Iridium nanoparticles supported on polyaniline nanotubes for peroxidase mimicking towards total antioxidant capacity assay of fruits and vegetables

In this study, a straightforward approach is presented for the first time to anchor Ir nanoparticles on the surface of uniform polyaniline (PANi) nanotubes (NTs), which can be used as an efficient peroxidase (POD)-like catalyst. The morphology and chemical structure of the PANi-Ir nanocomposite are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), Raman and X-ray photoelectron spectroscopy (XPS) measurements. Owing to the strong interaction between Ir nanoparticles and PANi, a remarkable catalytic enhancement is achieved compared to the bare Ir black catalyst and individual PANi NTs, dominating withan electron transfer mechanism. Furthermore, an efficient colorimetric sensor for ascorbic acid (AA) is developed with a low detection limit of 1.0 μM (S/N = 3), and a total antioxidant capacity (TAC) sensing platform is also constructed for the rigorous detection and analysis of fruits and vegetables.

Lactic acid responsive sequential production of hydrogen peroxide and consumption of glutathione for enhanced ferroptosis tumor therapy

Ferroptosis is characterized by the lethal accumulation of lipid reactive oxygen species (ROS), which has great potential for tumor therapy. However, developing new ferroptosis-inducing strategies by combining nanomaterials with small molecule inducers is important. In this study, an enzyme-gated biodegradable natural-product delivery system based on lactate oxidase (LOD)-gated biodegradable iridium (Ir)-doped hollow mesoporous organosilica nanoparticles (HMONs) loaded with honokiol (HNK) (HNK@Ir-HMONs-LOD, HIHL) is designed to enhance ferroptosis in colon tumor therapy. After reaching the tumor microenvironment, the outer LOD dissociates and releases the HNK to induce ferroptosis. Moreover, the released dopant Ir4+ and disulfide-bridged organosilica frameworks deplete intracellular glutathione (GSH), which is followed by GSH-mediated Ir(IV)/Ir(III) conversion. This leads to the repression of glutathione peroxidase 4 (GPX4) activity and decomposition of intratumoral hydrogen peroxide (H2O2) into hydroxyl radicals (•OH) by Ir3+-mediated Fenton-like reactions. Moreover, LOD efficiently depletes lactic acid to facilitate the generation of H2O2 and boost the Fenton reaction, which in turn enhances ROS generation. With the synergistic effects of these cascade reactions and the release of HNK, notable ferroptosis efficacy was observed both in vitro and in vivo. This combination of natural product-induced and lactic acid-responsive sequential production of H2O2 as well as the consumption of glutathione may provide a new paradigm for achieving effective ferroptosis-based cancer therapy.

Monitoring the Mitochondrial Viscosity Changes During Cuproptosis with Iridium(III) Complex Probe via In Situ Phosphorescence Lifetime Imaging

Cuproptosis is a novel copper-dependent form of programmed cell death, displaying important regulatory functions in many human diseases, including cancer. However, the relationship between the changes in mitochondrial viscosity, a key factor associated with cellular malfunction, and cuproptosis is still unclear. Herein, we prepared a phosphorescent iridium (Ir) complex probe for precisely monitoring the changes of mitochondrial viscosity during cuprotosis via phosphorescence lifetime imaging. The Ir complex probe possessed microsecond lifetimes (up to 1 μs), which could be easily distinguished from cellular autofluorescence to improve the imaging contrast and sensitivity. Benefiting from the long phosphorescence lifetime, excellent viscosity selectivity, and mitochondrial targeting abilities, the Ir complex probe could monitor the increase in the mitochondrial viscosity during cuproptosis (from 46.8 to 68.9 cP) in a quantitative manner. Moreover, through in situ fluorescence imaging, the Ir complex probe successfully monitored the increase in viscosity in zebrafish treated with lipopolysaccharides or elescolomol-Cu2+, which were well-known cuproptosis inducers. We anticipate that this new Ir complex probe will be a useful tool for in-depth understanding of the biological effects of mitochondrial viscosity during cuproptosis.

A Ferroptosis-Inducing Arsenene-Iridium Nanoplatform for Synergistic Immunotherapy in Pancreatic Cancer

Due to multidrug resistance and the high risk of recurrence, effective and less toxic alternative pancreatic cancer treatments are urgently needed. Pancreatic cancer cells are highly resistant to apoptosis but sensitive to ferroptosis. In this study, an innovative nanoplatform (AsIr@PDA) was developed by electrostatic adsorption of a cationic iridium complex (IrFN) onto two-dimensional (2D) arsenene nanosheets. This nanoplatform exhibits superior ferroptosis-inducing effects with high drug loading capacity and, importantly, excellent anti-cancer immune activation function, leading to efficient elimination of pancreatic tumors with no observable side effects. Interestingly, AsIr@PDA significantly prevents the recurrence of pancreatic cancer in vivo when compared with a cisplatin-loaded nanoplatform. This designed nanoplatform demonstrated superior therapeutic efficacy by synergistic ferroptosis-induced chemotherapy with immunotherapy via an all-in-one strategy, providing new insights for future pancreatic cancer therapy.

Ligand Regulation Strategy to Modulate ROS Nature in a Rhodamine-Iridium(III) Hybrid System for Phototherapy

The efficacy of photodynamic therapy (PDT) is highly dependent on the photosensitizer features. The reactive oxygen species (ROS) generated by photosensitizers is proven to be associated with immunotherapy by triggering immunogenic cell death (ICD) as well. In this work, we establish a rhodamine-iridium(III) hybrid model functioning as a photosensitizer to comprehensively understand its performance and potential applications in photodynamic immunotherapy. Especially, the correlation between the ROS generation efficiency and the energy level of the Ir(III)-based excited state (T1'), modulated by the cyclometalating (C∧N) ligand, is systematically investigated and correlated. We prove that in addition to the direct population of the rhodamine triplet state (T1) formed through the intersystem crossing process with the assistance of a heavy Ir(III) metal center, the fine-tuned T1' state could act as a relay to provide an additional pathway for promoting the cascade energy transfer process that leads to enhanced ROS generation ability. Moreover, type I ROS can be effectively produced by introducing sulfur-containing thiophene units in C∧N ligands, providing a stronger M1 macrophage-activation efficiency under hypoxia to evoke in vivo antitumor immunity. Overall, our work provides a fundamental guideline for the molecular design and exploration of advanced transition-metal-based photosensitizers for biomedical applications.

Light-harvesting iridium (III) complex-sensitized NiO photocathode for photoelectrochemical bioanalysis

A novel iridium (III) complex bearing boron dipyrromethene (Bodipy) as the light-harvesting antenna has been synthesized and is firstly employed as photosensitizer to assemble a dye-sensitized NiO photocathode. The assembled photocathode exhibits significantly improved photoelectrochemical (PEC) performance. Integrating the prepared photocathode with hybridization chain reaction (HCR)--based signal amplification strategy, a cathodic PEC biosensor is proposed for the detection of microRNA-133a (miRNA-133a). In the presence of the target, HCR is triggered to form long duplex concatamers on the photocathode, which allows numerous manganese porphyrins (MnPP) to bind in the dsDNA groove. With the help of H2O2, MnPP with peroxidase-like activity catalyzes 4--chloro-1-naphthol (4-CN) to produce benzo--4--chlorohexadienone (4-CD) precipitate on the electrode, leading to a significant decrease of photocurrent signal. The decreased photocurrent correlates linearly with the target concentration from 0.1 fM to 1 nM with a detection limit of 66.2 aM (S/N = 3). The proposed PEC strategy exhibits delightful selectivity, reproducibility and stability.

Three new red neutral and ionic iridium(III) complexes based on the same main ligand and auxiliary ligand but with different counterions for solution-processed organic light-emitting diodes

Three new neutral and ionic phosphorescent iridium(III) complexes were successfully prepared using 1-(6-methoxynaphthalen-2-yl)isoquinoline as the main ligand, while the auxiliary ligand was 2-(2-1H-imidazolyl)pyridine. Three complexes (Ir1, Ir2, Ir3) showed red emission, peaking at 610, 609, and 615 nm, respectively, and they exhibited good solubility and excellent photophysical properties in different solvents, which is suitable to prepare organic light-emitting diodes (OLEDs) by solution method. Among the three OLEDs prepared by iridium(III) complexes using the solution method, the device based on Ir2 possessed better electroluminescent properties, and its maximum brightness, current efficiency (CE), power efficiency (PE), and the maximum external quantum efficiency (EQE) were 507.2 cd m-2 , 0.14 cd A-1 , 0.06 lm W-1 , and 0.14%. respectively, proving that the three complexes have a certain of potential for OLEDs applications and are expected to expand the applications of iridium(III) complexes for OLEDs.

A "turn-on" red cyclometalated iridium (III) complex for long-term tracking the diffusion of CORM-2 in cells and zebrafish

Transition metal carbonyl compound of CO releasing molecules (CORMs) are widely used to treat arthritis, tumor and immune. They play a physiological role by directly acting on target tissues to release CO for disease treatment without matrix metabolism after dissolution. It is important to track the level and diffusion process of CORMs in vivo to control CO dose and distribution, facilitating to understand the roles of CORMs in disease treatment. Herein, we designed two red ring Ir1/2 complexes with a large stokes shift. Both Ir1 and Ir2 complexes probes can sensitively and selectively respond to CORM-2. The probe Ir1 exhibits rapid reaction with CORM-2 in Phosphate Buffered Saline within 1 min, showing a detection limitation of 0.13 μM and manifesting a linear relationship with the CORM-2 concentration from 0 to 70 μM at λem = 618 nm. Due to low toxicity even after 12 h exposure and fluorescence stability, this probe has been successfully used for continuous tracking the diffusion process of CORM-2 in living cells for up to 60 min and visualizing CORM-2 distribution in zebrafish. Additionally, this probe showed a good capacity for deep penetration (126 μm), suggesting the potential in detecting CORM-2 in living tissues.

Enantio- and Diastereodivergent Cyclopropanation of Allenes by Directed Evolution of an Iridium-Containing Cytochrome

Alkylidene cyclopropanes (ACPs) are valuable synthetic intermediates because of their constrained structure and opportunities for further diversification. Although routes to ACPs are known, preparations of ACPs with control of both the configuration of the cyclopropyl (R vs S) group and the geometry of the alkene (E vs Z) are unknown. We describe enzymatic cyclopropanation of allenes with ethyl diazoacetate (EDA) catalyzed by an iridium-containing cytochrome (Ir(Me)-CYP119) that controls both stereochemical elements. Two mutants of Ir(Me)-CYP119 identified by 6-codon (6c, VILAFG) saturation mutagenesis catalyze the formation of (E)-ACPs with -93% to >99% ee and >99:1 E/Z ratio with just three rounds of 96 mutants. By four additional rounds of mutagenesis, an enzyme variant was identified that forms (Z)-ACPs with up to 94% ee and a 28:72 E/Z ratio. Computational studies show that the orientation of the carbene unit dictated by the mutated positions accounts for the stereoselectivity.

Perfluorinated Iridium Catalyst for Signal Amplification by Reversible Exchange Provides Metal-Free Aqueous Hyperpolarized [1-13C]-Pyruvate

Hyperpolarized (HP) carbon-13 [13C] enables the specific investigation of dynamic metabolic and physiologic processes via in vivo MRI-based molecular imaging. As the leading HP metabolic agent, [1-13C]pyruvate plays a pivotal role due to its rapid tissue uptake and central role in cellular energetics. Dissolution dynamic nuclear polarization (d-DNP) is considered the gold standard method for the production of HP metabolic probes; however, development of a faster, less expensive technique could accelerate the translation of metabolic imaging via HP MRI to routine clinical use. Signal Amplification by Reversible Exchange in SHield Enabled Alignment Transfer (SABRE-SHEATH) achieves rapid hyperpolarization by using parahydrogen (p-H2) as the source of nuclear spin order. Currently, SABRE is clinically limited due to the toxicity of the iridium catalyst, which is crucial to the SABRE process. To mitigate Ir contamination, we introduce a novel iteration of the SABRE catalyst, incorporating bis(polyfluoroalkylated) imidazolium salts. This novel perfluorinated SABRE catalyst retained polarization properties while exhibiting an enhanced hydrophobicity. This modification allows the easy removal of the perfluorinated SABRE catalyst from HP [1-13C]-pyruvate after polarization in an aqueous solution, using the ReD-SABRE protocol. The residual Ir content after removal was measured via ICP-MS at 177 ppb, which is the lowest reported to date for pyruvate and is sufficiently safe for use in clinical investigations. Further improvement is anticipated once automated processes for delivery and recovery are initiated. SABRE-SHEATH using the perfluorinated SABRE catalyst can become an attractive low-cost alternative to d-DNP to prepare biocompatible HP [1-13C]-pyruvate formulations for in vivo applications in next-generation molecular imaging modalities.

Recent Advances in Organometallic NIR Iridium(III) Complexes for Detection and Therapy

Iridium(III) complexes are emerging as a promising tool in the area of detection and therapy due to their prominent photophysical properties, including higher photostability, tunable phosphorescence emission, long-lasting phosphorescence, and high quantum yields. In recent years, much effort has been devoted to develop novel near-infrared (NIR) iridium(III) complexes to improve signal-to-noise ratio and enhance tissue penetration. In this review, we summarize different classes of organometallic NIR iridium(III) complexes for detection and therapy, including cyclometalated ligand-enabled NIR iridium(III) complexes and NIR-dye-conjugated iridium(III) complexes. Moreover, the prospects and challenges for organometallic NIR iridium(III) complexes for targeted detection and therapy are discussed.

[Imaging of In Vivo Oxygen Tension Based on Phosphorescence Lifetime Microscopy]

Molecular oxygen plays essential roles in aerobic organisms as a terminal electron acceptor in the electron transport chain in mitochondria. The intracellular oxygen concentration of the entire body is strictly regulated by a balance between the supply of oxygen from blood vessels and the consumption of oxygen in mitochondria. The disruption of oxygen homeostasis in the body often results in serious pathologies such as cancer, cerebral infarction, and chronic kidney disease, and thus considerable effort has been devoted to the development of suitable techniques allowing the qualitative and quantitative detection of tissue oxygen levels. This review focuses on recent advances in the visualization of oxygen levels in tissue based on phosphorescence lifetime measurements using exogenously small molecular oxygen probes. Specially, I introduce the principle of oxygen sensing by means of phosphorescence quenching, recent advances in intracellular and intravascular oxygen probes based on iridium(III) complexes, a system for measuring phosphorescence lifetime combined with confocal scanning microscopy, and the applications of these technologies to in vivo oxygen measurements, emphasizing the usefulness of iridium(III) complexes as biological oxygen probes.

FRET Luminescent Probe for the Ratiometric Imaging of Peroxynitrite in Rat Brain Models of Epilepsy-Based on Organic Dye-Conjugated Iridium(III) Complex

Epilepsy is a chronic neurological disorder characterized by recurrent seizures globally, imposing a substantial burden on patients and their families. The pathological role of peroxynitrite (ONOO-), which can trigger oxidative stress, inflammation, and neuronal hyperexcitability, is critical in epilepsy. However, the development of reliable, in situ, and real-time optical imaging tools to detect ONOO- in the brain encounters some challenges related to the depth of tissue penetration, background interference, optical bleaching, and spectral overlapping. To address these limitations, we present Ir-CBM, a new one-photon and two-photon excitable and long-lived ratiometric luminescent probe designed specifically for precise detection of ONOO- in epilepsy-based on the Förster resonance energy transfer mechanism by combining an iridium(III) complex with an organic fluorophore. Ir-CBM possesses the advantages of rapid response, one-/two-photon excitation, and ratiometric luminescent imaging for monitoring the cellular levels of ONOO- and evaluating the effects of different therapeutic drugs on ONOO- in the brain of an epilepsy model rat. The development and utilization of Ir-CBM offer valuable insights into the design of ratiometric luminescent probes. Furthermore, Ir-CBM serves as a rapid imaging and screening tool for antiepileptic drugs, thereby accelerating the exploration of novel antiepileptic drug screening and improving preventive and therapeutic strategies in epilepsy research.

Protocol for (E)-selective semihydrogenation of alkynes using iridium-based catalyst

In this protocol, we describe highly (E)-selective alkyne semihydrogenation employing commercially available iridium complex and a bidentate phosphine ligand. We provide steps for (E)-stilbene synthesis, remaining formic acid neutralization, and determination of the (Z)/(E) ratio using gas chromatography analysis. We then detail (E)-stilbene purification using a short pad of silica and NMR analysis. The protocol is compatible with a wide range of functionalities and different types of alkynes. For complete details on the use and execution of this protocol, please refer to Kusy et al. (2022).1.

Multifunctional IrOx Neural Probe for In Situ Dynamic Brain Hypoxia Evaluation

Perioperative cerebral hypoxia and neonatal hypoxia-ischemic encephalopathy are the main triggers that lead to temporary or permanent brain dysfunction. The pathogenesis is intimately correlated to neural activities and the pH of the microenvironment, which calls for a high demand for in situ multitype physiological signal acquisition in the brain. However, conventional pH sensing neural interfaces cannot obtain the characteristics of multimodes, multichannels, and high spatial resolution of physiological signals simultaneously. Here, we report a multifunctional implantable iridium oxide (IrOx) neural probe (MIIONP) combined with electrophysiology recording, in situ pH sensing, and neural stimulation for real-time dynamic brain hypoxia evaluation. The neural probe modified with IrOx films exhibits outstanding electrophysiology recording and neural stimulation performance and long-term stable high spatial pH sensing resolution of about 100 μm, and the cytotoxicity of IrOx microelectrodes was investigated as well. In addition, 4 weeks' tracking of the same neuron firing and instantaneous population spike captured during electrical stimulation was achieved by MIIONP. Finally, in a mouse brain hypoxia model, the MIIONP has demonstrated the capability of synchronous in situ recording of the pH and neural firing changes in the brain, which has a valuable application in dynamic brain disease evaluation through real-time acquisition of multiple physiological signals.

Novel Electrochemiluminescent Biosensor to Ultrasensitively Detect U94 Gene in Human Herpesvirus 6 Using Metal-Organic Framework-Based Nanoemitters Comprising Iridium(III) Complexes via One-Pot Coordination Reaction Strategy

The detection of the U94 gene in human herpesvirus 6 is crucial for early diagnosis of HHV-6 infections, which could induce acute febrile illness in infants. In this work, the first ultrasensitive electrochemiluminescence (ECL) biosensor for detecting U94 gene in Human Herpesvirus 6 was successfully designed by utilizing efficient novel metal-organic framework (MOF)-based ECL nanoemitters comprising iridium(III) complexes (Ir-ZIF-8-NH2) synthesized via one-pot coordination reaction strategy as an ECL indicator and a target-catalyzed hairpin assembly (CHA) signal amplification strategy. The as-prepared ECL indicator Ir-ZIF-8-NH2 exhibited an approximately 2.7-fold ECL intensity compared with its small molecular analogue of emissive iridium(III) complex named IrppymIM formed by in situ coordination reaction between iridium(III) solvent complex and imidazole ligands. In addition, a target-catalyzed hairpin assembly (CHA) strategy was employed to further improve the sensitivity of the proposed ECL biosensor, which demonstrated a wide linear range from 1 fM to 1 μM and the limit of detection as low as 0.113 fM (S/N = 3). Significantly, this biosensor was successfully applied to detect U94 gene in plasmids and real virus samples. The recoveries were in the range of 97.0-109.0% for plasmids and 95.7-107.5% for real virus samples with a relative standard deviation (RSD) of 1.87-2.53%. These satisfactory experimental results from the proposed ECL biosensor in this work would inevitably promote the development of new time/cost-effective and sensitive methods to detect HHV-6 with a major global health threat and substantial burden on healthcare in the future.

A cell-impermeable luminogenic probe for near-infrared imaging of prostate-specific membrane antigen in prostate cancer microenvironments

Prostate-specific membrane antigen (PSMA) imaging probes are a promising tool for the diagnosis and image-guided surgery of prostate cancer (PCa). However, PSMA-specific luminescence probes for PCa detection and heterogeneity studies with high imaging contrast are lacking. Here, we report the first near-infrared (NIR) iridium(III) complex for the wash-free and specific imaging of PSMA in PCa cells and spheroids. The conjugation of a PSMA inhibitor, Lys-urea-Glu, to an iridium(III) complex synergizes the PSMA-specific affinity and biocompatibility of the inhibitor with the desirable photophysical properties of the iridium(III) complex, including NIR emission (670 nm), high photostability and a large Stokes shift. The cellular impermeability of the probe along with its strong binding affinity to PSMA enhances its specificity for PSMA, enabling the washing-free luminescent imaging of membrane PSMA with lower cytotoxicity. The probe was successfully applied for selectively visualizing PSMA-expressing cells and for the imaging of PSMA in a multicellular PCa model with good imaging penetration, indicating its potential use in complicated and heterogeneous tumor microenvironments. Furthermore, the probe showed good imaging performance in the PCa-bearing tumor mice via targeting PSMA in vivo. This work provides a novel strategy for the development of highly sensitive and specific NIR probes for PSMA in biological systems in vitro, which is of great significance for the precise diagnosis of PCa and for elucidating PCa heterogeneity.

A Mitochondria-Localized Iridium(III) Complex for Simultaneous Two-Photon Phosphorescence Lifetime Imaging of Downstream Products N2O3 and ONOO- of Endogenous Nitric Oxide

Nitric oxide (NO) serves as a ubiquitous and fundamental signaling molecule involved in intricate effects on both physiological and pathological processes. NO, biosynthesized by nitric oxide synthase (NOS) or generated from nitrite, can form nitrosation reagent N2O3 (4NO + O2 = 2N2O3) through its oxidation or quickly produce peroxynitrite anion ONOO- (NO + •O2- = ONOO-) by reacting with superoxide anion (•O2-). However, most of the existing luminescent probes for NO just focus on specificity and utilize only a single signal to distinguish products N2O3 or ONOO-. In most of the present work, they differentiate one product from another simply by fluorescence signal or fluorescence intensity, which is not enough to distinguish accurately the behavior of NO in living cells. Herein, a new mitochondria-targeted and two-photon near-infrared (NIR) phosphorescent iridium(III) complex, known as Ir-NBD, has been designed for accurate detection and simultaneous imaging of two downstream products of endogenous NO, i.e., N2O3 and ONOO-. Ir-NBD exhibits a rapid response to N2O3 and ONOO- in enhanced phosphorescence intensity, increased phosphorescence lifetime, and an exceptionally high two-photon cross-section, reaching values of 78 and 85 GM, respectively, after the reaction. Furthermore, we employed multiple imaging methods, phosphorescence intensity imaging, and phosphorescence lifetime imaging together to image even distinguish N2O3 and ONOO- by probe Ir-NBD. Thus, coupled with its excellent photometrics, Ir-NBD enabled the detection of the basal level of intracellular NO accurately by responding to N2O3 and ONOO- in the lipopolysaccharide-stimulated macrophage model in virtue of fluorescence signal and phosphorescence lifetime imaging, revealing precisely the endogenous mitochondrial NO distribution during inflammation in a cell environment.

A Switch-On Affinity-Based Iridium(III) Conjugate Probe for Imaging Mitochondrial Glutathione S-Transferase in Breast Cancer Cells

Glutathione S-transferase is heterogeneously expressed in breast cancer cells and is therefore emerging as a potential diagnostic biomarker for studying the heterogeneity of breast cancers. However, available fluorescent probes for GSTs depend heavily on GSTs-catalyzed glutathione (GSH) nucleophilic substitution reactions, making them susceptible to interference by the high concentration of nucleophilic species in the cellular environment. Moreover, the functions of subcellular GSTs are generally overlooked due to the lack of suitable luminescence probes. Herein, we report a highly selective affinity-based luminescence probe 1 for GST in breast cancer cells through tethering a GST inhibitor, ethacrynic acid, to an iridium(III) complex. Compared to activity-based probes which require the use of GSH, this probe could image GST-pi in the mitochondria by directly adducting to GST-pi (or potentially GST-pi/GS) in living cells. Probe 1 possesses desirable photophysical properties including a lifetime of 911 ns, a Stokes shift of 343 nm, and high photostability. The "turn on" luminescence mode of the probe enables highly selective detection of the GST with a limit of detection of 1.01 μM, while its long emission lifetime allows sensitive detection in organic dye-spiked autofluorescence samples by a time-resolved mode. The probe was further applied to specifically and quantitatively visualize MDA-MB-231 cells via specific binding to mitochondrial GST, and could differentiate breast cell lines based on their expression levels of GST. To the best of our knowledge, this probe is the first affinity-based iridium(III) imaging probe for the subcellular GST. Our work provides a valuable tool for unmasking the diverse roles of a subcellular GST in living systems, as well as for studying the heterogeneity of breast cancers.

Exosome camouflaged coordination-assembled Iridium(III) photosensitizers for apoptosis-autophagy-ferroptosis induced combination therapy against melanoma

Melanoma represents the most fatal form of skin cancer due to its resistance mechanisms and high capacity for the development of metastases. Among other medicinal techniques, photodynamic therapy is receiving increasing attention. Despite promising results, the application of photodynamic therapy is inherently limited due to interference from melanin, poor tissue penetration of photosensitizers, low loading into drug delivery systems, and a lack of tumor selectivity. To overcome these limitations, herein, the coordination-driven assembly of Ir(III) complex photosensitizers with Fe(III) ions into nanopolymers for combined photodynamic therapy and chemodynamic therapy is reported. While remaining stable under physiological conditions, the nanopolymers dissociated in the tumor microenvironment. Upon exposure to light, the Ir(III) complexes produced singlet oxygen and superoxide anion radicals, inducing cell death by apoptosis and autophagy. The Fe(III) ions were reduced to Fe(II) upon depletion of glutathione and reduction of the GPX4 levels, triggering cell death by ferroptosis. To provide tumor selectivity, the nanopolymers were further camouflaged with exosomes. The generated nanoparticles were found to eradicate a melanoma tumor as well as inhibit the formation of metastases inside a mouse model.

Electrochemiluminescence bioassay with anti-fouling ability for determination of matrix metalloproteinase 9 secreted from living cells under external stimulation

An electrochemiluminescence (ECL) bioassay with high sensitivity and anti-fouling ability was developed for determination of matrix metalloproteinase 9 (MMP-9) secreted from living cells under external stimulation. A peptide with sequence of CLGRMGLPGK and a new cyclometalated iridium(III) complex bearing carboxyl group, (pq)2Ir(dcbpy) (pq = 2-phenylquinoline, dcbpy = 2,2'-bipyridyl-4,4'-dicarboxyli acid, abbreviated as Ir) were employed as molecular recognition substrate and ECL emitter, respectively. The peptide was labelled with the Ir to form Ir-peptide as ECL probe. Ir-peptide was self-assembled onto Nafion and gold nanoparticles (AuNPs) modified glassy carbon electrode (AuNPs/Nafion/GCE) and then both of 6-mercapto-1-hexanol (MCH) and zwitterionic peptide as blocking reagents were co-assembled on Ir-peptide/AuNPs/Nafion/GCE to form an anti-fouling ECL peptide-based biosensor. MMP-9 can be quantified in the range 1.0-50 ng·mL-1 with a detection limit of 0.50 ng·mL-1 based on the decreased ECL intensity. Relative standard derivation was 2.3% for six fabricated anti-fouling ECL peptide-based biosensors after reaction with 50 ng·mL-1 MMP-9. The anti-fouling ECL peptide-based biosensor can be used to monitor MMP-9 secreted from living cells under external stimulation. 96.0%-108.0% of recoveries were obtained in 60-diluted cell culture media. This study demonstrates that the ECL biosensor by the combination of iridium(III) complex-based sensitive ECL method and the anti-fouling interface provides a promising way for the determination of MMP-9 in biological sample, which is viable in clinical diagnosis and point-of-care test of protease.

Highly Selective Nitrite Hydrogenation to Ammonia over Iridium Nanoclusters: Competitive Adsorption Mechanism

Wet denitrification is a promising approach to control nitrogen oxides (NOx) produced in fossil fuel combustion. Yet, the highly concentrated nitrite (NO2-) wastewater generated poses a major threat to the aqueous environment. Here, iridium nanoclusters (d = 1.63 nm) deposited on TiO2 were applied for NO2- reduction to ammonia (NRA), showing an exceptional NH4+ selectivity of 95% and a production rate of 20.51 mgN·L-1·h-1, which held significant potential for NO2- wastewater purification and ammonia resource recovery. Notably, an interesting non-first-order NO2- hydrogenation kinetics was observed, which was further confirmed to result from the competitive adsorption mechanism between H2 and NO2- over iridium. The NRA pathways on the Ir(111) surface were explored via density functional theory calculations with the NO2-* → NO* → HNO* → HNOH* → H2NOH* → NH2* → NH3* identified as the most energetically favorable pathway and the NO* → HNO* confirmed as the rate-determining step. In situ DRIFTS further experimentally verified the generation of HNO* intermediate during NO* hydrogenation on Ir(111). To verify NRA kinetics at varied NO2- concentrations or H2 pressures, a kinetic model was derived based on the Langmuir-Hinshelwood competitive adsorption mechanism. These findings provide mechanistic insights into the NRA pathways on Ir nanocatalysts, which will be beneficial for wet denitrification waste stream decontamination and valorization.

Luminescent iridium(III) porphyrin complexes as near-infrared-emissive biological probes

We report herein the design, synthesis and characterisation of a series of luminescent iridium(III) porphyrin complexes [Ir(ttp)(CH2CH2OH)] (H2ttp = 5,10,15,20-tetra-4-tolylporphyrin) (1), [Ir(tpp-Ph-NO2)(CO)Cl] (H2tpp-Ph-NO2 = 5-(4-((4-nitrophenoxy)carbonyloxymethyl)phenyl)-10,15,20-triphenylporphyrin) (2), [Ir(tpp-COOMe)(Py)2](Cl) (H2tpp-COOMe = 5-(4-methoxycarbonylphenyl)-10,15,20-triphenylporphyrin; Py = pyridine) (3) and [Ir(tpp-COOH)(Py)2](Cl) (H2tpp-COOH = 5-(4-carboxylphenyl)-10,15,20-triphenylporphyrin) (4). All the complexes displayed long-lived near-infrared (NIR) emission attributed to an excited state of mixed triplet intraligand (3IL) (π → π*) (porphyrin) and triplet metal-to-ligand charge transfer (3MLCT) (dπ(Ir) → π*(porphyrin)) character. The cytotoxicity of the complexes toward HeLa cells was examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cationic complexes 3 and 4 exhibited higher cytotoxic activity toward HeLa cells than their neutral counterparts 1 and 2. Cellular uptake studies by inductively coupled plasma-mass spectrometry (ICP-MS) and laser-scanning confocal microscopy (LSCM) indicated that complexes 3 and 4 showed higher cellular uptake efficiencies than complexes 1 and 2 due to their cationic charge, and they were enriched in the perinuclear region of the cells with negligible nuclear uptake. Additionally, the carboxyl complex 4 was used to label a model protein bovine serum albumin (BSA) via an amidation reaction. The resultant luminescent protein conjugate 4-BSA displayed similar photophysical properties and intracellular localisation behaviour to its parent complex. The results of this work will contribute to the development of luminescent iridium(III) porphyrin complexes and related bioconjugates as NIR-emissive probes for bioimaging applications.

Highly Active Single-Atom Nanozymes with High-Loading Iridium for Sensitive Detection of Pesticides

Single-atom nanozymes (SAzymes) are novel mimic-enzyme materials with atomically doped active sites. They play a pivotal role in the field of nanozymes because of their excellent catalytic activities, high utilization efficiency of the metal atoms, and simple model of active sites. Herein, the peroxidase (POD)-like SAzymes with high-loading iridium (Ir) (5.31%) on graphene oxide (GO) nanosheets [Ir(III)/GO] were prepared through a coordination reaction between the Ir(III) complex and the oxygen-containing groups in GO. The preparation strategy avoids nitrogen doping and pyrolysis procedures which are the usually used strategies to improve the GO-based enzyme mimic activity. Ascribed to the highly active Ir atoms, Ir(III)/GO SAzymes demonstrate outstanding POD-like activity without the oxidase-like activity. In advantage of the excellent POD-like activity, a simple and sensitive colorimetric pesticide detection platform is established. The developed sensing platform offers an excellent "switch-on" pirimicarb (PIB) detection in the linear range of 10-300 nM with a limit of detection (LOD) of 2.81 nM. Moreover, the detection platform was fabricated into a portable test kit, which is composed of a test swab and sample processing tube. In the aid of a color-reading APP, the test kit can detect PIB with the LOD of 3.31 nM. It is astonishing to get this excellent detection sensitivity just using the simple colorimetric strategy. This work not only provides a novel strategy to synthesize Ir-based SAzymes but also exhibits the super capability of Ir(III)/GO in the biosensing field.

Directionally In Situ Self-Assembled Iridium(III)-Polyimine Complex-Encapsulated Metal-Organic Framework Two-Dimensional Nanosheet Electrode To Boost Electrochemiluminescence Sensing

Manufacturing electrochemiluminescence (ECL) electrodes to detect analytes with high performance in the aqueous phase for water-insoluble metal complexes is a great challenge. Here, a directional self-assembling avenue for in situ fabricating iridium(III)-polyimine complex-encapsulated metal-organic framework (MOF) two-dimensional electrode Hf-MOF/Ir2PD/APS/ITO is developed. The electrode displayed bright red ECL emission with high stability in the aqueous phase and specific adsorption toward ssDNA against dsDNA and mNs. That is to say, a "high-performance and multifunctional ECL electrode" is presented and explored for sensitive detection of acetamiprid (Ace) with a limit of detection of 0.0025 nM, where Ace-aptamer recognition-switched Exonuclease III-mediated digestion to make large numbers of Fc-labeled ssDNA transform into Fc-mNs. Furthermore, the proposed method was triumphantly employed to monitor the change in the residual concentration of Ace in pakchoi. This work breaks through the bottleneck of metal complex-based ECL emission in organic solvents and provides a novel strategy to develop high-performance ECL sensors.

Concise Enantioselective Total Synthesis of Isopavine Alkaloids

Herein, we report a concise asymmetric total synthesis of isopavine alkaloids, which feature a special azabicyclo[3.2.2]nonane tetracyclic skeleton. The key steps include iridium-catalyzed asymmetric hydrogenation of unsaturated carboxylic acids, Curtius rearrangement, and Eschweiler-Clarke methylation, which enable an enantioselective approach to isopavine alkaloids in 6-7 linear steps. Furthermore, for the first time, isopavine alkaloids, especially (-)-reframidine (3), are found to display effective antiproliferative effects on various cancer cell lines.

Sustainable magnetically recoverable Iridium-coated Fe3O4 nanoparticles for enhanced catalytic reduction of organic pollutants in water

The reduction of nitroarenes to aromatic amines is one of the potential pathways to remediate the hazardous impact of toxic nitroarenes on the aquatic environment. Aromatic amines obtained from the reduction of nitroaromatics are not only less toxic than nitroaromatics but also act as important intermediates in the synthesis of dyes, drugs, pigments, herbicides, and polymers. There is a huge demand for the development of cost-effective, and eco-friendly catalysts for the efficient reduction of nitroarenes. In the present study, Fe₃O₄@trp@Ir nanoparticles were explored as efficient catalysts for the reduction of nitroarenes. Fe₃O₄@trp@Ir magnetic nanoparticles were fabricated by surface coating of Fe₃O₄ with tryptophan and iridium by co-precipitation method. As-prepared Fe₃O₄@trp@Ir nanoparticles are environmentally benign efficient catalysts for reducing organic pollutants such as 4-nitrophenol (4-NP), 4-nitroaniline (4-NA), and 1-bromo-4-nitrobenzene (1-B-4-NB). The key parameters that affect the catalytic activity like temperature, catalyst loading, and the concentration of reducing agent NaBH₄ were optimized. The obtained results proved that Fe₃O₄@trp@Ir is an efficient catalyst for reducing nitroaromatics at ambient temperature with a minimal catalyst loading of 0.0025%. The complete conversion of 4-nitrophenol to 4-aminophenol took only 20 s with a minimal catalyst loading of 0.0025% and a rate constant of 0.0522 s^-1. The high catalytic activity factor (1.040 s^-1 mg^-1) and high turnover frequency (9 min^-1) obtained for Fe₃O₄@trp@Ir nanocatalyst highlight the possible synergistic effect of the two metals (Fe and Ir). The visible-light photocatalytic degradation of 4-NP was also investigated in the presence of Fe₃O₄@trp@Ir. The photocatalytic degradation of 4-NP by Fe₃O₄@trp@Ir is completed in 20 min with 95.15% efficiency, and the rate of photodegradation of 4-NP (0.1507 min^-1) is about twice the degradation rate of 4-NP in the dark (0.0755 min^-1). The catalyst was recycled and reused for five cycles without significant reduction in the conversion efficiency of the catalyst.

Tracking chromatin state changes using nanoscale photo-proximity labelling

Interactions between biomolecules underlie all cellular processes and ultimately control cell fate. Perturbation of native interactions through mutation, changes in expression levels or external stimuli leads to altered cellular physiology and can result in either disease or therapeutic effects1,2. Mapping these interactions and determining how they respond to stimulus is the genesis of many drug development efforts, leading to new therapeutic targets and improvements in human health1. However, in the complex environment of the nucleus, it is challenging to determine protein-protein interactions owing to low abundance, transient or multivalent binding and a lack of technologies that are able to interrogate these interactions without disrupting the protein-binding surface under study3. Here, we describe a method for the traceless incorporation of iridium-photosensitizers into the nuclear micro-environment using engineered split inteins. These Ir-catalysts can activate diazirine warheads through Dexter energy transfer to form reactive carbenes within an approximately 10 nm radius, cross-linking with proteins in the immediate micro-environment (a process termed µMap) for analysis using quantitative chemoproteomics4. We show that this nanoscale proximity-labelling method can reveal the critical changes in interactomes in the presence of cancer-associated mutations, as well as treatment with small-molecule inhibitors. µMap improves our fundamental understanding of nuclear protein-protein interactions and, in doing so, is expected to have a significant effect on the field of epigenetic drug discovery in both academia and industry.

Boosting Ferroptosis Therapy with Iridium Single-Atom Nanocatalyst in Ultralow Metal Content

Nanocatalysts are promising tumor therapeutics due to their ability to induce reactive oxygen species in the tumor microenvironment. Although increasing metal loading can improve catalytic activity, the quandary of high metal content versus potential systemic biotoxicity remains challenging. Here, a fully exposed active site strategy by site-specific anchoring of single iridium (Ir) atoms on the outer surface of a nitrogen-doped carbon composite (Ir single-atom catalyst (SAC)) is reported to achieve remarkable catalytic performance at ultralow metal content (≈0.11%). The Ir SAC exhibits prominent dual enzymatic activities to mimic peroxidase and glutathione peroxidase, which catalyzes the conversion of endogenous H2 O2 into •OH in the acidic TME and depletes glutathione (GSH) simultaneously. With an advanced support of GSH-trapping platinum(IV) and encapsulation with a red-blood-cell membrane, this nanocatalytic agent (Pt@IrSAC/RBC) causes intense lipid peroxidation that boosts tumor cell ferroptosis. The Pt@IrSAC/RBC demonstrates superior therapeutic efficacy in a mouse triple-negative mammary carcinoma model, resulting in complete tumor ablation in a single treatment session with negligible side effects. These outcomes may provide valuable insights into the design of nanocatalysts with high performance and biosafety for biomedical applications.

Imaging mitochondrial palladium species in living cells with a NIR iridium(III) complex

The wide use of palladium (Pd) raises the concern about environmental pollution and human diseases, evoking the need for the development of detection methods for Pd species. However, the development of near-infrared (NIR) luminescence probes for subcellular Pd species remains challenging. In this work, we presented a NIR iridium(III) complex-based luminescence probe for the detection of Pd⁰ species through incorporating an allyl group and amino group into the N^N ligand. We found that the probe was capable of detecting Pd⁰ species with a limit of detection (LOD) of 0.5 μM. Importantly, cell imaging experiments showed that the probe is applicable for visualizing mitochondrial Pd⁰ ions in living cells, which are also suitable for Pd(II) species. To the best of our knowledge, this is the first NIR luminescence imaging probe for the detection of mitochondria Pd species in living cells, paving the way for studying subcellular distributions and related toxicity analysis of exogenous Pd species in living cells.

BSA-templated synthesis of Ir/Gd bimetallic oxide nanotheranostics for MR/CT imaging-guided photothermal and photodynamic synergistic therapy

Precision medicine urges the development of theranostics which can efficiently integrate precise diagnosis and effective therapy. In this study, a facile synthesis of Ir/Gd bimetallic oxide nanotheranostics (termed BSA@Gd₂O₃/IrO₂ NPs) with good biocompatibility was demonstrated using a biomineralization method where bovine serum albumin (BSA) served as a versatile template. BSA@Gd₂O₃/IrO₂ NPs exhibited high longitudinal relaxivity (5.2 mM^-1 s^-1) and X-ray absorption capability (14.5 Hu mM^-1), illustrating them to be a good contrast agent for magnetic resonance (MR) and computed tomography (CT) dual-modal imaging. Moreover, BSA@Gd₂O₃/IrO₂ NPs can act as not only a photothermal conversion agent with ultrahigh efficiency (66.7%) as well as a good photosensitizer, but also an effective catalase to decompose endogenous H₂O₂ to produce O₂, thus relieving hypoxia and enhancing the phototherapeutic effect. Both in vitro and in vivo experiments demonstrated the high effectiveness of BSA@Gd₂O₃/IrO₂ NPs in MR/CT dual-modal imaging and photothermal and photodynamic synergistic tumor treatments. This work sheds new light on the development of versatile nanotheranostic systems using mild and robust biomineralization methods.

An antifouling gel-protected iridium needle sensor: Long-term, on-site monitoring of copper in seawater

Copper (Cu), a natural micronutrient with ecotoxicological significance, is involved in the carbon and nitrogen cycles occurring in marine ecosystems. Here, we developed a novel, antifouling gel-protected iridium (Ir) needle electrode modified with gold nanoparticles (G-IrNS) for long-term continuous and steady Cu monitoring. The gel formed an efficient membrane that effectively prevented the fouling of the sensing surface and displayed anti-convective properties, ensuring that mass transport toward the sensor surface was wholly controlled via diffusion. The repeatability, reproducibility, and stability of G-IrNS showed that it was suitable for long-term and on-site monitoring of Cu in seawater. Cu concentrations were successfully measured via fixed-point continuous monitoring for >2 weeks and onboard continuous monitoring in Bohai Sea using one sensor. Moreover, the relationship between Cu concentrations measured on-site via G-IrNS and its dissolved concentration in Bohai Sea was evaluated. G-IrNS can be applied to other metal ions as well, especially for long-term automatic on-site monitoring, thereby providing a basis for further research.

Aptamer recognition-promoted specific intercalation of iridium complexes in G-quadruplex DNA for label-free and enzyme-free phosphorescence analysis of kanamycin

In consideration of relevance of antibiotic with food security, it is extremely desirable to propose sensitive and credible methods for antibiotic screening. Nevertheless, most of known approaches are developed based on fluorescence technique, which suffered from the interferences of background fluorescence and autoluminescence, and tedious labeling procedures, ascribing to the deficiency of high-performance and multifunctional dyes. Herein, we developed a novel iridium (III) complex (Ir-QAU)-based aptamer-promoted phosphorescence sensor for label-free, enzyme-free and highly sensitive detection of target antibiotic (kanamycin, Kan) based on target-switched hybridizing chain reaction (HCR). Ir-QAU was elaborately devised to present a signal-on response to G-quadruplex (G4) DNA against other DNAs due to its specific intercalation in G4 DNA and subsequent restriction of intra-molecular rotation. The recognition of H1 by Kan promoted the formation of Kan@H1 complexes, which hybridized with H2 and H3 via toehold-mediated hybridization reaction, subsequently switching HCR to produce large numbers of G4 DNA. Compared to Kan absence, abundant Ir-QAU was locked in G4 DNA to yield a significantly increased luminescence, which switches the luminescence analysis process of Kan with a limit of detection down to 0.38 pM. Furthermore, the Ir-QAU-based sensor was triumphantly applied to detect Kan in milk sample. We anticipate this work will disclose a new way to development of high-efficiency and practical luminescence sensor, and show a great potential for antibiotic-related food security.

Efficacy of Nanoparticles in dose enhancement with high dose rate of Iridium-192 and Cobalt-60 radionuclide sources in the Treatment of Cancer: A systematic review

ABSTRACTS

A key challenge in radiation therapy is to maximize the radiation dose to cancer cells while minimizing damage to healthy tissues. In recent years, the introduction of remote after-loading technology such as high-dose-rate (HDR) brachytherapy becomes the safest and more precise way of radiation delivery compared to classical low-dose-rate (LDR) brachytherapy. However, the axially symmetric dose distribution of HDR with single channel cylindrical applicator, the physical "dead-space" with multichannel applicators, and shielding material heterogeneities are the main challenges of HDR brachytherapy. Thus, this review aimed to quantitatively evaluate the dose enhancement factor (DEF) produced by high atomic number nanoparticles (NPs) which increases the interaction probability of photons mainly through the photoelectric effect induced in the great number of atoms contained in each nanoparticle. The NPs loaded to the target volume create a local intensification effect on the target tissue that allows imparting the prescribed therapeutic dose using lower fluxes of irradiation and spare the surrounding healthy tissues. An electronic database such as PubMed/Medline, Embase, Scopus, and Google Scholar was searched to retrieve the required articles. Unpublished articles were also reached by hand from available sources. The dose is increased using the high atomic number of nanoparticle elements under the high dose iridium radionuclide whereas the cobalt-60 radionuclide source did not. However, much work is required to determine the dose distribution outside the target organ or tumor to spare the surrounding healthy tissues for the iridium source and make compressive work to have more data for the cobalt source.

Iridium Tungstate Nanozyme-Mediated Hypoxic Regulation and Anti-inflammation for Duplex Imaging Guided Photothermal Therapy of Metastatic Breast Tumors

Metastasis of breast cancer is key to poor prognosis and high mortality. However, the excess reactive oxygen species (ROS) and inflammatory response induced by photothermal therapy (PTT) further aggravate tumor metastasis. Meanwhile, the hypoxic tumor microenvironment promotes tumor cells to metastasize to distant organs. Herein, the intrinsic limitations of PTT for metastatic tumor have been addressed by fabricating polyethylene glycol modified iridium tungstate (IrWO_x-PEG) nanoparticles. The as-designed IrWO_x-PEG nanoparticles displayed good photothermal (PT) conversion ability for duplex photoacoustic/PT imaging guided PTT and multienzyme mimetic feature for broad-spectrum ROS scavenging. On the one hand, IrWO_x-PEG effectively removed excess ROS generated during PTT and reduced inflammation. On the other hand, owing to the catalase-like activity, it preferentially triggered the catalytic production of oxygen by decomposing ROS, leading to relieving of the hypoxic microenvironment. Hence, under bimodal imaging guidance, IrWO_x-PEG induced PTT completely eliminated in situ breast cancer in 4T1 tumor-bearing mice with no observable system toxicity, as well as further restricting tumor metastasis to other vital organs (lungs) by ROS scavenging, anti-inflammation, and regulating hypoxic microenvironment. We anticipate that this work will lead to new treatment strategies for other metastatic cancers.

Ir Cluster-Anchored MOFs as Peroxidase-Mimetic Nanoreactors for Diagnosing Hydrogen Peroxide-Related Biomarkers

Exploring multifaceted and highly sensitive biosensors is a major challenge in biotechnology and medical diagnosis. Here, we create a new iridium (Ir) cluster-anchored metal-organic framework (MOF, namely, Ir_NCs@Ti-MOF via a coordination-assisted strategy) as a peroxidase (POD)-mimetic nanoreactor for colorimetrically diagnosing hydrogen peroxide-related biomarkers. Owing to the Ir_NCs-N/O coordination of Ti-MOF and unique enzymatic properties of Ir clusters, the Ir_NCs@Ti-MOF exhibits exceptional and exclusive POD-mimetic activities (K_m = 3.94 mM, V_max = 1.70 μM s^-1, and turnover number = 39.64 × 10^-3 s^-1 for H₂O₂), thus demonstrating excellent POD-mimetic detecting activity and also super substrate selectivity, which is considerably more efficient than recently reported POD mimetics. Colorimetric studies disclose that this Ir_NCs@Ti-MOF-based nanoreactor shows multifaceted and efficient diagnosing activities and substrate selectivity, such as a limit of detection (LOD): 14.12 μM for H₂O₂ at a range of 0-900 μM, LOD: 3.41 μM for l-cysteine at a range of 0-50 μM, and LOD: 20.0 μM for glucose at a range of 0-600 μM, which enables an ultrasensitive and visual determination of abundant H₂O₂-related biomarkers. The proposed design will not only provide highly sensitive and cheap colorimetric biosensors in medical resource-limited areas but also offer a new path to engineering customizable enzyme-mimetic nanoreactors as a powerful tool for accurate and rapid diagnosis.

Catalytic Gold-Iridium Nanoparticles as Labels for Sensitive Colorimetric Lateral Flow Assay

The colorimetric lateral flow assay (CLFA, also known as test strip) is a widely used point-of-care diagnostic technology. It has been a challenge to significantly improve the detection sensitivity of CLFA without involving additional equipment and/or compromising its simplicity. In this work, we break through the detection limit barrier of CLFA by developing a type of catalytic nanoparticles (NPs) used as labels. Specifically, the NPs were engineered by coating conventional gold NPs (AuNPs) with iridium (Ir) to form an Au-Ir core-shell structure. Such Au-Ir NPs possess ultrahigh peroxidase-like catalytic activities. A single Au-Ir NP can generate up to 10⁷ colored molecules per second by catalyzing peroxidase substrates. The strong color signal from the catalysis ensures a high sensitivity of associated CLFA. The Au-Ir NP-based CLFA was successfully applied to the detection of two different cancer biomarkers that achieved limits of detection at the low picogram per milliliter level, hundreds of times lower than those of conventional AuNP-based CLFA.

Development of a NIR iridium(III) complex for self-calibrated and luminogenic detection of boron trifluoride

Boron trifluoride (BF3) is a potential environmental pollutant, and excess exposure to it may cause human diseases. However, the sensitive, rapid and accurate detection of BF3 for on-site purposes is still a challenge. In this work, we developed the first NIR iridium(III)-based probe with dual emission and a Stokes shift of 370 nm for self-calibrated and luminogenic detection of BF3. This probe exhibited a strong luminescence enhancement at around 650 nm to BF3 (0-100 μM) with almost no change in luminescence at 475 nm, displaying a 220-fold I650 nm/I475 nm enhancement at 100 μM of BF3 with a detection limit of 0.35 μM. Moreover, the probe showed a fast response time of less than 5 s to BF3 along with an obvious color change under UV irradiation for visual detection. Importantly, the desirable photophysical properties of the iridium(III)-based probe can be harnessed for time-resolved detection of BF3 in the presence of the fluorescence background. The applicability of the probe was further verified in an organic solvent waste-spiked system and on a glass pane. This work will provide a solid basis for the development of sensitive and on-site BF3 sensing toolkits for environmental monitoring.

Self-Amplifying Iridium(III) Photosensitizer for Ferroptosis-Mediated Immunotherapy Against Transferrin Receptor-Overexpressing Cancer

Photoimmunotherapy is attractive for cancer treatment due to its spatial controllability and sustained responses. This work presents a ferrocene-containing Ir(III) photosensitizer (IrFc1) that can bind with transferrin and be transported into triple-negative breast cancer (TNBC) cells via a transferrin receptor-mediated pathway. When the ferrocene in IrFc1 is oxidized by reactive oxygen species, its capability to photosensitize both type I (electron transfer) and type II (energy transfer) pathways is activated through a self-amplifying process. Upon irradiation, IrFc1 induces the generation of lipid oxidation to cause ferroptosis in TNBC cells, which promotes immunogenic cell death (ICD) under both normoxia and hypoxia. In vivo, IrFc1 treatment elicits a CD8⁺ T-cell response, which activates ICD in TNBC resulting in enhanced anticancer immunity. In summary, this work reports a small molecule-based photosensitizer with enhanced cancer immunotherapeutic properties by eliciting ferroptosis through a self-amplifying process.

Iridium-Catalyzed and pH-Dependent Reductions of Nitroalkenes to Ketones

A highly chemoselective conversion of α,β-disubstituted nitroalkenes to ketones is developed. An acid-compatible iridium catalyst serves as the key to the conversion. At a 2500 S/C ratio, nitroalkenes were readily converted to ketones in up to 72% isolated yields. A new mechanistic mode involving the reduction of nitroalkene to nitrosoalkene and N-alkenyl hydroxylamine is proposed. This conversion is ready to amplify to a gram-scale synthesis. The pH value plays an indispensable role in controlling the chemoselectivity.

Synthesis of a Thiazole Library via an Iridium-Catalyzed Sulfur Ylide Insertion Reaction

A library of thiazoles and selenothiazoles were synthesized via Ir-catalyzed ylide insertion chemistry. This process is a functional group, particularly heterocycle-substituent tolerant. This was applied to the synthesis of fanetizole, an anti-inflammatory drug, and a thiazole-containing drug fragment that binds to the peptidyl-tRNA hydrolase (Pth) in Neisseria gonorrheae bacteria.

Bioactive Iridium Nanoclusters with Glutathione Depletion Ability for Enhanced Sonodynamic-Triggered Ferroptosis-Like Cancer Cell Death

Ferroptosis is a regulated form of necrotic cell death that involves the accumulation of lipid peroxide (LPO) species in an iron- and reactive oxygen species (ROS)-dependent manner. Previous investigations have reported that ferroptosis-based cancer therapy can overcome the limitations of traditional therapeutics targeting the apoptosis pathway. However, it is still challenging to enhance the antitumor efficacy of ferroptosis due to intrinsic cellular regulation. In this study, a ferroptosis-inducing agent, i.e., chlorin e6 (Ce6)-conjugated human serum albumin-iridium oxide (HSA-Ce6-IrO₂ , HCIr) nanoclusters, is developed to achieve sonodynamic therapy (SDT)-triggered ferroptosis-like cancer cell death. The sonosensitizing role of both Ce6 and IrO₂ within the HCIr nanoclusters exhibits highly efficient ¹ O₂ generation capacity upon ultrasound stimulation, which promotes the accumulation of LPO and subsequently induces ferroptosis. Meanwhile, the HCIr can deplete glutathione (GSH) by accelerating Ir (IV)-Ir (III) transition, which further suppresses the activity of glutathione peroxidase 4 (GPX4) to enhance the ferroptosis efficacy. Through in vitro and in vivo experiments, it is demonstrated that HCIr possesses tremendous capacity to reduce the intracellular GSH content, which enhances SDT-triggered ferroptosis-like cancer cell death. Thus, an iridium-nanoclusters-based ferroptosis-inducing agent is developed, providing a promising strategy for inducing ferroptosis-like cancer cell death.

Deactivation of cyanobacteria blooms and simultaneous recovery phosphorus through electrolysis method

A novel method for remediating eutrophic lakes through electrolysis was made possible by one titanium (Ti) mesh, which serves as a cathode and two anodes of Ti mesh coated with ruthenium (IV) oxide and iridium (IV) oxide (RuO₂-IrO₂/Ti). Once the three-electrode components RuO₂-IrO₂/Ti and Ti are stabilized, they can carry out electrolytic reaction to control cyanobacteria blooms and assist with the remediation of eutrophic water. The order of influence on the theoretical energy consumption involved in removing algae is as follows: The electrode spacing was more effective than electrode voltage, which proved more effective than electrolysis time through the orthogonal test method. Thus, an electrode spacing of 60 mm, an electrode voltage of 30 V, and an electrolysis time of 12 h are the optimal electrolysis methods used to remove cyanobacterial blooms. The strong acidic environment produced by the anode increased the concentration of hydroxyl radical (•OH) and other strong oxidizing substances, which were the main roles that made cyanobacteria bloom inactivation. The electrolysis reaction was conducive to the transformation of organophosphorus in cyanobacterial blooms to dissolved inorganic phosphorus (DIP) in water. Some DIP was most deposited on the cathode after electro-depositing enhanced the removal of P in water with the 12-h prolonged electrolysis time. Meanwhile, it was beneficial to reduce the total nitrogen (TN) and ammonia nitrogen (NH₃-N) in the water. Thus, electrolysis proved to be an effective way to the inactivation of cyanobacteria blooms and simultaneously recover P as the concentration became higher.

Real-time acoustic monitoring with telemetry to mitigate potential effects of seismic survey sounds on marine mammals: a case study offshore Sakhalin Island

Exxon Neftegas Ltd. (ENL) carried out three 4D seismic surveys during the summer of 2015. Seismic operations in two of these fields (Odoptu and Chayvo) ensonified the nearshore feeding area of Korean-Okhotsk (western) gray whales (Eschrichtius robustus), potentially disturbing feeding activities. Following model-based optimization of the source design to minimize its lateral acoustic footprint, pre-season modeling was used to compute the acoustic exposure along each survey line. Real-time acoustic data facilitated implementation of mitigation measures aimed to minimize disturbance of whales. Acoustic data originated from underwater recorders deployed on the seafloor. Two complementary approaches were used to transmit recorded sound data to a computer housed at the Central Post (CP), where decisions regarding mitigation shut downs were made. In the first approach, a limited bandwidth (2-2000 Hz) sampling of the data was transmitted via cable to a surface buoy, which relayed these data to a shore station up to 15 km away via digital VHF telemetry. At the shore station, acoustic impulses from the seismic surveys were processed to compute impulse characteristics in the form of estimates of sound exposure level and peak sound pressure level, as well as one-minute-average 1/3-octave power spectral density coefficients, which were then transmitted to the CP via the internet. In the second, the pulse characteristics were computed through algorithms running on an onboard processor in each recorder's surface buoy and sent directly to the CP computer via an Iridium satellite uplink. Both methods of data transfer proved viable, but Iridium transmission achieved the goal without the need for any shore based relay stations and is therefore more operationally efficient than VHF transmission. At the CP, analysts used the real-time acoustic data to calibrate and adjust the output of pre-season acoustical model runs. The acoustic footprint for the active seismic source, advancing synchronously with the motion of the seismic vessel and changing as the sound propagation environment changed, was computed from the calibrated and adjusted model output and integrated through the software Pythagoras with locations of gray whales provided by shore-based observers. This enabled analysts to require air gun array shutdowns before whales were exposed to mean square sound pressure levels greater than the behavioral response threshold of 163 dB re 1 μPa². The method described here provides a realistic means of mitigating the possible effects of air guns at a behavioral response level, whereas most seismic surveys rely on pre-established mitigation radii to manage the risk of injury to a whale.

A cationic iridium(III) complex containing a thiosemicarbazide unit: Synthesis and application for turn-on chemiluminescent detection of Hg2

A novel cationic iridium(III) complex [(ppy)₂Ir(bPCPC)]PF₆ (ppy: 2-phenylpyridine; bPCPC: 2-([2,2'-bipyridine]-4-carbonyl)-N-phenylhydrazinecarbothioamide) containing a thiosemicarbazide unit was designed and synthesized. The thiosemicarbazide unit was a sensitive functional group to Hg²⁺, when it reacted with Hg²⁺, it was desulphurized and thus led to the formation of 1,3,4-oxadiazole, [(ppy)₂Ir(bPCPC)]PF₆ resultantly was used as a "turn-on" chemodosimeter for luminescent detection of Hg²⁺ in DMF/PBS buffer solution at pH = 7-11. Except for Ag⁺, recognition capability of [(ppy)₂Ir(bPCPC)]PF₆ to Hg²⁺ was not interfered by other common metal ions (Co²⁺, Li⁺, Zn²⁺, Pb²⁺, K⁺, Al³⁺, Na⁺, Mn²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Cr³⁺, Ba²⁺, Mg²⁺, Ni²⁺ and Ca²⁺). The detection limit was 1.83 × 10^-9 mol∙L^-1 (0.37 ppb), which indicated the complex was a highly sensitive chemiluminescent detection reagent of Hg²⁺.

Ir(III)-Based Agents for Monitoring the Cytochrome P450 3A4 Active Site Occupancy

Cytochromes P450 (CYPs) are a superfamily of enzymes responsible for biosynthesis and drug metabolism. Monitoring the activity of CYP3A4, the major human drug-metabolizing enzyme, is vital for assessing the metabolism of pharmaceuticals and identifying harmful drug-drug interactions. Existing probes for CYP3A4 are irreversible turn-on substrates that monitor activity at specific time points in end-point assays. To provide a more dynamic approach, we designed, synthesized, and characterized emissive Ir(III) and Ru(II) complexes that allow monitoring of the CYP3A4 active-site occupancy in real time. In the bound state, probe emission is quenched by the active-site heme. Upon displacement from the active site by CYP3A4-specific inhibitors or substrates, these probes show high emission turn-on. Direct probe binding to the CYP3A4 active site was confirmed by X-ray crystallography. The lead Ir(III)-based probe has nanomolar Kd and high selectivity for CYP3A4, efficient cellular uptake, and low toxicity in CYP3A4-overexpressing HepG2 cells.

Multiaxial fields improve SABRE efficiency by preserving hydride order

Signal Amplification By Reversible Exchange (SABRE) and the heteronuclear variant, X-SABRE, increase the sensitivity of magnetic resonance techniques using order derived from reversible binding of para-hydrogen. One current limitation of SABRE is suboptimal polarization transfer over the lifetime of the complex. Here, we demonstrate a multiaxial low-field pulse sequence which allows optimal polarization build-up during a low-field "evolution" pulse, followed by a high-field "mixing" pulse which permits proton decoupling along an orthogonal axis. This preserves the singlet character of the hydrides while allowing exchange to replenish the ligands on the iridium catalyst. This strategy leads to a 2.5-fold improvement over continuous field SABRE SHEATH experimentally which was confirmed with numerical simulation.

Blue Phosphorescence and Hyperluminescence Generated from Imidazo[4,5-b]pyridin-2-ylidene-Based Iridium(III) Phosphors

Four isomeric, homoleptic iridium(III) metal complexes bearing 5-(trifluoromethyl)imidazo[4,5-b]pyridin-2-ylidene and 6-(trifluoromethyl)imidazo[4,5-b]pyridin-2-ylidene-based cyclometalating chelates are successfully synthesized. The meridional isomers can be converted to facial isomers through acid induced isomerization. The m-isomers display a relatively broadened and red-shifted emission, while f-isomers exhibit narrowed blue emission band, together with higher photoluminescent quantum yields and reduced radiative lifetime relative to the mer-counterparts. Maximum external quantum efficiencies of 13.5% and 22.8% are achieved for the electrophosphorescent devices based on f-tpb1 and m-tpb1 as dopant emitter together with CIE coordinates of (0.15, 0.23) and (0.22, 0.45), respectively. By using f-tpb1 as the sensitizing phosphor and t-DABNA as thermally activated delayed fluorescence (TADF) terminal emitter, hyperluminescent OLEDs are successfully fabricated, giving high efficiency of 29.6%, full width at half maximum (FWHM) of 30 nm, and CIE coordinates of (0.13, 0.11), confirming the efficient Förster resonance energy transfer (FRET) process.

An Enhanced Photothermal Therapeutic Iridium Hybrid Platform Reversing the Tumor Hypoxic Microenvironment

As hypoxia is closely associated with tumor progression, proliferation, invasion, metastasis, and strong resistance to therapy, regulating and overcoming the hypoxia tumor microenvironment are two increasingly important aspects of tumor treatment. Herein, we report a phototherapeutic platform that uses the organic photosensitizer diketopyrrolopyrrole (DPP) derivative and inorganic iridium salts (IrCl₃) with photothermal activity and the capacity to decompose H₂O₂ efficiently. The characterization of their photophysical properties proved that DPP-Ir nanoparticles are capable of remarkable near-infrared (NIR) absorption, and compared to DPP nanoparticles, the photothermal conversion efficiency (PCE) increases from 42.1% in DPP nanoparticles to 67.0% in DPP-Ir nanoparticles. The hybrid nanoparticles utilize the catalytic decomposition of endogenous H₂O₂ to produce oxygen for the downregulation of the hypoxia-inducible factor 1 subunit alpha (HIF-1α) protein, which could reverse the tumor hypoxic microenvironment. Benefiting from the excellent optical properties and good biocompatibility, the hybrid platform exhibits efficient photothermal therapeutic effects as well as good biological safety. In conclusion, such a hybrid platform could improve photothermal therapy against cancer.

A Rising Interest in the Development of Metal Complexes in Cancer Immunotherapy

Metal complexes have shown great potential in cancer immunotherapy. This review briefly introduces the basic concepts and strategies of cancer immunotherapy and summarizes the recent discoveries on the immune effects of traditional platinum-based anticancer compounds. In addition, we also outline the latest research progresses on metal complexes for cancer immunotherapy focusing on platinum, ruthenium, iridium, rhenium and copper complexes. Finally, the research perspectives and unsolved problems on the applications of metallo-anticancer agents in cancer immunotherapy are purposed.