PET and NIR optical imaging using self-illuminating (64)Cu-doped chelator-free gold nanoclusters

Exploring innovative strides in radiolabeled nanoparticle progress for multimodality cancer imaging and theranostic applications

Multimodal imaging unfolds as an innovative approach that synergistically employs a spectrum of imaging techniques either simultaneously or sequentially. The integration of computed tomography (CT), magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), positron emission tomography (PET), and optical imaging (OI) results in a comprehensive and complementary understanding of complex biological processes. This innovative approach combines the strengths of each method and overcoming their individual limitations. By harmoniously blending data from these modalities, it significantly improves the accuracy of cancer diagnosis and aids in treatment decision-making processes. Nanoparticles possess a high potential for facile functionalization with radioactive isotopes and a wide array of contrast agents. This strategic modification serves to augment signal amplification, significantly enhance image sensitivity, and elevate contrast indices. Such tailored nanoparticles constructs exhibit a promising avenue for advancing imaging modalities in both preclinical and clinical setting. Furthermore, nanoparticles function as a unified nanoplatform for the co-localization of imaging agents and therapeutic payloads, thereby optimizing the efficiency of cancer management strategies. Consequently, radiolabeled nanoparticles exhibit substantial potential in driving forward the realms of multimodal imaging and theranostic applications. This review discusses the potential applications of molecular imaging in cancer diagnosis, the utilization of nanotechnology-based radiolabeled materials in multimodal imaging and theranostic applications, as well as recent advancements in this field. It also highlights challenges including cytotoxicity and regulatory compliance, essential considerations for effective clinical translation of nanoradiopharmaceuticals in multimodal imaging and theranostic applications.

Superluminal Molecular and Nanomaterial Probes Based on Fast Ions or Electrons

This work reviews the progression of chemical analysis via Cherenkov emissions, i.e., Cherenkov Photometry and Cherenkov Emission Spectroscopy, from its introduction in the literature up to modern developments. In presenting the history of this field, we aim to consolidate the literature, both for reference and contextualization. We present an argument aiming to untangle why this corner of research has seen little progress while so many other directly related aspects of Cherenkov research have flourished, as well as speak to the progress of the field in recent years and prospective direction in years to come.

Highly intense NIR emissive Cu4Pt2 bimetallic clusters featuring Pt(i)-Cu4-Pt(i) sandwich kernel

Metal nanoclusters (NCs) capable of near-infrared (NIR) photoluminescence (PL) are gaining increasing interest for their potential applications in bioimaging, cell labelling, and phototherapy. However, the limited quantum yield (QY) of NIR emission in metal NCs, especially those emitting beyond 800 nm, hinders their widespread applications. Herein, we present a bright NIR luminescence (PLQY up to 36.7%, ∼830 nm) bimetallic Cu4Pt2 NC, [Cu4Pt2(MeO-C6H5-C[triple bond, length as m-dash]C)4(dppy)4]2+ (dppy = diphenyl-2-pyridylphosphine), with a high yield (up to 67%). Furthermore, by modifying the electronic effects of R in RC[triple bond, length as m-dash]C- (R = MeO-C6H5, F-C6H5, CF3-C6H5, Nap, and Biph), we can effectively modulate phosphorescence properties, including the PLQY, emission wavelength, and excited state decay lifetime. Experimental and computational studies both demonstrate that in addition to the electron effects of substituents, ligand modification enhances luminescence intensity by suppressing non-radiation transitions through intramolecular interactions. Simultaneously, it allows the adjustment of emitting wavelengths by tuning the energy gaps and first excited triplet states through intermolecular interactions of ligand substituents. This study provides a foundation for rational design of the atomic-structures of alloy metal NCs to enhance their PLQY and tailor the PL wavelength of NIR emission.

Translocator Protein 18 kDa (TSPO): A Promising Molecular Target for Image-Guided Surgery of Solid Cancers

The translocator protein 18-kDa (TSPO) is a mitochondrial membrane protein that is previously identified as the peripheral benzodiazepine receptor (PBR). Furthermore, it plays a significant role in a diverse range of biochemical processes, including steroidogenesis, mitochondrial cholesterol transport, cell survival and death, cell proliferation, and carcinogenesis. Several investigations also reported its roles in various types of cancers, including colorectal, brain, breast, prostate, and lung cancers, as well as melanoma. According to a previous study, the expression of TSPO was upregulated in cancer cells, which corresponds to an aggressive phenotype and/or poor prognosis. Consequently, the potential for crafting diagnostic and prognostic tools with a focus on TSPO holds great potential. In this context, several radioligands designed to target this protein have been identified, and some of the candidates have advanced to clinical trials. In recent years, the use of hybrid probes with radioactive and fluorescence molecules for image-guided surgery has exhibited promising results in animal and human studies. This indicates that the approach can serve as a valuable surgical navigator during cancer surgery. The current hybrid probes are built from various molecular platforms, including small molecules, nanoparticles, and antibodies. Although several TSPO-targeted imaging probes have been developed, their development for image-guided surgery of cancers is still limited. Therefore, this review aims to highlight recent findings on the involvement of TSPO in carcinogenesis, as well as provide a new perspective on the potential application of TSPO-targeted hybrid probes for image-guided surgery.

β-Galactosidase-Activated and Red Light-Induced RNA Modification Strategy for Prolonged NIR Fluorescence/PET Bimodality Imaging

Improving the retention of small-molecule-based therapeutic agents in tumors is crucial to achieve precise diagnosis and effective therapy of cancer. Herein, we propose a β-galactosidase (β-Gal)-activated and red light-induced RNA modification (GALIRM) strategy for prolonged tumor imaging. A β-Gal-activatable near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probe 68Ga-NOTA-FCG consists of a triaaza triacetic acid chelator NOTA for 68Ga-labeling, a β-Gal-activated photosensitizer CyGal, and a singlet oxygen (1O2)-susceptible furan group for RNA modification. Studies have demonstrated that the probe emits an activated NIR FL signal upon cleavage by endogenous β-Gal overexpressed in the lysosomes, which is combined with the PET imaging signal of 68Ga allowing for highly sensitive imaging of ovarian cancer. Moreover, the capability of 68Ga-NOTA-FCG generating 1O2 under 690 nm illumination could be simultaneously unlocked, which can trigger the covalent cross-linking between furan and nucleotides of cytoplasmic RNAs. The formation of the probe-RNA conjugate can effectively prevent exocytosis and prolong retention of the probe in tumors. We thus believe that this GALIRM strategy may provide entirely new insights into long-term tumor imaging and efficient tumor treatment.

Copper Nanoclusters as Novel Podium for Cancer Detection, Imaging, and Therapy Applications

Nanoclusters (NCs) are meticulously small, kinetically stable, crystalline materials which hold immense potential as multifaceted catalysts for a broad range of biomedical applications. Metal NCs are atomically precise and exist within the range of Fermi wavelength of electrons. They are highly advantageous as functional materials as their physicochemical properties can be customized to meet specific requirements. Copper NCs (CuNCs) are emerging as an efficient substitute to the other existing metal NCs. The synthesis of CuNCs is highly methodical, fast, cost effective and does not involve any complicated manipulation. On the contrary to gold and silver NCs, copper is a vital trace element for humans that can be excreted easily out the body. Further, the relatively inexpensiveness and easy availability of copper aids in potential nanotechnological applications in large quantity. As such, CuNCs have attracted great interest among the research community recently. The modern developments in the strategy, synthesis, surface modifications, and use of CuNCs in diagnosis of disease, imaging and treatment have been discussed in the present review. Approaches to regulate and augment the emission of CuNCs, challenges and drawbacks have also been considered. This review brings to light the multifarious applications of CuNCs and their potential as emerging theranostic agents. It is anticipated that the visions and directions for translating existing developments in CuNCs from the laboratory to the clinic can be further improved and enhanced.

Biological Interaction and Imaging of Ultrasmall Gold Nanoparticles

The ultrasmall gold nanoparticles (AuNPs), serving as a bridge between small molecules and traditional inorganic nanoparticles, create significant opportunities to address many challenges in the health field. This review discusses the recent advances in the biological interactions and imaging of ultrasmall AuNPs. The challenges and the future development directions of the ultrasmall AuNPs are presented.

Nanotheranostics in cancer lymph node metastasis: The long road ahead

Lymph node metastasis (LNM) significantly impacts the prognosis of cancer patients. Despite significant advancements in diagnostic techniques and treatment modalities, clinical challenges continue to persist in the realm of LNM. These include difficulties in early diagnosis, limited treatment efficacy, and potential side effects and injuries associated with treatment. Nanotheranostics, a field within nanotechnology, seamlessly integrates diagnostic and therapeutic functionalities. Its primary goal is to provide precise and effective disease diagnosis and treatment simultaneously. The development of nanotheranostics for LNM offers a promising solution for the stratified management of patients with LNM and promotes the advancement of personalized medicine. This review introduces the mechanisms of LNM and challenges in its diagnosis and treatment. Furthermore, it demonstrates the advantages and development potential of nanotheranostics, focuses on the challenges nanotheranostics face in its application, and provides an outlook on future trends. We consider nanotheranostics a promising strategy to improve clinical effectiveness and efficiency as well as the prognosis of cancer patients with LNM.

A Thiol-Michael Approach Towards Versatile Functionalized Cyclic Titanium-Oxo Clusters

In expanding our research activities of superlattice engineering, designing new giant molecules is the necessary first step. One attempt is to use inorganic transition metal clusters as building blocks. Efficient functionalization of chemically precise transition metal clusters, however, remains a great challenge to material scientists. Herein, we report an efficient thiol-Michael addition approach for the modifications of cyclic titanium-oxo cluster (CTOC). Several advantages, including high efficiency, mild reaction condition, capability of complete addition, high atom economy, as well as high functional group tolerance were demonstrated. This approach can afford high yields of fully functionalized CTOCs, which provides a powerful platform for achieving versatile functionalization of precise transition metal clusters and further applications.

Nanoparticles labeled with gamma-emitting radioisotopes: an attractive approach for in vivo tracking using SPECT imaging

Providing accurate molecular imaging of the body and biological process is critical for diagnosing disease and personalizing treatment with the minimum side effects. Recently, diagnostic radiopharmaceuticals have gained more attention in precise molecular imaging due to their high sensitivity and appropriate tissue penetration depth. The fate of these radiopharmaceuticals throughout the body can be traced using nuclear imaging systems, including single-photon emission computed tomography (SPECT) and positron emission tomography (PET) modalities. In this regard, nanoparticles are attractive platforms for delivering radionuclides into targets because they can directly interfere with the cell membranes and subcellular organelles. Moreover, applying radiolabeled nanomaterials can decrease their toxicity concerns because radiopharmaceuticals are usually administrated at low doses. Therefore, incorporating gamma-emitting radionuclides into nanomaterials can provide imaging probes with valuable additional properties compared to the other carriers. Herein, we aim to review (1) the gamma-emitting radionuclides used for labeling different nanomaterials, (2) the approaches and conditions adopted for their radiolabeling, and (3) their application. This study can help researchers to compare different radiolabeling methods in terms of stability and efficiency and choose the best way for each nanosystem.

Investigation of the interaction between the functionalized mesoporous silica nanocarriers and bovine serum albumin via multi-spectroscopy

It is well known that the physicochemical properties of nanocarriers, which are closely related to the surface modification of nanoparticles, have crucial impacts on their biological effects. Herein, the interaction between functionalized degradable dendritic mesoporous silica nanoparticles (DDMSNs) and bovine serum albumin (BSA) was investigated for probing into the nanocarriers' potential toxicity using multi-spectroscopy such as ultraviolet/visible (UV/Vis), synchronous fluorescence, Raman and circular dichroism (CD) spectroscopy. BSA, owing to its structural homology and high sequence similarity with HSA, was employed as the model protein to study the interactions with DDMSNs, amino-modified DDMSNs (DDMSNs-NH₂) and hyaluronic acid (HA) coated nanoparticles (DDMSNs-NH₂-HA). It was found that the static quenching behavior of DDMSNs-NH₂-HA to BSA was accompanied by an endothermic and hydrophobic force-driven thermodynamic process, which was confirmed by fluorescence quenching spectroscopic studies and thermodynamic analysis. Furthermore, the conformational variations of BSA upon interaction with nanocarriers were observed by combination of UV/Vis, synchronous fluorescence, Raman and CD spectroscopy. The microstructure of amino residues in BSA changed due to the existence of nanoparticles, for example, the amino residues and hydrophobic groups exposed to microenvironment and the alpha helix (α-helix) content of BSA decreased. Specially, through thermodynamic analysis, the diverse binding modes and driving forces between nanoparticles and BSA were discovered because of different surface modifications on DDMSNs, DDMSNs-NH₂ and DDMSNs-NH₂-HA. We believe that this work can promote the interpretation of mutual impact between nanoparticles and biomolecules, which will be in favor of predicting the biological toxicity of nano-DDS and engineering functionalized nanocarriers.

Nanoparticle biodistribution coefficients: A quantitative approach for understanding the tissue distribution of nanoparticles

The objective of this manuscript is to provide quantitative insights into the tissue distribution of nanoparticles. Published pharmacokinetics of nanoparticles in plasma, tumor and 13 different tissues of mice were collected from literature. A total of 2018 datasets were analyzed and biodistribution of graphene oxide, lipid, polymeric, silica, iron oxide and gold nanoparticles in different tissues was quantitatively characterized using Nanoparticle Biodistribution Coefficients (NBC). It was observed that typically after intravenous administration most of the nanoparticles are accumulated in the liver (NBC = 17.56 %ID/g) and spleen (NBC = 12.1 %ID/g), while other tissues received less than 5 %ID/g. NBC values for kidney, lungs, heart, bones, brain, stomach, intestine, pancreas, skin, muscle and tumor were found to be 3.1 %ID/g, 2.8 %ID/g, 1.8 %ID/g, 0.9 %ID/g, 0.3 %ID/g, 1.2 %ID/g, 1.8 %ID/g, 1.2 %ID/g, 1.0 %ID/g, 0.6 %ID/g and 3.4 %ID/g, respectively. Significant variability in nanoparticle distribution was observed in certain organs such as liver, spleen and lungs. A large fraction of this variability could be explained by accounting for the differences in nanoparticle physicochemical properties such as size and material. A critical overview of published nanoparticle physiologically-based pharmacokinetic (PBPK) models is provided, and limitations in our current knowledge about in vitro and in vivo pharmacokinetics of nanoparticles that restrict the development of robust PBPK models is also discussed. It is hypothesized that robust quantitative assessment of whole-body pharmacokinetics of nanoparticles and development of mathematical models that can predict their disposition can improve the probability of successful clinical translation of these modalities.

Radiolabeled nanomaterial for cancer diagnostics and therapeutics: principles and concepts

In the last three decades, radiopharmaceuticals have proven their effectiveness for cancer diagnosis and therapy. In parallel, the advances in nanotechnology have fueled a plethora of applications in biology and medicine. A convergence of these disciplines has emerged more recently with the advent of nanotechnology-aided radiopharmaceuticals. Capitalizing on the unique physical and functional properties of nanoparticles, radiolabeled nanomaterials or nano-radiopharmaceuticals have the potential to enhance imaging and therapy of human diseases. This article provides an overview of various radionuclides used in diagnostic, therapeutic, and theranostic applications, radionuclide production through different techniques, conventional radionuclide delivery systems, and advancements in the delivery systems for nanomaterials. The review also provides insights into fundamental concepts necessary to improve currently available radionuclide agents and formulate new nano-radiopharmaceuticals.

Cerenkov radiation-activated probes for deep cancer theranostics: a review

Cerenkov radiation (CR) from radionuclides and megavoltage X-ray radiation can act as an in situ light source for deep cancer theranostics, overcoming the limitations of external light sources. Despite the blue-weighted emission and low quantum yield of CR, activatable probes-mediated CR can enhance the in-vivo diagnostic signals by Cerenkov resonance energy transfer and also can produce therapeutic effects by reactive species generation/drug release, greatly promoting the biomedical applications of CR. In this review, we describe the principles and sources of CR, construction of CR-activated probes and their application to tumor optical imaging and therapy. Finally, future prospects for the design and biomedical application of CR-activated probes are discussed.

Application of Cherenkov radiation in tumor imaging and treatment

Cherenkov radiation (CR) is the characteristic blue glow that is generated during radiotherapy or radioisotope decay. Its distribution and intensity naturally reflect the actual dose and field of radiotherapy and the location of radioisotope imaging agents in vivo. Therefore, CR can represent a potential in situ light source for radiotherapy monitoring and radioisotope-based tumor imaging. When used in combination with new imaging techniques, molecular probes or nanomedicine, CR imaging exhibits unique advantages (accuracy, low cost, convenience and fast) in tumor radiotherapy monitoring and imaging. Furthermore, photosensitive nanomaterials can be used for CR photodynamic therapy, providing new approaches for integrating tumor imaging and treatment. Here the authors review the latest developments in the use of CR in tumor research and discuss current challenges and new directions for future studies.

Gold nanoparticles targeting the autophagy-lysosome system to combat the inflammation-compromised osteogenic potential of periodontal ligament stem cells: From mechanism to therapy

Although substantial data indicate that the osteogenic potential of periodontal ligament stem cells (PDLSCs) is compromised under inflammatory conditions, the underlying mechanism remains largely unexplored. In this study, we found that both the autophagy levels and autophagic flux levels were decreased in PDLSCs incubated under inflammatory conditions (I-PDLSCs). Based on the increased expression of LC3 II (at an autophagy level) and decreased accumulation of LC3 II (at an autophagic flux level) in I-PDLSCs, we speculated that the disruption of I-PDLSC autophagy arose from dysfunction of the cellular autophagy-lysosome system. Subsequently, our hypothesis was demonstrated by inhibited autophagosome-lysosome fusion, damaged lysosomal function, and suppressed activation of transcription factor EB (TFEB, a master regulator of the autophagy-lysosome system) in I-PDLSCs and verified by TFEB overexpression in I-PDLSCs. We found that gold nanoparticle (Au NP) treatment rescued the osteogenic potential of I-PDLSCs by restoring the inflammation-compromised autophagy-lysosome system. In this context, Au NP ceased to be effective when TFEB was knocked down in PDLSCs. Our data demonstrate the crucial role of the autophagy-lysosome system in cellular osteogenesis under inflammatory conditions and suggest a new target for rescuing inflammation-induced cell dysfunction using nanomaterials to aid cell biology and tissue regeneration.

Optimal Physicochemical Properties of Antibody-Nanoparticle Conjugates for Improved Tumor Targeting

Tumor-targeted antibody (mAb)/fragment-conjugated nanoparticles (NPs) represent an innovative strategy for improving the local delivery of small molecules. However, the physicochemical properties of full mAb-NPs and fragment-NPs-that is, NP material, size, charge, as well as the targeting antibody moiety, and the linker conjugation strategies-remain to be optimized to achieve an efficient tumor targeting. A meta-analysis of 161 peer-reviewed studies is presented, which describes the use of tumor-targeted mAb-NPs and fragment-NPs from 2009 to 2021. The use of these targeted NPs is confirmed to result in significantly greater tumor uptake of NPs than that of naked NPs (7.9 ± 1.9% ID g^-1 versus 3.2 ± 0.6% ID g^-1 , respectively). The study further demonstrates that for lipidic NPs, fragment-NPs provide a significantly higher tumor uptake than full mAb-NPs. In parallel, for both polymeric and organic/inorganic NPs, full mAb-NPs yield a significant higher tumor uptake than fragment-NPs. In addition, for both lipidic and polymeric NPs, the tumor uptake is improved with the smallest sizes of the conjugates. Finally, the pharmacokinetics of the conjugates are demonstrated to be driven by the NPs and not by the antibody moieties, independently of using full mAb-NPs or fragment-NPs, confirming the importance of optimizing the NP design to improve the tumor uptake.

PET/Fluorescence Imaging: An Overview of the Chemical Strategies to Build Dual Imaging Tools

Molecular imaging is a biomedical research discipline that has quickly emerged to afford the observation, characterization, monitoring, and quantification of biomarkers and biological processes in living organism. It covers a large array of imaging techniques, each of which provides anatomical, functional, or metabolic information. Multimodality, as the combination of two or more of these techniques, has proven to be one of the best options to boost their individual properties, hence offering unprecedented tools for human health. In this review, we will focus on the combination of positron emission tomography and fluorescence imaging from the specific perspective of the chemical synthesis of dual imaging agents. Based on a detailed analysis of the literature, this review aims at giving a comprehensive overview of the chemical strategies implemented to build adequate imaging tools considering radiohalogens and radiometals as positron emitters, fluorescent dyes mostly emitting in the NIR window and all types of targeting vectors.

Application of nanotechnology in medical diagnosis and imaging

Nanotechnology has tremendously impacted the advancement in imaging, early detection, diagnosis, and prognosis of diseases by improving upon existing clinically relevant technologies. The unique biophysical properties of the nanoparticles enable contrast enhancement to improve biomedical imaging while our ability to manipulate nanoparticles for molecular level specificity enables tissue-specific diagnosis. Importantly, subtle variation in size or composition of the nanoparticles can result in great changes in their optical, magnetic or electrical properties that allows unique possibility of multiplexing. This concise but focused review summarizes the important classes of nanoparticles that have been actively used in improving our ability to image diseased tissues and have contributed to develop technologies that has led to early detection and diagnosis of diseases.

Engineered Repeat Protein Hybrids: The New Horizon for Biologic Medicines and Diagnostic Tools

ConspectusThe last decades have witnessed unprecedented scientific breakthroughs in all the fields of knowledge, from basic sciences to translational research, resulting in the drastic improvement of the lifespan and overall quality of life. However, despite these great advances, the treatment and diagnosis of some diseases remain a challenge. Inspired by nature, scientists have been exploring biomolecules and their derivatives as novel therapeutic/diagnostic agents. Among biomolecules, proteins raise much interest due to their high versatility, biocompatibility, and biodegradability.Protein binders (binders) are proteins that bind other proteins, in certain cases, inhibiting or modulating their action. Given their therapeutic potential, binders are emerging as the next generation of biopharmaceuticals. The most well-known example of binders are antibodies, and inspired by them researchers have developed alternative binders using protein design approaches. Protein design can be based on naturally occurring proteins in which, by means of rational design or combinatorial approaches, new binding interfaces can be engineered to obtain specific functions or based on de novo proteins emerging from state-of-the-art computational methodologies.Among the novel designed proteins, a class of engineered repeat proteins, the consensus tetratricopeptide repeat (CTPR) proteins, stand out due to their stability and robustness. The CTPR unit is a helix-turn-helix motif constituted of 34 amino acids, of which only 8 are essential to ensure correct folding of the structure. The small number of conserved residues of CTPR proteins leaves plenty of freedom for functional mutations, making them a base scaffold that can be easily and reproducibly tailored to endow desired functions to the protein. For example, the introduction of metal-binding residues (e.g., histidines, cysteines) drives the coordination of metal ions and the subsequent formation of nanomaterials. Additionally, the CTPR unit can be conjugated with other peptides/proteins or repeated in tandem to encode larger CTPR proteins with superhelical structures. These properties allow for the design of both binder and nanomaterial-coordination modules as well as their combination within the same molecule, making the CTPR proteins, as we have demonstrated in several recent examples, the ideal platform to develop protein-nanomaterial hybrids. Generally, the fusion of two distinct materials exploits the best properties of each; however, in protein-nanomaterial hybrids, the fusion takes on a new dimension as new properties arise.These hybrids have ushered the use of protein-based nanomaterials as biopharmaceuticals beyond their original therapeutic scope and paved the way for their use as theranostic agents. Despite several reports of protein-stabilized nanomaterials found in the literature, these systems offer limited control in the synthesis and properties of the grown nanomaterials, as the protein acts just as a stabilizing agent with no significant functional contribution. Therefore, the rational design of protein-based nanomaterials as true theranostic agents is still incipient. In this context, CTPR proteins have emerged as promising scaffolds to hold simultaneously therapeutic and diagnostic functions through protein engineering, as it has been recently demonstrated in pioneering in vitro and in vivo examples.

One-pot synthesis of 68Ga-doped ultrasmall gold nanoclusters for PET/CT imaging of tumors

Gold nanoclusters (AuNCs) have attracted much attention for tumor theranostics in recent years because of their ability of renal clearance and to escape the reticuloendothelial system (RES) sequestration. In this study, we presented a novel method to synthesize ⁶⁸Ga-doped (labeled) AuNCs by simultaneous reduction of ⁶⁸GaCl₃ and HAuCl₄ by glutathione. As synthesized ⁶⁸Ga-doped, glutathione-coated AuNCs (⁶⁸Ga-GSH@AuNCs) were ultrasmall in size (<2 nm), highly stable under physiological conditions and renally clearable, and had high efficiency for tumor targeting. To demonstrate the universality of this ⁶⁸Ga labeling method and further enhance tumor targeting efficiency, arginine-glycine-aspartate (RGD)-containing peptide was introduced as co-reductant to synthesize RGD peptide and glutathione co-coated, ⁶⁸Ga-labeled AuNCs (⁶⁸Ga-RGD-GSH@AuNCs). Introduction of RGD peptide did not interfere the synthesis process but significantly enhanced the tumor targeting efficiency of the AuNCs. Our study demonstrated that it was feasible to label AuNCs with gallium-68 by direct reduction of the radioisotope and HAuCl₄ with reductant peptides, holding a great potential for clinical translation for PET/CT detection of tumors.

Bioorthogonal chemistry in metal clusters: a general strategy for the construction of multifunctional probes for bioimaging in living cells and in vivo

Multifunctional bioimaging probes based on metal clusters have multiple characteristics of metal clusters and functional conjugates, and their development has broad application prospects in the fields of biomedical imaging and tumor diagnosis. However, current bioconjugation methods on metal clusters are time-consuming and have low reaction efficiency, which hinders the construction of bioimaging probes with multifunctional components. Here, we report a concise and promising design strategy to realize the simple and efficient introduction of functional conjugates through bioorthogonal reactions based on azido-functionalized metal clusters. Based on this strategy, taking the probe FA-Cu_C@BSA-Cy5 as an example, we demonstrated the design of a copper cluster-based multifunctional near-infrared (NIR) fluorescent probe and its real-time imaging application in vivo. Through the strain-promoted azide-alkyne cycloaddition (SPAAC) reaction, the tumor-specific targeting ligand folic acid (FA) and fluorophore (Cy5) can be chemically conjugated to azido-functionalized Cu_C@BSA-N₃ quickly and efficiently under biocompatible conditions. The prepared probe showed numerous advantages of metal clusters, including good stability, ultra-small particle size and low toxicity and rapid renal clearance. At the same time, FA-modified FA-Cu_C@BSA-Cy5 can specifically target KB cells with high FR expression, and in vivo fluorescence imaging shows higher tumor accumulation. The construction of the azido functional metal cluster platform can be extended to various metal clusters with functional probes and prodrugs, thereby providing more promising candidates for future medical diagnoses.

A perspective on the radiopharmaceutical requirements for imaging and therapy of glioblastoma

Despite numerous clinical trials and pre-clinical developments, the treatment of glioblastoma (GB) remains a challenge. The current survival rate of GB averages one year, even with an optimal standard of care. However, the future promises efficient patient-tailored treatments, including targeted radionuclide therapy (TRT). Advances in radiopharmaceutical development have unlocked the possibility to assess disease at the molecular level allowing individual diagnosis. This leads to the possibility of choosing a tailored, targeted approach for therapeutic modalities. Therapeutic modalities based on radiopharmaceuticals are an exciting development with great potential to promote a personalised approach to medicine. However, an effective targeted radionuclide therapy (TRT) for the treatment of GB entails caveats and requisites. This review provides an overview of existing nuclear imaging and TRT strategies for GB. A critical discussion of the optimal characteristics for new GB targeting therapeutic radiopharmaceuticals and clinical indications are provided. Considerations for target selection are discussed, i.e. specific presence of the target, expression level and pharmacological access to the target, with particular attention to blood-brain barrier crossing. An overview of the most promising radionuclides is given along with a validation of the relevant radiopharmaceuticals and theranostic agents (based on small molecules, peptides and monoclonal antibodies). Moreover, toxicity issues and safety pharmacology aspects will be presented, both in general and for the brain in particular.

Gold nanoclusters: An ultrasmall platform for multifaceted applications

Gold nanoclusters (Au NCs) with a core size below 2 nm form an exciting class of functional nano-materials with characteristic physical and chemical properties. The properties of Au NCs are more prominent and extremely different from their bulk counterparts. The synthesis of Au NCs is generally assisted by template or ligand, which impart excellent cluster stability and high quantum yield. The tunable and sensitive physicochemical properties of Au NCs open horizons for their advanced applications in various interdisciplinary fields. In this review, we briefly summarize the solution phase synthesis and origin of the characteristic properties of Au NCs. A vast review of recent research work introducing biosensors based on Au NCs has been presented along with their specifications and detection limits. This review also highlights recent progress in the use of Au NCs as bio-imaging probe, enzyme mimic, temperature sensing probe and catalysts. A speculation on present challenges and certain future prospects have also been provided to enlighten the path for advancement of multifaceted applications of Au NCs.

Synergistic integration of metal nanoclusters and biomolecules as hybrid systems for therapeutic applications

Therapeutic nanoparticles are designed to enhance efficacy, real-time monitoring, targeting accuracy, biocompatibility, biodegradability, safety, and the synergy of diagnosis and treatment of diseases by leveraging the unique physicochemical and biological properties of well-developed bio-nanomaterials. Recently, bio-inspired metal nanoclusters (NCs) consisting of several to roughly dozens of atoms (<2 nm) have attracted increasing research interest, owing to their ultrafine size, tunable fluorescent capability, good biocompatibility, variable metallic composition, and extensive surface bio-functionalization. Hybrid core-shell nanostructures that effectively incorporate unique fluorescent inorganic moieties with various biomolecules, such as proteins (enzymes, antigens, and antibodies), DNA, and specific cells, create fluorescently visualized molecular nanoparticle. The resultant nanoparticles possess combinatorial properties and synergistic efficacy, such as simplicity, active bio-responsiveness, improved applicability, and low cost, for combination therapy, such as accurate targeting, bioimaging, and enhanced therapeutic and biocatalytic effects. In contrast to larger nanoparticles, bio-inspired metal NCs allow rapid renal clearance and better pharmacokinetics in biological systems. Notably, advances in nanoscience, interfacial chemistry, and biotechnologies have further spurred researchers to explore bio-inspired metal NCs for therapeutic purposes. The current review presents a comprehensive and timely overview of various metal NCs for various therapeutic applications, with a special emphasis on the design rationale behind the use of biomolecules/cells as the main scaffolds. In the different hybrid platform, we summarize the current challenges and emerging perspectives, which are expected to offer in-depth insight into the rational design of bio-inspired metal NCs for personalized treatment and clinical translation.

Systematic imaging in medicine: a comprehensive review

Systematic imaging can be broadly defined as the systematic identification and characterization of biological processes at multiple scales and levels. In contrast to "classical" diagnostic imaging, systematic imaging emphasizes on detecting the overall abnormalities including molecular, functional, and structural alterations occurring during disease course in a systematic manner, rather than just one aspect in a partial manner. Concomitant efforts including improvement of imaging instruments, development of novel imaging agents, and advancement of artificial intelligence are warranted for achievement of systematic imaging. It is undeniable that scientists and radiologists will play a predominant role in directing this burgeoning field. This article introduces several recent developments in imaging modalities and nanoparticles-based imaging agents, and discusses how systematic imaging can be achieved. In the near future, systematic imaging which combines multiple imaging modalities with multimodal imaging agents will pave a new avenue for comprehensive characterization of diseases, successful achievement of image-guided therapy, precise evaluation of therapeutic effects, and rapid development of novel pharmaceuticals, with the final goal of improving human health-related outcomes.

Radiolabeling strategies and pharmacokinetic studies for metal based nanotheranostics

Radiolabeled metal-based nanoparticles (MNPs) have drawn considerable attention in the fields of nuclear medicine and molecular imaging, drug delivery, and radiation therapy, given the fact that they can be potentially used as diagnostic imaging and/or therapeutic agents, or even as theranostic combinations. Here, we present a systematic review on recent advances in the design and synthesis of MNPs with major focuses on their radiolabeling strategies and the determinants of their in vivo pharmacokinetics, and together how their intended applications would be impacted. For clarification, we categorize all reported radiolabeling strategies for MNPs into indirect and direct approaches. While indirect labeling simply refers to the use of bifunctional chelators or prosthetic groups conjugated to MNPs for post-synthesis labeling with radionuclides, we found that many practical direct labeling methodologies have been developed to incorporate radionuclides into the MNP core without using extra reagents, including chemisorption, radiochemical doping, hadronic bombardment, encapsulation, and isotope or cation exchange. From the perspective of practical use, a few relevant examples are presented and discussed in terms of their pros and cons. We further reviewed the determinants of in vivo pharmacokinetic parameters of MNPs, including factors influencing their in vivo absorption, distribution, metabolism, and elimination, and discussed the challenges and opportunities in the development of radiolabeled MNPs for in vivo biomedical applications. Taken together, we believe the cumulative advancement summarized in this review would provide a general guidance in the field for design and synthesis of radiolabeled MNPs towards practical realization of their much desired theranostic capabilities. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Nanoparticles for Cerenkov and Radioluminescent Light Enhancement for Imaging and Radiotherapy

Cerenkov luminescence imaging and Cerenkov photodynamic therapy have been developed in recent years to exploit the Cerenkov radiation (CR) generated by radioisotopes, frequently used in Nuclear Medicine, to diagnose and fight cancer lesions. For in vivo detection, the endpoint energy of the radioisotope and, thus, the total number of the emitted Cerenkov photons, represents a very important variable and explains why, for example, ⁶⁸Ga is better than ¹⁸F. However, it was also found that the scintillation process is an important mechanism for light production. Nanotechnology represents the most important field, providing nanosctructures which are able to shift the UV-blue emission into a more suitable wavelength, with reduced absorption, which is useful especially for in vivo imaging and therapy applications. Nanoparticles can be made, loaded or linked to fluorescent dyes to modify the optical properties of CR radiation. They also represent a useful platform for therapeutic agents, such as photosensitizer drugs for the production of reactive oxygen species (ROS). Generally, NPs can be spaced by CR sources; however, for in vivo imaging applications, NPs bound to or incorporating radioisotopes are the most interesting nanocomplexes thanks to their high degree of mutual colocalization and the reduced problem of false uptake detection. Moreover, the distance between the NPs and CR source is crucial for energy conversion. Here, we review the principal NPs proposed in the literature, discussing their properties and the main results obtained by the proponent experimental groups.

Gold nanoparticles against respiratory diseases: oncogenic and viral pathogens review

Nanoscale size-dependent properties give nanomaterials unique specifications that are robust in many applications of human medicine. Gold nanoparticles (AuNPs) have recently gained attention because of their unique optical, physical and electrical properties. AuNPs increase the efficacy of biomedical applications in diagnostic treatments for infectious diseases, by targeting or labeling target cells/bioactive compounds. However, it is imperative to develop the regimens for more accurate diagnostic tools, preventive care and effective therapy. Our critical and comprehensive review presents emerging avenues of molecular diagnostics as well as therapeutics translated into clinical approaches. This manuscript critically reviews the rampant future of AuNPs in the diagnosis and treatment of the most important diseases, such as cancer and viruses of respiratory system.

Synthesis, Properties, and Biological Applications of Metallic Alloy Nanoparticles

Metallic alloy nanoparticles are synthesized by combining two or more different metals. Bimetallic or trimetallic nanoparticles are considered more effective than monometallic nanoparticles because of their synergistic characteristics. In this review, we outline the structure, synthesis method, properties, and biological applications of metallic alloy nanoparticles based on their plasmonic, catalytic, and magnetic characteristics.

In Vivo Repeatedly Activated Persistent Luminescence Nanoparticles by Radiopharmaceuticals for Long-Lasting Tumor Optical Imaging

Persistent luminescence nanoparticles (PLNPs) with rechargeable near-infrared afterglow properties attract much attention for tumor diagnosis in living animals since they can avoid tissue autofluorescence and greatly improve the signal-to-background ratio. Using UV, visible light, or X-ray as excitation sources to power up persistent luminescence (PL) faces the challenges such as limited tissue penetration, inefficient charging capability, or tissue damage caused by irradiation. Here, it is proved that radiopharmaceuticals can efficiently excite ZnGa₂ O₄ :Cr³⁺ nanoparticles (ZGCs) for both fluorescence and afterglow luminescence via Cerenkov resonance energy transfer as well as ionizing radiation. ¹⁸ F-FDG, a clinically approved tumor-imaging radiopharmaceutical with a short decay half-life around 110 min, is successfully used as the internal light source to in vivo excite intravenously injected ZGCs for tumor luminescence imaging over 3 h. The luminescence with similar decay time can be re-obtained for multiple times upon injection of ¹⁸ F-FDG at any time needed with no health concern. It is believed this strategy can not only provide tumor luminescence imaging with high sensitivity, high contrast, and long decay time at desired time, but also guarantee the patients much less radiation exposure, greatly benefiting image-guided surgery in the future.

Peptide and protein modified metal clusters for cancer diagnostics

The biomedical features of metal clusters have been explored in tumor diagnostic applications in recent years. Peptide or protein protected metal clusters with low toxicity, ultra-small size and good biocompatibility are ideal bioanalytical tools, and exhibit better cancer diagnostic properties that have been attractive to oncologists. This perspective provides a rigorous but succinct overview of cancer diagnosis as a working concept for metal clusters by reporting the latest significant advances in the applications of metal clusters in tumor-related bioanalysis and diagnosis. The materials design principles, bioanalytical mechanisms and biomedical applications of metal clusters are described, and then the potential challenges and prospects of metal clusters in cancer diagnosis are discussed. A perspective addressing the role of metal clusters in this field is required to understand their effects and functions, as well as for the scientific community to further advance the development of metal clusters for broader diagnostic applications.

Meta-Analysis of Nanoparticle Delivery to Tumors Using a Physiologically Based Pharmacokinetic Modeling and Simulation Approach

Numerous studies have engineered nanoparticles with different physicochemical properties to enhance the delivery efficiency to solid tumors, yet the mean and median delivery efficiencies are only 1.48% and 0.70% of the injected dose (%ID), respectively, according to a study using a nonphysiologically based modeling approach based on published data from 2005 to 2015. In this study, we used physiologically based pharmacokinetic (PBPK) models to analyze 376 data sets covering a wide range of nanomedicines published from 2005 to 2018 and found mean and median delivery efficiencies at the last sampling time point of 2.23% and 0.76%ID, respectively. Also, the mean and median delivery efficiencies were 2.24% and 0.76%ID at 24 h and were decreased to 1.23% and 0.35%ID at 168 h, respectively, after intravenous administration. While these delivery efficiencies appear to be higher than previous findings, they are still quite low and represent a critical barrier in the clinical translation of nanomedicines. We explored the potential causes of this poor delivery efficiency using the more mechanistic PBPK perspective applied to a subset of gold nanoparticles and found that low delivery efficiency was associated with low distribution and permeability coefficients at the tumor site (P < 0.01). We also demonstrate how PBPK modeling and simulation can be used as an effective tool to investigate tumor delivery efficiency of nanomedicines.

Tandem Dye-Doped Nanoparticles for NIR Imaging via Cerenkov Resonance Energy Transfer

The detection of the Cerenkov radiation (CR) is an emerging preclinical imaging technique which allows monitoring the in vivo distribution of radionuclides. Among its possible advantages, the most interesting is the simplicity and cost of the required instrumentation compared, e.g., to that required for PET scans. On the other hand, one of its main drawbacks is related to the fact that CR, presenting the most intense component in the UV-vis region, has a very low penetration in biological tissues. To address this issue, we present here multifluorophoric silica nanoparticles properly designed to efficiently absorb the CR radiation and to have a quite high fluorescence quantum yield (0.12) at 826 nm. Thanks to a highly efficient series of energy transfer processes, each nanoparticle can convert part of the CR into NIR light, increasing its detection even under 1.0-cm thickness of muscle.

Gold nanoclusters elicit homeostatic perturbations in glioblastoma cells and adaptive changes of lysosomes

Unique physicochemical features place gold nanoclusters at the forefront of nanotechnology for biological and biomedical applications. To date, information on the interactions of gold nanoclusters with biological macromolecules is limited and restricts their use in living cells. Methods: Our multidisciplinary study begins to fill the current knowledge gap by focusing on lysosomes and associated biological pathways in U251N human glioblastoma cells. We concentrated on lysosomes, because they are the intracellular destination for many nanoparticles, regulate cellular homeostasis and control cell survival. Results: Quantitative data presented here show that gold nanoclusters (with 15 and 25 gold atoms), surface-modified with glutathione or PEG, did not diminish cell viability at concentrations ≤1 µM. However, even at sublethal concentrations, gold nanoclusters modulated the abundance, positioning, pH and enzymatic activities of lysosomes. Gold nanoclusters also affected other aspects of cellular homeostasis. Specifically, they stimulated the transient nuclear accumulation of TFEB and Nrf2, transcription factors that promote lysosome biogenesis and stress responses. Moreover, gold nanoclusters also altered the formation of protein aggregates in the cytoplasm. The cellular responses elicited by gold nanoclusters were largely reversible within a 24-hour period. Conclusions: Taken together, this study explores the subcellular and molecular effects induced by gold nanoclusters and shows their effectiveness to regulate lysosome biology. Our results indicate that gold nanoclusters cause homeostatic perturbations without marked cell loss. Notably, cells adapt to the challenge inflicted by gold nanoclusters. These new insights provide a framework for the further development of gold nanocluster-based applications in biological sciences.

Radiolabeling nanomaterials for multimodality imaging: New insights into nuclear medicine and cancer diagnosis

Nuclear medicine imaging has been developed as a powerful diagnostic approach for cancers by detecting gamma rays directly or indirectly from radionuclides to construct images with beneficial characteristics of high sensitivity, infinite penetration depth and quantitative capability. Current nuclear medicine imaging modalities mainly include single-photon emission computed tomography (SPECT) and positron emission tomography (PET) that require administration of radioactive tracers. In recent years, a vast number of radioactive tracers have been designed and constructed to improve nuclear medicine imaging performance toward early and accurate diagnosis of cancers. This review will discuss recent progress of nuclear medicine imaging tracers and associated biomedical imaging applications. Radiolabeling nanomaterials for rational development of tracers will be comprehensively reviewed with highlights on radiolabeling approaches (surface coupling, inner incorporation and interface engineering), providing profound understanding on radiolabeling chemistry and the associated imaging functionalities. The applications of radiolabeled nanomaterials in nuclear medicine imaging-related multimodality imaging will also be summarized with typical paradigms described. Finally, key challenges and new directions for future research will be discussed to guide further advancement and practical use of radiolabeled nanomaterials for imaging of cancers.

Radionuclide-Activated Nanomaterials and Their Biomedical Applications

Radio-nanomedicine, or the use of radiolabeled nanoparticles in nuclear medicine, has attracted much attention in the last few decades. Since the discovery of Cerenkov radiation and its employment in Cerenkov luminescence imaging, the combination of nanomaterials and Cerenkov radiation emitters has been revolutionizing the way nanomaterials are perceived in the field: from simple inert carriers of radioactivity to activatable nanomaterials for both diagnostic and therapeutic applications. Herein, we provide a comprehensive review on the types of nanomaterials that have been used to interact with Cerenkov radiation and the gamma and beta scintillation of radionuclides, as well as on their biological applications.

Characterization and validation of multimodal annihilation-gamma/near-infrared/visible laparoscopic system

Minimally invasive robotic surgery using fluorescence-guided images with a video laparoscope has been widely used because of its advantages of small incision, fast recovery time, and efficiency. However, the penetration depth limitation of fluorescence is a disadvantage caused by the absorption and scattering in tissues and blood cells. If this limitation can be overcome by additional imaging modalities, the surgical procedure can be quite efficient and precise. High-energy annihilation-gamma photons have a stronger penetration capability than visible and fluorescence photons. To characterize and validate a multimodal annihilation-gamma/near-infrared (NIR)/visible laparoscopic imaging system, an internal detector composed of an annihilation-gamma detector and an optical system was assembled inside a surgical stainless pipe with an outer diameter of 15.8 mm and an external detector with a dimension of 100  ×  100  mm2 placed at the opposite side of the internal detector. Integrated images of 511-keV gamma rays, NIR fluorescence, and visible light were obtained simultaneously. The 511-keV gamma image could be clearly seen with the acquisition of 5 s, while NIR and visible images could be presented in real time. This multimodal system has the potential for improving the surgery time and the quality of patient care.

Cu-doped quantum dots: a new class of near-infrared emitting fluorophores for bioanalysis and bioimaging

Transition metal ion-doped quantum dots (QDs) exhibit unique optical and photophysical properties that offer significant advantages over undoped QDs, such as larger Stokes shift to avoid self-absorption/energy transfer, longer excited-state lifetimes, wider spectral window, and improved chemical and thermal stability. Among the doped QDs emitters, Cu is widely introduced into the doped QDs as novel, efficient, stable, and tunable optical materials that span a wide spectrum from blue to near-infrared (NIR) light. Their unique physical and chemical characteristics enable the use of Cu-doped QDs as NIR labels for bioanalysis and bioimaging. In this review, we discuss doping mechanisms and optical properties of Cu-doped QDs that are capable of NIR emission. Applications of Cu-doped QDs in in vitro biosensing and in in vivo bioimaging are highlighted. Moreover, a prospect of the future of Cu-doped QDs for bioanalysis and bioimaging are also summarized.

Gold nanoclusters as a contrast agent for image-guided surgery of head and neck tumors

With the objective to evaluate the potential of ultra-small gold (Au) nanoclusters (NCs) for optical image-guided surgery, we synthesized and characterized AuNCs shelled by zwitterionic or pegylated ligands. The toxicity of the different AuNCs was evaluated on the Head and Neck Squamous Cell Carcinoma (HNSCC) CAL-33 and SQ20B cell lines in vitro. The safer AuNCs were administrated intravenously to mice for the determination of the pharmacokinetic properties. Biodistributions were performed on orthotopic CAL-33 HNSCC-bearing mice. Finally, the AuNCs were used for image-guided surgery, allowing the increase of the survival time vs. control animals, and the number of animals without any local recurrence.

Comparative study of core- and surface-radiolabeling strategies for the assembly of iron oxide nanoparticle-based theranostic nanocomposites

This work highlights the superiority of the surface-radiolabeling strategy over the core-labeling strategy in the assembly of radioactive iron oxide nanoparticle (IONP)-based nanocomposites for use in multimodal imaging and targeted therapy. It also implies a possible overestimation of the labeling stability in previous studies and points out directions for further optimization.

Multimodality Imaging Agents with PET as the Fundamental Pillar

Positron emission tomography (PET) provides quantitative information in vivo with ultra-high sensitivity but is limited by its relatively low spatial resolution. Therefore, PET has been combined with other imaging modalities, and commercial systems such as PET/computed tomography (CT) and PET/magnetic resonance (MR) have become available. Inspired by the emerging field of nanomedicine, many PET-based multimodality nanoparticle imaging agents have been developed in recent years. This Minireview highlights recent progress in the design of PET-based multimodality imaging nanoprobes with an aim to overview the major advances and key challenges in this field and substantially improve our knowledge of this fertile research area.