Silica-Encapsulated Perovskite Nanocrystals for X-ray-Activated Singlet Oxygen Production and Radiotherapy Application

Enhanced stability and optical performance of CsPbBr3@FAPbBr3 core-shell perovskite nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs), particularly CsPbBr3, have attracted considerable attention due to their remarkable optical properties, positioning them as promising candidates for optoelectronics and bioimaging. Despite their potential, challenges such as environmental degradation and structural instability persist. Core-shell architectures and encapsulation have emerged as effective strategies to address these issues. Here, we propose a double-shelling strategy aimed at the improvement of the optical properties of perovskite NCs and their stability under harsh environmental conditions. We demonstrate the synthesis of CsPbBr3@FAPbBr3 core-shell NCs, combining a luminescent CsPbBr3 core with a stabilizing FAPbBr3 shell via a hot-injection method. This approach allows for a significant enhancement of the photoluminescence quantum yield, extension of photoluminescence lifetimes, and improvement of the photo- and thermostability of NCs. For further reinforcement of moisture resistance, we encapsulated the core-shell NCs in a SiO2 shell to preserve their photoluminescence responses under one- and two-photon excitation in water and isopropanol. Additionally, the increased two-photon absorption cross-section of these NCs combined with water stability suggests their strong suitability for multiphoton imaging applications. This dual-shelling strategy offers a stable, high-performance perovskite-based nanomaterial, expanding the application potential of lead halide perovskite nanocrystals in light-emitting devices and bioimaging technologies.

Recent Advances and Challenges in Metal Halide Perovskite Quantum Dot-Embedded Hydrogels for Biomedical Application

Metal halide perovskite quantum dots (MHP QDs), as a kind of fluorescent material, have attracted much attention due to their excellent photoluminescence (PL) quantum yield (QY), narrow full width at half maximum (FWHM), broad absorption, and tunable emission wavelength. However, the instability and biological incompatibility of MHP QDs greatly hinder their application in the field of biomedicine. Hydrogels are three-dimensional polymer networks that are widely used in biomedicine because of their high transparency and excellent biocompatibility. This review not only introduces the latest research progress in improving the mechanical and optical properties of hydrogels/MHP QDs but also combines it with the existing methods for enhancing the stability of MHP QDs in hydrogels, aiming to provide new ideas for researchers in material selection and methods for constructing MHP QD-embedded hydrogels. Finally, their application prospects and future challenges are introduced.

Cutting-Edge Developments in Metal Halide Perovskites Core/Shell Heterocrystals: from Photodetectors to Biomedical Applications

In recent years, the performance of metal halide perovskite (MHP)-based detectors (photon, biomedical, and X-ray detection) has significantly improved, resulting in higher carrier mobilities, longer carrier diffusion lengths, and excellent absorption coefficients. However, the widespread adoption of halide perovskites has been hindered by issues related to their stability and toxicity. Various strategies have been adopted to address these challenges, focusing on enhancing ambient stability and reducing toxicity by encapsulating MHPs within stable and robust host materials, such as silicon compounds, metal oxides, chalcogenides, and lead-free perovskites. This review focuses on recent developments in hybrid nanostructure-based detectors (photon, biomedical, and X-ray), particularly core/shell architectures, and provides a comprehensive analysis of techniques for mitigating degradation due to light and oxygen exposure, UV irradiance, and thermal effects. This review enhances the understanding of current advancements in core/shell-based detectors.

Double Layer SiO2-Coated Water-Stable Halide Perovskite as a Promising Antimicrobial Photocatalyst under Visible Light

Halide perovskite nanocrystals (HPNCs) have emerged as promising materials for various light harvesting applications due to their exceptional optical and electronic properties. However, their inherent instability in water and biological fluids has limited their use as photocatalysts in the aqueous phase. In this study, we present highly water-stable SiO2-coated HPNCs as efficient photocatalysts for antimicrobial applications. The double SiO2 layer coating method confers long-term structural and optical stability to HPNCs in water, while the in situ synthesis of lead- and bismuth-based perovskite NCs into the SiO2 shell enhances their versatility and tunability. We demonstrate that the substantial generation of singlet oxygen via energy transfer from HPNCs enables efficient photoinduced antibacterial efficacy under aqueous conditions. More than 90% of Escherichia coli was inactivated under mild visible light irradiation for 6 h. The excellent photocatalytic antibacterial performance suggests that SiO2-coated HPNCs hold great potential for various aqueous phase photocatalytic applications.

Surface functionalized perovskite nanocrystals: a design strategy for organelle-specific fluorescence lifetime multiplexing

Fluorescent molecules or materials with high photoluminescence quantum yields and stability towards photobleaching are ideally suited for multiplex imaging. Despite complying with such properties, perovskite nanocrystals (Pv-NCs) are rarely used for bioimaging owing to their toxicity and limited stability in aqueous media and towards human physiology. We aim to address these deficiencies by designing core-shell structures with Pv-NCs as the core and surface-engineered silica as the shell (SiO2@Pv-NCs) since silica is recognized as a biologically benign carrier material and is known to be excreted through urine. The post-grafting methodology is adopted for developing [SiO2@Pv-NCs]tpm and [SiO2@Pv-NCs]tsy (tpm: triphenylphosphonium ion, tsy: tosylsulfonamide) for specific imaging of mitochondria and endoplasmic reticulum (ER) of the live HeLa cell, respectively. A subtle difference in their average fluorescence decay times ([SiO2@Pv-NCs]tpm: tpm τ av = 3.1 ns and [SiO2@Pv-NCs]tsy: tsy τ av = 2.1 ns) is used for demonstrating a rare example of perovskite nanocrystals in fluorescence lifetime multiplex imaging.

Dual Passivation Strategy for Highly Stable Blue-Luminescent CsPbBr3 Nanoplatelets

Blue-emitting colloidal CsPbX3 (X = Br, Cl, or I) perovskite nanocrystals have emerged as one of the most fascinating materials for optoelectronic applications. However, their applicability is hindered by poor stability and a low photoluminescence efficiency. Herein, highly stable CsPbBr3 nanoplatelets exhibiting intense blue luminescence are fabricated by employing a strategy in which the morphology is regulated and the surface is subjected to dual passivation through the incorporation of zirconium acetylacetonate [Zr(acac)4]. The passivated CsPbBr3 nanocrystals exhibit adjustable light emission from green to dark blue and a controllable morphology from nanocubes (NCs) to nanoplatelets (NPLs) and nanorods accomplished by varying the content of Zr(acac)4. The optimized NPLs are characterized by a bright blue emission with a central wavelength of 459 nm and a high photoluminescence quantum yield of 90%. The addition of Zr(acac)4 in the synthesis of CsPbBr3 induces oriented growth with a two-dimensional morphology. The Zr(acac)4 can repair the surface defects of the nanocrystal surface, and the surface is also capped with the Zr(OH)4 cluster layer. Therefore, the passivated blue-emitting NPLs exhibit outstanding stability compared to that of pristine NPLs during long-term storage and exposure to light. This work provides a novel strategy for fabricating highly stable PNCs with deep-blue emission and widens their potential applications in blue-emitting optoelectronic devices.

Photoluminescence Enhancement in Silica-Confined Ligand-Free Perovskite Nanocrystals by Suppression of Silanol-Induced Traps and Phase Impurities

The detriments of intrinsic silanol groups in mesoporous silica to the photoluminescence (PL) of lead halide perovskite nanocrystals (LHP NCs) confined in the template have never been determined and clearly elucidated. Here, we disclose that silanol-induced Cs+ and Br- deficiencies prompt the generation of traps and CsPb2Br5 impurities. The temperature-dependent PL spectra verify the higher energetic barrier of trap states in CsPbBr3 NCs confined in silanol-rich mesoporous silica. Femtosecond transient absorption spectra reveal the trapped state mediates a broadband photoinduced absorption and long-lived decay pathway of CsPbBr3 NCs in silanol-rich templates. A remarkable improvement (up to 160-fold) in PL quantum yields is realized by simple silanol elimination. This work demonstrates the detrimental effects of silanol sites on the PL properties of LHP NCs impregnated in mesoporous silica and provides a new perspective for the ligand-free synthesis of high-quality LHP NCs in mesoporous templates by facile impregnation for practical applications.

Organosilicon-Based Ligand Design for High-Performance Perovskite Nanocrystal Films for Color Conversion and X-ray Imaging

Perovskite nanocrystals (PNCs) bear a huge potential for widespread applications, such as color conversion, X-ray scintillators, and active laser media. However, the poor intrinsic stability and high susceptibility to environmental stimuli including moisture and oxygen have become bottlenecks of PNC materials for commercialization. Appropriate barrier material design can efficiently improve the stability of the PNCs. Particularly, the strategy for packaging PNCs in organosilicon matrixes can integrate the advantages of inorganic-oxide-based and polymer-based encapsulation routes. However, the inert long-carbon-chain ligands (e.g., oleic acid, oleylamine) used in the current ligand systems for silicon-based encapsulation are detrimental to the cross-linking of the organosilicon matrix, resulting in performance deficiencies in the nanocrystal films, such as low transparency and large surface roughness. Herein, we propose a dual-organosilicon ligand system consisting of (3-aminopropyl)triethoxysilane (APTES) and (3-aminopropyl)triethoxysilane with pentanedioic anhydride (APTES-PA), to replace the inert long-carbon-chain ligands for improving the performance of organosilicon-coated PNC films. As a result, strongly fluorescent PNC films prepared by a facile solution-casting method demonstrate high transparency and reduced surface roughness while maintaining high stability in various harsh environments. The optimized PNC films were eventually applied in an X-ray imaging system as scintillators, showing a high spatial resolution above 20 lp/mm. By designing this promising dual organosilicon ligand system for PNC films, our work highlights the crucial influence of the molecular structure of the capping ligands on the optical performance of the PNC film.

Long live(d) CsPbBr3 superlattices: colloidal atomic layer deposition for structural stability

Superlattice formation afforded by metal halide perovskite nanocrystals has been a phenomenon of interest due to the high structural order induced in these self-assemblies, an order that is influenced by the surface chemistry and particle morphology of the starting building block material. In this work, we report on the formation of superlattices from aluminum oxide shelled CsPbBr3 perovskite nanocrystals where the oxide shell is grown by colloidal atomic layer deposition. We demonstrate that the structural stability of these superlattices is preserved over 25 days in an inert atmosphere and that colloidal atomic layer deposition on colloidal perovskite nanocrystals yields structural protection and an enhancement in photoluminescence quantum yields and radiative lifetimes as opposed to gas phase atomic layer deposition on pre-assembled superlattices or excess capping group addition. Structural analyses found that shelling resulted in smaller nanocrystals that form uniform supercrystals. These effects are in addition to the increasingly static capping group chemistry initiated where oleic acid is installed as a capping ligand directly on aluminum oxide. Together, these factors lead to fundamental observations that may influence future superlattice assembly design.

A pH-Sensitive Nanoparticle as Reactive Oxygen Species Amplifier to Regulate Tumor Microenvironment and Potentiate Tumor Radiotherapy

Background

Radiotherapy is a widely used clinical tool for tumor treatment but can cause systemic toxicity if excessive radiation is administered. Although numerous nanoparticles have been developed as radiosensitizers to reduce the required dose of X-ray irradiation, they often have limitations, such as passive reliance on radiation-induced apoptosis in tumors, and little consider the unique tumor microenvironment that contributes radiotherapy resistance.

Methods

In this study, we developed and characterized a novel self-assembled nanoparticle containing dysprosium ion and manganese ion (Dy/Mn-P). We systematically investigated the potential of Dy/Mn-P nanoparticles (NPs) as a reactive oxygen species (ROS) amplifier and radiosensitizer to enhance radiation therapy and modulate the tumor microenvironment at the cellular level. Additionally, we evaluated the effect of Dy/Mn-P on the stimulator of interferon genes (STING), an innate immune signaling pathway.

Results

Physicochemical analysis demonstrated the prepared Dy/Mn-P NPs exhibited excellent dispersibility and stability, and degraded rapidly at lower pH values. Furthermore, Dy/Mn-P was internalized by cells and exhibited selective toxicity towards tumor cells compared to normal cells. Our findings also revealed that Dy/Mn-P NPs improved the tumor microenvironment and significantly increased ROS generation under ionizing radiation, resulting in a ~70% increase in ROS levels compared to radiation therapy alone. This enhanced ROS generation inhibited ~92% of cell clone formation and greatly contributed to cytoplasmic DNA exposure. Subsequently, the activation of the STING pathway was observed, leading to the secretion of pro-inflammatory immune factors and maturation of dendritic cells (DCs).

Conclusion

Our study demonstrates that Dy/Mn-P NPs can potentiate tumor radiotherapy by improving the tumor microenvironment and increasing endogenous ROS levels within the tumor. Furthermore, Dy/Mn-P can amplify the activation of the STING pathway during radiotherapy, thereby triggering an anti-tumor immune response. This novel approach has the potential to expand the application of radiotherapy in tumor treatment.

Robust Organogel Scintillator for Self-healing and Ultra-flexible X-ray Imaging

Metal halide scintillators serve as promising candidates for X-ray detection due to their high attenuation coefficients, high light yields, and low-cost solution-processable characteristics. However, the issues of humidity/thermal quenching and mechanical fragility, remain obstacles to the broad and diversified development of metal halide scintillators. Here, this work reports a lead-free, water-stable, stretchable, and self-healing (ethylenebis-triphenylphosphonium manganese (II) bromide (C38 H34 P2 )MnBr4 organogel scintillator that meets X-ray imaging in complex scenarios. The robust organogel scintillator can be stretched with elongation up to 1300% while maintaining the scintillation properties. Activated by the dynamic hydrogen bonds and coordination bonds design, the organogel scintillator exhibits excellent self-healing properties at room temperature to alleviate the vignetting problem of the rigid scintillator films, the X-ray imaging resolution can reach 16.7 lp mm-1 . The organogel scintillator can also realize flexible and self-healing X-ray imaging in water, providing a design path for portable devices in harsh conditions.

Aqueous-Based Inorganic Colloidal Halide Perovskites Customizing Liquid Scintillators

Compared to solid scintillators and organic liquid scintillators, aqueous-based liquid scintillators (AbLS) have more superiority in highly flexible scalability, yet are now limited by their low light yield (≈100 photons MeV-1 ). Here, aqueous-based inorganic colloidal halide perovskites with high photoluminescence quantum yield (PLQY) of three primary color luminescence up to 88.1% (red), 96% (green), and 81.8% (blue) are respectively synthesized, and a new generation of colloidal perovskite-mediated AbLS (PAbLS) with light yield increased in comparison with the commercial scintillator AbLS is fabricated. This paper exhibits that the excellent PLQY and colloidal dispersion of halide perovskites benefit from poly(ethylene glycol) modification and this modification ensures the vacancy inhibition and formation of defect-free surfaces in an aqueous solution. Moreover, their high luminescent emission can be maintained for 100 days at low temperatures, and such modification also promises the heat-to-cold customization of operating temperature even in ice below 0 °C. Finally, depending on the light yield of around 3058 and 8037 photons MeV-1 at room temperature and low temperature, PAbLS with shape/size scalability exhibit their robust radiation hardness (dose rate as high as 23 mGy s-1 ) and conceptual application potential in high-energy ray radiation detection from every angle of 360°.

Ultrafast and Radiation-Hard Lead Halide Perovskite Nanocomposite Scintillators

The use of scintillators for the detection of ionizing radiation is a critical aspect in many fields, including medicine, nuclear monitoring, and homeland security. Recently, lead halide perovskite nanocrystals (LHP-NCs) have emerged as promising scintillator materials. However, the difficulty of affordably upscaling synthesis to the multigram level and embedding NCs in optical-grade nanocomposites without compromising their optical properties still limits their widespread use. In addition, fundamental aspects of the scintillation mechanisms are not fully understood, leaving the scientific community without suitable fabrication protocols and rational guidelines for the full exploitation of their potential. In this work, we realize large polyacrylate nanocomposite scintillators based on CsPbBr3 NCs, which are synthesized via a novel room temperature, low waste turbo-emulsification approach, followed by their in situ transformation during the mass polymerization process. The interaction between NCs and polymer chains strengthens the scintillator structure, homogenizes the particle size distribution and passivates NC defects, resulting in nanocomposite prototypes with luminescence efficiency >90%, exceptional radiation hardness, 4800 ph/MeV scintillation yield even at low NC loading, and ultrafast response time, with over 30% of scintillation occurring in the first 80 ps, promising for fast-time applications in precision medicine and high-energy physics. Ultrafast radioluminescence and optical spectroscopy experiments using pulsed synchrotron light further disambiguate the origin of the scintillation kinetics as the result of charged-exciton and multiexciton recombination formed under ionizing excitation. This highlights the role of nonradiative Auger decay, whose potential impact on fast timing applications we anticipate via a kinetic model.