Polystyrene-Core, Silica-Shell Scintillant Nanoparticles for Low-Energy Radionuclide Quantification in Aqueous Media

Abstract

β-particle emitting radionuclides are useful molecular labels due to their abundance in biomolecules. Detection of β-emission from H,S, and P, important biological isotopes, is challenging due to the low energies (E ≤ 300 keV) and short penetration depths (≤0.6 mm) in aqueous media. The activity of biologically relevant β-emitters is usually measured in liquid scintillation cocktail (LSC), a mixture of energy-absorbing organic solvents, surfactants, and scintillant fluorophores, which places significant limitations on the ability to acquire time-resolved measurements directly in aqueous biological systems. As an alternative to LSC, we developed polystyrene-core, silica-shell nanoparticle scintillators (referred to as nanoSCINT) for quantification of low-energy β-particle emitting radionuclides directly in aqueous solutions. The polystyrene acts as an absorber for energy from emitted β-particles and can be loaded with a range of hydrophobic scintillant fluorophores, leading to photon emission at visible wavelengths. The silica shell serves as a hydrophilic shield for the polystyrene core, enabling dispersion in aqueous media and providing better compatibility with water-soluble analytes. While polymer and inorganic scintillating microparticles are commercially available, their large size and/or high density complicates effective dispersion throughout the sample volume. In this work, nanoSCINT nanoparticles were prepared and characterized. nanoSCINT responds to H,S, and P directly in aqueous solutions, does not exhibit a change in scintillation response between pH 3.0 and 9.5 or with 100 mM NaCl, and can be recovered and reused for activity measurements in bulk aqueous samples, demonstrating the potential for reduced production of LSC waste and reduced total waste volume during radionuclide quantification. The limits of detection for 1 mg/mL nanoSCINT are 130 nCi/mL forH, 8 nCi/mL for S, and<1 nCi/mL for P.

Mechanistic Insights and Controlled Synthesis of Radioluminescent ZnSe Quantum Dots Using a Microfluidic Reactor

“…RL spectra of ZnSe cores exposed to X-rays reveal that ZnSe nanocrystals are also radioluminescent materials for radiation detection (Figure a). Furthermore, the RL intensity increases linearly as a function of the current applied in the X-ray tube (Figure b), i.e., RL intensity is linearly proportional to the fluence/dose rate of X-rays, which is highly desirable . The RL emission band shifts according to the nanocrystal size (Figure c), evidencing that this emission is associated to confined excitons.…”

“…Furthermore, the RL intensity increases linearly as a function of the current applied in the X-ray tube (Figure 8b), i.e., RL intensity is linearly proportional to the fluence/dose rate of X-rays, which is highly desirable. 49 The RL emission band shifts according to the nanocrystal size (Figure 8c), evidencing that this emission is associated to confined excitons. Although the quantum yield of the as-synthesized cores is relatively low, RL is detected.…”

“…Besides investigating the absorbance and PL properties of heavy-metal-free semiconductor nanocrystals, some applications in biomedicine also require investigation of the radioluminescence (RL) emission. − RL is the light emitted by the investigated materials when exposed to ionizing radiation, like X-rays. , Particularly, the ionization caused by X-rays produces electron–hole pairs in the insulator and semiconducting materials that can recombine leading to light emission in the UV–visible region. , This luminescent process is also called scintillation, X-ray luminescence, or X-ray-excited optical luminescence. , RL-emitting nanocrystals have recently been employed for the development of new cancer therapies combining radiation and photodynamic therapy (X-ray-activated photodynamic therapy). ,,, In these treatments, the energy harvested by the RL-emitting nanocrystals from the radiation therapy X-ray beam is transferred to photosensitizers and produces reactive oxygen species . In addition, because the intensity of RL is proportional to the dose rate of X-rays, RL can also be used for assessing doses of ionizing radiation in industrial and medical applications …”

“…47,52 RL-emitting nanocrystals have recently been employed for the development of new cancer therapies combining radiation and photodynamic therapy (X-ray-activated photodynamic therapy). 47,49,53,54 In these treatments, the energy harvested by the RL-emitting nanocrystals from the radiation therapy X-ray beam is transferred to photosensitizers and produces reactive oxygen species. 47 In addition, because the intensity of RL is proportional to the dose rate of X-rays, 51 RL can also be used for assessing doses of ionizing radiation in industrial and medical applications.…”

Synthesis and characterization of magnetic nanoparticles for biomedical applications

“…As it can be seen this nanocomposite exposed to X-rays (2 mA to 10 mA) presents radioluminescence emission (Figure 4.12 (a)). Furthermore, a linear increase of the radioluminescence intensity of nanocomposite as a function of the current applied in the X-ray tube (dose rate of X-rays) can be observed (Figure 4.12 (b)), which is highly desirable for biomedical applications [192,193]. However, the peaks in X-ray luminescence of IONPs/OA/AN/PVA are shifted to red compared to its fluorescence, what is also attractive for biological applications because of the decrease in scattering and longer propagation in biological tissues.…”