Sub-10 nm Water-Dispersible β-NaGdF4:X% Eu3+ Nanoparticles with Enhanced Biocompatibility for in Vivo X-ray Luminescence Computed Tomography

Strong Persistent Luminescence NaYF4-based Nanoparticles Combined with Manipulated Hyperfractionated Irradiation for X-ray-Excited Photodynamic Therapy Enhancement

X-ray-excited photodynamic therapy (X-PDT), a novel synergistic therapy combining radiotherapy (RT) with photodynamic therapy (PDT), demonstrates not only more effective therapeutic outcomes but also overcomes the limitation of PDT's shallow penetration depth. Persistent luminescence nanoparticles (PLNPs) have been employed in X-PDT due to their unique afterglow emission, which yields more light to achieve more effective PDT outcomes using the same irradiation dose. However, at present, persistent luminescent materials used in X-PDT are mainly bulk crystals characterized by a nonuniform size and morphology, which are not suitable for biomedical applications, and the presence of excessive surface defects reduces the luminescence efficiency and the persistent luminescence duration. Herein, the NaYF4:Tb@NaYF4 core-shell nanoparticles with enhanced luminescence and afterglow performance and uniform morphology were prepared via the optimized solvothermal method. Their X-ray excitation optical luminescence (XEOL) and persistent luminescence (XEPL) intensities were enhanced more than 5.2 times and 3.5 times, respectively. The PLNPs were modified with a water-soluble AEP ligand and piggybacked with the photosensitizer Rose Bengal (RB) to construct an efficient X-PDT nanocoupling system. To fully utilize the afterglow of PLNPs, a unique hyperfractionated irradiation plan was designed, and the ROS yield was increased by nearly 50% at the same irradiation dose. In vivo therapeutic efficacy validation using the B16-F10-bearing C57 mouse model demonstrated that hyperfractionated irradiation combined with PLNPs showed significant therapeutic advantages. At a total dose of 2 Gy, the tumor inhibition rate was enhanced from 67.5% to 85% compared to the conventional irradiation strategy. Pathological analysis showed no significant histological damage in major organs, attesting to its negligible side effects. This study offers a novel modality, with both nanoparticles and irradiation strategy improvement, to further improve the X-PDT therapeutic efficacy and reduce side effects.

Development of Biocompatible, UV and NIR Excitable Nanoparticles with Multiwavelength Emission and Enhanced Colloidal Stability

The development of functional nanoprobes for biomedical applications is highly important in the field of modern nanotechnology. Due to strict requirements, such as the ability to be excited using irradiation, which allows deep tissue penetration, nonblinking behavior, and good optical and colloidal stability, the choice of nanoparticles is limited, and their synthesis is challenging. Among all of the functional nanoprobes for biomedical purposes, upconverting nanoparticles, especially those with more complex architectures (e.g., core-shell or core-shell-shell), are the most promising candidates. This study demonstrates advanced synthetic routes for constructing biocompatible nanoprobes with tunable optical properties and colloidal stability. The core-shell-shell architecture of the nanoprobes allows excitation from at least four sources, such as 272 and 394 nm of near-ultraviolet (near-UV) irradiation and 980 and 808 nm near-infrared (NIR) lasers. Furthermore, Gd-matrix-based nanoprobes doped with lanthanide ions (Nd3+, Yb3+, Tm3+, and Eu3+) are known for their paramagnetic properties for magnetic resonance imaging (MRI) imaging as well as upconversion luminescence with diverse emission bands across the entire visible spectrum. This feature is highly desirable for photodynamic therapy applications, as the upconversion emission of the proposed nanoprobes could overlap with the absorption band of commonly used photosensitizers and could potentially result in an efficient energy transfer process and enhanced generation of reactive oxygen species or singlet oxygen.

Preventive effect of sea bass protein-based high internal phase Pickering emulsion loaded with astaxanthin on DEHP-induced liver lipid metabolism disorder

The present study was to investigate the effect of the astaxanthin high internal phase Pickering emulsion (H-AXT) on DEHP-induced liver lipid metabolism disorder and to demonstrate its possible protective mechanism. We have developed an antioxidant activity emulsion system to deliver astaxanthin into the liver to maximize its ability to protect the liver. In vitro, H-AXT intervention inhibited oxidative stress restored the level of mitochondrial membrane potential to 90 % of that of normal LO2 cells, and alleviated the imbalance of energy metabolism by protecting mitochondrial structure and function. Based on metabonomics, it was proved that H-AXT inhibited triglyceride accumulation by antagonizing lipid metabolism disorder. In DEHP-induced mice, H-AXT intervention mitigated liver damage by inhibiting oxidative stress and inflammatory reaction, and alleviated metabolic dysfunction by regulating lipid levels and inhibiting fat accumulation. Meanwhile, H-AXT alleviated DEHP-induced testicular tissue damage and maintained the integrity of testicular tissue. The encapsulation of the emulsion system effectively promoted the liver uptake of astaxanthin to prevent liver diseases associated with metabolic disorders.

Cone-beam x-ray luminescence computed tomography (CB-XLCT) prototype development and performance evaluation

This study developed a prototype for a rotational cone-beam x-ray luminescence computed tomography (CB-XLCT) system, considering its potential application in pre-clinical theranostic imaging. A geometric calibration method applicable to both imaging chains (XL and CT) was also developed to enhance image quality. The results of systematic performance evaluations were presented to assess the feasibility of commercializing XLCT technology. Monte Carlo GATE simulation was performed to determine the optimal imaging conditions for nanophosphor particles (NPs) irradiated by 70 kV x-rays. We acquired a low-dose transmission x-ray tube and designed a prone positioning platform and a rotating gantry, using mice as targets from commercial small animalμ-CT systems. We then employed the image cross-correlation (ICC) automatic geometric calibration method to calibrate XL and CT images. The performance of the system was evaluated through a series of phantom experiments with a linearity of 0.99, and the contrast-to-noise ratio (CNR) between hydroxyl-apatite (HA) and based epoxy resin is 19.5. The XL images of the CB-XLCT prototype achieved a Dice similarity coefficient (DICE) of 0.149 for a distance of 1 mm between the two light sources. Finally, the final XLCT imaging results were demonstrated using the Letter phantoms with NPs. In summary, the CB-XLCT prototype developed in this study showed the potential to achieve high-quality imaging with acceptable radiation doses for small animals. The performance of CT images was comparable to current commercial machines, while the XL images exhibited promising results in phantom imaging, but further efforts are needed for biomedical applications.

Automated Restarting Fast Proximal Gradient Descent Method for Single-View Cone-Beam X-ray Luminescence Computed Tomography Based on Depth Compensation

Single-view cone-beam X-ray luminescence computed tomography (CB-XLCT) has recently gained attention as a highly promising imaging technique that allows for the efficient and rapid three-dimensional visualization of nanophosphor (NP) distributions in small animals. However, the reconstruction performance is hindered by the ill-posed nature of the inverse problem and the effects of depth variation as only a single view is acquired. To tackle this issue, we present a methodology that integrates an automated restarting strategy with depth compensation to achieve reconstruction. The present study employs a fast proximal gradient descent (FPGD) method, incorporating L0 norm regularization, to achieve efficient reconstruction with accelerated convergence. The proposed approach offers the benefit of retrieving neighboring multitarget distributions without the need for CT priors. Additionally, the automated restarting strategy ensures reliable reconstructions without the need for manual intervention. Numerical simulations and physical phantom experiments were conducted using a custom CB-XLCT system to demonstrate the accuracy of the proposed method in resolving adjacent NPs. The results showed that this method had the lowest relative error compared to other few-view techniques. This study signifies a significant progression in the development of practical single-view CB-XLCT for high-resolution 3-D biomedical imaging.

Novel Sol-Gel Route to Prepare Eu3+-Doped 80SiO2-20NaGdF4 Oxyfluoride Glass-Ceramic for Photonic Device Applications

Oxyfluoride glass-ceramics (OxGCs) with the molar composition 80SiO₂-20(1.5Eu³⁺: NaGdF₄) were prepared with sol-gel following the "pre-crystallised nanoparticles route" with promising optical results. The preparation of 1.5 mol % Eu³⁺-doped NaGdF₄ nanoparticles, named 1.5Eu³⁺: NaGdF₄, was optimised and characterised using XRD, FTIR and HRTEM. The structural characterisation of 80SiO₂-20(1.5Eu³⁺: NaGdF₄) OxGCs prepared from these nanoparticles' suspension was performed by XRD and FTIR revealing the presence of hexagonal and orthorhombic NaGdF₄ crystalline phases. The optical properties of both nanoparticles' phases and the related OxGCs were studied by measuring the emission and excitation spectra together with the lifetimes of the ⁵D₀ state. The emission spectra obtained by exciting the Eu³⁺-O^2- charge transfer band showed similar features in both cases corresponding the higher emission intensity to the ⁵D₀→⁷F₂ transition that indicates a non-centrosymmetric site for Eu³⁺ ions. Moreover, time-resolved fluorescence line-narrowed emission spectra were performed at a low temperature in OxGCs to obtain information about the site symmetry of Eu³⁺ in this matrix. The results show that this processing method is promising for preparing transparent OxGCs coatings for photonic applications.

Fast and Inexpensive Separation of Bright Phosphor Particles from Commercial Sources by Gravitational and Centrifugal Sedimentation for Deep Tissue X-ray Luminescence Imaging

X-ray luminescence tomography (XLT) detects X-ray scintillators contrast agents using a focused or collimated X-ray beam to provide high spatial resolution excitation through thick tissue. The approach requires bright nanophosphors that are either synthesized or purchased. However, currently available commercial nanophosphors are mostly composed of a polydisperse mixture of several micro- to nano-sized particles that are unsuitable for biomedical imaging applications because of their size and aggregated form. Here, we demonstrate a fast and robust method to obtain uniform nano to submicron phosphor particles from a commercial source of polydisperse Eu- and Tb-doped Gd2O2S particles by separating the smaller particles present using gravitational and centrifugal sedimentation. In contrast to ball milling for 15–60 min, which drastically degraded the particles’ brightness while reducing their size, our sedimentation method enabled the extraction of comparatively bright nanophosphors (≈100–300 nm in size) with a luminescence intensity of ≈10–20% of the several micron particles in the sample. Moreover, if scale up for higher yielding is required, the sedimentation process can be accelerated using fixed-angle and/or swinging bucket rotating centrifugation. Finally, after separation and characterization, nano and submicron phosphors were suspended and imaged through 5 mm thick porcine tissue using our in-house-built scanning X-ray induced luminescence chemical imaging (XELCI) system.

X-ray excited luminescence spectroscopy and imaging with NaGdF4:Eu and Tb

X-ray excited optical luminescence from nanophosphors can be used to selectively generate light in tissue for imaging and stimulating light-responsive materials and cells. Herein, we synthesized X-ray scintillating NaGdF4:Eu and Tb nanophosphors via co-precipitate and hydrothermal methods, encapsulated with silica, functionalized with biotin, and characterized by X-ray excited optical luminescence spectroscopy and imaging. The nanophosphors synthesized by co-precipitate method were ∼90 and ∼106 nm in diameter, respectively, with hydrothermally synthesized particles showing the highest luminescence intensity. More importantly, we investigated the effect of thermal annealing/calcination on the X-ray excited luminescence spectra and intensity. At above 1000 °C, the luminescence intensity increased, but particles fused together. Coating with a 15 nm thick silica shell prevented particle fusion and enabled silane-based chemical functionalization, although luminescence decreased largely due to the increased mass of non-luminescent material. We observed an increase in luminesce intensity with temperature until at 400 °C. At above 600 °C, NaGdF4:Eu@SiO2 converts to NaGd9Si6O26:Eu, an X-ray scintillator brighter than annealed NPs at 400 °C and dimmer than NPs synthesized using the hydrothermal method. The particles generate light through tissue and can be selectively excited using a focused X-ray source for imaging and light generation applications. The particles also act as MRI contrast agents for multi-modal localization.

Contrast agents for x-ray luminescence computed tomography

Imaging probes are an important consideration for any type of contrast agent-based imaging method. X-ray luminescence imaging (XLI) and x-ray luminescence computed tomography (XLCT) are both contrast agent-based imaging methods that employ x-ray excitable scintillating imaging probes that emit light to be measured for optical imaging. In this work, we compared the performance of several select imaging probes, both commercial and self-synthesized, for application in XLI/XLCT imaging. Commercially available cadmium telluride quantum dots (CdTe QDs) and europium-doped gadolinium oxysulfide (GOS:Eu) microphosphor as well as synthesized NaGdF4 nanophosphors doped with either europium or terbium were compared through their x-ray luminescence emission spectra, luminescence intensity, and also by performing XLCT scans using phantoms embedded with each of the imaging probes. Each imaging probe displayed a unique emission spectrum that was ideal for deep-tissue optical imaging. In terms of luminescence intensity, due to the large particle size, GOS:Eu had the brightest emission, followed by NaGdF4:Tb, NaGdF4:Eu, and finally the CdTe QDs. Lastly, XLCT scans showed that each imaging probe could be reconstructed with good shape and location accuracy.

Focused x-ray luminescence imaging system for small animals based on a rotary gantry

SIGNIFICANCE

The ability to detect and localize specific molecules through tissue is important for elucidating the molecular basis of disease and treatment. Unfortunately, most current molecular imaging tools in tissue either lack high spatial resolution (e.g., diffuse optical fluorescence tomography or positron emission tomography) or lack molecular sensitivity (e.g., micro-computed tomography, μCT). X-ray luminescence imaging emerged about 10 years ago to address this issue by combining the molecular sensitivity of optical probes with the high spatial resolution of x-ray imaging through tissue. In particular, x-ray luminescence computed tomography (XLCT) has been demonstrated as a powerful technique for the high-resolution imaging of deeply embedded contrast agents in three dimensions (3D) for small-animal imaging.

AIM

To facilitate the translation of XLCT for small-animal imaging, we have designed and built a small-animal dedicated focused x-ray luminescence tomography (FXLT) scanner with a μCT scanner, synthesized bright and biocompatible nanophosphors as contrast agents, and have developed a deep-learning-based reconstruction algorithm.

APPROACH

The proposed FXLT imaging system was designed using computer-aided design software and built according to specifications. NaGdF4 nanophosphors doped with europium or terbium were synthesized with a silica shell for increased biocompatibility and functionalized with biotin. A deep-learning-based XLCT image reconstruction was also developed based on the residual neural network as a data synthesis method of projection views from few-view data to enhance the reconstructed image quality.

RESULTS

We have built the FXLT scanner for small-animal imaging based on a rotational gantry. With all major imaging components mounted, the motor controlling the gantry can be used to rotate the system with a high accuracy. The synthesized nanophosphors displayed distinct x-ray luminescence emission, which enables multi-color imaging, and has successfully been bound to streptavidin-coated substrates. Lastly, numerical simulations using the proposed deep-learning-based reconstruction algorithm has demonstrated a clear enhancement in the reconstructed image quality.

CONCLUSIONS

The designed FXLT scanner, synthesized nanophosphors, and deep-learning-based reconstruction algorithm show great potential for the high-resolution molecular imaging of small animals.

Tb-Doped core-shell-shell nanophosphors for enhanced X-ray induced luminescence and sensitization of radiodynamic therapy

The development of radiation responsive materials, such as nanoscintillators, enables a variety of exciting new theranostic applications. In particular, the ability of nanophosphors to serve as molecular imaging agents in novel modalities, such as X-ray luminescence computed tomography (XLCT), has gained significant interest recently. Here, we present a radioluminescent nanoplatform consisting of Tb-doped nanophosphors with an unique core/shell/shell (CSS) architecture for improved optical emission under X-ray excitation. Owing to the spatial confinement and separation of luminescent activators, these CSS nanophosphors exhibited bright optical luminescence upon irradiation. In addition to standard physiochemical characterization, these CSS nanophosphors were evaluated for their ability to serve as energy mediators in X-ray stimulated photodynamic therapy, also known as radiodynamic therapy (RDT), through attachment of a photosensitizer, rose bengal (RB). Furthermore, cRGD peptide was used as a model targeting agent against U87 MG glioblastoma cells. In vitro RDT efficacy studies suggested the RGD-CSS-RB in combination with X-ray irradiation could induce enhanced DNA damage and increased cell killing, while the nanoparticles alone are well tolerated. These studies support the utility of CSS nanophosphors and warrants their further development for theranostic applications.

Review of in vivo optical molecular imaging and sensing from x-ray excitation

SIGNIFICANCE

Deep-tissue penetration by x-rays to induce optical responses of specific molecular reporters is a new way to sense and image features of tissue function in vivo. Advances in this field are emerging, as biocompatible probes are invented along with innovations in how to optimally utilize x-ray sources.

AIM

A comprehensive review is provided of the many tools and techniques developed for x-ray-induced optical molecular sensing, covering topics ranging from foundations of x-ray fluorescence imaging and x-ray tomography to the adaptation of these methods for sensing and imaging in vivo.

APPROACH

The ways in which x-rays can interact with molecules and lead to their optical luminescence are reviewed, including temporal methods based on gated acquisition and multipoint scanning for improved lateral or axial resolution.

RESULTS

While some known probes can generate light upon x-ray scintillation, there has been an emergent recognition that excitation of molecular probes by x-ray-induced Cherenkov light is also possible. Emission of Cherenkov radiation requires a threshold energy of x-rays in the high kV or MV range, but has the advantage of being able to excite a broad range of optical molecular probes. In comparison, most scintillating agents are more readily activated by lower keV x-ray energies but are composed of crystalline inorganic constituents, although some organic biocompatible agents have been designed as well. Methods to create high-resolution structured x-ray-optical images are now available, based upon unique scanning approaches and/or a priori knowledge of the scanned x-ray beam geometry. Further improvements in spatial resolution can be achieved by careful system design and algorithm optimization. Current applications of these hybrid x-ray-optical approaches include imaging of tissue oxygenation and pH as well as of certain fluorescent proteins.

CONCLUSIONS

Discovery of x-ray-excited reporters combined with optimized x-ray scan sequences can improve imaging resolution and sensitivity.

Y2O3: Eu3+/PMMA hybrid film as a converter for enhanced harvesting of broadband solar-blind UV light

At present, the most common materials for solar-blind UV light detectors are wide band-gap semiconductors, which generally have high requirements and complex methods for preparation. Ordinary semiconductor materials such as silicon, TiO₂, and Cu₂O were industrialized, but they were excluded for direct harvest of solar-blind UV light due to their inability to absorb solar-blind light photons. Here, inorganic-organic hybrid film of Y₂O₃:Eu³⁺/PMMA was used as a spectral converter to realize the detection of broadband solar-blind UV light by ordinary semiconductor, converting broadband solar-blind UV luminescence to visible luminescence based on down-conversion process, after which the visible luminescence was detected by the Si photo-resister. The results show that hybrid film based on rare earth luminescence materials is particularly valuable for broadband solar-blind UV detection.

Smart diagnostic nano-agents for cerebral ischemia

A summary of the latest developments on imaging techniques and smart nano-diagnostics used for ischemic stroke.

The feasibility of NaGdF4 nanoparticles as an x-ray fluorescence computed tomography imaging probe for the liver and lungs

PURPOSE

As a novel imaging modality, x-ray fluorescence computed tomography (XFCT) can provide distribution and concentration information of contrast agents containing high atomic number elements, such as iodine, gadolinium, barium, gold, and platinum. Since XFCT has a better sensitivity and detection limit of high-Z elements compared with traditional and spectral CT, it becomes a powerful quantitative imaging tool for biological studies. The main problem of current XFCT imaging is its low emission and detection efficiency of x-ray fluorescence (XRF) photons. Increasing XRF photons generation by choosing a high atomic element as a contrast agent is essential to improve the imaging quality of XFCT. Gadolinium emits at least a few times more of XRF photons than gold under the same x-ray excitation condition, leading to a detection limit at a level of sub-mg/mL as the next generation of clinical imaging modality. However, most current XFCT studies have utilized gadolinium salt as the contrast agent, which could not accumulate in organs or tumors efficiently, making in vivo XFCT imaging quite difficult. In this study, we present NaGdF₄ nanoparticles with ultra-small size as nanoprobes to test the feasibility for in vivo XFCT application for the first time.

METHODS

NaGdF₄ nanoparticles with different sizes (3-10 nm) were successfully synthesized via a coprecipitation process by controlling the reaction time at temperature of 290 °C. The morphology, crystal phase, chemical composition, and size of such NPs were further characterized with HR-TEM, XRD, and EDX. The abilities of XRF photons from different sizes of NPs were quantified by our customized XFCT imaging system. To access the in vivo application of as-synthesized NPs, such hydrophobic NPs capped OA molecules were further modified with AEP via a ligand-exchange process and characterized with FT-IR. For in vivo XFCT imaging, 0.1 mL of 30 mg/mL NPs were injected into nude mice via the tail vein. The Varian G-297 x-ray tube was set to 150 kV and 0.5 mA. The XRF photons were captured by a Kromek eV-3500 photon counting detector at each 8° for 10 s.

RESULT

The successfully synthesized NaGdF₄ nanoparticles (3-10 nm) were monodisperse, highly uniform spherical morphology and hexagonal crystalline phases. No significant influence on XRF photons yields or XFCT imaging quality were found by varying the nanoparticle size. The XRF photons were 2.5 times more emitted from NaGdF₄ nanoparticles (NPs) compared to gold nanoparticles, thereby leading to a better image quality. With the AEP surface modification, such NPs were readily adapted for use in in vivo XFCT applications with monodispersity in aqueous solution and negligible cytotoxicity. With the tail-vein injection, the liver, spleen, and lungs could be clearly imaged with XFCT at a sub-mg/mL level.

CONCLUSIONS

Such NaGdF₄ NPs, which were synthesized with coprecipitation process, were modified with AEP for in vivo XFCT applications. With both the phantom and in vivo experiments, such NPs were proved to be appropriate probes for XFCT application with the detection limit at a sub-mg/mL level. In the future research, such NPs could be further functionalized with targeting molecules for early-phase cancer detection.

Feasibility study of three-dimensional multiple-beam x-ray luminescence tomography

X-ray luminescence tomography (XLT) is a promising imaging technology based on x-ray beams, with high-resolution capability. We developed a fan-beam XLT system, where the x-ray beam scans the object at predefined directions and positions. As the scanning at one position needs to cover the object, the data acquisition time is usually long. To improve spatial resolution, we propose a three-dimensional multiple-beam x-ray luminescence imaging method, in which the x rays are modulated by an x-ray fence-modulation component. The proposed method can produce multiple x-ray beams and ensure spatial resolution along the longitudinal direction as well as the transverse plane. The proposed methods of single-source experiments can achieve 0.62 mm in location error and 0.87 in the dice coefficient while 1.32 mm in location error and 0.63 in the dice coefficient in the double-source experiment. The simulation experiments show that our proposed method can achieve better results at different depths than the traditional scanning method. It is also demonstrated that the best simulation results can be achieved with the smallest x-ray width.

Method for improving the spatial resolution of narrow x-ray beam-based x-ray luminescence computed tomography imaging

X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality which has the potential for achieving both high sensitivity and spatial resolution simultaneously. For the narrow x-ray beam-based XLCT imaging, based on previous work, a spatial resolution of about double the x-ray beam size can be achieved using a translate/rotate scanning scheme, taking step sizes equal to the x-ray beam width. To break the current spatial resolution limit, we propose a scanning strategy achieved by reducing the scanning step size to be smaller than the x-ray beam size. We performed four sets of numerical simulations and a phantom experiment using cylindrical phantoms and have demonstrated that our proposed scanning method can greatly improve the XLCT-reconstructed image quality compared with the traditional scanning approach. In our simulations, by using a fixed x-ray beam size of 0.8 mm, we were able to successfully reconstruct six embedded targets as small as 0.5 mm in diameter and with the same edge-to-edge distances by using a scanning step as small as 0.2 mm which is a 1.6 times improvement in the spatial resolution compared with the traditional approach. Lastly, the phantom experiment further demonstrated the efficacy of our proposed method in improving the XLCT image quality, with all image quality metrics improving as the step size decreased.

Quantitative Imaging of Gd Nanoparticles in Mice Using Benchtop Cone-Beam X-ray Fluorescence Computed Tomography System

Nanoparticles (NPs) are currently under intensive research for their application in tumor diagnosis and therapy. X-ray fluorescence computed tomography (XFCT) is considered a promising non-invasive imaging technique to obtain the bio-distribution of nanoparticles which include high-Z elements (e.g., gadolinium (Gd) or gold (Au)). In the present work, a set of experiments with quantitative imaging of GdNPs in mice were performed using our benchtop XFCT device. GdNPs solution which consists of 20 mg/mL NaGdF4 was injected into a nude mouse and two tumor-bearing mice. Each mouse was then irradiated by a cone-beam X-ray source produced by a conventional X-ray tube and a linear-array photon counting detector with a single pinhole collimator was placed on one side of the beamline to record the intensity and spatial information of the X-ray fluorescent photons. The maximum likelihood iterative algorithm with scatter correction and attenuation correction method was applied for quantitative reconstruction of the XFCT images. The results show that the distribution of GdNPs in each target slice (containing liver, kidney or tumor) was well reconstructed and the concentration of GdNPs deposited in each organ was quantitatively estimated, which indicates that this benchtop XFCT system provides convenient tools for obtaining accurate concentration distribution of NPs injected into animals and has potential for imaging of nanoparticles in vivo.

X-ray-activated nanosystems for theranostic applications

X-rays are widely applied in clinical medical facilities for radiotherapy (RT) and biomedical imaging. However, the sole use of X-rays for cancer treatment leads to insufficient radiation energy deposition due to the low X-ray attenuation coefficients of living tissues and organs, producing unavoidable excessive radiation doses with serious side effects to healthy body parts. Over the past decade, developments in materials science and nanotechnology have led to rapid progress in the field of X-ray-activated tumor-targeting nanosystems, which are able to tackle even systemic tumors and relieve the burden of exposure to large radiation doses. Additionally, novel imaging contrast agents and techniques have also been developed. In comparison with conventional external light sources (e.g., near infrared), the X-ray technique is ideal for the activation of nanosystems for cancer treatment and biomedical imaging applications due to its nearly unlimited penetration depth in living tissues and organisms. In this review, we systematically describe the interaction mechanisms between X-rays and nanosystems, and provide an overview of X-ray-sensitive materials and the recent progress on X-ray-activated nanosystems for cancer-associated theranostic applications.

Luminescent-Magnetic Cellulose Fibers, Modified with Lanthanide-Doped Core/Shell Nanostructures

Novel luminescent-magnetic cellulose microfibers were prepared by a dry-wet spinning method with the use of N-methylmorpholine-N-oxide. The synthesized luminescent-magnetic core/shell type nanostructures, based on the lanthanide-doped fluorides and magnetite nanoparticles (NPs)-Fe₃O₄/SiO₂/NH₂/PAA/LnF₃, were used as nanomodifiers of the fibers. Thanks to the successful incorporation of the bifunctional nanomodifiers into the cellulose structure, the functionalized fibers exhibited superior properties, that is, bright multicolor emission under UV light and strong magnetic response. By the use of the as-prepared fibers, the luminescent-magnetic thread was fabricated and used to sew and make a unique pattern in the glove material, as a proof of concept for advanced, multimodal cloths'/materials' protection against counterfeiting. The presence and uniform distribution of the modifier NPs in the polymer matrix were confirmed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis (EDX). The concentration of the modifier NPs in the fibers was determined by inductively coupled plasma mass spectrometry, EDX, and magnetic measurements. The luminescence characteristics of the materials were examined by photoluminescence spectroscopy, and their magnetic field-responsive behavior was investigated by a superconducting quantum interference device.

Spectral-resolved cone-beam X-ray luminescence computed tomography with principle component analysis

Cone-beam X-ray luminescence computed tomography (CB-XLCT) has become a promising technique for its higher utilization of X-ray and shorter scanning time compared to the narrow-beam XLCT, but it suffers from the low-spatial resolution that results in the insufficiency to resolve the adjacent multiple probes. In multispectral CB-XLCT, multiple probes show different emission behaviors in the dimension of the spectrum. In this work, a spectral-resolved CB-XLCT method combining multispectral CB-XLCT with principle component analysis (PCA) was proposed to improve the imaging resolution. Results of digital simulation and the phantom experiment illustrated that the proposed method was capable of resolving adjacent multiple probes accurately and had better performance than the common multispectral CB-XLCT with spectrum information priori.

Radioluminescence studies of colloidal oleate-capped β-Na(Gd,Lu)F4:Ln3+ nanoparticles (Ln = Ce, Eu, Tb)

We report on the synthesis, characterization, and radioluminescence quantification of several new varieties of nanoparticles with the general composition β-NaLnF4, incorporating known luminescent activator/sensitizer pairs. Using Monte Carlo modeling to complement luminescence measurements, we have calculated the radioluminescence yields and intrinsic conversion efficiencies of colloidally-dispersed nanoparticles by comparison to an organic liquid scintillator. While five of the compositions had low to modest radioluminescence yields relative to bulk materials, colloidal β-Na(Lu0.65Gd0.2Tb0.15)F4 displayed a strong output of 39 460 photons per MeV absorbed, comparable to some of the best non-hygroscopic bulk crystal scintillators and X-ray phosphors such as Gd2O2S:Tb. Measurements of β-Na(Lu0.65Gd0.2Tb0.15)F4 powder samples revealed persistent luminescence as well as stable charge trapping, warranting further investigation.

Cone-beam x-ray luminescence computed tomography based on x-ray absorption dosage

With the advances of x-ray excitable nanophosphors, x-ray luminescence computed tomography (XLCT) has become a promising hybrid imaging modality. In particular, a cone-beam XLCT (CB-XLCT) system has demonstrated its potential in in vivo imaging with the advantage of fast imaging speed over other XLCT systems. Currently, the imaging models of most XLCT systems assume that nanophosphors emit light based on the intensity distribution of x-ray within the object, not completely reflecting the nature of the x-ray excitation process. To improve the imaging quality of CB-XLCT, an imaging model that adopts an excitation model of nanophosphors based on x-ray absorption dosage is proposed in this study. To solve the ill-posed inverse problem, a reconstruction algorithm that combines the adaptive Tikhonov regularization method with the imaging model is implemented for CB-XLCT reconstruction. Numerical simulations and phantom experiments indicate that compared with the traditional forward model based on x-ray intensity, the proposed dose-based model could improve the image quality of CB-XLCT significantly in terms of target shape, localization accuracy, and image contrast. In addition, the proposed model behaves better in distinguishing closer targets, demonstrating its advantage in improving spatial resolution.

Synthesis and luminescence properties of Eu3+-activated BiF3 nanoparticles for optical thermometry and fluorescence imaging in rice root

The luminescence, optical thermometric properties, phytotoxicity, and fluorescence imaging in plant cells of Eu³⁺-activated BiF₃ nanoparticles were systematically studied. Under the excitation of near-ultraviolet light, the prepared compounds emitted visible red light arising from the intra-4f transitions of Eu³⁺ ions. By employing the fluorescence intensity ratio technique, the temperature sensing performance of the synthesized nanoparticles was investigated and the maximum sensitivity was demonstrated to be 3.4 × 10⁻⁵ K⁻¹ at 443 K. Furthermore, the rice root, which was treated with Eu³⁺-activated BiF₃ nanoparticles, showed similar primary root elongation and crown root number to the seedlings cultivated in the MS0 medium without nanoparticles, indicating the relatively low phytotoxicity of the resultant samples to the rice root. Additionally, the results of the toxicity-related gene levels and phenotypes also demonstrated the low phytotoxicity of the as-prepared nanoparticles to the plant cells. Ultimately, with the help of the red emission of Eu³⁺ ions, the studied compounds were found to be accumulated in the division and differentiation regions of the rice root rather than transferred to the above-ground tissues. These results suggest that the Eu³⁺-activated BiF₃ nanoparticles may have potential applications in non-invasive optical temperature sensors and fluorescence probes in plant cells.

The luminescence, optical thermometric properties, phytotoxicity, and fluorescence imaging in plant cells of Eu³⁺-activated BiF₃ nanoparticles were systematically studied.