Single Crystal CdSe X-ray Detectors with Ultra-High Sensitivity and Low Detection Limit

Selective Photochromic Response to Low-Dose X-ray Radiation Detection in One-Dimensional Cadmium-Viologen Complexes

Photochromic viologen-based materials have emerged as one of the most promising candidates for the development of X-ray light detection applications, including medical diagnosis and treatment, environmental radiation inspection, and industrial crack detection. However, the design and construction of low-dose X-ray-sensitive complexes remains an immense challenge, especially for the in-depth dissection of their response mechanisms. Herein, by using N,N'-4,4'-bipyridiniodipropionate (CV) as functional sensitive structural units and cadmium as heavy atoms, two cadmium-viologen complexes with one-dimensional chained structures, namely, [Cd₂Cl₄(CV)(H₂O)₂]_n (1) and [CdBr₂(CV)]_n (2), have been constructed, which exhibit a remarkable and selective photochromic response to low-dose X-ray radiation detection. Compound 1 is visually sensitive to both X-ray and UV light due to the more accessible photoinduced electron transfer (ET) pathways, while compound 2 only shows a slight color-changing process in response to UV light, in conformity with UV-vis absorbance analyses and kinetic studies. Surprisingly, compound 2 has longer ET pathways than 1, but not in response to high-energy X-ray light, seeming to contradict the previous phenomena. On further analysis, the key point in achieving X-ray-sensitive behavior should be a good balance among the electron donor-acceptor distance, intermolecular interaction, and X-ray absorbing capacity, as verified by density functional theory (DFT) and X-ray absorption strength calculations, X-ray photoelectron spectra, electron paramagnetic resonance measurements, and independent gradient model analysis. In particular, compound 1 is unprecedentedly sensitive to soft X-ray radiation, accompanied by an X-ray detection limit of as low as 2.91 Gy. These findings push forward the further development of low-dose X-ray sensing materials.

In Vivo Quantitative Assessment of a Radiation Dose Based on Ratiometric Photoacoustic Imaging of Tumor Apoptosis

Accurately assessing the radiation level of tumors and surrounding tissues is of great significance for the optimization of clinical therapeutic interventions as well as minimizing the radiation-induced side effects. Therefore, the development of noninvasive and sensitive biological dosimeters is vital to achieve quantitative detection of a radiation dose in a living system. Herein, as a proof of concept, we report a tumor-targeted and caspase-3-activatable NIR fluorogenic probe AcDEVD-Cy-RGD consisting of a hemicyanine fluorophore as a signal reporter, a caspase-3 specific Asp-Glu-Val-Asp (DEVD) peptide, and a cyclic Arg-Gly-Asp peptide (cRGD) for tumor targeting. Upon cleavage with activated caspase-3, this probe not only displays the lighted-up NIR fluorescence, but also ratiometric photoacoustic (PA₇₁₀/PA₆₈₀) signals concurrently in a caspase-3 concentration-dependent manner, allowing for sensitive and quantitative detection of caspase-3 activity through both fluorescence and PA imaging, which provides the possibility for real-time monitoring of tumor cell apoptosis in a living system. More notably, we utilized this probe to successfully realize the direct visualization of tumor response to chemo- or radiotherapy and, for the first time, achieve the accurate estimation of radiation doses imparted to the tumors. We thus believe that our current strategy would offer an attractive and valuable means for the precise assessment of locally delivered radiation doses in various clinical settings.

A High-Sensitivity Flexible Direct X-ray Detector Based on Bi2O3/PDMS Nanocomposite Thin Film

The characteristics of mechanical flexibility, low health risk, and simple processing of polymer nanocomposite materials make them potentially applicable as flexible X-ray detectors. In this study, we report on a high sensitivity, environmentally friendly, and flexible direct X-ray detector using polymer nanocomposite material consisting of bismuth oxide (Bi₂O₃) nanoparticles and polydimethylsiloxane (PDMS). This detector was realized by printing patterned Ag electrodes on the polymer nanocomposite material. The response of PDMS to X-rays was verified for the first time, and the effect of doping different contents of Bi₂O₃ nanoparticles on the performance of the device was tested. The optoelectronic performance of the optimized detector indicated a high sensitivity (203.58 μC Gy_air⁻¹ cm⁻²) to low dose rate (23.90 μGy_air s⁻¹) at a 150 V bias voltage and the X-ray current density (J_X-ray) was 10,000-fold higher than the dark current density (J_dark). The flexible direct X-ray detector could be curled for 10,000 cycles with slight performance degradation. The device exhibited outstanding stability after storage for over one month in air. Finally, this device provides new guidance for the design of high-performance flexible direct X-ray detectors.