Monitoring pH-triggered drug release from radioluminescent nanocapsules with X-ray excited optical luminescence

Nanomaterials for light-mediated therapeutics in deep tissue

Light-mediated therapeutics, including photodynamic therapy, photothermal therapy and light-triggered drug delivery, have been widely studied due to their high specificity and effective therapy. However, conventional light-mediated therapies usually depend on the activation of light-sensitive molecules with UV or visible light, which have poor penetration in biological tissues. Over the past decade, efforts have been made to engineer nanosystems that can generate luminescence through excitation with near-infrared (NIR) light, ultrasound or X-ray. Certain nanosystems can even carry out light-mediated therapy through chemiluminescence, eliminating the need for external activation. Compared to UV or visible light, these 4 excitation modes penetrate more deeply into biological tissues, triggering light-mediated therapy in deeper tissues. In this review, we systematically report the design and mechanisms of different luminescent nanosystems excited by the 4 excitation sources, methods to enhance the generated luminescence, and recent applications of such nanosystems in deep tissue light-mediated therapeutics.

Surface-Doped Zinc Gallate Colloidal Nanoparticles Exhibit pH-Dependent Radioluminescence with Enhancement in Acidic Media

As abnormal acidic pH symbolizes dysfunctions of cells, it is highly desirable to develop pH-sensitive luminescent materials for diagnosing disease and imaging-guided therapy using high-energy radiation. Herein, we explored near-infrared-emitting Cr-doped zinc gallate ZnGa₂O₄ nanoparticles (NPs) in colloidal solutions with different pH levels under X-ray excitation. Ultrasmall NPs were synthesized via a facile hydrothermal method by controlling the addition of ammonium hydroxide precursor and reaction time, and structural characterization revealed Cr dopants on the surface of NPs. The synthesized NPs exhibited different photoluminescence and radioluminescence mechanisms, confirming the surface distribution of activators. It was observed that the colloidal NPs emit pH-dependent radioluminescence in a linear relationship, and the enhancement reached 4.6-fold when pH = 4 compared with the colloidal NPs in the neutral solution. This observation provides a strategy for developing new biomaterials by engineering activators on the nanoparticle surfaces for potential pH-sensitive imaging and imaging-guided therapy using high-energy radiation.

Advancing X-ray Luminescence for Imaging, Biosensing, and Theragnostics

X-ray luminescence is an optical phenomenon in which chemical compounds known as scintillators can emit short-wavelength light upon the excitation of X-ray photons. Since X-rays exhibit well-recognized advantages of deep penetration toward tissues and a minimal autofluorescence background in biological samples, X-ray luminescence has been increasingly becoming a promising optical tool for tackling the challenges in the fields of imaging, biosensing, and theragnostics. In recent years, the emergence of nanocrystal scintillators have further expanded the application scenarios of X-ray luminescence, such as high-resolution X-ray imaging, autofluorescence-free detection of biomarkers, and noninvasive phototherapy in deep tissues. Meanwhile, X-ray luminescence holds great promise in breaking the depth dependency of deep-seated lesion treatment and achieving synergistic radiotherapy with phototherapy.In this Account, we provide an overview of recent advances in developing advanced X-ray luminescence for applications in imaging, biosensing, theragnostics, and optogenetics neuromodulation. We first introduce solution-processed lead halide all-inorganic perovskite nanocrystal scintillators that are able to convert X-ray photons to multicolor X-ray luminescence. We have developed a perovskite nanoscintillator-based X-ray detector for high-resolution X-ray imaging of the internal structure of electronic circuits and biological samples. We further advanced the development of flexible X-ray luminescence imaging using solution-processable lanthanide-doped nanoscintillators featuring long-lived X-ray luminescence to image three-dimensional irregularly shaped objects. We also outline the general principles of high-contrast in vivo X-ray luminescence imaging which combines nanoscintillators with functional biomolecules such as aptamers, peptides, and antibodies. High-quality X-ray luminescence nanoprobes were engineered to achieve the high-sensitivity detection of various biomarkers, which enabled the avoidance of interference from the biological matrix autofluorescence and photon scattering. By marrying X-ray luminescence probes with stimuli-responsive materials, multifunctional theragnostic nanosystems were constructed for on-demand synergistic gas radiotherapy with excellent therapeutic effects. By taking advantage of the capability of X-rays to penetrate the skull, we also demonstrated the development of controllable, wireless optogenetic neuromodulation using X-ray luminescence probes while obviating damage from traditional optical fibers. Furthermore, we discussed in detail some challenges and future development of X-ray luminescence in terms of scintillator synthesis and surface modification, mechanism studies, and their other potential applications to provide useful guidance for further advancing the development of X-ray luminescence.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Combining X-ray excited optical luminescence and X-ray absorption spectroscopy for correlative imaging on the nanoscale

X-ray absorption and optical luminescence can both provide valuable but very different information on the chemical and physical properties of materials. Although it is known that the spectral characteristics of many materials are highly heterogeneous on the micro- and/or nanoscale, no methodology has so far been shown to be capable of spatially resolving both full X-ray absorption and X-ray excited optical luminescence (XEOL) spectra on the nanoscale in a correlative manner. For this purpose, the scanning transmission X-ray microscope at the HERMES beamline of the SOLEIL synchrotron was equipped with an optical detection system capable of recording high-resolution XEOL spectra using a 40 nm soft X-ray probe. The functionality of the system was demonstrated by analyzing ZnO powder dispersions - showing simultaneously the X-ray linear dichroism and XEOL behavior of individual submicrometric ZnO crystallites.

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.

An Overview of Gadolinium-Based Oxide and Oxysulfide Particles: Synthesis, Properties, and Biomedical Applications

In the last decade, the publications presenting novel physical and chemical aspects of gadolinium-based oxide (Gd2O3) and oxysulfide (Gd2O2S) particles in the micro- or nano-scale have increased, mainly stimulated by the exciting applications of these materials in the biomedical field. Their optical properties, related to down and upconversion phenomena and the ability to functionalize their surface, make them attractive for developing new probes for selective targeting and emergent bioimaging techniques, either for biomolecule labeling or theranostics. Moreover, recent reports have shown interesting optical behavior of these systems influenced by the synthesis methods, dopant amount and type, particle shape and size, and surface functionality. Hence, this review presents a compilation of the latest works focused on evaluating the optical properties of Gd2O3 and Gd2O2S particles as a function of their physicochemical and morphological properties; and also on their novel applications as MRI contrast agents and drug delivery nanovehicles, discussed along with their administration routes, biodistribution, cytotoxicity, and clearance mechanisms. Perspectives for this field are also identified and discussed.

Strategies for Preparing Different Types of Lipid Polymer Hybrid Nanoparticles in Targeted Tumor Therapy

At present, cancer is one of the most common diseases in the world, causing a large number of deaths and seriously affecting people's health. The traditional treatment of cancer is mainly surgery, radiotherapy or chemotherapy. Conventional chemotherapy is still an important treatment, but it has some shortcomings, such as poor cell selectivity, serious side effects, drug resistance and so on. Nanoparticle administration can improve drug stability, reduce toxicity, prolong drug release time, prolong system half-life, and bring broad prospects for tumor therapy. Lipid polymer hybrid nanoparticles (LPNs), which combine the advantages of polymer core and phospholipid shell to form a single platform, have become multi-functional drug delivery platforms. This review introduces the basic characteristics, structure and preparation methods of LPNs, and discusses targeting strategies of LPNs in tumor therapy in order to overcome the defects of traditional drug therapy.

Wireless Optogenetic Modulation of Cortical Neurons Enabled by Radioluminescent Nanoparticles

While offering high-precision control of neural circuits, optogenetics is hampered by the necessity to implant fiber-optic waveguides in order to deliver photons to genetically engineered light-gated neurons in the brain. Unlike laser light, X-rays freely pass biological barriers. Here we show that radioluminescent Gd₂(WO₄)₃:Eu nanoparticles, which absorb external X-rays energy and then downconvert it into optical photons with wavelengths of ∼610 nm, can be used for the transcranial stimulation of cortical neurons expressing red-shifted, ∼590-630 nm, channelrhodopsin ReaChR, thereby promoting optogenetic neural control to the practical implementation of minimally invasive wireless deep brain stimulation.

Interfacial Photo-Cross-Linking: Simple but Powerful Approach for Fabricating Capsule Polymer Particles with Tunable pH-Responsive Controlled Release Capability

Herein, we describe capsule polymer particles with precisely controlled pH-responsive release properties prepared directly via the interfacial photo-cross-linking of spherical poly(2-diethylaminoethyl methacrylate-co-2-cinnamoylethyl methacrylate) (P(DEAEMA-CEMA)) particles. In the interfacial photo-cross-linking, photoreactive cinnamoyl groups in the polymer particles were cross-linked via [2π + 2π] cycloaddition reactions at the polymer/water interface, showing that the shell-cross-linked hollow polymer particles can be directly prepared from spherical polymer particles. The approach has fascinating advantages such as using minimal components, simplicity, and not requiring sacrificial template particles and toxic solvents. The following important observations are made: (I) encapsulated materials were stably retained in the capsule particles under neutral pH conditions; (II) encapsulated materials were released from the capsule particles under acidic pH conditions; (III) the release kinetics of encapsulated materials were controlled by the pH conditions; i.e., immediate and sustained release was achieved by varying the acidity of the aqueous media; (IV) the photoirradiation time did not significantly affect the release kinetics under different pH conditions; and (V) the pH-responsive release properties were regulated by changing the polymer composition in P(DEAEMA-CEMA). Furthermore, by exploiting the pH-responsiveness, capsule particles are successfully obtained via an all-aqueous process from spherical polymer particles. The advantages of the all-aqueous encapsulation process allowed the water-soluble biomacromolecules such as DNA and saccharides to be successfully encapsulated in the P(DEAEMA-CEMA) hollow particles. With this simple interfacial photo-cross-linking strategy, we envision the ready synthesis of sophisticated particulate materials for broad application in advanced research fields.

Development of dispersible radioluminescent silicate nanoparticles through a sacrificial layer approach

X-rays offer low tissue attenuation with high penetration depth when used in medical applications and when coupled with radioluminescent nanoparticles, offer novel theranostic opportunities. In this role, the ideal scintillator requires a high degree of crystallinity for an application relevant radioluminescence, yet a key challenge is the irreversible aggregation of the particles at most crystallization temperatures. In this communication, a high temperature multi-composite reactor (HTMcR) process was successfully developed to recrystallize monodisperse scintillating particulates by employing a core-multishell architecture. The core-shell morphology of the particles consisted of a silica core over-coated with a rare earth (Re = Y³⁺, Lu³⁺, Ce³⁺) oxide shell. This core-shell assembly was then encapsulated within a poly(divinylbenzene) shell which was converted to glassy carbon during the annealing & crystallization of the silica/rare earth oxide core-shell particle. This glassy carbon acted as a delamination layer and prevented the irreversible aggregation of the particles during the high temperature crystallization step. A subsequent low temperature annealing step in an air environment removed the glassy carbon and resulted in radioluminescent nanoparticles. Two monodisperse nanoparticle systems were synthesized using the HTMcR process including cerium doped Y₂Si₂O₇ and Lu₂Si₂O₇ with radioluminescence peaks at 427 and 399 nm, respectively. These particles may be employed as an in vivo light source for a noninvasive X-ray excited optogenetics.

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.

A brief review on solid lipid nanoparticles: part and parcel of contemporary drug delivery systems

Drug delivery technology has a wide spectrum, which is continuously being upgraded at a stupendous speed. Different fabricated nanoparticles and drugs possessing low solubility and poor pharmacokinetic profiles are the two major substances extensively delivered to target sites. Among the colloidal carriers, nanolipid dispersions (liposomes, deformable liposomes, virosomes, ethosomes, and solid lipid nanoparticles) are ideal delivery systems with the advantages of biodegradation and nontoxicity. Among them, nano-structured lipid carriers and solid lipid nanoparticles (SLNs) are dominant, which can be modified to exhibit various advantages, compared to liposomes and polymeric nanoparticles. Nano-structured lipid carriers and SLNs are non-biotoxic since they are biodegradable. Besides, they are highly stable. Their (nano-structured lipid carriers and SLNs) morphology, structural characteristics, ingredients used for preparation, techniques for their production, and characterization using various methods are discussed in this review. Also, although nano-structured lipid carriers and SLNs are based on lipids and surfactants, the effect of these two matrixes to build excipients is also discussed together with their pharmacological significance with novel theranostic approaches, stability and storage.

Multimodal gadolinium oxysulfide nanoparticles for bioimaging: A comprehensive biodistribution, elimination and toxicological study

For some years now, gadolinium oxysulfide nanoparticles (NPs) appear as strong candidates for very efficient multimodal in vivo imaging by: 1) Magnetic Resonance (MRI), 2) X-ray Computed Tomography (CT) and 3) photoluminescence imaging. In this paper, we present a selection of results centered on the evaluation of physico-chemical stability, toxicity, bio-distribution and excretion mechanisms of Gd₂O₂S:Ln³⁺ nanoparticles intravenously injected in rats. Two formulations are here tested with a common matrix and different dopants: Gd₂O₂S:Eu³⁺_5% and Gd₂O₂S:Yb³⁺_4%/Tm³⁺_0.1%. The NPs appear to be almost insoluble in pure water and human plasma but corrosion/degradation phenomenon appears in acidic conditions classically encountered in cell lysosomes. Whole body in vivo distribution, excretion and toxicity evaluation revealed a high tolerance of nanoparticles with a long-lasting imaging signal associated with a slow hepatobiliary clearance and very weak urinary excretion. The results show that the majority of the injected product (>60%) has been excreted through the feces after five months. Experiments have evidenced that the NPs mainly accumulate in macrophage-rich organs, that is mainly liver and spleen and to a lesser extent lungs and bones (mainly marrow). No significant amounts have been detected in other organs such as heart, kidneys, brain, intestine and skin. Gd₂O₂S:Ln³⁺ NPs appeared to be very well tolerated up to 400 mg/kg when administered intravenously. STATEMENT OF SIGNIFICANCE: Since 2011, we have focused our work on Gd₂O₂S nanoparticles (NPs) for multimodal bioimaging using fluorescence, Magnetic Resonance Imaging (MRI) and Computed Tomography with very efficient results already published. However, since the European Medicines Agency has concluded its review of gadolinium contrast agents, confirming recommendations to restrict the use of some linear gadolinium agents used in MRI, a particular attention must be paid to any new contrast media containing gadolinium. Therefore, we present in this paper a compilation of studies about toxicity, bio-distribution and excretion mechanisms of Gd₂O₂S:Ln³⁺ NPs intravenously injected into rats. We also present an in vitro kinetic study of NPs degradation in aqueous and biological media to provide some information on chemical and biological stability.

Metal Oxysulfides: From Bulk Compounds to Nanomaterials

This review summarizes the syntheses and applications of metal oxysulfides. Bulk compounds of rare earth and transition metals are discussed in the section Introduction. After a presentation of their main properties and applications, their structures are presented and their syntheses are discussed. The section Bulk Materials and Their Main Applications is dedicated to the growing field of nanoscaled metal oxysulfides. Synthesis and applications of lanthanide-based nanoparticles are more mature and are discussed first. Then, works on transition-metal based nanoparticles are presented and discussed. Altogether, this review highlights the opportunities offered by metal oxysulfides for application in a range of technological fields, in relation with the most advanced synthetic routes and characterization techniques.

Multilayer capsules made of weak polyelectrolytes: a review on the preparation, functionalization and applications in drug delivery

Multilayer capsules have been of great interest for scientists and medical communities in multidisciplinary fields of research, such as drug delivery, sensing, biomedicine, theranostics and gene therapy. The most essential attributes of a drug delivery system are considered to be multi-functionality and stimuli responsiveness against a range of external and internal stimuli. Apart from the highly explored strong polyelectrolytes, weak polyelectrolytes offer great versatility with a highly controllable architecture, unique stimuli responsiveness and easy tuning of the properties for intracellular delivery of cargo. This review describes the progress in the preparation, functionalization and applications of capsules made of weak polyelectrolytes or their combination with biopolymers. The selection of a sacrificial template for capsule formation, the driving forces involved, the encapsulation of a variety of cargo and release based on different internal and external stimuli have also been addressed. We describe recent perspectives and obstacles of weak polyelectrolyte/biopolymer systems in applications such as therapeutics, biosensing, bioimaging, bioreactors, vaccination, tissue engineering and gene delivery. This review gives an emerging outlook on the advantages and unique responsiveness of weak polyelectrolyte based systems that can enable their widespread use in potential applications.

Principal Component Analysis Based Dynamic Cone Beam X-Ray Luminescence Computed Tomography: A Feasibility Study

Cone beam X-ray luminescence computed tomography (CB-XLCT) is a promising imaging technique in studying the physiological and pathological processes in small animals. However, the dynamic bio-distributions of probes in small animal, especially in adjacent targets are still hard to be captured directly from dynamic CB-XLCT. In this paper, a 4D temporal-spatial reconstruction method based on principal component analysis (PCA) in the projection space is proposed for dynamic CB-XLCT. First, projections of angles in each 3D frame are compressed to reduce the noises initially. Then a temporal PCA is performed on the projection data to decorrelate the 4D problem into separate 3D problems in the PCA domain. In the PCA domain, the difference between dynamic behaviors of multiple targets can be reflected by the first several principal components which can be further used for fast and improved reconstruction by a restarted Tikhonov regularization method. At last, by discarding the principal components mainly reflecting noise, the concentration series of targets are recovered from the first few reconstruction results with a mask as the constraint. The numerical simulation and phantom experiment demonstrate that the proposed method can resolve multiple targets and recover the dynamic distributions with high computation efficiency. The proposed method provides new feasibility for imaging dynamic bio-distributions of probes in vivo.

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.

Fabrication of Hybrid Nanostructures Based on Fe3O4 Nanoclusters as Theranostic Agents for Magnetic Resonance Imaging and Drug Delivery

Combining anticancer drugs with inorganic nanocrystals to construct multifunctional hybrid nanostructures has become a powerful tool for cancer treatment and tumor suppression. However, it remains a critical challenge to synthesize compact, multifunctional nanostructures with improved functionality and reproducibility. In this study, we report the fabrication of magnetite hybrid nanostructures employing Fe3O4 nanoparticles (NPs) to form multifunctional magnetite nanoclusters (NCs) by combining an oil-in-water microemulsion assembly and a layer-by-layer (LBL) method. The Fe3O4 NCs were firstly prepared via a microemulsion self-assembly technique. Then, polyelectrolyte layers composed of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) and doxorubicin hydrochloride (DOX) were capped on Fe3O4 NCs to construct the Fe3O4 NC/PAH/PSS/DOX hybrid nanostructures via LBL method. The as-prepared hybrid nanostructures loaded with DOX demonstrated the pH-responsive drug release and higher cytotoxicity towards human lung cancer (A549) cells in vitro and can serve as T2-weighted magnetic resonance imaging (MRI) contrast agents, which can significantly improve T2 relaxivity and lead to a better cellular MRI contrast effect. The loaded DOX emitting red signals under excitation with 490 nm are suitable for bioimaging applications. This work provides a novel strategy to build a Fe3O4-based multifunctional theranostic nanoplatform with T2-weighted MRI, fluorescence imaging, and drug delivery.

Breaking the Depth Dependence by Nanotechnology-Enhanced X-Ray-Excited Deep Cancer Theranostics

The advancements in nanotechnology have created multifunctional nanomaterials aimed at enhancing diagnostic accuracy and treatment efficacy for cancer. However, the ability to target deep-seated tumors remains one of the most critical challenges for certain nanomedicine applications. To this end, X-ray-excited theranostic techniques provide a means of overcoming the limits of light penetration and tissue attenuation. Herein, a comprehensive overview of the recent advances in nanotechnology-enhanced X-ray-excited imaging and therapeutic methodologies is presented, with an emphasis on the design of multifunctional nanomaterials for contrast-enhanced computed tomography (CT) imaging, X-ray-excited optical luminescence (XEOL) imaging, and X-ray-excited multimodal synchronous/synergistic therapy. The latter is based on the concurrent use of radiotherapy with chemotherapy, gas therapy, photodynamic therapy, or immunotherapy. Moreover, the featured biomedical applications of X-ray-excited deep theranostics are discussed to highlight the advantages of X-ray in high-sensitivity detection and efficient elimination of malignant tumors. Finally, key issues and technical challenges associated with this deep theranostic technology are identified, with the intention of advancing its translation into the clinic.

Toolbox for In Vivo Imaging of Host-Parasite Interactions at Multiple Scales

Animal models have for long been pivotal for parasitology research. Over the last few years, techniques such as intravital, optoacoustic and magnetic resonance imaging, optical projection tomography, and selective plane illumination microscopy developed promising potential for gaining insights into host-pathogen interactions by allowing different visualization forms in vivo and ex vivo. Advances including increased resolution, penetration depth, and acquisition speed, together with more complex image analysis methods, facilitate tackling biological problems previously impossible to study and/or quantify. Here we discuss advances and challenges in the in vivo imaging toolbox, which hold promising potential for the field of parasitology.

Radioluminescence in biomedicine: physics, applications, and models

The electromagnetic spectrum contains different frequency bands useful for medical imaging and therapy. Short wavelengths (ionizing radiation) are commonly used for radiological and radionuclide imaging and for cancer radiation therapy. Intermediate wavelengths (optical radiation) are useful for more localized imaging and for photodynamic therapy (PDT). Finally, longer wavelengths are the basis for magnetic resonance imaging and for hyperthermia treatments. Recently, there has been a surge of interest for new biomedical methods that synergize optical and ionizing radiation by exploiting the ability of ionizing radiation to stimulate optical emissions. These physical phenomena, together known as radioluminescence, are being used for applications as diverse as radionuclide imaging, radiation therapy monitoring, phototherapy, and nanoparticle-based molecular imaging. This review provides a comprehensive treatment of the physics of radioluminescence and includes simple analytical models to estimate the luminescence yield of scintillators and nanoscintillators, Cherenkov radiation, air fluorescence, and biologically endogenous radioluminescence. Examples of methods that use radioluminescence for diagnostic or therapeutic applications are reviewed and analyzed in light of these quantitative physical models of radioluminescence.

Nanoparticle Binding to Urokinase Receptor on Cancer Cell Surface Triggers Nanoparticle Disintegration and Cargo Release

Cancer cell expresses abundant surface receptors. These receptors are important targets for cancer treatment and imaging applications. Our goal here is to develop nanoparticles with cargo loading and tumor targeting capability.

Methods: A peptide targeting at cancer cell surface receptor (urokinase receptor, uPAR) was expressed in fusion with albumin (diameter of ~7 nm), and the fusion protein was assembled into nanoparticles with diameter of 40 nm, either in the presence or absence of cargo molecules, by a novel preparation method. An important feature of this method is that the nanoparticles were stabilized by hydrophobic interaction of the fusion protein and no covalent linking agent was used in the preparation. The stability, the cargo release, in vitro and in vivo properties of such formed nanoparticles were characterized by transmission electron microscopy, dynamic light scattering, gel shift assay, laser scanning confocal microscopy and 3D fluorescent molecular tomography.

Results: The nanoparticles were stable for more than two weeks in aqueous buffer, even in the buffer containing 10% fetal bovine serum. Interestingly, in the presence of urokinase receptor, the uPAR-targeting nanoparticle disintegrated into 7.5 nm fragments and released its cargo, but not the non-targeting nanoparticles made from albumin by the same preparation method. Such nanoparticles also showed higher uptake and cytotoxicity to the receptor-expressing cancer cells in vitro and higher tumor accumulation in xenografted tumor-bearing mice in vivo compared to the non-targeting nanoparticles.

Conclusion: Our results demonstrate a new function of cell surface receptor as a responsive trigger to disassemble nanoparticles, besides its common use to enrich targeting agents. Such nanoparticles were thus named receptor-responsive nanoparticles (RRNP).

Imaging and therapeutic applications of persistent luminescence nanomaterials

The development of probes for biomolecular imaging and diagnostics is a very active research area. Among the different imaging modalities, optics emerged since it is a noninvasive and cheap imaging technique allowing real time imaging. In vitro, this technique is very useful however in vivo, fluorescence suffers from low signal-to-noise ratio due to tissue autofluorescence under constant excitation. To address this limitation, novel types of optical nanoprobes are actually being developed and among them, persistent luminescence nanoparticles (PLNPs), with long lasting near-infrared (NIR) luminescence capability, allows doing optical imaging without constant excitation and so without autofluorescence. This review will begin by introducing the physical phenomenon associated to the long luminescence decay of such nanoprobes, from minutes to hours after ceasing the excitation. Then we will show how this property can be used to develop in vivo imaging probes and also more recently nanotheranostic agents. Finally, preliminary data on their biocompatibility will be mentioned and we will conclude by envisioning on the future applications and improvements of such nanomaterials.

Noninvasive real-time monitoring of local drug release using nano-Au-absorbed self-decomposable SiO2 carriers

Real time monitoring of drug release at specific local sites by a non-invasive imaging method is critical in patient-specific drug administration in order to avoid insufficient or excess drug dosing. In the present work, we designed a specific carrier system for such a purpose using self-decomposable SiO2 nanoparticles (NPs) with the drug being loaded in the center and Au NPs on the SiO2 NPs as the imaging agent. We discovered a correlation between the drug release from the carrier and the morphological evolution of Au NPs, which also left the carrier and changed their aggregation states along with the drug release process. This finding enabled the real time monitoring of the drug release at local sites (e.g. tumor) in a quantitative manner by recording the CT signal evolution of the Au NPs, as demonstrated in vivo using mice bearing Colo-205 xenografts. The present work provided a promising platform for non-invasive real time tracking on the localized drug release, enabling a variety of personalized therapeutic applications.

Ga Ion-Enhanced and Particle Shape-Dependent Generation of Reactive Oxygen Species in X-ray-Irradiated Composites

The reported results test the effects of the collective behavior hypothesized to contribute to the production of more reactive oxygen species (ROS) in vitro and result in an enhanced radiosensitization. The role of particle shape in composites with gallium oxyhydroxide (GaOOH) particles and Matrigel is studied. Particles of two different shapes are embedded into the gel to understand only the materials effect on the generation of ROS rather than cell penetrating variations. The paper reports materials characterization by scanning electron microscopy and X-ray diffraction. The stability of the particles within the composite is assessed by quantification of leached metal using inductively coupled plasma mass spectrometry. The amount of ROS in each construct under variable radiation conditions is quantified in the presence and absence of PC12 cells seeded on top of the composites. The viability of cells is also recorded under different in vitro conditions. The collective materials characterization and the results from the bioassays are used to explain the role of anisotropy on the radiosensitization of nanostructures containing Ga. The presence of Ga ions in composites can have a radiosensitizing effect, and the amount of the available Ga³⁺ determines the magnitude of the radiosensitization. The shape of the particles determines the stability in aqueous solutions and release of Ga³⁺ that triggers ROS production. The concentration and shape of Ga-containing materials can be combined to generate an additive effect by increasing the amount of available free metal ions in solution. The studies with GaOOH containing composites enable one to explore the role of key parameters that lead to an increased efficiency of radiation treatments.

Gamma rays excited radioluminescence tomographic imaging

Background

Radionuclide-excited luminescence imaging is an optical radionuclide imaging strategy to reveal the distributions of radioluminescent nanophosphors (RLNPs) inside small animals, which uses radioluminescence emitted from RLNPs when excited by high energy rays such as gamma rays generated during the decay of radiotracers used in clinical nuclear medicine imaging. Currently, there is no report of tomographic imaging based on radioluminescence.

Methods

In this paper, we proposed a gamma rays excited radioluminescence tomography (GRLT) to reveal three-dimensional distributions of RLNPs inside a small animal using radioluminescence through image reconstruction from surface measurements of radioluminescent photons using an inverse algorithm. The diffusion equation was employed to model propagations of radioluminescent photons in biological tissues with highly scattering and low absorption characteristics.

Results

Phantom and artificial source-implanted mouse model experiments were employed to test the feasibility of GRLT, and the results demonstrated that the ability of GRLT to reveal the distribution of RLNPs such as Gd₂O₂S:Tb using the radioluminescent signals when excited by gamma rays produced from ^99mTc.

Conclusions

With the emerging of targeted RLNPs, GRLT can provide new possibilities for in vivo and noninvasive examination of biological processes at cellular levels. Especially, combining with Cerenkov luminescence imaging, GRLT can achieve dual molecular information of RLNPs and nuclides using single optical imaging technology.

Thermometry properties of Er, Yb-Gd2O2S microparticles: dependence on the excitation mode (cw versus pulsed excitation) and excitation wavelength (980 nm versus 1500 nm)

Herein, we present a first report on the luminescence thermometry properties of Er, Yb doped Gd₂O₂S microparticles under near infrared up-conversion excitation at 980 and 1500 nm measured in the 280-800 K interval. The thermometry properties are assessed using both cw and ns pulsed excitation as well as tuning the excitation wavelength across Yb and Er absorption profiles. For low cw (300 mW cm^-1) and pulsed ns (400 ÷ 550 mW cm^-1) excitation modes, no thermal load is observed. At room-temperature (280 K), the maximum relative sensitivity values are comparable under pulsed excitation at 980 and 1500 nm, around ∼0.01 and ∼0.008% K^-1, respectively. In addition, a relative intense up-conversion emission at 980 nm under excitation at 1500 nm is measured. Our findings evidence attractive up-conversion and thermometry properties Er, Yb doped Gd₂O₂S under near-infrared excitation and highlight the need to explore further these properties in the nanoparticulate regime.

High-efficiency X-ray luminescence in Eu3+-activated tungstate nanoprobes for optical imaging through energy transfer sensitization

X-ray luminescence optical imaging has been recognized as a powerful technique for medical diagnosis due to its deep penetration and low auto-fluorescence in tissues. However, the low luminescence efficiency of current X-ray luminescence nanoprobes remains a major hurdle for sensitive bioimaging in practical medical applications. Here we present a new kind of energy transfer-sensitized X-ray luminescence nanoprobe (PEG-NaGd(WO₄)₂:Eu) for highly effective optical bioimaging. Under X-ray excitation, the tungstate host absorbs the X-ray photons and then transfers the energy to the Eu³⁺ luminescence center, thus enhancing the luminescence efficiency of the nanoprobes for high sensitivity optical in vivo imaging. Moreover, the shortened T₁ relaxation response of Gd³⁺ ions and X-ray attenuation capability of W atoms enable the nanoprobes to serve as efficient contrast agents for magnetic resonance imaging (MRI) and computed tomography (CT) imaging. Therefore, combined with the MRI, CT and X-ray luminescence imaging capabilities, the present PEG-NaGd(WO₄)₂:Eu nanoprobes could be used as promising multimodal imaging contrast agents in biological systems.

Short-wave near-infrared emissive GdPO4:Nd3+theranostic probe forin vivobioimaging beyond 1300 nm

The optical probes working in the second near-infrared (NIR-II) window have attracted increasing research interest for their advantages of high tissue penetration depth, low autofluorescence, and unprecedentedly improved imaging sensitivity and spatial resolution. Therefore, it is of great significance to design a new nanoplatform by integration of NIR-II optical imaging and drug delivery functions. Herein, a multifunctional nanoplatform based on GdPO₄:Nd³⁺ yolk–shell sphere was developed for dual-modal in vivo NIR-II/X-ray bioimaging and pH-responsive drug delivery. The in vivo NIR-II bioimaging and real-time tracking presented that these probes were mainly accumulated in liver and spleen. Moreover, owing to the large X-ray absorption coefficient of Gd³⁺, these probes are successfully used as superior X-ray imaging agents than iobitridol. The in vivo toxicity assessments demonstrate the low biotoxicity of the GdPO₄:Nd³⁺ spheres in living animals. More importantly, apart from the excellent dual-modal bioimaging, these yolk–shell-structured probes were also used as ideal nanotransducer for pH-responsive drug delivery of doxorubicin (DOX). These findings open up the opportunity of designing theranostic nanoplatform with integration of imaging-based diagnosis and therapy.

A multifunctional theranostic nanoplatform based on GdPO₄:Nd³⁺ yolk–shell sphere was developed for dual-modal in vivo NIR-II/X-ray bioimaging and pH-responsive drug delivery.

Soft X-ray activated NaYF4:Gd/Tb scintillating nanorods for in vivo dual-modal X-ray/X-ray-induced optical bioimaging

Lanthanide (Ln) nanocrystals using soft X-ray as an excitation source have received significant research interest due to the advantages of unlimited penetration depth of X-ray light. In this study, we demonstrated an efficient scintillator based on NaYF₄:Gd nanorods (denoted as NRs) doped with different contents of terbium (Tb) ions for optical bioimaging under X-ray irradiation. The experimental results showed that the emission intensity was correlated to the doping contents of Tb³⁺, and the largest emission intensity was achieved by doping 15% Tb under excitation by soft X-ray light. In addition, the emission intensity of the as-prepared NRs can be significantly improved by increasing the excitation power and irradiation times of the X-ray. Owing to the efficient X-ray-induced emission, these NRs were successfully used as probes for X-ray-induced optical bioimaging with high sensitivity. In addition, the dual-modal X-ray imaging and X-ray induced optical bioimaging were performed on a mouse, which indicated that the NRs were promising dual-modal bioprobes. Therefore, the X-ray activation nature of the designed NRs makes them promising probes for biomedicine and X-ray-induced photodynamic therapy (PDT) applications owing to the unlimited penetration depth of X-ray excitation source and absence of autofluorescence.

LiGa5O8:Cr-based theranostic nanoparticles for imaging-guided X-ray induced photodynamic therapy of deep-seated tumors

Using X-ray as the irradiation source, a photodynamic therapy process can be initiated from under deep tissues. This technology, referred to as X-ray induced PDT, or X-PDT, holds great potential to treat tumors at internal organs. To this end, one question is how to navigate the treatment to tumors with accuracy with external irradiation. Herein we address the issue with a novel, LiGa₅O₈: Cr (LGO:Cr)-based nanoscintillator, which emits persistent, near-infrared X-ray luminescence. This permits deep-tissue optical imaging that can be employed to guide irradiation. Specifically, we encapsulated LGO:Cr nanoparticles and a photosensitizer, 2,3-naphthalocyanine, into mesoporous silica nanoparticles. The nanoparticles were conjugated with cetuximab and systemically injected into H1299 orthotopic non-small cell lung cancer tumor models. The nanoconjugates can efficiently home to tumors in the lung, confirmed by monitoring X-ray luminescence from LGO:Cr. Guided by the imaging, external irradiation was applied, leading to efficient tumor suppression while minimally affecting normal tissues. To the best of our knowledge, the present study is the first to demonstrate, with systematically injected nanoparticles, that X-PDT can suppress growth of deep-seated tumors. The imaging guidance is also new to X-PDT, and is significant to the further transformation of the technology.

XEOL spectroscopy of lanthanides in aqueous solution

As part of an ongoing study of the electronic interactions between solute and solvent molecules, a method for X-ray excited optical luminescence (XEOL) analysis of aqueous solutions was developed at the double-crystal monochromator beamline (DCM) of the Canadian Synchrotron Radiation Facility (CSRF). It was tested using a series of solutions containing lanthanide ions. The samples were contained in a sample holder for liquids with a 3 μm Mylar window separating them from the vacuum (≤3 × 10−6 torr, 1 torr = 133.3224 Pa) in the solid state absorption chamber of the DCM beamline. Terbium, samarium, and dysprosium have 4 intense and narrow luminescence peaks between 450 and 700 nm, well separated from the luminescence peak of the Mylar window between 300 and 425 nm. The intensity of the rare earth (RE3+) luminescence peaks was lower for the solutions than for solid RECl3·6H2O. In part, this was caused by the lower RE3+ concentration in the solutions than in the solid. In addition, the solvent (water) acts as a quencher. The disorder and the molecular motion in the solution increase the availability of nonradiative de-excitation pathways. A high concentration of SO42− in the solution enhanced the luminescence intensity, probably by inhibiting some nonradiative de-excitation pathways. This study has shown that it is in principle possible to investigate the luminescence of aqueous solutions with XEOL spectroscopy. Furthermore, it is possible to use this technique as a quantitative analytical tool for concentrated luminescent solutions and to study the shielding effects of anions in the solution that increase the luminescence intensity.

Sensitivity evaluation and selective plane imaging geometry for x-ray-induced luminescence imaging

PURPOSE

X-ray-induced luminescence (XIL) is a hybrid x-ray/optical imaging modality that employs nanophosphors that luminescence in response to x-ray irradiation. X-ray-activated phosphorescent nanoparticles have potential applications in radiation therapy as theranostics, nanodosimeters, or radiosensitizers. Extracting clinically relevant information from the luminescent signal requires the development of a robust imaging model that can determine nanophosphor distributions at depth in an optically scattering environment from surface radiance measurements. The applications of XIL in radiotherapy will be limited by the dose-dependent sensitivity at depth in tissue. We propose a novel geometry called selective plane XIL (SPXIL), and apply it to experimental measurements in optical gel phantoms and sensitivity simulations.

METHODS

An imaging model is presented based on the selective plane geometry which can determine the detected diffuse optical signal for a given x-ray dose and nanophosphor distribution at depth in a semi-infinite, optically homogenous material. The surface radiance in the model is calculated using an analytical solution to the extrapolated boundary condition. Y₂ O₃ :Eu³⁺ nanoparticles are synthesized and inserted into various optical phantom in order to measure the luminescent output per unit dose for a given concentration of nanophosphors and calibrate an imaging model for XIL sensitivity simulations. SPXIL imaging with a dual-source optical gel phantom is performed, and an iterative Richardson-Lucy deconvolution using a shifted Poisson noise model is applied to the measurements in order to reconstruct the nanophosphor distribution.

RESULTS

Nanophosphor characterizations showed a peak emission at 611 nm, a linear luminescent response to tube current and nanoparticle concentration, and a quadratic luminescent response to tube voltage. The luminescent efficiency calculation accomplished with calibrated bioluminescence mouse phantoms determines 1.06 photons were emitted per keV of x-ray radiation absorbed per g/mL of nanophosphor concentration. Sensitivity simulations determined that XIL could detect a concentration of 1 mg/mL of nanophosphors with a dose of 1 cGy at a depth ranging from 2 to 4 cm, depending on the optical parameters of the homogeneous diffuse optical environment. The deconvolution applied to the SPXIL measurements could resolve two sources 1 cm apart up to a depth of 1.75 cm in the diffuse phantom.

CONCLUSIONS

We present a novel imaging geometry for XIL in a homogenous, diffuse optical environment. Basic characterization of Y₂ O₃ :Eu³⁺ nanophosphors are presented along with XIL/SPXIL measurements in optical gel phantoms. The diffuse optical imaging model is validated using these measurements and then calibrated in order to execute initial sensitivity simulations for the dose-depth limitations of XIL imaging. The SPXIL imaging model is used to perform a deconvolution on a dual-source phantom, which successfully reconstructs the nanophosphor distributions.

X-ray-Activated Near-Infrared Persistent Luminescent Probe for Deep-Tissue and Renewable in Vivo Bioimaging

Near-infrared (NIR) persistent luminescence nanoparticles (PLNPs) are considered as new alternative optical probes due to being free of autofluorescence, benefited from the self-sustained emission after excitation and high signal-to-noise ratio. However, the NIR-emitted PLNPs always present a short decay time and require excitation by ultraviolet or visible light with a short penetrable depth, remarkably hindering their applications for in vivo long-term tracking and imaging. Therefore, it is important to develop NIR-emitted PLNPs with in vivo activation nature by new excitation sources with deeper penetrating depths. Here, we propose a new type of X-ray-activated ZnGa₂O₄:Cr PLNPs (X-PLNPs) with efficient NIR persistent emission and rechargeable activation features, in which both the excitation and emission possess a high penetrable nature in vivo. These X-PLNPs exhibit long-lasting, up to 6 h, NIR emission at 700 nm after the stoppage of the X-ray excitation source. More importantly, the designed X-PLNPs can be readily reactivated by a soft X-ray excitation source with low excitation power (45 kVp, 0.5 mA) to restore in vivo bioimaging signals even at 20 mm depth. Renewable in vivo whole-body bioimaging was also successfully achieved via intravenous injection/oral administration of X-PLNPs after in situ X-ray activation. This is the first time that NIR-emitted PLNPs have been demonstrated to be recharged by X-ray light for deep-tissue in vivo bioimaging, which paves the way for in vivo renewable bioimaging using PLNPs and makes the PLNPs more competitive in bioimaging area.

Bright X-ray and up-conversion nanophosphors annealed using encapsulated sintering agents for bioimaging applications

Nanophosphors are promising contrast agents for deep tissue optical imaging applications because they can be excited by X-ray and near infrared light that penetrates deeply through tissue and generates almost no autofluorescence background in the tissue. For these bioimaging applications, the nanophosophors should ideally be small, monodispersed and brightly luminescent. However, most methods used to improve luminescence yield by annealing the particles to reduce crystal and surface defects (e.g. using flux or sintering agents) also cause particle fusion or require multiple component core-shell structures. Here, we report a novel method to prepare bright, uniformly sized X-ray nanophosphors (Gd2O2S:Eu or Tb) and upconversion nanophosphors (Y2O2S: Yb/Er, or Yb/Tm) with large crystal domain size without causing aggregation. A core-shell nanoparticle is formed, with NaF only in the core. We observe that increasing the NaF sintering agent concentration up to 7.6 mol% increases both crystal domain size and luminescence intensity (up to 40% of commercial microphosphors) without affecting the physical particticle diameter. Above 7.6 mol%, particle fusion is observed. The annealing is insensitive to the cation (Na+ or K+) but varies strongly with anion, with F->Cl->CO32->Br->I-. The luminescence depends strongly on crystal domain size. The data agree reasonably well with a simple domain surface quenching model, although the size-dependence suggests additional quenching mechanisms within small domains. The prepared bright nanophosphors were subsequently functionalized with PEG-folic acid to target MCF-7 breast cancer cells which overexpress folic acid receptors. Both X-ray and upconversion nanophosphors provided low background and bright luminescence which was imaged through 1 cm chicken breast tissue at a low dose of nanophosphors 200 µL (0.1 mg/mL). We anticipate these highly monodispersed and bright X-ray and upconversion nanophosphors will have significant potential for tumor targeted imaging.

Reduction-Responsive Carbon Dots for Real-Time Ratiometric Monitoring of Anticancer Prodrug Activation in Living Cells

Anticancer prodrugs have been extensively investigated to lower toxic side effects of common chemotherapeutic agents in biomedical fields. To illustrate the activation mechanism of anticancer prodrugs, fluorescent dyes or single-emission intensity alteration-based approaches have been widely used. However, fluorescent dyes often suffer from poor photostability and chemical stability, and single-emission intensity alteration-based methods cannot avoid the influence from uncontrolled microenvironment changes in living samples. To overcome these obstacles, herein, a fluorescence resonance energy transfer (FRET)-based ratiometric approach was successfully developed for real-time monitoring of anticancer prodrug activation. Excitation-wavelength-dependent and full-color-emissive carbon dots (CDs) were used as drug nanocarriers and FRET donor, and a cisplatin(IV) prodrug was selected as the model drug and the linker to load the Dabsyl quencher on the surface of CDs. Owing to the FRET effect, the blue fluorescence of CDs was effectively quenched by the Dabsyl unit. Under reductive conditions in solution or in living cells for the reduction of cisplatin(IV) prodrug to Pt(II) species, the blue fluorescence of CDs increased over time, without apparent intensity change for green or red fluorescence. Thus, the gradually enhanced intensity ratio of blue-to-green or blue-to-red fluorescence could be indicative of the real-time reduction of the cisplatin(IV) prodrug to cytotoxic Pt(II) species. This ratiometric method could exclude the influence from complex biological microenvironments by using green or red fluorescence of CDs as an internal reference, which provides new insights into the activation of the cisplatin(IV) prodrug and offers a great opportunity to design safe and effective anticancer therapeutics.

Current Multistage Drug Delivery Systems Based on the Tumor Microenvironment

The development of traditional tumor-targeted drug delivery systems based on EPR effect and receptor-mediated endocytosis is very challenging probably because of the biological complexity of tumors as well as the limitations in the design of the functional nano-sized delivery systems. Recently, multistage drug delivery systems (Ms-DDS) triggered by various specific tumor microenvironment stimuli have emerged for tumor therapy and imaging. In response to the differences in the physiological blood circulation, tumor microenvironment, and intracellular environment, Ms-DDS can change their physicochemical properties (such as size, hydrophobicity, or zeta potential) to achieve deeper tumor penetration, enhanced cellular uptake, timely drug release, as well as effective endosomal escape. Based on these mechanisms, Ms-DDS could deliver maximum quantity of drugs to the therapeutic targets including tumor tissues, cells, and subcellular organelles and eventually exhibit the highest therapeutic efficacy. In this review, we expatiate on various responsive modes triggered by the tumor microenvironment stimuli, introduce recent advances in multistage nanoparticle systems, especially the multi-stimuli responsive delivery systems, and discuss their functions, effects, and prospects.

Cone Beam X-ray Luminescence Computed Tomography Based on Bayesian Method

X-ray luminescence computed tomography (XLCT), which aims to achieve molecular and functional imaging by X-rays, has recently been proposed as a new imaging modality. Combining the principles of X-ray excitation of luminescence-based probes and optical signal detection, XLCT naturally fuses functional and anatomical images and provides complementary information for a wide range of applications in biomedical research. In order to improve the data acquisition efficiency of previously developed narrow-beam XLCT, a cone beam XLCT (CB-XLCT) mode is adopted here to take advantage of the useful geometric features of cone beam excitation. Practically, a major hurdle in using cone beam X-ray for XLCT is that the inverse problem here is seriously ill-conditioned, hindering us to achieve good image quality. In this paper, we propose a novel Bayesian method to tackle the bottleneck in CB-XLCT reconstruction. The method utilizes a local regularization strategy based on Gaussian Markov random field to mitigate the ill-conditioness of CB-XLCT. An alternating optimization scheme is then used to automatically calculate all the unknown hyperparameters while an iterative coordinate descent algorithm is adopted to reconstruct the image with a voxel-based closed-form solution. Results of numerical simulations and mouse experiments show that the self-adaptive Bayesian method significantly improves the CB-XLCT image quality as compared with conventional methods.

Intrinsically 89Zr-labeled Gd2O2S:Eu nanophosphors with high in vivo stability for dual-modality imaging

Radioluminescence imaging (RLI) employs high energy particles from radioisotope decay for in situ excitation of selected nanophosphors. Co-injection of radiopharmaceuticals and nanophosphors suffers from suboptimal RL efficiency owing to the large separation between the source and the emitter. In addition, vastly different pharmacokinetic profiles of the two further impede the practical applications of this approach. To overcome the above challenges, chelator-free radiolabeled nanophosphors with excellent RL efficiency and dual-modality imaging capabilities have been proposed. Abundant O2- donors on Gd2O2S:Eu could intrinsically chelate oxophilic radionuclide 89Zr with ~80 % labeling yield. Positron emission tomography demonstrated superb long-term radiostability of [89Zr]Gd2O2S:Eu@PEG nanoparticles in vivo, and a conventional optical imaging system was used to study radiouminescence properties of [89Zr]Gd2O2S:Eu@PEG nanoparticles in vitro and in vivo.

Shape induced acid responsive heat triggered highly facilitated drug release by cube shaped magnetite nanoparticles

This paper reports a very simple yet better method for synthesis of cube shaped magnetite nanoparticles (MNPs) and their application in the drug delivery system (DDS). Structural analysis was done by XRD measurements to confirm the phase of the material, and morphological information was obtained through TEM analysis to confirm the shape and size of the particles. It has been shown that these particles can be decomposed in acid medium. These acid-decomposable magnetite nano-particles have been used for heat triggered, remote-controlled, on demand delivery and release of a cancer drug doxorubicin for research and therapeutic purposes. Here, we have shown that the pH stimulated and heat-triggered release of drug from our MNPs significantly enhances the release efficiency. In this case, we observe that pH induced release is far better in comparison to heat-triggered release. From these inspiring results, it may be expected that this methodology may become a significant step towards the development of a pH-sensitive heat triggered drug delivery system minimizing drug toxicity.

Cone Beam X-Ray Luminescence Tomography Imaging Based on KA-FEM Method for Small Animals

Cone beam X-ray luminescence tomography can realize fast X-ray luminescence tomography imaging with relatively low scanning time compared with narrow beam X-ray luminescence tomography. However, cone beam X-ray luminescence tomography suffers from an ill-posed reconstruction problem. First, the feasibility of experiments with different penetration and multispectra in small animal has been tested using nanophosphor material. Then, the hybrid reconstruction algorithm with KA-FEM method has been applied in cone beam X-ray luminescence tomography for small animals to overcome the ill-posed reconstruction problem, whose advantage and property have been demonstrated in fluorescence tomography imaging. The in vivo mouse experiment proved the feasibility of the proposed method.

Two-photon sensitized hollow Gd2O3:Eu(3+) nanocomposites for real-time dual-mode imaging and monitoring of anticancer drug release

New two-photon sensitized multifunctional nanocomposites were designed for dual-mode imaging and real-time drug release monitoring by photoluminescence (PL) and magnetic resonance imaging (MRI). By drug loading based on coordination effect, PL signals of Eu(3+) and MRI signals of Gd(3+) can be stabilized and enhanced, respectively, which then display excellent linear decreases on drug release.

Synthesis of Hollow Mesoporous Silica Nanorods with Controllable Aspect Ratios for Intracellular Triggered Drug Release in Cancer Cells

Here, we have reported a straightforward and effective synthetic strategy for synthesis of aspect-ratios-controllable mesoporous silica nanorods with hollow structure (hMSR) and its application for transcription factor (TF)-responsive drug delivery intracellular. Templating by an acid-degradable nickel hydrazine nanorods (NHNT), we have first synthesized the hollow dense silica nanorods and then coated on a mesoporous silica layer. Subsequently, the dense silica layer was removed by the surface-protected etching method and the hollow structure of hMSR was finally formed. The aspect ratios of the hMSR can be conveniently controlled by regulating the aspect ratios of NHNT. Four different hMSR with aspect ratios of ca. 2.5, ca. 5.3, ca. 8.1, and ca. 9.0 has been obtained. It was demonstrated that the as-prepared hMSRs have good stability, high drug loading capacity, and fast cell uptake capability, which makes them to a potential nanocarrier for drug delivery. As the paradigm, hMSR with an aspect ratio of ca. 8.1 was then applied for TF-responsive intracellular anticancer drug controlled release by using a Ag(+)-stabilized molecular switch of triplex DNA (TDNA) as capping agents and probes for TFs recognition. In the presence of TF, the pores of hMSR can be unlocked by the TFs induced disassembly of TDNA, leading to the leakage of DOX. The research in vitro displayed that this system has a TFs-triggered DOX release, and the cytotoxicity in L02 normal cells was lower than that of HeLa cells. We hope that this developed hMSR-based system will promote the development of cancer therapy in related fields.

Intrinsically Zirconium-89 Labeled Gd2 O2 S:Eu Nanoprobes for In Vivo Positron Emission Tomography and Gamma-Ray-Induced Radioluminescence Imaging

The engineering of a novel dual-modality imaging probe is reported here by intrinsically labeling zirconium-89 ((89) Zr, a positron emission radioisotope with a half-life of 78.4 h) to PEGylated Gd2 O2 S:Eu nanophorphors, forming [(89) Zr]Gd2 O2 S:Eu@PEG for in vivo positron emission tomography/radioluminescence lymph node mapping.