Gd-encapsulated carbonaceous dots with efficient renal clearance for magnetic resonance imaging

Alginate mediated functional aggregation of gold nanoclusters for systemic photothermal therapy and efficient renal clearance

For renal clearable nanoagents, it is challenging to delay the renal clearance to acquire efficient tumor accumulation. Herein, we report sodium alginate (SA) stabilized gold (Au) NCs. The Au NCs are of high biocompatibility and renal clearable. Contributed from the ligands of SA, the half-life (t_1/2) of Au NCs is prolonged to ∼9.3 h, enhancing the tumor accumulation rate to 10.4 %ID/g. In tumor microenvironment (TME), the Au NCs are stimulated to functionally aggregate, which switches on the photothermal effect. Animal experiments prove that Au NCs aggregates are efficient photothermal therapy (PTT) agents for both local treatment of single tumors and systemic treatment of double-tumor models without causing noticeable side effects, confirming the biosecurity of Au NCs and systemic PTT. The switchable strategy of PTT may signify the establishment of a new systemic therapeutic methodology.

Hyaluronic Acid-Functionalized Gadolinium Oxide Nanoparticles for Magnetic Resonance Imaging-Guided Radiotherapy of Tumors

Inaccuracy localization and intrinsic radioresistance of solid tumors seriously hindered the clinical implementation of radiotherapy. In this study, we fabricated hyaluronic acid-functionalized gadolinium oxide nanoparticles (HA-Gd₂O₃ NPs) via one-pot hydrothermal process for effective magnetic resonance (MR) imaging and radiosensitization of tumors. By virtue of HA functionalization, the as-prepared HA-Gd₂O₃ NPs with a diameter of 105 nm showed favorable dispersibility in water, low cytotoxicity, and excellent biocompatibility and readily entered into the cytoplasm of cancer cells by HA receptor-mediated endocytosis. Importantly, HA-Gd₂O₃ NPs exhibited high longitudinal relaxivity (r₁) 6.0 mM^-1S^-1 as MRI contrast agents and radiosensitization enhancement in a dose-dependent manner. These finds demonstrated that as-synthesized HA-Gd₂O₃ NPs as bifunctional theranostic agents have great potential in tumors diagnosis and radiotherapy.

A plausible way for excretion of metal nanoparticles via active targeting

Even so, the metal nanoparticles (metal NPs) have attractive optical and biomedical applications, the translation of metal NPs into the clinical practice remains a challenge due to their severe accumulation in the body. Active targeting to renal podocytes opens the door for enhancing kidney targeting and clearance. The goal of this study was to assess the excretion of larger particle size through kidney podocyte via active targeting. To reach this goal, PEGylated quantum dots (QDs) were coated with vapreotide (VAP) for selectively reaching somatostatin receptors (SSTRs) expressed in the podocyte cells. This QDs-VAP was tested on isolated primary podocytes, while the flow cytometry (FACS), confocal microscopy (CLSM), and inductively coupled plasma mass spectrometry (ICP-MS) were used to confirm this hypothesis. The results showed highly specific interactions with podocyte cells as detected by FACS, and CLSM. Moreover, ICP-MS demonstrated higher amount of QDs in the podocyte cells one-hour post-incubation (67.99% ID/g tissue), while the unmodified QDs did not accumulate. This study confirmed that QDs-VAP can target the podocyte's SSTRs then can be cleared via podocyte cells. Moreover, these results are considered as a highly promising approach for future therapy, targeting, clearance, and diagnosis of podocyte-associated diseases.

Single-layer boron-doped graphene quantum dots for contrast-enhanced in vivo T1-weighted MRI

Gadolinium (Gd)-based chelates are used as clinical T1 contrast agents for magnetic resonance imaging (MRI) due to their demonstrated high sensitivity and positive contrast enhancement capability. However, there has been an increasing safety concern about their use in medicine because of the toxicity of the metal ions released from these contrast agents when used in vivo. Although significant effort has been made in developing metal-free MRI contrast agents, none have matched the magnetic properties achieved by the gold standard clinical contrast agent, Gd diethylene penta-acetic acid (Gd-DTPA). Here, we report the development of a single-layer, boron-doped graphene quantum dot (termed SL-BGQD) that demonstrates better T1 contrast enhancement than Gd-DTPA. The SL-BGQD is shown to provide significantly higher positive contrast enhancement than the Gd-DTPA contrast agent in imaging vital organs, including kidneys, liver, and spleen, and especially, vasculatures. Further, our results show that the SL-BQGD is able to bypass the blood-brain barrier and allows sustained imaging for at least one hour with a single injection. Hematological and histopathological analyses show that the SL-BGQD demonstrates a non-toxic profile in wild-type mice and may, therefore, serve as an improved, safer alternative to currently available clinical MRI contrast agents.

Rapid, facile, reagentless, and room-temperature conjugation of monolayer MoS2 nanosheets with dual-fluorophore-labeled flares as nanoprobes for ratiometric sensing of TK1 mRNA in living cells

Surface functionalization of MoS₂ nanosheets with FRET-based flares was conducted for ratiometric sensing and imaging of TK1 mRNA in HeLa and MCF-7 cells.

Tumor Targeting Strategies of Smart Fluorescent Nanoparticles and Their Applications in Cancer Diagnosis and Treatment

Advantages such as strong signal strength, resistance to photobleaching, tunable fluorescence emissions, high sensitivity, and biocompatibility are the driving forces for the application of fluorescent nanoparticles (FNPs) in cancer diagnosis and therapy. In addition, the large surface area and easy modification of FNPs provide a platform for the design of multifunctional nanoparticles (MFNPs) for tumor targeting, diagnosis, and treatment. In order to obtain better targeting and therapeutic effects, it is necessary to understand the properties and targeting mechanisms of FNPs, which are the foundation and play a key role in the targeting design of nanoparticles (NPs). Widely accepted and applied targeting mechanisms such as enhanced permeability and retention (EPR) effect, active targeting, and tumor microenvironment (TME) targeting are summarized here. Additionally, a freshly discovered targeting mechanism is introduced, termed cell membrane permeability targeting (CMPT), which improves the tumor-targeting rate from less than 5% of the EPR effect to more than 50%. A new design strategy is also summarized, which is promising for future clinical targeting NPs/nanomedicines design. The targeting mechanism and design strategy will inspire new insights and thoughts on targeting design and will speed up precision medicine and contribute to cancer therapy and early diagnosis.

Polyethylenimine-Based Nanogels for Biomedical Applications

Nanogels (NGs) are 3-dimensional (3D) networks composed of hydrophilic or amphiphilic polymer chains, allowing for effective and homogeneous encapsulation of drugs, genes, or imaging agents for biomedical applications. Polyethylenimine (PEI), possessing abundant positively charged amine groups, is an ideal platform for the development of NGs. A variety of effective PEI-based NGs have been designed and much effort has been devoted to study the relationship between the structure and function of the NGs. In particular, PEI-based NGs can be prepared either using PEI as the major NG component or using PEI as a crosslinker. This review reports the recent progresses in the design of PEI-based NGs for gene and drug delivery and for bioimaging applications with a target focus to tackle the diagnosis and therapy of cancer.

Fluorescent carbon dots functionalization

Carbon dots (CDs), as a new type of luminescent zero-dimensional carbon nanomaterial, have been applied in a variety of fields. Currently, functionalization of CDs is an extremely useful method for effectively tuning their intrinsic structure and surface state. Heteroatom doping and surface modification are two functionalization strategies for improving the photophysical performance and broadening the range of applications for fluorescent CDs. Heteroatom doping in CDs can be used to tune their intrinsic properties, which has received significant research interests because of its simplicity. Surface modification can be applied for varying active sites and the functional groups on the CDs surface, which can endow fluorescent CDs with the unique properties resulting from functional ligand. In this review, we summarize the structural and physicochemical properties of functional CDs. We focused our review on the latest developments in functionalization strategies for CDs and discuss the detailed characteristics of different functionalization methods. Ultimately, we hope to inform researchers on the latest progress in functionalization of CDs and provide perspectives on future developments for functionalization of CDs and their potential applications.

Fluorine and Nitrogen Co-Doped Carbon Dot Complexation with Fe(III) as a T1 Contrast Agent for Magnetic Resonance Imaging

Commercial gadolinium-based materials have been widely used as contrast agents for magnetic resonance imaging (MRI), but the high toxicity of leaking free Gd³⁺ ions still raises biosafety concerns. Here, we develop a novel, safe, and efficient MRI contrast agent based on a stable Fe(III) complex of fluorine and nitrogen co-doped carbon dots (F,N-CDs) that was prepared from glucose and levofloxacin by a simple microwave-assisted thermal decomposition method. The obtained Fe³⁺@F,N-CD complex exhibits higher longitudinal relaxivity ( r₁ = 5.79 mM^-1·s^-1) than that of the control samples of the Fe³⁺@CD complex ( r₁ = 4.23 mM^-1 s^-1) and free Fe³⁺ ( r₁ = 1.59 mM^-1 s^-1) in aqueous solution, as assessed by a 1.5 T NMR analyzer. More importantly, the Fe³⁺@F,N-CD complex is very stable with a large coordination constant of 1.06 × 10⁷ in aqueous medium. While incubated with HeLa cells, the Fe³⁺@F,N-CD complex shows clear MR images, demonstrating that it has potential to be an excellent MRI contrast agent. Furthermore, in vivo MRI experiments indicate that the Fe³⁺@F,N-CD complex provides high-resolution MRI pictures of 4T1 tumor bearing BALB/c mice 15 min after injection and can be completely excreted 2 h after administration. No cytotoxicity was observed with F,N-CDs and Fe concentration up to 0.2 mg/mL and 0.3 mM in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation assay, respectively. The possible mechanism of the enhanced MRI effect of the Fe³⁺@F,N-CD complex is therefore proposed. The extremely low toxicity, high r₁ relaxivity, strong photoluminescence, and low synthetic cost enable the Fe³⁺@F,N-CD complex to be a safe and promising T₁-weighted MRI contrast agent for clinical applications.

Probing the biological obstacles of nanomedicine with gold nanoparticles

Despite massive growth in nanomedicine research to date, the field still lacks fundamental understanding of how certain physical and chemical features of a nanoparticle affect its ability to overcome biological obstacles in vivo and reach its intended target. To gain fundamental understanding of how physical and chemical parameters affect the biological outcomes of administered nanoparticles, model systems that can systematically manipulate a single parameter with minimal influence on others are needed. Gold nanoparticles are particularly good model systems in this case as one can synthetically control the physical dimensions and surface chemistry of the particles independently and with great precision. Additionally, the chemical and physical properties of gold allow particles to be detected and quantified in tissues and cells with high sensitivity. Through systematic biological studies using gold nanoparticles, insights toward rationally designed nanomedicine for in vivo imaging and therapy can be obtained. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

A magnetofluorescent boron-doped carbon dots as a metal-free bimodal probe

High-resolution observation of biological process is vital for biological researches and diagnosing diseases, which requires accurate diagnosis that involves coordinating imaging technologies such as fluorescence and magnetic resonance (MR). Nowadays, metal-based labels have been used for dual modality imaging. However, heavy metal ions are not environment-and organism-friendly. Therefore, it is a desirable to fabricate a metal-free label with fluorescence and MR properties. Herein, we synthesized boron-doped carbon dots (B-CDs) with dual modal properties through a one-pot solvothermal process. Compared with boron-free CDs, B-CDs exhibited apparent red-shift fluoresence emission, higher fluorescence intensity, and higher longitudinal relaxivity (r₁ = 5.13 mM^-1 s^-1). It demonstrated that boron doping can enhance the fluorescence intensity of CDs, and maybe lead to form paramagnetic centers. The fluorescence and MR imaging of B-CDs make them a prospective label for clinical applications as a result of their oversimplified synthesis process, low cost, good biocompatibility and low toxicity. It will open a new window for building novel imaging labels.

Nanoparticles to mediate X-ray-induced photodynamic therapy and Cherenkov radiation photodynamic therapy

Photodynamic therapy (PDT) has emerged as an attractive option for cancer treatment. However, conventional PDT is activated by light that has poor tissue penetration depths, limiting its applicability in the clinic. Recently the idea of using X-ray sources to activate PDT and overcome the shallow penetration issue has garnered significant interest. This can be achieved by external beam irradiation and using a nanoparticle scintillator as transducer. Alternatively, research on exploiting Cherenkov radiation from radioisotopes to activate PDT has also begun to flourish. In either approach, the most auspicious success is achieved using nanoparticles as either a scintillator or a photosensitizer to mediate energy transfer and radical production. Both X-ray induced PDT (X-PDT) and Cherenkov radiation PDT (CR-PDT) contain a significant radiation therapy (RT) component and are essentially PDT and RT combination. Unlike the conventional combination, however, in X-PDT and CR-PDT, one energy source simultaneously activates both processes, making the combination always in synchronism and the synergy potential maximized. While still in early stage of development, X-PDT and CR-PDT address important issues in the clinic and hold great potential in translation. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Preparation of gadolinium doped carbon dots for enhanced MR imaging and cell fluorescence labeling

Gadolinium doped carbon dots (Gd-CDs) were prepared as a dual-modal imaging agent for enhanced MR imaging and cell fluorescence imaging. The Gd-CDs were synthesized via one-step solvent free technique with Gd-DTPA and l-arginine as the Gd and carbon sources with a quantum yield of 57.78%. The Gd-CDs exhibited good crystal structure, excellent aqueous dispersity, high colloidal stability, intense fluorescence and low cytotoxicity. The bio-TEM images revealed that the Gd-CDs could be easily internalized by cancer cells and escape from the endosomes. Furthermore, the Gd-CDs demonstrated wonderful multi-color fluoresence cell labeling ability at various excitation wavelength and much better MR contrast effect compared with commercial Gd-DTPA with a high r₁ relaxivity value 6.27 mM^-1s^-1. In addition, Gd-CDs exhibited brighter MR signal than Gd-DTPA in the animal MR imaging test. Finally, the Gd-CDs also indicated low long-term toxicity by the serum biochemistry analysis. Thus, these results indicated that Gd-CDs would be an excellent dual-modal imaging probe for enhanced MR imaging and fluorescence imaging.

Development of hollow ferrogadolinium nanonetworks for dual-modal MRI guided cancer chemotherapy

The development of hollow ferrogadolinium nanonetworks has not been reported for nanomedicine application until now. In this study, we developed a hollow and porous ferrogadolinium nanonetwork structure using the one-pot solvothermal method. This nanoparticle could be simultaneously used as a T₁ and T₂ dual-modal magnetic resonance imaging (MRI) contrast agent. In addition, the hollow lumen and abundant pores of the nanonetworks maximized the loading capacity and conferred the nanoplatforms for suitable anticancer drug loading capacity. Using these nanonetworks, MRI and anticancer experiments were conducted in vitro and satisfactory dual-modal MRI and cancer chemotherapy results were obtained. Therefore, the nanonetworks with dual-modal MRI and drug loading abilities effectively complement the ferrogadolinium composites' library and hold great promise in nanomedicine for simultaneous cancer diagnosis and chemotherapy.

This multifunctional nanomaterial with a nanonetwork architecture can be used for dual-modal MRI guided cancer chemotherapy.

Full-color emissive carbon-dots targeting cell walls of onion for in situ imaging of heavy metal pollution

Full-colour emissive carbon-dots were prepared and applied in targeting onion CWs for in situ imaging of heavy metal pollution.

Enhancement of mitochondrial ROS accumulation and radiotherapeutic efficacy using a Gd-doped titania nanosensitizer

Radiotherapy is an extensively used treatment modality in the clinic and can kill malignant cells by generating cytotoxic reactive oxygen species (ROS). Unfortunately, excessive dosages of radiation are typically required because only a small proportion of the radiative energy is adsorbed by the soft tissues of a tumor, which results in the nonselective killing of normal cells and severe systemic side effects. An efficient nanosensitizer that makes cancer cells more sensitive to radiotherapy under a relatively low radiation dose would be highly desirable.

Methods: In this study, we developed a Gd-doped titania nanosensitizer that targets mitochondria to achieve efficient radiotherapy. Upon X-ray irradiation, the nanosensitizer triggers a “domino effect” of ROS accumulation in mitochondria. This overabundance of ROS leads to mitochondrial permeability transition and ultimately irreversible cell apoptosis. Confocal laser imaging, western blotting and flow cytometry analysis were used to explore the biological process of intrinsic apoptosis induced by the nanosensitizer. Clonogenic survival assay, cell migration and invasion experiments were employed to evaluate the radiosensitizing effect of the nanosensitizer in vitro. Finally, to evaluate the therapeutic outcome of the nanosensitizer in vivo, MCF-7 tumor model was used.

Results: Confocal laser images and western blotting data demonstrated that the nanosensitizer in conjunction with X-ray irradiation could induce cell apoptosis in ROS-mediated apoptotic signal pathways. A clonogenic survival assay revealed that cells treated with the prepared nanosensitizer exhibited a lower number of viable cell colonies than that of the nontargeted group under X-ray irradiation. Notably, with only a single dose of radiotherapy, the mitochondria-targeted nanosensitizer elicited the complete ablation of tumors in a mouse model.

Conclusion: The designed nanosensitizer in combination with X-ray radiation exposure could be used for radiotherapy against cancer in living cells and in vivo. Moreover, the nanosensitizer with mitochondria targeting played a pivotal role in triggering a “domino effect” of ROS and cell apoptosis. The current strategy could provide new opportunities in designing efficient radiosensitizers for future cancer therapy.

Targeted tumor dual mode CT/MR imaging using multifunctional polyethylenimine-entrapped gold nanoparticles loaded with gadolinium

We report the construction and characterization of polyethylenimine (PEI)-entrapped gold nanoparticles (AuNPs) chelated with gadolinium (Gd) ions for targeted dual mode tumor CT/MR imaging in vivo. In this work, polyethylene glycol (PEG) monomethyl ether-modified PEI was sequentially modified with Gd chelator and folic acid (FA)-linked PEG (FA-PEG) was used as a template to synthesize AuNPs, followed by Gd(III) chelation and acetylation of the remaining PEI surface amines. The formed FA-targeted PEI-entrapped AuNPs loaded with Gd (FA-Gd-Au PENPs) were well characterized in terms of structure, composition, morphology, and size distribution. We show that the FA-Gd-Au PENPs with an Au core size of 3.0 nm are water dispersible, colloidally stable, and noncytotoxic in a given concentration range. Thanks to the coexistence of Au and Gd elements within one nanoparticulate system, the FA-Gd-Au PENPs display a better X-ray attenuation property than clinical iodinated contrast agent (e.g. Omnipaque) and reasonable r1 relaxivity (1.1 mM-1s-1). These properties allow the FA-targeted particles to be used as an efficient nanoprobe for dual mode CT/MR imaging of tumors with excellent FA-mediated targeting specificity. With the demonstrated organ biocompatibility, the designed FA-Gd-Au PENPs may hold a great promise to be used as a nanoprobe for CT/MR dual mode imaging of different FA receptor-overexpressing tumors.

Gadolinium-Encapsulated Graphene Carbon Nanotheranostics for Imaging-Guided Photodynamic Therapy

Photosensitizers (PS) are an essential component of photodynamic therapy (PDT). Conventional PSs are often porphyrin derivatives, which are associated with high hydrophobicity, low quantum yield in aqueous solutions, and suboptimal tumor-to-normal-tissue (T/N) selectivity. There have been extensive efforts to load PSs into nanoparticle carriers to improve pharmacokinetics. The approach, however, is often limited by PS self-quenching, pre-mature release, and nanoparticle accumulation in the reticuloendothelial system organs. Herein, a novel, nanoparticle-based PS made of gadolinium-encapsulated graphene carbon nanoparticles (Gd@GCNs), which feature a high 1 O2 quantum yield, is reported. Meanwhile, Gd@GCNs afford strong fluorescence and high T1 relaxivity (16.0 × 10-3 m-1 s-1 , 7 T), making them an intrinsically dual-modal imaging probe. Having a size of approximately 5 nm, Gd@GCNs can accumulate in tumors through the enhanced permeability and retention effect. The unbound Gd@GCNs cause little toxicity because Gd is safely encapsulated within an inert carbon shell and because the particles are efficiently excreted from the host through renal clearance. Studies with rodent tumor models demonstrate the potential of the Gd@GCNs to mediate image-guided PDT for cancer treatment. Overall, the present study shows that Gd@GCNs possess unique physical, pharmaceutical, and toxicological properties and are an all-in-one nanotheranostic tool with substantial clinical translation potential.

Doped Carbon Dots for Sensing and Bioimaging Applications: A Minireview

In the last decade, carbon dots (C-dots, CDs) or carbon quantum dots (CQDs) have attracted a considerable amount of attention from the scientific community as a low cost and biocompatible alternative to semiconductor quantum dots. In particular, doped C-dots have excellent fluorescent properties that have been successfully utilized for numerous applications. In this minireview, we overview the recent advances on the synthesis of doped C-dots derived from carbon-rich sources and their potential applications for biomedical and sensing applications. In addition, we will also discuss some challenges and outline some future perspectives of this exciting material.

Tumor-targeting CuS nanoparticles for multimodal imaging and guided photothermal therapy of lymph node metastasis

Precise diagnosis of lymph node metastasis to guide lymphadenectomy is highly important for gastric cancer therapy in clinics. Though surgical dissection of regional metastatic lymph nodes remains the only way for gastric cancer therapy, the extended dissection may cause unavoidable postoperative risk of complications. It is still lack of effective method enabling the accurate removal of metastatic gastric cancer cells in lymph nodes with minimum injuries to normal tissue. Herein, we report a new fluorescent copper sulfide (CuS) nanoparticle (RGD-CuS-Cy5.5) enabling both non-invasive multimodality imaging and targeting photothermal therapy (PTT) of metastatic gastric cancer cells in lymph nodes. We demonstrate that RGD-CuS-Cy5.5 can easily drain into sentinel lymph nodes (SLN) after injection into primary tumors, and selectively enter into metastatic gastric MNK45 tumor cells via αvβ3 integrin-mediated endocytosis. The resulting strong near-infrared (NIR) fluorescence and computed tomography (CT) contrast in metastatic SLN compared to normal SLN can precisely differentiate SLN metastasis of gastric cancers. Guided by the imaging, localized PTT with RGD-CuS-Cy5.5 is conducted upon irradiation with an 808 nm laser, resulting in complete removal of metastatic gastric tumor cells in SLN without obvious toxicity. Moreover, RGD-CuS-Cy5.5 can also allow for the rapid and non-invasive self-monitoring of PTT efficacy against metastatic SLNs in living mice. This study highlights the potential of using RGD-CuS-Cy5.5 for imaging-guided and targeting PTT of SLN metastasis in vivo, which may be applicable for the metastatic gastric cancer therapy in clinics.

STATEMENT OF SIGNIFICANCE

RGD-CuS-Cy5.5 nanoparticles possess NIR fluorescence and CT signals for in vivo bimodality imaging of lymph node metastasis. Strong photothermal property under irradiation at 808 nm for efficient PTT. Easy drain into sentinel lymph nodes and selective enter metastatic gastric cancer cells via αvβ3 integrin-mediated endocytosis. Rapid and non-invasive monitoring of therapeutic efficacy against lymph node metastasis.

Surface impact on nanoparticle-based magnetic resonance imaging contrast agents

Magnetic resonance imaging (MRI) is one of the most widely used diagnostic tools in the clinic. To improve imaging quality, MRI contrast agents, which can modulate local T1 and T2 relaxation times, are often injected prior to or during MRI scans. However, clinically used contrast agents, including Gd3+-based chelates and iron oxide nanoparticles (IONPs), afford mediocre contrast abilities. To address this issue, there has been extensive research on developing alternative MRI contrast agents with superior r1 and r2 relaxivities. These efforts are facilitated by the fast progress in nanotechnology, which allows for preparation of magnetic nanoparticles (NPs) with varied size, shape, crystallinity, and composition. Studies suggest that surface coatings can also largely affect T1 and T2 relaxations and can be tailored in favor of a high r1 or r2. However, the surface impact of NPs has been less emphasized. Herein, we review recent progress on developing NP-based T1 and T2 contrast agents, with a focus on the surface impact.

Contrast agents in dynamic contrast-enhanced magnetic resonance imaging

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a noninvasive method to assess angiogenesis, which is widely used in clinical applications including diagnosis, monitoring therapy response and prognosis estimation in cancer patients. Contrast agents play a crucial role in DCE-MRI and should be carefully selected in order to improve accuracy in DCE-MRI examination. Over the past decades, there was much progress in the development of optimal contrast agents in DCE-MRI. In this review, we describe the recent research advances in this field and discuss properties of contrast agents, as well as their advantages and disadvantages. Finally, we discuss the research perspectives for improving this promising imaging method.

Metal-Phenolic Encapsulated Mesoporous Silica Nanoparticles for pH-Responsive Drug Delivery and Magnetic Resonance Imaging

The anticancer drug doxorubicin (DOX) is locked in the mesoporous silica nanoparticle by coating FeIII-TA polymer, and its burst release can be achieved under acidic environment, along with the decreased longitudinal relaxivity. This nanoplatform shows great potential to monitoring the drug delivery process and the fate of the nanocarrier.

Hyperthemia-Promoted Cytosolic and Nuclear Delivery of Copper/Carbon Quantum Dot-Crosslinked Nanosheets: Multimodal Imaging-Guided Photothermal Cancer Therapy

Copper-containing nanomaterials have been applied in various fields because of their appealing physical, chemical, and biomedical properties/functions. Herein, for the first time, a facile, room-temperature, and one-pot method of simply mixing copper ions and sulfur-doped carbon dots (CDs) is developed for the synthesis of copper/carbon quantum dot (or CD)-crosslinked nanosheets (CuCD NSs). The thus-obtained CuCD NSs with the size of 20-30 nm had a high photothermal conversion efficiency of 41.3% and good photothermal stability. Especially, after coating with thiol-polyethylene glycol and fluorescent molecules, the resultant CuCD NSs could selectively target tumor tissues and realize multimodal (photoacoustic, photothermal, and fluorescence) imaging-guided cancer therapy. More importantly, our CuCD NSs exhibited laser-triggered cytosolic delivery, lysosomal escape, and nuclear-targeting properties, which greatly enhanced their therapeutic efficacy. The significantly enhanced tumor accumulation of CuCD NSs after in situ tumor-site laser irradiation was also observed in in vivo experiments. These in vitro and in vivo events occurring during the continuous laser irradiation have not been observed. Overall, this work develops a CD-assisted synthetic method of photothermal nanoagents for triple-modal imaging-guided phototherapy and deepens our understanding of the action mechanism of photothermal therapy, which will promote the development of nanomedicine and beyond.

NIRF/PA/CT multi-modality imaging guided combined photothermal and photodynamic therapy based on tumor microenvironment-responsive nanocomposites

We developed a novel nanocomposite as a single nanoplatform (AlPc-MoS₂@SiO₂-CS) for photothermal and photodynamic therapy of tumors.

In Vivo X-ray Imaging of Transport of Renal Clearable Gold Nanoparticles in the Kidneys

With more and more engineered nanoparticles (NPs) being designed renal clearable for clinical translation, fundamental understanding of their transport in the different compartments of kidneys becomes increasingly important. Here, we report noninvasive X-ray imaging of renal clearable gold NPs (AuNPs) in normal and nephropathic kidneys. By quantifying the transport kinetics of the AuNPs in cortex, medulla and pelvis of the normal and injured kidneys, we found that ureteral obstruction not just blocked the NP elimination through the ureter but also slowed down their transport from the medulla to pelvis and enhanced the cellular uptake. Moreover, the transport kinetics of the NPs and renal anatomic details can be precisely correlated with local pathological lesion. These findings not only advance our understandings of the nano-bio interactions in kidneys but also offer a new pathway to noninvasively image kidney dysfunction and local injuries at the anatomical level.

Spherical Polyelectrolyte Brushes as a Novel Platform for Paramagnetic Relaxation Enhancement and Passive Tumor Targeting

A novel platform for the development of highly efficient magnetic resonance imaging (MRI) contrast agents has been demonstrated. New contrast agents are designed and produced through electrostatic self-assembly of cationic gadolinium(III) complexes onto anionic spherical polyelectrolyte brushes (SPB). The structurally well-defined SPB are composed of polystyrene core and polyacrylic acid brush layer, where numerous binding sites and confined microenvironments are available for the embedment of the gadolinium(III) contrast agents. Both in vitro and in vivo experiments show excellent biocompatibility and relaxometric performance of these SPB-based gadolinium hybrid materials. The enhanced relaxivity value is up to 86.2 mM^-1 s^-1 per Gd, a remarkably high record value at 1.5 T magnetic field. In vivo imaging displays a prolonged blood circulation time and massive accumulation of the contrast agents at the tumor region due to the enhanced permeability and retention effect. The SPB-based gadolinium hybrid materials not only broaden the horizons of new MRI contrast agents, but also have a great potential for tumor diagnosis.

Paramagnetic Properties of Metal-Free Boron-Doped Graphene Quantum Dots and Their Application for Safe Magnetic Resonance Imaging

A boron-doped graphene quantum dot (B-GQD) as a metal-free multimodal contrast agent (CA) for safe magnetic resonance imaging and fluorescence imaging is reported. In vivo T1 -weighted magnetic resonance images show that B-GQDs induce significant contrast enhancement on the heart, liver, spleen, and kidney, and sustain for more than 1 h, about 10 times longer than Gd-based CAs currently used in clinic.

A high-yield and versatile method for the synthesis of carbon dots for bioimaging applications

A facile and versatile molten-salt method was developed to prepare hydrosoluble carbon dots (CDs) from various precursors, in high yields and on a large scale. Citric acid-based CDs (CA-CDs) were obtained in a maximum yield of 39.6% and exhibited a high fluorescence quantum yield of 20.8% without any passivation. The CA-CDs showed little cytotoxicity even at a concentration as high as 800 μg mL^-1. In addition, CA-CDs could be used as multicolour fluorescence imaging agents in vitro with blue, green, and red fluorescence emissions at excitation wavelengths of 405, 488, and 543 nm, respectively. Moreover, the CA-CDs could be chelated with gadolinium ions (Gd³⁺) to construct Gd-CA-CDs for dual-mode magnetic resonance and fluorescence imaging. The Gd-CA-CDs showed good water dispersibility, excellent biocompatibility, a strong fluorescence quantum yield of 13.1%, and a high magnetic resonance relaxivity of 22.45 mM^-1 s^-1. The molten-salt method was demonstrated to be applicable to other precursors, such as sodium lignosulphonate, sucrose, glucose, and p-phenylenediamine, and the maximum yield of the four as-prepared CDs was as high as 66.7%, which is much higher than the value reported in previous studies. This study proves that the molten-salt synthesis is a versatile method to obtain CDs in high yields, which will promote the application of CDs in the field of bioimaging.

Renal clearable noble metal nanoparticles: photoluminescence, elimination, and biomedical applications

Metal nanoparticles have demonstrated broad and promising biomedical applications in research laboratories, but how to fulfill their promises in the clinical practices demands extensive effort to minimize their non-specific accumulation in the body. In the past 6 years, we have developed a class of renal clearable noble metal nanoparticles with tunable visible and near-infrared emission, which can behave like small molecular contrast agents to be effectively eliminated through the kidneys. By taking advantage of the unique clearance pathway, we were able to gain some fundamental understanding of how engineering nanoparticles cleared out of the body through urinary system. Moreover, they also provided unique opportunities in early cancer detection and kidney functional imaging that were often challenging to be achieved with non-renal clearable nanoparticles and small molecular probes. In this review, we summarize key factors that govern in the renal clearance of luminescent noble metal nanoparticles and their strengths in cancer targeting and kidney functional imaging. At the end, we also outline several key challenges that need to be addressed before they can be considered in the clinical practices. WIREs Nanomed Nanobiotechnol 2017, 9:e1453. doi: 10.1002/wnan.1453 For further resources related to this article, please visit the WIREs website.

Gadolinium oxysulfide-coated gold nanorods with improved stability and dual-modal magnetic resonance/photoacoustic imaging contrast enhancement for cancer theranostics

Gold nanorods (GNRs) are emerging as a promising nanoplatform for cancer theranostics because of their unique optical properties. However, they still suffer from many limitations, such as high cytotoxicity, low thermodynamic and biological stability, and a tedious process for integrating other imaging modalities, for further practical biomedical applications. In this work, a strategy by one-step coating of Gd₂O₂S around GNRs is reported to address these limitations of GNRs. After the coating of the Gd₂O₂S shell, the as-fabricated Gd₂O₂S coated GNRs (GNRs@Gd₂O₂S) show enhanced biocompatibility and photostability, and tunable localized surface plasmon resonance. The strong absorption in the near-infrared region renders GNRs@Gd₂O₂S outstanding photoacoustic imaging and photothermal therapy capabilities. Moreover, owing to the T₁ shortening ability of Gd₂O₂S, the GNRs@Gd₂O₂S also show an excellent T₁ MRI contrast performance. The GNRs@Gd₂O₂S thus can serve as a versatile nanoplatform for cancer theranostics combining dual-modal imaging and photothermal therapy.

Sequential growth of CaF2:Yb,Er@CaF2:Gd nanoparticles for efficient magnetic resonance angiography and tumor diagnosis

It is a significant challenge to develop nanoscale magnetic resonance imaging (MRI) contrast agents with high performance of relaxation.

Facile synthesis of gold/gadolinium-doped carbon quantum dot nanocomposites for magnetic resonance imaging and photothermal ablation therapy

Composites of gold nanomaterials and imaging agents show promise in cancer therapy.

One-pot synthesis of gadolinium-doped carbon quantum dots for high-performance multimodal bioimaging

A high-performance fluorescence (FL)/magnetic resonance (MR) imaging probe is synthesized by doping Gd³⁺ into carbon quantum dots via a one-pot pyrolysis process, and its dual-modality applications are demonstrated by the use of HeLa cells and mice as models.

Manganese-iron layered double hydroxide: a theranostic nanoplatform with pH-responsive MRI contrast enhancement and drug release

A manganese-iron layered double hydroxide serves as a pH-responsive nanoplatform for simultaneous MRI contrast enhancement and drug delivery.

Enhancing MRI of liver metastases with a zwitterionized biodegradable dendritic contrast agent

The MRI enhanced by a zwitterionized dendritic contrast agent clearly indicates metastatic tumors in the liver.

Tailoring Renal Clearance and Tumor Targeting of Ultrasmall Metal Nanoparticles with Particle Density

Identifying key factors that govern the in vivo behavior of nanomaterials is critical to the clinical translation of nanomedicines. Overshadowed by size-, shape-, and surface-chemistry effects, the impact of the particle core density on clearance and tumor targeting of inorganic nanoparticles (NPs) remains largely unknown. By utilizing a class of ultrasmall metal NPs with the same size and surface chemistry but different densities, we found that the renal-clearance efficiency exponentially increased in the early elimination phase while passive tumor targeting linearly decreased with a decrease in particle density. Moreover, lower-density NPs are more easily distributed in the body and have shorter retention times in highly permeable organs than higher-density NPs. The density-dependent in vivo behavior of metal NPs likely results from their distinct margination in laminar blood flow, which opens up a new path for precise control of nanomedicines in vivo.