Ultrasensitive magnetic resonance imaging of systemic reactive oxygen species in vivo for early diagnosis of sepsis using activatable nanoprobes

Cu(II)-induced magnetic resonance tuning and enhanced magnetic relaxation switching immunosensor for sensitive detection of chlorpyrifos and Salmonella

Magnetic relaxation switching (MRS) biosensors have been recognized as useful analytical tools for a range of targets; however, traditional MRS biosensors are limited by the "prozone effect", resulting in a narrow linear range and low sensitivity. Herein, we proposed a paramagnetic Cu2+-induced magnetic resonance tuning (MRET) strategy, based on which Cu2+ ions and magnetic nanoparticles (MNPs) were adopted to construct a Cu-MNP-mediated MRS (Cu-M-MRS) immunosensor with Cu2+ ions acting as a quencher and MNPs as an enhancer. An Fe3O4@polydopamine-secondary antibody conjugate was prepared and used to correlate the amount of Cu2+ ions to the target concentration through an immunoassay. Based on the immunoreaction, the Cu-M-MRS immunosensor enabled the sensitive detection of chlorpyrifos (0.05 ng/mL, a 77-fold enhancement in sensitivity compared with the traditional MRS immunosensor) and Salmonella (50 CFU/mL). The proposed MRET strategy effectively improved the sensitivity and accuracy of the MRS immunosensor, offering a promising and versatile platform for food safety detection.

Nanomaterial-Based Repurposing of Macrophage Metabolism and Its Applications

Macrophage immunotherapy represents an emerging therapeutic approach aimed at modulating the immune response to alleviate disease symptoms. Nanomaterials (NMs) have been engineered to monitor macrophage metabolism, enabling the evaluation of disease progression and the replication of intricate physiological signal patterns. They achieve this either directly or by delivering regulatory signals, thereby mapping phenotype to effector functions through metabolic repurposing to customize macrophage fate for therapy. However, a comprehensive summary regarding NM-mediated macrophage visualization and coordinated metabolic rewiring to maintain phenotypic equilibrium is currently lacking. This review aims to address this gap by outlining recent advancements in NM-based metabolic immunotherapy. We initially explore the relationship between metabolism, polarization, and disease, before delving into recent NM innovations that visualize macrophage activity to elucidate disease onset and fine-tune its fate through metabolic remodeling for macrophage-centered immunotherapy. Finally, we discuss the prospects and challenges of NM-mediated metabolic immunotherapy, aiming to accelerate clinical translation. We anticipate that this review will serve as a valuable reference for researchers seeking to leverage novel metabolic intervention-matched immunomodulators in macrophages or other fields of immune engineering.

Microenvironment-triggered cascade metal-polyphenolic nanozyme for ROS/NO synergistic hyperglycemic wound healing

Wound infection of hyperglycemic patient often has extended healing period and increased probability due to the high glucose level. However, achieving precise and safe therapy of the hyperglycemic wound with specific wound microenvironment (WME) remains a major challenge. Herein, a WME-activated smart L-Arg/GOx@TA-Fe (LGTF) nanozymatic system composed of generally recognized as safe (GRAS) compound is engineered. The nanozymatic system combining metal-polyphenol nanozyme (tannic acid-Fe3+, TA-Fe) and natural enzyme (glucose oxidase, GOx) can consume the high-concentration glucose, generating reactive oxygen species (ROS) and nitric oxide (NO) in situ to synergistically disinfect hyperglycemia wound. In addition, glucose consumption and gluconic acid generation can lower glucose level to promote wound healing and reduce the pH of WME to enhance the catalytic activities of the LGTF nanozymatic system. Thereby, low-dose LGTF can perform remarkable synergistic disinfection and healing effect towards hyperglycemic wound. The superior biosafety, high catalytic antibacterial and beneficial WME regulating capacity demonstrate this benign GRAS nanozymatic system is a promising therapeutic agent for hyperglycemic wound.

Developments and Trends of Nanotechnology Application in Sepsis: A Comprehensive Review Based on Knowledge Visualization Analysis

Sepsis, a common life-threatening clinical condition, continues to have high morbidity and mortality rates, despite advancements in management. In response, significant research efforts have been directed toward developing effective strategies. Within this scope, nanotechnology has emerged as a particularly promising field, attracting significant interest for its potential to enhance disease diagnosis and treatment. While several reviews have highlighted the use of nanoparticles in sepsis, comprehensive studies that summarize and analyze the hotspots and research trends are lacking. To identify and further promote the development of nanotechnology in sepsis, a bibliometric analysis was conducted on the relevant literature, assessing research trends and hotspots in the application of nanomaterials for sepsis. Next, a comprehensive review of the subjectively recognized research hotspots in sepsis, including nanotechnology-enhanced biosensors and nanoscale imaging for sepsis diagnostics, and nanoplatforms designed for antimicrobial, immunomodulatory, and detoxification strategies in sepsis therapy, is elucidated, while the potential side effects and toxicity risks of these nanomaterials were discussed. Particular attention is given to biomimetic nanoparticles, which mimic the biological functions of source cells like erythrocytes, immune cells, and platelets to evade immune responses and effectively deliver therapeutic agents, demonstrating substantial translational potential. Finally, current challenges and future perspectives of nanotechnology applications in sepsis with a view to maximizing their great potential in the research of translational medicine are also discussed.

Azo Reductase Activated Magnetic Resonance Tuning Probe with "Switch-On" Property for Specific and Sensitive Tumor Imaging in Vivo

Cancer remains a threat to human health. However, if tumors can be detected in the early stage, then the effectiveness of cancer treatment could be significantly improved. Therefore, it is worthwhile to develop more sensitive and accurate cancer diagnostic methods. Herein, we demonstrated an azo reductase (AzoR)-activated magnetic resonance tuning (MRET) probe with a "switch-on" property for specific and sensitive tumor imaging in vivo. Specifically, Gd-labeled DNA1 (DNA1-Gd) and cyclodextrin-coated magnetic nanoparticles (MNP-CD) were employed as enhancer and quencher of MRET, respectively, while DNA2, an azobenzene (Azo) group-modified aptamer (AS1411), served as a linker between enhancer and quencher to construct the MRET probe of MNP@DNA(1-2)-Gd. In tumor tissues with high-level AzoR, the T1-weighted magnetic resonance signal of the MRET probe could be restored by intelligently regulating the switch from "OFF" to "ON" after activation with AzoR, thus accurately indicating the location of the tumor accurately. Moreover, the tumor with a 4 times smaller size than that of the normal tumor model could be imaged based on the proposed MRET probe. The as-proposed MRET-based magnetic resonance imaging strategy not only achieves tumor imaging accurately but also shows promise for early diagnosis of tumors, which might improve patients' survival rates and provide an opportunity for image-guided biomedical applications in the future.

hROS-Responsive Behavior for Long-Term Stability of Cellulosic Gold Nanoclusters

Understanding the gold core-ligand interaction in gold nanoclusters (GNCs) is essential for the on-demand tailoring of their photoluminescence properties and long-term stability. Here, inspired by the suckers arranged directionally on the tentacles of octopus, a series of GNCs with regulating ligand structures are grown and stabilized on the cellulose nanocrystals (CNCs). The carboxylated CNCs providing an electron-rich environment to promote the luminescence of GNCs and stabilize it within a long-term of 1 year through anchoring and diluting effects, and the highest quantum yields reaches 31.02% in ultrapure water. Interestingly, this bionic preparation strategy is generally applicable to various ligands for tailoring on-demand hROS-responsive and nonresponsive GNCs to construct tunable-emission wavelength dual GNCs ratiometric probes. The results show that designing a specific ligand structure to inhibit the transformation of Au-Au to Au (I)-ligand in GNCs is crucial to regulate the hROS-responsive characteristics. As expected, the interfacial compatible dual GNCs ratiometric probe with a hROS limit of detection of 0.74 µmol L-1 can diagnose certain diseases through intracellular hROS imaging. This work provides important insights for understanding the gold core-ligand interaction in GNCs during the oxidation process triggered by intracellular hROS.

The Emerging Role of Ferroptosis in Sepsis, Opportunity or Challenge?

Sepsis is a syndrome in multi-organ dysfunction triggered by a deleterious immunological reaction of the body to a condition caused by infection, surgery, or trauma. Currently, sepsis is thought to be primarily associated with abnormal immune responses resulting in organ microcirculatory disturbances, cellular mitochondrial dysfunction, and induced cell death, although the exact pathogenesis of sepsis is still inconclusive. In recent years, the role of abnormal metabolism of trace nutrients in the pathogenesis of sepsis has been investigated. Ferroptosis is a type of cell death that relies on iron and is characterized by unique morphological, biochemical, and genetic features. Unlike other forms of cell death, such as autophagy, apoptosis, necrosis, and pyroptosis, ferroptosis is primarily driven by lipid peroxidation. Ferroptosis cells may be immunogenic, amplify inflammatory responses, cause more cell death, and ultimately induce multi-organ failure. An increasing number of studies have indicated the significance of ferroptosis in sepsis and its role in reducing inflammation. The effectiveness of sepsis treatment has been demonstrated by the use of drugs that specifically target molecules associated with the ferroptosis pathway, including ferroptosis inhibitors. Nevertheless, there is a scarcity of studies investigating the multi-organ dysfunction caused by ferroptosis in sepsis. This article presents a summary and evaluation of recent progress in the role of ferroptosis through molecularly regulated mechanisms and its potential mechanisms of action in the multi-organ dysfunction associated with sepsis. It also discusses the current challenges and prospects in understanding the connection between sepsis and ferroptosis, and proposes innovative ideas and strategies for the treatment of sepsis.

Toward quantification of hypoxia using fluorinated EuII/III-containing ratiometric probes

Hypoxia is a prognostic biomarker of rapidly growing cancers, where the extent of hypoxia is an indication of tumor progression and prognosis; therefore, hypoxia is also used for staging while performing chemo- and radiotherapeutics for cancer. Contrast-enhanced MRI using EuII-based contrast agents is a noninvasive method that can be used to map hypoxic tumors, but quantification of hypoxia using these agents is challenging due to the dependence of signal on the concentration of both oxygen and EuII. Here, we report a ratiometric method to eliminate concentration dependence of contrast enhancement of hypoxia using fluorinated EuII/III-containing probes. We studied three different EuII/III couples of complexes containing 4, 12, or 24 fluorine atoms to balance fluorine signal-to-noise ratio with aqueous solubility. The ratio between the longitudinal relaxation time (T1) and 19F signal of solutions containing different ratios of EuII- and EuIII-containing complexes was plotted against the percentage of EuII-containing complexes in solution. We denote the slope of the resulting curves as hypoxia indices because they can be used to quantify signal enhancement from Eu, that is related to oxygen concentration, without knowledge of the absolute concentration of Eu. This mapping of hypoxia was demonstrated in vivo in an orthotopic syngeneic tumor model. Our studies significantly contribute toward improving the ability to radiographically map and quantify hypoxia in real time, which is critical to the study of cancer and a wide range of diseases.

Flavonoid-Conjugated Gadolinium Complexes as Anti-Inflammatory Theranostic Agents

In this study, we designed, synthesized, and evaluated gadolinium compounds conjugated with flavonoids as potential theranostic agents for the treatment of inflammation. These novel theranostic agents combine a molecular imaging agent and one of three flavonoids (galangin, chrysin, and 7-hydroxyflavone) as anti-inflammatory drugs as a single integrated platform. Using these agents, MR imaging showed contrast enhancement (>10 in CNR) at inflamed sites in an animal inflammation model, and subsequent MR imaging used to monitor the therapeutic efficacy of these integrated agents revealed changes in inflamed regions. The anti-inflammatory effects of these agents were demonstrated both in vitro and in vivo. Furthermore, the antioxidant efficacy of the agents was evaluated by measuring their reactive oxygen species scavenging properties. For example, Gd-galangin at 30 μM showed a three-fold higher ROS scavenging of DPPH. Taken together, our findings provide convincing evidence to indicate that flavonoid-conjugated gadolinium compounds can be used as potentially efficient theranostic agents for the treatment of inflammation.

Designing Protein-Based Probes for Sensing Biological Analytes with Magnetic Resonance Imaging

Genetically encoded sensors provide unique advantages for monitoring biological analytes with molecular and cellular-level specificity. While sensors derived from fluorescent proteins represent staple tools in biological imaging, these probes are limited to optically accessible preparations owing to physical curbs on light penetration. In contrast to optical methods, magnetic resonance imaging (MRI) may be used to noninvasively look inside intact organisms at any arbitrary depth and over large fields of view. These capabilities have spurred the development of innovative methods to connect MRI readouts with biological targets using protein-based probes that are in principle genetically encodable. Here, we highlight the state-of-the-art in MRI-based biomolecular sensors, focusing on their physical mechanisms, quantitative characteristics, and biological applications. We also describe how innovations in reporter gene technology are creating new opportunities to engineer MRI sensors that are sensitive to dilute biological targets.

Vanadium nitride@carbon nanofiber composite: Synthesis, cascade enzyme mimics and its sensitive and selective colorimetric sensing of superoxide anion

Nanozymes featuring with favorable activity, good stability and easy scale-up production, are promising to replace natural enzymes for various applications. However, it remains a challenge to explore the cascade reactions of multi-enzyme mimics, aiming at synergistic catalysis for various applications. Herein, vanadium nitride nanoparticles deposited on carbon nanofibers (VN@CNFs) composite was facilely prepared by typical electrospinning route with subsequently ammonia reduction process. The nanocomposite showed excellent peroxidase (POD)-like and superoxide dismutase (SOD)-like activities. Additionally, their catalytic mechanisms were systematically researched. Coupling of SOD-like with POD-like as cascade enzyme, a selective and sensitive colorimetric detection of superoxide anion (O₂^•-) was explored, which has two linear parts, 0.05-30 μM and 30-250 μM O₂^•- with the LOD of 0.0167 μM (S/N = 3). The as-proposed method was applicable to practical samples detection with satisfactory accuracy and recovery. Therefore, the VN@CNFs composite shows great prospect in biosensing, superoxide anion removal and biocatalysis.

Biodegradable AuNP-Based Plasmonic Nanogels as Contrast Agents for Computed Tomography and Photoacoustics

Gold nanoparticles (AuNP) are well-established contrast agents in computed tomography (CT) and photoacoustic imaging (PAI). A wide variety of AuNP sizes, shapes, and coatings have been reported for these applications. However, for clinical translation, AuNP should be excretable to avoid long-term accumulation and possible side effects. Sub-5 nm AuNP have the benefit to be excretable through kidney filtration, therefore their loading in biodegradable nanogels holds promise to result in contrast agents that have long circulation times in the vasculature and subsequent biodegradation for excretion. Polyphosphazenes are intrinsically biodegradable polymers capable of forming nanogels with high payloads, and to release their payloads upon degradation. The significant development in polyphosphazenes that have tailored degradation kinetics, and their formulation with drugs or contrast agents, has shown potential as a biodegradable platform for imaging vasculature and endogenous molecules, by combination of CT and PA modalities. Therefore, we herein present methods for the formulation of AuNP assemblies loaded in nanogels composed of biodegradable polyphosphazenes, with a size range from 50 to 200 nm. We describe protocols for their characterization by UV-vis spectroscopy, Fourier-transform infrared spectroscopy, various microscopy techniques, elemental quantification by induced coupling plasma optical emission spectroscopy and contrast production in both CT and PAI. Finally, we detail the methods to investigate their effect on cells, distribution in cells and imaging properties for detection of endogenous molecules.

The Design of Abnormal Microenvironment Responsive MRI Nanoprobe and Its Application

Magnetic resonance imaging (MRI) is often used to diagnose diseases due to its high spatial, temporal and soft tissue resolution. Frequently, probes or contrast agents are used to enhance the contrast in MRI to improve diagnostic accuracy. With the development of molecular imaging techniques, molecular MRI can be used to obtain 3D anatomical structure, physiology, pathology, and other relevant information regarding the lesion, which can provide an important reference for the accurate diagnosis and treatment of the disease in the early stages. Among existing contrast agents, smart or activatable nanoprobes can respond to selective stimuli, such as proving the presence of acidic pH, active enzymes, or reducing environments. The recently developed environment-responsive or smart MRI nanoprobes can specifically target cells based on differences in the cellular environment and improve the contrast between diseased tissues and normal tissues. Here, we review the design and application of these environment-responsive MRI nanoprobes.

Tumor microenvironment-responsive polydopamine-based core/shell nanoplatform for synergetic theranostics

Theranostic agents that integrate diagnostic and therapeutic modalities have drawn extensive attention due to their ability to deliver real-time imaging-guided tumor treatment. Herein, a novel core-shell polydopamine (PDA)-based theranostic agent (PDA@TA-Fe) was fabricated via a two-step strategy. Upon 808 nm and 1064 nm laser irradiation, this agent exhibited high photothermal conversion efficiencies of 29% and 41%, respectively. After endocytosis into tumor cells, the TA-Fe shell of PDA@TA-Fe gradually disintegrated in the weakly acidic tumor microenvironment (TME), and released the TA as an acidity-activated reductant that could reduce Fe3+ to Fe2+. Subsequently, the generated Fe2+ reacted with H2O2 to generate toxic hydroxyl radicals (˙OH) via the Fenton reaction, which induced the apoptosis of tumor cells and achieved the chemodynamic therapy (CDT). The heat produced by photothermal therapy (PTT) accelerated the ˙OH generation to achieve a synergetic effect of CDT/PTT. In vivo tumor-xenograft imaging and therapeutic assays demonstrated obvious contrast enhancement at the tumor site in the T1/T2-weighted MR imaging and efficient tumor suppression achieved after the intravenous injection of this agent because of the enhanced permeation and retention (EPR) effect. This study offered a new strategy to design an "all-in-one" nanoplatform for T1/T2 MR imaging-guided synergistic cancer treatment of CDT/PTT.

The effects of sepsis on endothelium and clinical implications

ABSTRACT

Sepsis accounts for nearly 700 000 deaths in Europe annually and is caused by an overwhelming host response to infection resulting in organ failure. The endothelium is an active contributor to sepsis and as such represents a major target for therapy. During sepsis, endothelial cells amplify the immune response and activate the coagulation system. They are both a target and source of inflammation and serve as a link between local and systemic immune responses. In response to cytokines produced by immune cells, the endothelium expresses adhesion molecules and produces vasoactive compounds, inflammatory cytokines, and chemoattractants, thus switching from an anticoagulant to procoagulant state. These responses contribute to local control of infection, but systemic activation can lead to microvascular thrombosis, capillary permeability, hypotension, tissue hypoxia, and ultimately tissue damage. This review focuses on the role of the endothelium in leucocyte adhesion and transmigration as well as production of reactive oxygen and nitrogen species, microRNAs and cytokines, formation of signalling microparticles, and disseminated intravascular coagulation. We also discuss alterations in endothelial permeability and apoptosis. Finally, we review the diagnostic potential of endothelial markers and endothelial pathways as therapeutic targets for this devastating disease.

Nanotools for Sepsis Diagnosis and Treatment

Sepsis is one of the leading causes of death worldwide with high mortality rates and a pathological complexity hindering early and accurate diagnosis. Today, laboratory culture tests are the epitome of pathogen recognition in sepsis. However, their consistency remains an issue of controversy with false negative results often observed. Clinically used blood markers, C reactive protein (CRP) and procalcitonin (PCT) are indicators of an acute-phase response and thus lack specificity, offering limited diagnostic efficacy. In addition to poor diagnosis, inefficient drug delivery and the increasing prevalence of antibiotic-resistant microorganisms constitute significant barriers in antibiotic stewardship and impede effective therapy. These challenges have prompted the exploration for alternative strategies that pursue accurate diagnosis and effective treatment. Nanomaterials are examined for both diagnostic and therapeutic purposes in sepsis. The nanoparticle (NP)-enabled capture of sepsis causative agents and/or sepsis biomarkers in biofluids can revolutionize sepsis diagnosis. From the therapeutic point of view, currently existing nanoscale drug delivery systems have proven to be excellent allies in targeted therapy, while many other nanotherapeutic applications are envisioned. Herein, the most relevant applications of nanomedicine for the diagnosis, prognosis, and treatment of sepsis is reviewed, providing a critical assessment of their potentiality for clinical translation.

Phenol-like group functionalized graphene quantum dots structurally mimicking natural antioxidants for highly efficient acute kidney injury treatment

Acute kidney injury (AKI) is a syndrome characterized by rapid loss of renal excretory function with high in-hospital mortality. The excess generation of reactive oxygen species (ROS) in the kidneys during AKI has been considered a major cause of renal failure. Currently available antioxidants for AKI treatment often lack the required antioxidative efficacy or renal accumulation rate. Herein, inspired by the structure of natural phenolic antioxidants, phenol-like group functionalized graphene quantum dots (h-GQDs) with both high ROS scavenging efficacy and renal specificity are constructed for AKI antioxidative therapy. Similar to natural polyphenols, the abundant phenol-like groups on h-GQDs are demonstrated to be the active components exerting antioxidative effects. Further exhaustive mechanistic investigations indicate that the ultrahigh antioxidative activity of h-GQDs originates not solely from the phenol-like groups, but also from the synergy between adjacent phenol-like groups, as well as the removal of unfavorable carbonyl groups on h-GQDs. In AKI mice, h-GQDs can effectively protect the kidneys from oxidative injury with only a one-sixteenth dose of the clinical antioxidant N-acetylcysteine (NAC) and show no evidence of toxicity. The findings of this study will facilitate development of high-performance carbon-based antioxidative platforms via structure–activity relationships for treating AKI and other ROS-related diseases.

Phenol-like group functionalized graphene quantum dots that structurally mimic natural antioxidants are constructed as high-efficacy reactive oxygen species scavengers for acute kidney injury antioxidative therapy.

An Oxidation-Enhanced Magnetic Resonance Imaging Probe for Visual and Specific Detection of Singlet Oxygen Generated in Photodynamic Cancer Therapy In Vivo

Singlet oxygen is regarded as the primary cytotoxic agent in cancer photodynamic therapy (PDT). Despite the advances in optical methods to image singlet oxygen, it remains a challenge for in vivo application due to the limited tissue penetration depth of light. Up to date, no singlet oxygen-specific magnetic resonance imaging (MRI) probe has been reported. Herein, a T₂ -weighted MRI probe is reported to visually detect singlet oxygen generated in PDT in vitro and in vivo. The MRI probe Ce6/Fe₃ O₄ -M is constructed by co-encapsulation of photosensitizer Ce6 and Fe₃ O₄ nanoparticles in mPEG₂₀₀₀ -TK-C₁₆ micelles. Thioketal (TK) linker in the probe is highly sensitive to singlet oxygen, but lowly sensitive to other reactive oxygen species (ROS) existing in physiological and pathological environments. Singlet oxygen, generated with light irradiation, triggers the cleavage of TK, which leads to loss of surface polyethylene glycol, increment of the hydrophobicity, and aggregation of Fe₃ O₄ nanoparticles. Subsequently, negatively enhanced T₂ -weighted MRI signal is obtained for visual detection of singlet oxygen in the solution, cancer cells, and in vivo. This oxidation responsive MRI probe is expected to hold great promise in evaluating the ability of photosensitizers to generate singlet oxygen and in predicting the therapeutic efficacies of PDT in vivo.

Early stratification of radiotherapy response by activatable inflammation magnetic resonance imaging

Tumor heterogeneity is one major reason for unpredictable therapeutic outcomes, while stratifying therapeutic responses at an early time may greatly benefit the better control of cancer. Here, we developed a hybrid nanovesicle to stratify radiotherapy response by activatable inflammation magnetic resonance imaging (aiMRI) approach. The high Pearson's correlation coefficient R values are obtained from the correlations between the T1 relaxation time changes at 24-48 h and the ensuing adaptive immunity (R = 0.9831) at day 5 and the tumor inhibition ratios (R = 0.9308) at day 18 after different treatments, respectively. These results underscore the role of acute inflammatory oxidative response in bridging the innate and adaptive immunity in tumor radiotherapy. Furthermore, the aiMRI approach provides a non-invasive imaging strategy for early prediction of the therapeutic outcomes in cancer radiotherapy, which may contribute to the future of precision medicine in terms of prognostic stratification and therapeutic planning.

Carbon dot targeting to nitrogen signaling molecules for inhibiting neuronal death

Ultrasmall carbon dot with targeting ability to nitrogen signaling molecules inhibit neuronal death by regulating the activity of endogenous enzymes.

In situ and real-time imaging of superoxide anion and peroxynitrite elucidating arginase 1 nitration aggravating hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion (IR) injury is dynamically regulated by intertwined superoxide anion (O2-)-peroxynitrite (ONOO-) cascaded molecules. Arginase 1 involves in O2-/ONOO- fluctuations and is strongly connected to IR injury. A few probes have been innovated to measure intracellular O2- or ONOO- by fluorescent imaging separately, but revealing the definite link of O2-, ONOO- and arginase 1 in situ remains unidentified in hepatic IR. Thus, a well-designed dual-color two-photon fluorescence probe (CyCA) was created for the in situ real-time detection of O2--ONOO-. Surprisingly, CyCA exhibited a suitable combination of high specificity, preeminent sensitivity, exclusive mitochondria-targeting and fast-response. On the basis of remarkable advantages, we successfully applied CyCA to visualize endogenous O2- and ONOO- in living cells and mice. The synergistic elevation of mitochondrial O2--ONOO- in IR mice was observed for the first time. Furthermore, three tyrosine nitration-sites in arginase 1 caused by ONOO- were identified in proteomic analysis, which was never reported previously. Attractively, nitro-modified arginase 1 could further promote ONOO- formation, ultimately exacerbating the intracellular redox imbalance and IR injury. These new findings decipher direct molecular links of O2--ONOO--arginase 1, and suggest effective strategies for the prevention and treatment of IR injury.

Reactivity-Based Organic Theranostic Bioprobes

Reactivity-based organic bioprobes have been increasingly designed and developed in the last couple of years to address important questions in numerous fields, particularly in biology and medicine. Contrary to the conventional lock-and-key bioprobes, which rely on molecular recognition to probe biological systems and impart sensing specificity, reactivity-based bioprobes capitalize on molecular reactivity for selective target detection. In fact, reactivity-based sensing exploits the intrinsic differences in chemical reactivity to differentiate various chemical species possessing similar size and shape in biological systems. This unique sensing mechanism has been effective for the detection of a wide range of chemical analytes in living cells, tissues, and animals, although bioprobes with additional functionalities are increasingly required in the quest to unravel and understand the complex biological systems. This is why the integration of diagnostic and therapeutic functions in one theranostic platform has become a continuous pursuit in the development of bioprobes in recent years. To this end, numerous design and synthetic approaches have been explored, notably that combining different organic materials with distinct functionalities into one integrated system, also known as "all-in-one" strategy. Nevertheless, the "all-in-one" strategy is prone to design complexity and unsatisfactory reproducibility. To minimize these undesirable hurdles, the deliberate design and engineering of simple organic molecules with multiple functionalities have been actively pursued, leading to the emergence of a unique approach known as "one-for-all" strategy. A prominent example of this approach leverages on fluorogens with aggregation-induced emission (AIE) characteristic. Through smart molecular engineering, we and other groups have recently shown that conventional organic AIE fluorogens can be specifically tailored to offer both imaging and therapeutic functionalities, such as photosensitizing ability to facilitate photodynamic therapy. The creation of this new class of versatile organic theranostic bioprobes with simultaneous imaging and therapeutic capabilities has further enabled image-guided chemotherapy and image-guided photodynamic therapy. Essentially, from this endeavor, replacing the fluorophores of conventional reactivity-based bioprobes with multifunctional molecules will yield reactivity-based organic theranostic bioprobes with enhanced capabilities and improved performance. In this Account, we summarize the latest advancement of reactivity-based theranostic bioprobes. To start with, we discuss the fundamental differences between conventional lock-and-key and reactivity-based sensing mechanisms, followed by general design routes of reactivity-based organic theranostic bioprobes. We then describe our efforts in recent years in formulating reactivity-based organic biosensing/imaging probes and multifunctional theranostic probes as well as in utilizing these bioprobes in detecting various chemical species in living systems, such as free radicals and toxins, and in diagnosing and treating cancer and bacterial infections. Finally, we highlight current challenges and opportunities in the conclusions and outlook section. With this Account, we seek to further stimulate research activities and closer collaborations among the research fields of chemistry, materials, and biology to push the boundary of this emerging field and promote reactivity-based theranostics for practical applications and clinical translations.

Renal-Clearable Porphyrinic Metal-Organic Framework Nanodots for Enhanced Photodynamic Therapy

Nanoscale porphyrinic metal-organic frameworks (NMOFs) have emerged as promising therapeutic platforms for the photodynamic therapy (PDT) of cancer in recent years. However, the relatively large sizes of current NMOFs ranging from tens to hundreds of nanometers usually lead to inefficient body clearance and unsatisfactory PDT effect, thus amplifying their long-term toxicity and restricting their further usage. To overcome these shortcomings, herein, ultrasmall porphyrinic metal-organic framework nanodots (MOF QDs) prepared from NMOFs are rationally synthesized via a facile method and used as renal-clearable nanoagents for the enhanced PDT of cancer. Compared with the precursor NMOFs, our well-prepared MOF QDs can generate 2-fold effective toxic reactive oxygen species (ROS) upon the same light irradiation and greatly decrease the inefficacy of PDT caused by the inefficient use of ROS generated from the interior of NMOFs. Meanwhile, the IC₅₀ value of ultrasmall MOF QDs is nearly one-third that of NMOFs, and in vivo results demonstrate that our MOF QDs exhibit better PDT efficacy than NMOFs under the same treatment owing to their overcoming the limited ROS diffusion distance. Significantly, these ultrasmall MOF QDs show efficient tumor accumulation and rapid renal clearance in vivo, indicating their potential in biomedical utility. Last but not least, comprehensive investigations of long-term toxicity of these MOF QDs well demonstrate their overall safety. Therefore, this study will offer valuable insight into the development of safe and high-performance PDT nanoplatforms for further clinical translation.

Activatable Hybrid Polyphosphazene-AuNP Nanoprobe for ROS Detection by Bimodal PA/CT Imaging

Overproduction of reactive oxygen species (ROS) is often related to inflammation or cancer and can cause tissue damage. Probes that have been previously reported to image ROS typically rely on imaging techniques that have low depth penetration in tissue, thus limiting their use to superficial disease sites. We report herein a novel formulation of hybrid nanogels loaded with gold nanoparticles (AuNP) to produce contrast for computed tomography (CT) and photoacoustics (PA), both being deep-tissue imaging techniques. The polyphosphazene polymer has been designed to selectively degrade upon ROS exposure, which triggers a switch-off of the PA signal by AuNP disassembly. This ROS-triggered degradation of the nanoprobes leads to a significant decrease in the PA contrast, thus allowing ratiometric ROS imaging by comparing the PA to CT signal. Furthermore, ROS imaging using these nanoprobes was applied to an in vitro model of inflammation, that is, LPS-stimulated macrophages, where ROS-triggered disassembly of the nanoprobe was confirmed via reduction of the PA signal. In summary, these hybrid nanoprobes are a novel responsive imaging agent that have the potential to image ROS overproduction by comparing PA to CT contrast.

Aggregation-induced emission-active Au nanoclusters for ratiometric sensing and bioimaging of highly reactive oxygen species

A nanoprobe based on aggregation-induced emission-active Au nanoclusters for ratiometric sensing and bioimaging of highly reactive oxygen species is constructed.