-Filled Silicone Nanocomposites Deliver Real-Time Readout of Diagnostic X-Ray Doses

Medical imaging runs on a paradox: the machines that reveal what is happening inside the human body expose patients to radiation that must be measured with meticulous care. Dosimetry, the science of quantifying absorbed radiation dose, has long depended on bulky detectors, passive films that require chemical processing, or semiconductor chips that degrade with each readout. A team of physicists from Yazd University and the Nuclear Science and Technology Research Institute in Iran now reports a deceptively simple alternative — a flexible, lead-free silicone rubber loaded with bismuth oxide nanoparticles that converts X-ray exposure directly into a measurable electrical current, in real time. The study, published in Scientific Reports, describes a nanocomposite that could give clinicians an immediate, bendable readout of the dose delivered during diagnostic imaging.

The material at the heart of the work is room-temperature-vulcanizing silicone, designated RTV-2, a two-part elastomer that cures into a soft, stable, and radiation-tolerant matrix. On its own, silicone is a poor X-ray absorber at the low photon energies used in diagnostic imaging. The researchers changed that by dispersing nanoparticles of bismuth trioxide — Bi2O3 — into the polymer at weight fractions ranging from zero to 60 percent. Bismuth is a heavy element with a high atomic number, which makes it exceptionally efficient at interacting with X-ray photons in the tens of kiloelectronvolt range typical of medical imaging. Crucially, the team avoided lead, sidestepping the toxicity and disposal problems that shadow conventional high-Z materials in radiation applications.

Fabrication relied on solution casting, a technique in which the nanoparticles are dispersed in a solvent, mixed into the silicone precursors, and then allowed to cure into sheets. The concentration of Bi2O3 proved to be the tuning knob for sensitivity: as the loading increased, the photocurrent generated under X-ray illumination rose steadily, reaching roughly 1.66 nanoamperes at the highest loading of 60 weight percent, compared with about 0.56 nanoamperes for pure silicone. That corresponds to a threefold enhancement, a significant jump for a passive polymer system operated at room temperature without any photoconductive gain engineering.

Getting nanoparticles to distribute evenly inside a viscous polymer is notoriously difficult, because particles tend to clump into aggregates that create weak points and inhomogeneous response. The researchers therefore subjected their composites to a battery of structural and morphological checks. X-ray diffraction confirmed that the bismuth oxide retained its monoclinic crystal structure inside the silicone, while scanning electron microscopy and energy-dispersive X-ray spectroscopy with elemental mapping showed the nanorods dispersed uniformly through the amorphous elastomer matrix. Fourier-transform infrared and Raman spectroscopy verified that the chemical bonds of the silicone were undisturbed by the filler, and thermogravimetric analysis demonstrated that the composites remain thermally stable well beyond the temperatures encountered in clinical settings.

The dosimetric testing was carried out with a COMET MXR 320/26 X-ray tube operating at dose rates between 2.8 and 12 milligray per minute, the range relevant to diagnostic exposures. Current-voltage measurements taken at 4.8 milligray per minute revealed a highly linear response across applied voltages from minus 400 to plus 400 volts, which simplifies calibration enormously: a linear detector means the measured signal can be translated directly into dose without complex correction algorithms. At the maximum bias of 400 volts, the devices achieved a signal-to-noise ratio of approximately 1900, meaning the radiation-induced current stands far above the random electrical noise floor — a key figure of merit for detecting the very small signals associated with low-dose imaging.

Repeatability is where many candidate detector materials stumble. A dosimeter that gives a different answer each time it is exposed is clinically useless, no matter how sensitive. The nanocomposite devices delivered a standard deviation of just 2.3 percent over ten consecutive irradiation cycles, indicating that the material’s response is stable across repeated use rather than drifting or fatiguing as charges become trapped in the polymer network. For a flexible organic-inorganic hybrid operating without cooling or annealing steps between measurements, that level of consistency is notable.

To benchmark their results, the authors compared the normalized sensitivity of their detectors — photocurrent per unit dose rate — with commercial metal-oxide-semiconductor field-effect transistor dosimeters, which typically register around 0.1 to 1 nanoampere per milligray. The silicone-bismuth oxide composites achieved roughly 0.35 nanoamperes per milligray per minute, equivalent to about 878 nanocoulombs per milligray per cubic centimeter when normalized by volume, placing them competitively among reported Bi2O3-polymer systems and commercial devices. The comparison matters because MOSFET dosimeters, while well established, accumulate permanent damage with each readout and have finite lifetimes, whereas the nanocomposite response is a transient photocurrent that resets with each exposure.

The physical mechanism underlying the signal is worth unpacking. When diagnostic X-ray photons strike the bismuth oxide nanoparticles, their high atomic number promotes photoelectric absorption, ejecting energetic electrons that can travel into the surrounding silicone matrix. Under an applied electric field, these liberated charge carriers drift toward the electrodes, producing the measured photocurrent. The silicone acts both as an insulating host that prevents dark current from swamping the signal and as a flexible structural scaffold, so the detector can be conformed to curved surfaces — a phantom, a piece of imaging equipment, or potentially a patient — without losing function.

The appeal of a lead-free, real-time, flexible dosimeter extends beyond radiology departments. Quality assurance of imaging equipment, occupational monitoring of staff, and verification of dose delivery in interventional procedures where fluoroscopic exposure can be prolonged all stand to benefit from a detector that reads out continuously, tolerates bending, and contains no toxic heavy metals. The nanocomposite approach also suggests a broader design principle: pairing low-density polymers with high-Z nanoparticles to engineer radiation sensitivity without sacrificing mechanical workability.

The authors are careful to note that this is not yet a bedside technology. Their study demonstrates sensitivity, linearity, repeatability, and an impressive signal-to-noise ratio under laboratory conditions, but long-term stability and mechanical durability remain to be established before the composites could be certified for clinical use. Silicone can age, nanoparticles can migrate, and any detector intended to safeguard patient health must survive years of sterilization, handling, and storage without its calibration drifting. Still, the trajectory is clear: a threefold sensitivity gain from simply tuning nanoparticle loading, achieved in a material that costs little to produce and cures at room temperature, offers a credible route toward dosimeters that are as flexible and disposable as the medical devices they accompany. As diagnostic imaging continues to expand worldwide, and with it the imperative to track every milligray, this silicone-bismuth nanocomposite suggests that the next generation of radiation dosimeters may look less like instruments and more like the soft materials of the body they protect.

Subject of Research: Real-time X-ray dosimetry using bismuth oxide nanoparticle-loaded silicone nanocomposites for diagnostic radiation

Article Title: Investigation of the dosimetric characteristics of real-time silicone/Bi2O3 nanocomposites for the diagnostic level X-rays

Article References: Keyvani, F., Gholamzadeh, L., Malekie, S., & Kashian, S. (2026). Investigation of the dosimetric characteristics of real-time silicone/Bi2O3 nanocomposites for the diagnostic level X-rays. Scientific Reports. https://doi.org/10.1038/s41598-026-76522-9

Image Credits: AI Generated

DOI: 10.1038/s41598-026-76522-9

Keywords: X-ray dosimetry, bismuth oxide nanoparticles, silicone nanocomposite, real-time radiation detector, diagnostic imaging, lead-free materials, photocurrent, signal-to-noise ratio, solution casting, radiation protection, nanocomposites, medical physics