Multifunctional Au I ‐based AIEgens: Manipulating Molecular Structures and Boosting Specific Cancer Cell Imaging and Theranostics

Strategically engineered Au(I) complexes for orchestrated tumor eradication via chemo-phototherapy and induced immunogenic cell death

Cancer is a significant cause of death around the world, and for many varieties, treatment is not successful. Therefore, there is a need for the development of innovative, efficacious, and precisely targeted treatments. Here, we develop a series of Au(I) complexes (1-4) through rational manipulation of ligand structures, thereby achieving tumor cell specific targeting and orchestrated tumor eradication via chemo-phototherapy and induced immunogenic cell death. A comprehensive exploration based on in vitro and in vivo female mice experimentation shows that complex 4 exhibits proficiency in specific tumor imaging, endoplasmic reticulum targeting, and has robust therapeutic capabilities. Mechanistic elucidation indicates that the anticancer effect derives from the synergistic actions of thioredoxin reductase inhibition, highly efficient reactive oxygen species production and immunogenic cell death. This work presents a report on a robust Au(I) complex integrating three therapeutic modalities within a singular system. The strategy presented in this work provides a valuable reference for the development of high-performance therapeutic agents.

Fast and easy detection of hypochlorite by a smartphone-based fluorescent turn-on probe: Applications to water samples, zebrafish and plant imaging

We have developed a fluorescent probe DBT-Cl ((E)-2-(2-(4-(diphenylamino)benzylidene) hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) for ClO- with an aggregation-induced emission (AIE) strategy depending on solvent polarity. DBT-Cl possessed a prominent solvatochromic emission property with intramolecular charge transfer (ICT) from the TPA (triphenylamine) to the amide group, which was studied by spectroscopic analysis and DFT calculations. These unique AIE properties of DBT-Cl led to the recognition of ClO- with high fluorescent selectivity. DBT-Cl quickly detected ClO- in less than 1 sec with a fluorescent color change from green to cyan. DBT-Cl had a low detection limit of 9.67 μM to ClO-. Detection mechanism of DBT-Cl toward ClO- was illustrated to be oxidative cleavage of DBT-Cl by 1H NMR titrations, ESI-mass, and DFT calculations. We established the viability for dependable detection of ClO- in actual water samples, as well as zebrafish and plant imaging. In particular, DBT-Cl was capable of easily monitoring ClO- through a smartphone application. Therefore, DBT-Cl assured a promising approach for a fast-responsive and multi-applicable ClO- probe in environmental and living organism systems.

Bonding states of gold/silver plasmonic nanostructures and sulfur-containing active biological ingredients in biomedical applications: a review

As one of the most instrumental components in the architecture of advanced nanomedicines, plasmonic nanostructures (mainly gold and silver nanomaterials) have been paid a lot of attention. This type of nanomaterial can absorb light photons with a specific wavelength and generate heat or excited electrons through surface resonance, which is a unique physical property. In innovative biomaterials, a significant number of theranostic (therapeutic and diagnostic) materials are produced through the conjugation of thiol-containing ingredients with gold and silver nanoparticles (Au and Ag NPs). Hence, it is essential to investigate Au/Ag-S interfaces precisely and determine the exact bonding states in the active nanobiomaterials. This study intends to provide useful insights into the interactions between Au/Ag NPs and thiol groups that exist in the structure of biomaterials. In this regard, the modeling of Au/Ag-S bonding in active biological ingredients is precisely reviewed. Then, the physiological stability of Au/Ag-based plasmonic nanobioconjugates in real physiological environments (pharmacokinetics) is discussed. Recent experimental validation and achievements of plasmonic theranostics and radiolabelled nanomaterials based on Au/Ag-S conjugation are also profoundly reviewed. This study will also help researchers working on biosensors in which plasmonic devices deal with the thiol-containing biomaterials (e.g., antibodies) inside blood serum and living cells.

Thioredoxin (Trx): A redox target and modulator of cellular senescence and aging-related diseases

Thioredoxin (Trx) is a compact redox-regulatory protein that modulates cellular redox state by reducing oxidized proteins. Trx exhibits dual functionality as an antioxidant and a cofactor for diverse enzymes and transcription factors, thereby exerting influence over their activity and function. Trx has emerged as a pivotal biomarker for various diseases, particularly those associated with oxidative stress, inflammation, and aging. Recent clinical investigations have underscored the significance of Trx in disease diagnosis, treatment, and mechanistic elucidation. Despite its paramount importance, the intricate interplay between Trx and cellular senescence-a condition characterized by irreversible growth arrest induced by multiple aging stimuli-remains inadequately understood. In this review, our objective is to present a comprehensive and up-to-date overview of the structure and function of Trx, its involvement in redox signaling pathways and cellular senescence, its association with aging and age-related diseases, as well as its potential as a therapeutic target. Our review aims to elucidate the novel and extensive role of Trx in senescence while highlighting its implications for aging and age-related diseases.

Synthesis of a Novel Gold(I) Complex and Evaluation of Its Anticancer Properties in Breast Cancer Cells

BACKGROUND

Platinum complexes are commonly used for cancer chemotherapy; however, they are not only highly-priced but also have various side effects. It is, therefore, important to design affordable anticancer drugs with minimal side effects.

METHODS

We synthesized a new gold(I) complex, PF6{(BDPEA)(TPPMS) digold(I)} (abbreviated as PBTDG) and tested its cytotoxicity in MCF-7 breast cancer cells. We also evaluated the effects of PBTDG on mitochondrial membrane potential, generation of reactive oxygen species (ROS) and apoptosis in breast cancer cells.

RESULTS

The IC50 values for PBTDG and sorafenib were found to be 1.48 μM and 4.45 μM, respectively. Exposure to PBTDG caused significant and concentration-dependent depletion of ATP and disruption of mitochondrial membrane potential. PBTDG induced 2.6, 3.6, and 5.7-fold apoptosis for 1 μM, 3 μM, and 10 μM concentrations, respectively. The induction of apoptosis by the same concentrations of sorafenib was 1.2, 1.3, and 1.6-fold, respectively. The low concentration of PBTDG (1 μM) induced the generation of ROS by 99.83%, which was significantly higher than the ROS generation caused by the same concentration of sorafenib (73.76%). The ROS induction caused by higher concentrations (5 μM) of PBTDG and sorafenib were 104.95% and 122.11%, respectively.

CONCLUSION

The lower concentration of PBTDG produced similar cytotoxicity and apoptotic effects that were caused by a comparatively higher concentration of known anticancer drug (sorafenib). The anticancer effects of PBTDG are attributed to its tendency to disrupt mitochondrial membrane potential, induction of apoptosis and generation of ROS. Further studies are warranted to test the anticancer effects of PBTDG in animal models of cancer.

A New Strategy to Elevate Absorptivity of AIEgens for Intensified NIR-II Emission and Synergized Multimodality Therapy

High-efficiency absorptivity is crucial for the construction of high-performance luminescent materials, especially the long-wavelength near-infrared II (NIR-II) materials; thus seeking an efficient and universal strategy to elevate the absorptivity is extremely important but is still an intractable challenge. In this work, a simple but efficient design strategy is discovered, involving the introduction of gold(I) unit that could effectively elevate the absorptivity of aggregation-induced-emission luminogens (AIEgens). As a result of the efficient elevation of absorptivity, the representative AIE-active TBTP-Au shows more superior NIR-II (1220 nm) luminescence, much higher photothermal conversion efficiency, and unique intracellular reactive oxygen species (ROS) generating ability compared with that of the TBTP ligand. Taking advantage of these improvements, the fabricated tumor-targeting TBTP-Au-cRGD nanoparticles achieve specific NIR-II tumorous imaging in vivo and exert high-efficiency cancer therapy via the synergistic chemotherapy and photothermal therapy. Thus, this work provides a new and efficient strategy to construct high-absorption luminescent materials and demonstrates the great potential of gold(I)-based AIEgens as multifunctional theranostic agents.

Gold(I)-N-Heterocyclic Carbene Synthons in Organometallic Synthesis

The prominent role of gold-N-heterocyclic carbene (NHC) complexes in numerous research areas such as homogeneous (photo)catalysis, medicinal chemistry and materials science has prompted organometallic chemists to design gold-based synthons that permit access to target complexes through simple synthetic steps under mild conditions. In this review, the main gold-NHC synthons employed in organometallic synthesis are discussed. Mechanistic aspects involved in their synthesis and reactivity as well as applications of gold-NHC synthons as efficient pre-catalysts, antitumor agents and/or photo-emissive materials are presented.

Thioredoxin Reductase and Organometallic Complexes: A Pivotal System to Tackle Multidrug Resistant Tumors?

Cancers classified as multidrug-resistant (MDR) are a family of diseases with poor prognosis despite access to increasingly sophisticated treatments. Several mechanisms explain these resistances involving both tumor cells and their microenvironment. It is now recognized that a multi-targeting approach offers a promising strategy to treat these MDR tumors. Inhibition of thioredoxin reductase (TrxR), a key enzyme in maintaining redox balance in cells, is a well-identified target for this approach. Auranofin was the first inorganic gold complex to be described as a powerful inhibitor of TrxR. In this review, we will first recall the main results obtained with this metallodrug. Then, we will focus on organometallic complexes reported as TrxR inhibitors. These include gold(I), gold(III) complexes and metallocifens, i.e., organometallic complexes of Fe and Os derived from tamoxifen. In these families of complexes, similarities and differences in the molecular mechanisms of TrxR inhibition will be highlighted. Finally, the possible relationship between TrxR inhibition and cytotoxicity will be discussed and put into perspective with their mode of action.

Coupling Probiotics with 2D CoCuMo-LDH Nanosheets as a Tumor-Microenvironment-Responsive Platform for Precise NIR-II Photodynamic Therapy

Photodynamic therapy (PDT) has become a promising cancer treatment approach with superior advantages. However, it remains a grand challenge to develop tumor microenvironment (TME)-responsive photosensitizers (PSs) for tumor-targeting precise PDT. Herein, the coupling Lactobacillus acidophilus (LA) probiotics with 2D CoCuMo layered-double-hydroxide (LDH) nanosheets (LA&LDH) is reported as a TME-responsive platform for precise NIR-II PDT. The CoCuMo-LDH nanosheets loaded on LA can be transformed from crystalline into amorphous through etching by the LA-metabolite-enabled low pH and overexpressed glutathione. The TME-induced in situ amorphization of CoCuMo-LDH nanosheets can boost its photodynamic activity for singlet oxygen (¹ O₂ ) generation under 1270 nm laser irradiation with relative ¹ O₂ quantum yield of 1.06, which is the highest among previously reported NIR-excited PSs. In vitro and in vivo assays prove that the LA&LDH can effectively achieve complete cell apoptosis and tumor eradication under 1270 nm laser irradiation. This study proves that the probiotics can be used as a tumor-targeting platform for highly efficient precise NIR-II PDT.

A Brain-Targeting NIR-II Ferroptosis System: Effective Visualization and Oncotherapy for Orthotopic Glioblastoma

Near-infrared-II (NIR-II) ferroptosis activators offer promising potentials in in vivo theranostics of deep tumors, such as glioma. However, most cases are nonvisual iron-based systems that are blind for in vivo precise theranostic study. Additionally, the iron species and their associated nonspecific activations might trigger undesired detrimental effects on normal cells. Considering gold (Au) is an essential cofactor for life and it can specifically bind to tumor cells, Au(I)-based NIR-II ferroptosis nanoparticles (TBTP-Au NPs) for brain-targeted orthotopic glioblastoma theranostics are innovatively constructed. It achieves the real-time visual monitoring of both the BBB penetration and the glioblastoma targeting processes. Moreover, it is first validated that the released TBTP-Au specifically activates the effective heme oxygenase-1-regulated ferroptosis of glioma cells to greatly extend the survival time of glioma-bearing mice. This new ferroptosis mechanism based on Au(I) may open a new way for the fabrication of advanced and high-specificity visual anticancer drugs for clinical trials.

Gold Complexes in Anticancer Therapy: From New Design Principles to Particle-Based Delivery Systems

The discovery of the medicinal properties of gold complexes has fuelled the design and synthesis of new anticancer metallodrugs, which have received special attention due to their unique modes of action. Current research in the development of gold compounds with therapeutic properties is predominantly focused on the molecular design of drug leads with superior pharmacological activities, e.g., by introducing targeting features. Moreover, intensive research aims at improving the physicochemical properties of gold compounds, such as chemical stability and solubility in the physiological environment. In this regard, the encapsulation of gold compounds in nanocarriers or their chemical grafting onto targeted delivery vectors could lead to new nanomedicines that eventually reach clinical applications. Herein, we provide an overview of the state-of-the-art progress of gold anticancer compounds, andmore importantly we thoroughly revise the development of nanoparticle-based delivery systems for gold chemotherapeutics.

Solvato-Controlled Assembly and Structural Transformation of Emissive Poly-NHC-Based Organometallic Cages and Their Applications in Amino Acid Sensing and Fluorescence Imaging

Stimuli-induced structural transformation of supramolecular cages has drawn increasing attention because of their sensitive feature to external variations as model systems to simulate biological processes. However, combining structural transformation and useful functions has remained a difficult task. This study reports the solvato-controlled self-assembly of two unique topologies with different emission characteristics, a water-soluble Ag₈ L₄ cage (A) and an Ag₄ L₂ cage (B), produced from the same sulfonate-pendant tetraphenylethene (TPE) bridged tetrakis-(1,2,4-triazolium) ligand. Both cages show interesting solvent-responsive reversible structural transformation, and the change of fluorescence signals can efficiently track the process. Additionally, water-soluble cage A exhibits unique properties in thermochromism, thiol amino acid sensing, and subcellular imaging in aqueous media.

Aurophilic Interactions of Dimeric Bisphosphine Gold(I) Complexes Pre-Organized by the Structure of the 1,5-Diaza-3,7-Diphosphacyclooctanes

The dimeric gold(I) chloride and gold(I) iodide complexes ([L2Au]Cl2 and L2AuI2) on the scaffold of the cyclic bisphosphine, namely 1,5-diaza-3,7-diphosphacyclooctane containing α-phenylbenzyl (benzhydryl) substituents at the nitrogen atoms, were synthesized. The obtained complexes were isolated as white crystalline powders. The single crystal XRD of the obtained complexes revealed the strong aurophilic interactions between two gold(I) atoms with the Au…Au distance values of 2.9977(6) and 3.1680(5) Å. The comparison of the gold complexes, based on the N,N-diaryl- and N,N-dibenzhydryl substituted 1,5-diaza-3,7-diphosphacyclooctanes, allowed to reveal the strong impact of the initial heterocycle conformation on the realization of the aurophilic interactions, where the geometry of N,N-dibenzhydryl substituted 1,5-diaza-3,7-diphosphacyclooctane, is pre-organized for the intramolecular aurophilic interactions of the complexes. The obtained complexes exhibit a bluish-green phosphorescence (λem 505 (-Cl) and 530(-I)) in the solid state at room temperature, originated by the metal-halide centered transitions, which was confirmed by the TDDFT calculations. It was found that the aurophilic interactions are realized in the ground and in the triplet excited states of the complexes. The slighter change of the geometry of the N,N-dibenzhydryl substituted gold(I) iodide complexes, under the transition from the ground state to the excited state, in comparison with their N,N-diaryl substituted analogues, results in the reduced values of the Stokes shift of luminescence (ca. 150 nm vs. 175 nm).

Structure and functions of Aggregation-Induced Emission-Photosensitizers in anticancer and antimicrobial theranostics

Photosensitizers with Aggregation-Induced Emission (AIE) can allow the efficient light-mediated generation of Reactive Oxygen Species (ROS) based on their complex molecular structure, while interacting with living cells. They achieve better tissue targeting and allow penetration of different wavelengths of Ultraviolet-Visible-Infrared irradiation. Not surprisingly, they are useful for fluorescence image-guided Photodynamic Therapy (PDT) against cancers of diverse origin. AIE-photosensitizers can also function as broad spectrum antimicrobials, capable of destroying the outer wall of microbes such as bacteria or fungi without the issues of drug resistance, and can also bind to viruses and deactivate them. Often, they exhibit poor solubility and cellular toxicity, which compromise their theranostic efficacy. This could be circumvented by using suitable nanomaterials for improved biological compatibility and cellular targeting. Such dual-function AIE-photosensitizers nanoparticles show unparalleled precision for image-guided detection of tumors as well as generation of ROS for targeted PDT in living systems, even while using low power visible light. In short, the development of AIE-photosensitizer nanoparticles could be a better solution for light-mediated destruction of unwanted eukaryotic cells and selective elimination of prokaryotic pathogens, although, there is a dearth of pre-clinical and clinical data in the literature.

Biotin-Targeted Au(I) Radiosensitizer for Cancer Synergistic Therapy by Intervening with Redox Homeostasis and Inducing Ferroptosis

The search for highly selective sensitizers with a novel mechanism for tumor targeting therapy is of considerable interest. In this work, we have developed a series of new biotin-targeted Au(I) complexes. Through systematic biological evaluation and comparison, biotinylated Au(I) complex 3a containing a triphenylphosphine ligand was screened, as it realized both prominent efficient inhibition and selective cytotoxicity to cancer cells, and the effect was better than that of popularly used auranofin. Meanwhile, complex 3a, as a potent radiosensitizer, enhances anticancer effects in vitro and in vivo and has sensitization selectivity. From the action mechanism study, we provide evidence that complex 3a could intervene in redox homeostasis through targeted binding and strong suppression of thioredoxin reductase (TrxR) and induce the ferroptosis death process, enabling it to sensitize tumor cells to radiotherapy. Thus, complex 3a has enormous potential as an efficient and specific radiosensitizing agent in cancer therapy.

Recent development of gold(I) and gold(III) complexes as therapeutic agents for cancer diseases

Metal complexes have demonstrated significant antitumor activities and platinum complexes are well established in the clinical application of cancer chemotherapy. However, the platinum-based treatment of different types of cancers is massively hampered by severe side effects and resistance development. Consequently, the development of novel metal-based drugs with different mechanism of action and pharmaceutical profile attracts modern medicinal chemists to design and synthesize novel metal-based agents. Among non-platinum anticancer drugs, gold complexes have gained considerable attention due to their significant antiproliferative potency and efficacy. In most situations, the gold complexes exhibit anticancer activities by targeting thioredoxin reductase (TrxR) or other thiol-rich proteins and enzymes and trigger cell death via reactive oxygen species (ROS). Interestingly, gold complexes were recently reported to elicit biochemical hallmarks of immunogenic cell death (ICD) as an ICD inducer. In this review, the recent progress of gold(I) and gold(III) complexes is comprehensively summarized, and their activities and mechanism of action are documented.

A multi-hit therapeutic nanoplatform for hepatocellular carcinoma: Dual stimuli-responsive drug release, dual-modal imaging, and in situ oxygen supply to enhance synergistic therapy

Nanomedicine has been widely studied for the diagnosis and treatment of hepatocellular carcinoma (HCC). How to synthesize a nanoplatform possessing a high synergistic therapeutic efficacy remains a challenge in this emerging research field. In this study, a convenient all-in-one therapeutic nanoplatform (FTY720@AM/T7-TL) is designed for HCC. This advanced nanoplatform consists of multiple functional elements, including gold-manganese dioxide nanoparticles (AM), tetraphenylethylene (T), fingolimod (FTY720), hybrid-liposome (L), and T7 peptides (T7). The nanoplatform is negatively charged at physiological pH and can transit to a positively charged state once moving to acidic pH environments. The specially designed pH-responsive charge-reversal nanocarrier prolongs the half-life of nanodrugs in blood and improves cellular uptake efficiency. The platform achieves a sustained and controllable drug release through dual stimulus-response, with pH as the endogenous stimulus and near-infrared as the exogenous stimulus. Furthermore, the nanoplatform realizes in situ O₂ generation by catalyzing tumor over-expressed H₂O₂, which alleviates tumor microenvironment hypoxia and improves photodynamic therapy. Both in vitro and in vivo studies show the prepared nanoplatform has good photothermal conversion, cellular uptake efficiency, fluorescence/magnetic resonance imaging capabilities, and synergistic anti-tumor effects. These results suggest that the prepared all-in-one nanoplatform has great potential for dual-modal imaging-guided synergistic therapy of HCC.

Brain-Targeted Aggregation-Induced-Emission Nanoparticles with Near-Infrared Imaging at 1550 nm Boosts Orthotopic Glioblastoma Theranostics

A remaining challenge in the treatment of glioblastoma multiforme (GBM) is surmounting the blood-brain barrier (BBB). Such a challenge prevents the development of efficient theranostic approaches that combine reliable diagnosis with targeted therapy. In this study, brain-targeted near-infrared IIb (NIR-IIb) aggregation-induced-emission (AIE) nanoparticles are developed via rational design, which involves twisting the planar molecular backbone with steric hindrance. The resulting nanoparticles can balance competing responsiveness demands for radiation-mediated NIR fluorescence imaging at 1550 nm and non-radiation NIR photothermal therapy (NIR-PTT). The brain-targeting peptide apolipoprotein E peptide (ApoE) is grafted onto these nanoparticles (termed as ApoE-Ph NPs) to target glioma and promote efficient BBB traversal. A long imaging wavelength 1550 nm band-pass filter is utilized to monitor the in vivo biodistribution and accumulation of the nanoparticles in a model of orthotopic glioma, which overcomes previous limitations in wavelength range and equipment. The results demonstrate that the ApoE-Ph NPs have a higher PTT efficiency and significantly enhanced survival of mice bearing orthotopic GBM with moderate irradiation (0.5 W cm^-2 ). Collectively, the work highlights the smart design of a brain-targeted NIR-II AIE theranostic approach that opens new diagnosis and treatment options in the photonic therapy of GBM.

Au nanoclusters modulated macrophages polarization and synoviocytes apoptosis for enhanced rheumatoid arthritis treatment

The persistent progression of synovial inflammation and cartilage destruction was contributed to the cross-talk of pro-inflammatory macrophages and activated fibroblast-like synoviocytes (FLS) in synovial microenvironment. In this work, a structurally...

Just Add the Gold: Aggregation-Induced-Emission Properties of Alkynylphosphinegold(I) Complexes Functionalized with Phenylene-Terpyridine Subunits

A series of organometallic complexes containing an alkynylphosphinegold(I) fragment and a phenylene-terpyridine moiety connected together by flexible linker have been prepared using the specially designed terpyridine ligands. The compounds were studied crystallographically to reveal that all of them contain a linearly coordinated Au(I) atom and a free terpyridine moiety. The different orientations of the molecules relative to each other in the solid state determine the multiple noncovalent interactions such as antiparallel ππ stacking, CH-π, and CH-Au, but no aurophilic interactions are realized. The organometallic Au(I) complexes obtained show fluorescence in the solution and dual singlet-triplet emission in the solid state. This means that their photophysical behavior is determined by both intermolecular lattice-defined interactions and Au(I) atom introduction. Density functional theory computational analysis supported the assignment of emission to intraligand electronic transitions only inside the phenylene-terpyridine part with no Au(I) involved. In addition, a study of the nature of the excited states for the "dimer" with an antiparallel orientation of the terpyridine fragment showed that this orientation leads to the generation of abstracted singlet and triplet states, lowering their energy in comparison with the monomer complex. Thus, the complexes obtained can be qualified as examples of Au(I)-containing organometallic aggregation-induced-emission luminogens.

A multifunctional AIE gold cluster-based theranostic system: tumor-targeted imaging and Fenton reaction-assisted enhanced radiotherapy

BACKGROUND

As cancer is one of the main leading causes of mortality, a series of monotherapies such as chemotherapy, gene therapy and radiotherapy have been developed to overcome this thorny problem. However, a single treatment approach could not achieve satisfactory effect in many experimental explorations.

RESULTS

In this study, we report the fabrication of cyclic RGD peptide (cRGD) modified Au₄-iron oxide nanoparticle (Au₄-IO NP-cRGD) based on aggregation-induced emission (AIE) as a multifunctional theranostic system. Besides Au₄ cluster-based fluorescence imaging and enhanced radiotherapy, iron oxide (IO) nanocluster could realize magnetic resonance (MR) imaging and Fenton reaction-based chemotherapy. Abundant toxic reactive oxygen species generated from X-ray irradiation and in situ tumor-specific Fenton reaction under acidic microenvironment leads to the apoptotic and necrotic death of cancer cells. In vivo studies demonstrated good biocompatibility of Au₄-IO NP-cRGD and a high tumor suppression rate of 81.1% in the synergistic therapy group.

CONCLUSIONS

The successful dual-modal imaging and combined tumor therapy demonstrated AIE as a promising strategy for constructing multifunctional cancer theranostic platform.

Metal-Based Aggregation-Induced Emission Theranostic Systems

Efficient theranostic systems can realize better outcomes in disease treatment because of precise diagnosis and the concomitant effective therapy. Aggregation-induced emission luminogens (AIEgens) are a unique type of organic emitters with intriguing photophysical properties in the aggregate state. Among the AIEgens studied for biomedical applications, so far, metal-based AIE systems have shown great potential in theranostics due to the enhanced multimodal bioimaging ability and therapeutic effect. This research field has been growing rapidly, and many rationally designed systems with promising activities to cancer and other diseases have been reported recently. In this review, we summarized the recent progress of metal-based AIE materials in bioimaging and biological theranostics, and deciphered the pertinent design strategies. We hope that this review can offer new insights into the development of this growing field.

A Protein-Binding Molecular Photothermal Agent for Tumor Ablation

Photothermal therapy usually requires a high power density to activate photothermal agent for effective treatment, which inevitably leads to damage to normal tissues and inflammation in tumor tissues. Herein, we rationally design a protein-binding strategy to build a molecular photothermal agent for photothermal ablation of tumor. The synthesized photothermal agent can covalently bind to the thiol groups on the intracellular proteins. The heat generated by the photothermal agent directly destroyed the bioactive proteins in the cells, effectively reducing the heat loss and the molecular leakage. Under a low power density of 0.2 W cm^-2 , the temperature produced by the photothermal agent was sufficient to induce apoptosis. In vitro and in vivo experiments showed that the therapeutic effect of photothermal therapy can be efficiently improved with the protein-binding strategy.

Making Aggregation-Induced Emission Luminogen More Valuable by Gold: Enhancing Anticancer Efficacy by Suppressing Thioredoxin Reductase Activity

Gold complexes have been recognized as potential anticancer agents against various kinds of diseases due to their inherent suppressions of antioxidant thioredoxin reductase (TrxR) activity. Herein, a powerful aggregation-induced emission luminogen (AIEgen), TBP-Au, was designed and synthesized by integrating an anticancer Au(I) moiety with an AIE-active photosensitizer (TBP), in which both the production and consumption routes of reactive oxygen species (ROS) were elaborately considered simultaneously to boost the anticancer efficacy. It has been demonstrated that TBP-Au could realize superior two-photon fluorescence imaging in tumor tissues with high resolution and deep penetration as well as long-term imaging in live animals due to its AIE property. In addition, the introduction of a special Au(I) moiety could tune the organelle specificity and efficiently facilitate the ROS-determined photodynamic therapy (PDT). More impressively, TBP-Au could efficiently eliminate cancer cells under light irradiation through the preconceived synergetic approaches from the PDT and the effective suppression of TrxR, demonstrating that TBP-Au holds great potential for precise cancer theranostics.

Noncovalent Self-Assembled Smart Gold(III) Porphyrin Nanodrug for Synergistic Chemo-Photothermal Therapy

Self-assembly is a powerful means to fabricate multifunctional smart nanotheranostics. However, the complicated preparation, toxicity of responsive carriers, and low loading efficiency of drug cargo hinder the outcome. Herein, we developed a responsive carrier-free noncovalent self-assembly strategy of a metallized Au(III) tetra-(4-pyridyl) porphine (AuTPyP) anticancer drug for the preparation of a heat/acid dual-stimulated nanodrug, and it generated a better photothermal effect than monomers under irradiation. The photothermal effect promoted the protonation of the hydrophobic pyridyl group and the following release into tumorous acidic microenvironments. With cRGD modification, the released drug induced the aggravation of intracellular reactive oxygen species (ROS) via the activity inhibition of thioredoxin reductase (TrxR) for synergistic chemo-photothermal therapy of tumors.

Aggregation-induced emission active metal complexes: a promising strategy to tackle bacterial infections

This Feature Article discusses the recent development of metal-based aggregation-induced emission luminogens for detection, discrimination and decimation of bacterial pathogens to tackle antimicrobial resistance.

Lighting Silver(I) Complexes for Solution-Processed Organic Light-Emitting Diodes and Biological Applications via Thermally Activated Delayed Fluorescence

Luminescent coinage metal complexes have shown promising applications as electroluminescent emitters, photocatalysts/photosensitizers, and bioimaging/theranostic agents, rendering them attractive alternatives to transition metal complexes based on iridium, ruthenium, and platinum that have extremely low earth abundance. In comparison to the widely studied Au(I) and Cu(I) complexes, Ag(I) complexes have seldom been explored in this field because of their inferior emission properties. Herein, we report a novel series of [Ag(N^N)(P^P)]PF₆ complexes exhibiting highly efficient thermally activated delayed fluorescence by using easily accessible neutral diamine ligands and commercially available ancillary diphosphine chelates. The photoluminescence quantum yields (PLQYs) of the Ag(I) emitters are ≤0.62 in doped films. The high PLQY with a large delayed fluorescence ratio enabled the fabrication of solution-processed organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 8.76%, among the highest values for Ag(I) emitter-based OLEDs. With superior emission properties and an excited state lifetime in the microsecond regime, together with its potent cytotoxicity, the selected Ag(I) complex has been used for simultaneous cell imaging and anticancer treatment in human liver carcinoma HepG2 cells, revealing the potential of luminescent Ag(I) complexes for biological applications such as theranostics.

pH-Responsive Au(i)-disulfide nanoparticles with tunable aggregation-induced emission for monitoring intragastric acidity

Aggregation-induced emission (AIE)-featuring Au(i) complexes are superior probes for physiological environment monitoring in living organisms owing to their excellent biocompatibility and efficient luminescent properties. However, the intrinsic obstacle of poor water stability and lack of response to biological stimuli greatly restrict their practical application in biological systems. Herein, water-stable and pH-responsive Au(i)-disulfide nanoparticles (NPs) with AIE characteristics were designed. The NPs were prepared by integrating a pH-responsive moiety, cysteine (Cys), into Au(i)-thiolate (SR) complexes, and the Au(i)-SR-Cys structure was formed through disulfide bonds. Hydrophilic Cys was located on the outer layer of the NPs, endowing the spherical NPs with high stability and remarkable monodispersity in water. In addition, Cys endowed the NPs with pH-responsive characteristics. These unique advantages enable them to hold great promise as luminescent probes to monitor intragastric acidity in an acid suppression therapy. To the best of our knowledge, this work is the first example of luminescent Au(i) materials to monitor physiological changes.