Highly efficient photothermal nanoagent achieved by harvesting energy via excited-state intramolecular motion within nanoparticles

Advances in Nanotechnology Development to Overcome Current Roadblocks in CAR-T Therapy for Solid Tumors

Chimeric antigen receptor T cell (CAR-T) therapy for the treatment of hematologic tumors has achieved remarkable success, with five CAR-T therapies approved by the United States Food and Drug Administration. However, the efficacy of CAR-T therapy against solid tumors is not satisfactory. There are three existing hurdles in CAR-T cells for solid tumors. First, the lack of a universal CAR to recognize antigens at the site of solid tumors and the compact tumor structure make it difficult for CAR-T cells to locate in solid tumors. Second, soluble inhibitors and suppressive immune cells in the tumor microenvironment can inhibit or even inactivate T cells. Third, low survival and proliferation rates of CAR-T cells in vivo significantly influence the therapeutic effect. As an emerging method, nanotechnology has a great potential to enhance cell proliferation, activate T cells, and restarting the immune response. In this review, we discuss how nanotechnology can modify CAR-T cells through variable methods to improve the therapeutic effect of solid tumors.

Copper-Selenocysteine Quantum Dots for NIR-II Photothermally Enhanced Chemodynamic Therapy

Chemodynamic therapy has been appealing for effective cancer treatment. Particularly, Fenton-like reactions catalyzed by Cu²⁺-based nanoparticles showed promising prospects. Herein, we fabricated copper-selenocysteine quantum dots (Cu-Sec QDs) with the majority of Cu⁺ by a facile and robust thermal titration process. No high temperature or pressure is needed for this synthetic route of QDs. The selenocysteine functioned as the reducing agent as well as the stabilizer, circumventing the poor water solubility and stability, leading to enhanced biocompatibility. The existence of Cu⁺ endowed the QDs the ability to catalyze the Fenton-like reaction without an extra reduction reaction of Cu²⁺ to Cu⁺. Moreover, the strong absorption in the near-infrared-II region (1000-1300 nm) of the final Cu-Sec QDs is in great favor of the chemodynamic therapy via the photothermally enhanced Fenton-like reaction. And the Cu-Sec QDs exhibited obvious cytotoxicity to various cancer cell lines. We believe that this facile and robust synthetic approach could open up another method for the fabrication of quantum dots toward the potential Fenton-like reaction-based applications in biological fields.

Semiconducting Polymer Nanoparticles with Intramolecular Motion-Induced Photothermy for Tumor Phototheranostics and Tooth Root Canal Therapy

Much effort is devoted to develop agents with superior photoacoustic/photothermal properties for improved disease diagnosis and treatment. Herein, a new fused two isoindigo (DIID)-based semiconducting conjugated polymer (named PBDT-DIID) is rationally designed and synthesized with a strong near-infrared absorption band ranging from 700 to 1000 nm. Water-dispersing nanoparticles (NPs) of PBDT-DIID are prepared with good biocompatibility and a rather high photothermal conversion efficiency (70.6%), as the active excited-state intramolecular twist around the central double bonds in DIID permits most of the absorbed excitation energy flow to heat deactivation pathway through internal conversion. The photoacoustic signal can be further magnified by incorporation of polylactide (PLA) in the NP core to confine the generated heat of PBDT-DIID within NPs. The resultant doped NPs show excellent performance in photoacoustic imaging-guided photothermal therapy in an orthotopic 4T1 breast tumor-bearing mouse model. It is also found that the photothermal effect of the PBDT-DIID NPs is safe and quite efficacious to highly improve the root canal treatment outcome by heating the 1% NaClO solution inside the root canal upon 808 nm laser irradiation in a human extracted tooth root canal infection model.

Evoking Highly Immunogenic Ferroptosis Aided by Intramolecular Motion-Induced Photo-Hyperthermia for Cancer Therapy

Immunogenic cell death (ICD) through apoptosis or necroptosis is widely adopted to improve the therapeutic effect in cancer treatment by triggering a specific antitumor immunity. However, the tumor resistance to apoptosis/necroptosis seriously impedes the therapeutic effect. Recently, ferroptosis featured with excessive lipid peroxidation is demonstrated capable of bypassing the apoptosis/necroptosis resistance to kill cancer cells. To date, numerous efficient ferroptosis inducers are developed and successfully utilized for sensitizing cancer cells to ferroptosis. Unfortunately, these inducers can hardly generate adequate immunogenicity during induction of ferroptotic cancer cell death, which distinctly attenuates the efficacy of triggering antitumor immune response, therefore leads to unsatisfactory therapeutic effect. Herein, a novel high-performance photothermal nanoparticle (TPA-NDTA NP) is designed by exploiting energy via excited-state intramolecular motion and employed for immensely assisting ferroptosis inducer to evoke highly efficient ICD through ferroptosis pathway. Tumor models with poor immunogenicity are used to demonstrate the tremendously enhanced therapeutic effect endowed by highly enhanced immunogenic ferroptosis in vitro and in vivo by virtue of the NPs. This study sheds new light on a previously unrecognized facet of boosting the immunogenicity of ferroptosis for achieving satisfactory therapeutic effect in cancer therapy.

One-Pot Synthesis of Customized Metal-Phenolic-Network-Coated AIE Dots for In Vivo Bioimaging

The integration of aggregation-induced emission luminogens (AIEgens) and inorganic constituents to generate multifunctional nanocomposites has attracted much attention because it couples the bright aggregate-state fluorescence of AIEgens with the diverse imaging modalities of inorganic constituents. Herein, a facile and universal strategy to prepare metal-phenolic-network (MPN)-coated AIE dots in a high encapsulation efficiency is reported. Through precise control on the nucleation of AIEgens and deposition of MPNs in tetrahydrofuran/water mixtures, termed as coacervation, core-shell MPN-coated AIE dots with bright emission are assembled in a one-pot fashion. The optical properties of MPN-coated AIE dots can be readily tuned by varying the incorporated AIEgens. Different metal ions, such as Fe³⁺ , Ti⁴⁺ , Cu²⁺ , Ni²⁺ , can be introduced to the nanoparticles. The MPN-coated AIE dots with a red-emissive AIEgen core are successfully used to perform magnetic resonance/fluorescence dual-modality imaging in a tumor-bearing mouse model and blood flow visualization in a zebrafish larva. It is believed that the present study provides a tailor-made nanoplatform to meet the individual needs of in vivo bioimaging.

Acceptor Planarization and Donor Rotation: A Facile Strategy for Realizing Synergistic Cancer Phototherapy via Type I PDT and PTT

Tumor hypoxia seriously impairs the therapeutic outcomes of type II photodynamic therapy (PDT), which is highly dependent upon tissue oxygen concentration. Herein, a facile strategy of acceptor planarization and donor rotation is proposed to design type I photosensitizers (PSs) and photothermal reagents. Acceptor planarization can not only enforce intramolecular charge transfer to redshift NIR absorption but also transfer the type of PSs from type II to type I photochemical pathways. Donor rotation optimizes photothermal conversion efficiency (PCE). Accordingly, three 3,6-divinyl-substituted diketopyrrolopyrrole (DPP) derivatives, 2TPAVDPP, TPATPEVDPP, and 2TPEVDPP, with different number of rotors were prepared. Experimental results showed that three compounds were excellent type I PSs, and the corresponding 2TPEVDPP nanoparticles (NPs) with the most rotors possessed the highest PCE. The photophysical properties of 2TPEVDPP NPs are particularly suitable for in vivo NIR fluorescence imaging-guided synergistic PDT/PTT therapy. The proposed strategy is helpful for exploiting type I phototherapeutic reagents with high efficacy for synergistic PDT and PTT.

Chemo-photothermal immunotherapy for eradication of orthotopic tumors and inhibition of metastasis by intratumoral injection of polydopamine versatile hydrogels

Cancer remains one of the leading causes of death globally and metastasis always leads to treatment failure. Here, we develop a versatile hydrogel loading photothermal agents, chemotherapeutics, and immune-adjuvants to eradicate orthotopic tumors and inhibit metastasis by combinational therapy. Hydrogel networks were synthesized via the thiol-Michael addition of polydopamine (PDA) with thiolated hyaluronic acid. PDA acted as a cross-linking agent and endowed the hydrogel with excellent photothermal property. Meanwhile, a chemotherapeutic agent, doxorubicin (DOX), was loaded in the hydrogel via π‒π stacking with PDA and an immune-adjuvant, CpG-ODN, was loaded via electrostatic interaction. The release of DOX from the hydrogel was initially slow but accelerated due to near infrared light irradiation. The hydrogels showed remarkably synergistic effect against 4T1 cancer cells and stimulated plenty of cytokines secreting from RAW264.7 cells. Moreover, the hydrogels eradicated orthotopic murine breast cancer xenografts and strongly inhibited metastasis after intratumoral injection and light irradiation. The high anticancer efficiency of this chemo-photothermal immunotherapy resulted from the strong synergistic effect of the versatile hydrogels, including the evoked host immune response. The combinational strategy of chemo-photothermal immunotherapy is promising for highly effective treatment of breast cancer.

Diradical-Featured Organic Small-Molecule Photothermal Material with High-Spin State in Dimers for Ultra-Broadband Solar Energy Harvesting

Organic materials with radical characteristics are gaining increasing attention, due to their potential implications in highly efficient utilization of solar energy. Manipulating intermolecular interactions is crucial for tuning radical properties, as well as regulating their absorption bands, and thus improving the photothermal conversion efficiency. Herein, a diradical-featured organic small-molecule croconium derivative, CR-DPA-T, is reported for highly efficient utilization of solar energy. Upon aggregation, CR-DPA-T exists in dimer form, stabilized by the strong intermolecular π-π interactions, and exhibits a rarely reported high-spin state. Benefiting from the synergic effects of radical characteristics and strong intermolecular π-π interactions, CR-DPA-T powder absorbs broadly from 300 to 2000 nm. In-depth investigations with transient absorption analysis reveal that the strong intermolecular π-π interactions can promote nonradiative relaxation by accelerating internal conversion and facilitating intermolecular charge transfer (ICT) between dimeric molecules to open up faster internal conversion pathways. Remarkably, CR-DPA-T powder demonstrates a high photothermal efficiency of 79.5% under 808 nm laser irradiation. By employing CR-DPA-T as a solar harvester, a CR-DPA-T-loaded flexible self-healing poly(dimethylsiloxane) (H-PDMS) film, named as H-PDMS/CR-DPA-T self-healing film, is fabricated and employed for solar-thermal applications. These findings provide a feasible guideline for developing highly efficient diradical-featured organic photothermal materials.

The fast-growing field of photo-driven theranostics based on aggregation-induced emission

Photo-driven theranostics, also known as phototheranostics, relying on the diverse excited-state energy conversions of theranostic agents upon photoexcitation represents a significant branch of theranostics, which ingeniously integrate diagnostic imaging and therapeutic interventions into a single formulation. The combined merits of photoexcitation and theranostics endow photo-driven theranostics with numerous superior features. The applications of aggregation-induced emission luminogens (AIEgens), a particular category of fluorophores, in the field of photo-driven theranostics have been intensively studied by virtue of their versatile advantageous merits of favorable biocompatibility, tuneable photophysical properties, unique aggregation-enhanced theranostic (AET) features, ideal AET-favored on-site activation ability and ready construction of one-for-all multimodal theranostics. This review summarised the significant achievements of photo-driven theranostics based on AIEgens, which were detailedly elaborated and classified by their diverse theranostic modalities into three groups: fluorescence imaging-guided photodynamic therapy, photoacoustic imaging-guided photothermal therapy, and multi-modality theranostics. Particularly, the tremendous advantages and individual design strategies of AIEgens in pursuit of high-performance photosensitizing output, high photothermal conversion and multimodal function capability by adjusting the excited-state energy dissipation pathways are emphasized in each section. In addition to highlighting AIEgens as promising templates for modulating energy dissipation in the application of photo-driven theranostics, current challenges and opportunities in this field are also discussed.

A Unique Multifunctional Nanoenzyme Tailored for Triggering Tumor Microenvironment Activated NIR-II Photoacoustic Imaging and Chemodynamic/Photothermal Combined Therapy

The accurate diagnosis and targeted therapy of malignant tumors face significant challenges. To address these, an oxidized molybdenum polyoxometalate-copper nanocomposite (Ox-POM@Cu) is designed and synthesized here. The doping with Cu determines the formation of oxygen vacancies, which can increase the carrier concentration in Ox-POM@Cu, accelerate electron transfer, and enhance the redox activity, thus playing an efficient catalytic role. The nanocomposite presents unique enzymatic functions characterized by a multielement catalytic activity in the tumor microenvironment (TME). In addition, it can be employed as an NIR-II photoacoustic imaging (PAI) probe and cancer therapy agent. First, it participates in a redox reaction with glutathione (GSH) in tumor tissues, activates the PAI and photothermal therapy functions via NIR-II irradiation, and depletes the GSH supply in cancerous cells. Subsequently, it catalyzes a Fenton-like reaction with H₂ O₂ in tumor tissues to form hydroxyl radicals, thereby performing a chemodynamic therapy function. The findings show that the developed nanoenzyme is very efficient in the diagnosis and treatment of malignant tumors. This work not only provides a new strategy for the design of TME-induced NIR-II PAI but also presents new insights into enhanced cancer therapy.

9,10-Phenanthrenequinone: A Promising Kernel to Develop Multifunctional Antitumor Systems for Efficient Type I Photodynamic and Photothermal Synergistic Therapy

Synergistic phototherapy provides a promising strategy to conquer the hypoxia and heterogeneity of tumors and realize a better therapeutic effect than monomodal photodynamic therapy (PDT) or photothermal therapy (PTT). The development of efficient multifunctional organic phototheranostic systems still remains a challenging task. Herein, 9,10-phenanthrenequinone (PQ) with strong electron-withdrawing ability is conjugated with the rotor-type electron-donating triphenylamine derivatives to create a series of tailor-made photosensitizers. The highly efficient Type I reactive oxygen species generation and outstanding photothermal conversion capacity are tactfully integrated into these PQ-cored photosensitizers. The underlying photophysical and photochemical mechanisms of the combined photothermal and Type I photodynamic effects are deciphered by experimental and theoretical methods and are closely associated with the active intramolecular bond stretching vibration, facilitated intersystem crossing, and specific redox cycling activity of the PQ core. Both in vitro and in vivo evaluations demonstrate that the nanoagents fabricated by these PQ-based photosensitizers are excellent candidates for Type I photodynamic and photothermal combined antitumor therapy. This study thus broadens the horizon for the development of high-performance PTT/Type I PDT nanoagents for synergistic phototheranostic treatments.

A Tumor-Targeting Near-Infrared Heptamethine Cyanine Photosensitizer with Twisted Molecular Structure for Enhanced Imaging-Guided Cancer Phototherapy

In recent years, cancer phototherapy has been extensively studied as noninvasive cancer treatment. To present efficient recognition toward cancer cells, most photosensitizers (PSs) are required to couple with tumor-targeted ligands. Interestingly, the heptamethine cyanine IR780 displays an intrinsic tumor-targeted feature even without modification. However, the photothermal efficacy and photostability of IR780 are not sufficient enough for clinical use. Herein, we involve a twisted structure of tetraphenylethene (TPE) between two molecules of IR780 to improve the photothermal conversion efficiency (PCE). The obtained molecule T780T shows strong near-infrared (NIR) fluorescence and improved PCE (38.5%) in the dispersed state. Also, the photothermal stability and ROS generation capability of T780T at the NIR range (808 nm) are both promoted. In the aqueous phase, the T780T was formulated into uniform nanoaggregates (∼200 nm) with extremely low fluorescence and PTT response, which would reduce in vivo imaging background and side effect of PTT response in normal tissues. After intravenous injection into tumor-bearing mice, the T780T nanoaggregates display high tumor accumulation and thus remarkably inhibit the tumor growth. Moreover, the enhanced photostability of the T780T allows for twice irradiation after one injection and leads to more significant tumor inhibition. In summary, our study presents a tumor-targeted small-molecule PS for efficient cancer therapy and brings a new design of heptamethine cyanine PS for potential clinical applications.

Cascade-responsive nano-assembly for efficient photothermal-chemo synergistic inhibition of tumor metastasis by targeting cancer stem cells

Metastasis has been widely recognized as the most lethal threats for cancer patients. Due to their special genetic and environmental context, cancer stem cells (CSCs) which are resistant to most cytotoxic drugs and radiation, are considered as the dominant culprit for metastasis. Thus, the efficient targeting and thorough elimination of CSCs are significantly urgent for the enhancement of therapeutic efficacy. Herein, we developed a facile and smart photothermal-chemo therapeutic nano-assembly system, of which the surface was modified by a sheddable PEG shell and acid-activatable pro-penetration peptide, to surmount the physiological barriers in targeting CSCs. A highly-efficient diradical-featured croconium-based photothermal agent and a natural cytotoxic heat shock protein (HSP) inhibitor were co-loaded in redox-sensitive chitosan matrices to realize the synergistic photothermal-chemo therapy. Within solid tumors, the PEG shell that prevents the nano-assembly from mononuclear phagocytic clearance could rapidly leave to expose the positively charged chitosan, and the detached iRGD could further actuate the tumor penetration of chitosan nanoparticles, and allow the CSCs targeting by selective recognition of CD44 protein. Owing to the HSP inhibition and chemo-sensitization, both the CSCs and non-CSCs could be thoroughly eliminated by the designed nano-assembly, largely inhibiting the tumor growth and metastasis. This work provides a potential strategy for CSCs-targeting drug delivery to solve the CSCs-related metastasis.

Optimizing Comprehensive Performance of Aggregation-Induced Emission Nanoparticles through Molecular Packing Modulation for Multimodal Image-Guided Synergistic Phototherapy

Fluorescent nanoparticles (NPs) with aggregation-induced emission (AIE) characteristics hold remarkable potential for image-guided phototherapy. The molecular packing is the key point for optimizing the performance of AIE luminogens (AIEgens) in the aggregated or solid state. However, so far, the packing mode of AIEgens in NPs is still vague, causing some challenges for understanding the relationship between the photophysical property and packing mode, as well as further optimizing the performance of NPs for biomedical applications. In this contribution, by simply controlling the length of alkoxy chains in the donor-acceptor conjugated OPTPA, a packing balance between the twisted molecular structure and effective π-conjugation is actualized. Subsequently, the possibility of amorphous-crystalline transition of AIEgens in the polymer-encapsulated NPs is presented for the first time, and the comprehensive performance of NPs is further optimized. Both in vitro and in vivo experiments indicate that crystalline AIEgen-based NPs are remarkably effective in trimodal imaging-guided synergistic phototherapy.

A Facile Strategy of Boosting Photothermal Conversion Efficiency through State Transformation for Cancer Therapy

Improving photothermal conversion efficiency (PCE) is critical to facilitate therapeutic performance during photothermal therapy (PTT). However, current strategies of prompting PCE always involve complex synthesis or modification of photothermal agents, thereby significantly inhibiting the practical applications and fundamental understanding of photothermal conversion. A facile strategy is herein present for boosting PCE by transforming photothermal agents from aggregated state to dispersed state. Compared to aggregated state, the developed photothermal agents with semiconducting nature can rotate freely in dispersed state, which allows for an efficient nonradiative dissipation through twisted intramolecular charge transfer (TICT) effect, consequentially offering excellent photothermal performance. Noteworthy, the state transformation can be achieved by virtue of releasing photothermal molecules from nanoparticles on the basis of a pH-responsive polymer nanocarrier, and the PCE is elevated from 43% to 60% upon changing the pH values from 7.4 to 5.0. Moreover, the nanoparticle disassembly and state transformation behaviors can also smoothly proceed in lysosome of cancer cells, demonstrating a distinct photothermal therapeutic performance for cancer ablation. It is hoped that this strategy of transforming state to boost PCE would be a new platform for practical applications of PTT technique.

PEG-Polymer Encapsulated Aggregation-Induced Emission Nanoparticles for Tumor Theranostics

In the field of tumor imaging and therapy, the aggregation-caused quenching (ACQ) effect of fluorescent dyes at high concentration is a great challenge. In this regard, the aggregation-induced emission luminogens (AIEgens) show great potential, since AIEgens effectively overcome the ACQ effect and have better fluorescence quantum yield, photobleaching resistance, and photosensitivity. Polyethylene glycol (PEG)-polymer is the most commonly used carrier to prepare nanoparticles (NPs). The advantage of PEGylation is that it can greatly prolong the metabolic half-life and reduce immunogenicity and toxicity. Considering that the hydrophobicity of most AIEgens hinders their application in organisms, the use of PEG-polymer encapsulation is an effective strategy to overcome this obstacle. Importantly, bioactive functional groups can be modified on PEG-polymers to enhance the biological effect of NPs. The combination of powerful AIEgens and PEG-polymers provides a new strategy for tumor imaging and therapy, which is promising for clinical application.

Aggregation-Induced Emission-Based Platforms for the Treatment of Bacteria, Fungi, and Viruses

The prevention and control of pathogenic bacteria, fungi, and viruses is a herculean task for all the countries since they greatly threaten global public health. Rapid detection and effective elimination of these pathogens is crucial for the treatment of related diseases. It is urgently demanded to develop new diagnostic and therapeutic strategies to combat bacteria, fungi, and viruses-induced infections. The emergence of aggregation-induced emission (AIE) luminogens (AIEgens) is a revolutionary breakthrough for the treatment of many diseases, including pathogenic infections. In this review, the main focus is on the applications of AIEgens for theranostic treatment of pathogenic bacteria, fungi, and viruses. Due to the AIE characteristic, AIEgens are promising fluorescent probes for the detection of bacteria, fungi, and viruses with excellent sensitivity and photostability. Moreover, AIEgen-based theranostic platforms can be fabricated by introducing bactericidal moieties or designing AIE photosensitizers and AIE photothermal agents. The current strategies and ongoing developments of AIEgens for the treatment of pathogenic bacteria, fungi, and viruses will be discussed in detail.

Boosting Photothermal Theranostics via TICT and Molecular Motions for Photohyperthermia Therapy of Muscle-Invasive Bladder Cancer

The development of photothermal agents with high photothermal conversion efficiency (PCE) can help to reduce drug and laser dosage, but still remains a big challenge. Herein, a novel approach is reported to design photothermal agents with high PCE values by promoting nonradiative heat generation processes through the cooperation of twisted intramolecular charge transfer (TICT) and molecular motions. Within the designed molecule 2DMTT-BBTD, the tetraphenylethenes act as molecular rotors, the long alkyl chain grafted thiophene helps to twist the molecular geometry to facilitate TICT state formation and preserve molecular motions in aggregate, while the strong electron-withdrawing BBTD unit enhances TICT effect. 2DMTT-BBTD exhibits NIR-absorption and a high PCE value of 74.8% under 808 nm laser irradiation. Gambogic acid (GA) which surmounts tumor cell thermotolerance by inhibiting heat shock protein 90 (HSP90) expression is coloaded into the nanoparticles, RGD peptide is further introduced to the nanoparticle surface to improve tumor accumulation. The resultant nanoparticles facilitate the effective low-temperature hyperthermia therapy of muscle-invasive bladder cancer (MIBC) with minimal damage to surrounding heathy tissues. This work delivers a new design concept for development of highly efficient photothermal agents, which also provides a safer approach for noninvasive treatment of MIBC and other malignant tumors.

Phototherapy and optical waveguides for the treatment of infection

With rapid emergence of multi-drug resistant microbes, it is imperative to seek alternative means for infection control. Optical waveguides are an auspicious delivery method for precise administration of phototherapy. Studies have shown that phototherapy is promising in fighting against a myriad of infectious pathogens (i.e. viruses, bacteria, fungi, and protozoa) including biofilm-forming species and drug-resistant strains while evading treatment resistance. When administered via optical waveguides, phototherapy can treat both superficial and deep-tissue infections while minimizing off-site effects that afflict conventional phototherapy and pharmacotherapy. Despite great therapeutic potential, exact mechanisms, materials, and fabrication designs to optimize this promising treatment option are underexplored. This review outlines principles and applications of phototherapy and optical waveguides for infection control. Research advances, challenges, and outlook regarding this delivery system are rigorously discussed in a hope to inspire future developments of optical waveguide-mediated phototherapy for the management of infection and beyond.

Recent Advances in Aggregation-Induced Emission Materials and Their Biomedical and Healthcare Applications

The emergence of the concept of aggregation-induced emission (AIE) has opened new opportunities in many research areas, such as biopsy analysis, biological processes monitoring, and elucidation of key physiological and pathological behaviors. As a new class of luminescent materials, AIE luminogens (AIEgens) possess many prominent advantages such as tunable molecular structures, high molar absorptivity, high brightness, large Stokes shift, excellent photostability, and good biocompatibility. The past two decades have witnessed a dramatic growth of research interest in AIE, and many AIE-based bioprobes with excellent performance have been widely explored in biomedical fields. This review summarizes some of the latest advancements of AIE molecular probes and AIE nanoparticles (NPs) with regards to biomedical and healthcare applications. According to the research areas, the review is divided into five sections, which are imaging and identification of cells and bacteria, photodynamic therapy, multimodal theranostics, deep tissue imaging, and fluorescence-guided surgery. The challenges and future opportunities of AIE materials in the advanced biomedical fields are briefly discussed. In perspective, the AIE-based bioprobes play vital roles in the exploration of advanced bioapplications for the ultimate goal of addressing more healthcare issues by integrating various cutting-edge modalities and techniques.

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.

Conjugated Organic Photothermal Films for Spatiotemporal Thermal Engineering

With the growth of photoenergy harvesting and thermal engineering, photothermal materials (PTMs) have attracted substantial interest due to their unique functions such as localized heat generation, spatiotemporal thermal controllability, invisibility, and light harvesting capabilities. In particular, π-conjugated organic PTMs show advantages over inorganic or metallic PTMs in thin film applications due to their large light absorptivity, ease of synthesis and tunability of molecular structures for realizing high NIR absorption, flexibility, and solution processability. This review is intended to provide an overview of organic PTMs, including both molecular and polymeric PTMs. A description of the photothermal (PT) effect and conversion efficiency (ηPT ) for organic films is provided. After that, the chemical structure and optical properties of organic PTMs are discussed. Finally, emerging applications of organic PT films from the perspective of spatiotemporal thermal engineering principles are illustrated.

Near infrared photothermal conversion materials: mechanism, preparation, and photothermal cancer therapy applications

Photothermal therapy (PTT) has been widely applied in cancer therapy as a result of its non-invasive, localized treatment and good therapeutic effect. In general, the final therapeutic effect of PTT mainly depends on the photothermal materials, which can be further considered to be determined by the photothermal conversion efficiency, biocompatibility, and photothermal stability of photothermal materials. In this review, photothermal materials including inorganic materials, organic materials, and organic-inorganic composite materials in recent years have been summarized in terms of the mechanism, preparation, and cancer therapy applications. In the end, the perspectives and obstacles in their further development are overviewed.

"Internal and External Combined" Nonradiative Decay-Based Nanoagents for Photoacoustic Image-Guided Highly Efficient Photothermal Therapy

Rational manipulation of nonradiative decay channels is of crucial significance to improve photothermal conversion efficiency (PCE) and design photothermal agents. We first used the "internal and external combined" nonradiative decay strategy to enhance PCE. Specifically, organic IR-Y6 NPs with strong NIR absorption and high molar extinction coefficient were prepared and characterized. By means of TD-DFT calculations and fs-TA spectroscopy, the dual nonradiative decay channels composed of the free rotor (external strategy) and ultrafast dark excited states (DESs) between S0 and S1 states (internal strategy) were proved, which significantly enhanced PCE, up to 66%. IR-Y6 NPs were applied to a mice tumor model for photoacoustic image-guided photothermal therapy, showing complete tumor ablation ability and good biocompatibility for the normal organs. This work is of significance to deeply understand the nonradiation decay mechanism and rational design of high-performance PTT agents.

A Borondifluoride-Complex-Based Photothermal Agent with an 80 % Photothermal Conversion Efficiency for Photothermal Therapy in the NIR-II Window

Small organic photothermal agents (SOPTAs) that absorb in the second near-infrared (NIR-II, 1000-1700 nm) window are highly desirable in photothermal therapy for their good biocompatibility and deeper tissue penetration. However, the design of NIR-II absorbing SOPTAs remains a great challenge. Herein, we report that molecular engineering of BF₂ complex via strengthening the donor-acceptor conjugation and increasing the intramolecular motions is an efficient strategy to achieve NIR-II absorbing SOPTAs with high photothermal performance. Based on this strategy, a BF₂ complex, BAF4, was designed and synthesized. BAF4 exhibits an intense absorption maximum at 1000 nm and negligible fluorescence. Notably, the nanoparticles of BAF4 achieve a high photothermal conversion efficiency value of 80 % under 1064 nm laser irradiation (0.75 W cm^-2 ). In vitro and in vivo studies reveal the great potential of BAF4 nanoparticles in photoacoustic imaging-guided photothermal therapy in the NIR-II window.

Quantitative Förster Resonance Energy Transfer: Efficient Light Harvesting for Sequential Photo-Thermo-Electric Conversion

Light is essential to all life on the earth. Thus, highly efficient light-harvesting systems with the sequential energy transfer process are significant for using solar energy in photosynthesis. For developing an efficient light-harvesting system, a liquid aggregation-induced emission (AIE) dye TPE-EA is obtained, as a donor and solvent, which can light up the aggregation caused quenching (ACQ) Nile Red (NiR, acceptor) to construct a quantitative Förster resonance energy transfer (FRET) system in NiR⊂TPE-EA. Impressively, this FRET pair shows an impressive photothermal effect, producing a peak temperature of 119 °C while excited by UV light, with 37.8% of conversion efficiency. NiR⊂TPE-EA is quite different from most other photothermal materials, which require excitation with long wavelength light (>520 nm). Therefore, NiR⊂TPE-EA firstly converts the solar into thermal energy and then into electric energy to achieve sequential photo-thermo-electric conversion. Such sequential conversion, suitable for being excited by sunlight, is anticipated to unlock new and smart approaches for capturing solar energy.

Remodeling of Tumor Microenvironment by Tumor-Targeting Nanozymes Enhances Immune Activation of CAR T Cells for Combination Therapy

Targeting B7-H3 chimeric antigen receptor (CAR) T cells has antitumor potential for therapy of non-small cell lung cancer (NSCLC) in preclinical studies. However, CAR T cell therapy remains a formidable challenge for the treatment of solid tumors due to the heterogeneous and immunosuppressive tumor microenvironment (TME). Nanozymes exhibit merits modulating the immunosuppression of the tumor milieu. Here, a synergetic strategy by combination of nanozymes and CAR T cells in solid tumors is described. This nanozyme with dual photothermal-nanocatalytic properties is endowed to remodel TME by destroying its compact structure. It is found that the B7-H3 CAR T cells infused in mice engrafted with the NSCLC cells have superior antitumor activity after nanozyme ablation of the tumor. Importantly, it is found that the changes altered immune-hostile cancer environment, resulting in enhanced activation and infiltration of B7-H3 CAR T cells. The first evidence that the process of combination nanozyme therapy effectively improves the therapeutic index of CAR T cells is presented. Thus, this study clearly supports that the TME-immunomodulated nanozyme is a promising tool to improve the therapeutic obstacles of CAR T cells against solid tumors.

Second near-infrared (NIR-II) imaging: a novel diagnostic technique for brain diseases

Imaging in the second near-infrared II (NIR-II) window, a kind of biomedical imaging technology with characteristics of high sensitivity, high resolution, and real-time imaging, is commonly used in the diagnosis of brain diseases. Compared with the conventional visible light (400-750 nm) and NIR-I (750-900 nm) imaging, the NIR-II has a longer wavelength of 1000-1700 nm. Notably, the superiorities of NIR-II can minimize the light scattering and autofluorescence of biological tissue with the depth of brain tissue penetration up to 7.4 mm. Herein, we summarized the main principles of NIR-II in animal models of traumatic brain injury, cerebrovascular visualization, brain tumor, inflammation, and stroke. Simultaneously, we encapsulated the in vivo process of NIR-II probes and their in vivo and in vitro toxic effects. We further dissected its limitations and following optimization measures.

Photochemical Synthesis of Nonplanar Small Molecules with Ultrafast Nonradiative Decay for Highly Efficient Phototheranostics

There has been much recent progress in the development of photothermal agents (PTAs) for biomedical and energy applications. Synthesis of organic PTAs typically involves noble metal catalysts and high temperatures. On the other hand, photochemical synthesis, as an alternative and green chemical technology, has obvious merits such as low cost, energy efficiency, and high yields. However, photochemical reactions have rarely been employed for the synthesis of PTAs. Herein, a facile and high-yield photochemical reaction is exploited for synthesizing nonplanar small molecules (NSMs) containing strong Michler's base donors and a tricyanoquinodimethane acceptor as high-performance PTAs. The synthesized NSMs show interesting photophysical properties including good absorption for photons of over 1000 nm wavelength, high near-infrared extinction coefficients, and excellent photothermal performance. Upon assembling the NSMs into nanoparticles (NSMN), they exhibit good biocompatibility, high photostability, and excellent photothermal conversion efficiency of 75%. Excited-state dynamic studies reveal that the NSMN has ultrafast nonradiative decay after photoexcitation. With these unique properties, the NSMN achieves efficient in vivo photoacoustic imaging and photothermal tumor ablation. This work demonstrates the superior potential of photochemical reactions for the synthesis of high-performance molecular PTAs.

Add the Finishing Touch: Molecular Engineering of Conjugated Small Molecule for High-Performance AIE Luminogen in Multimodal Phototheranostics

Phototheranostics based on luminogens with aggregation-induced emission (AIE) characteristics is captivating increasing research interest nowadays. However, AIE luminogens are inherently featured by inferior absorption coefficients (ε) resulting from the distorted molecular geometry. Besides, molecular innovation of long-wavelength light-excitable AIE luminogens with highly efficient phototheranostic outputs is an appealing yet significantly challenging task. Herein, on the basis of a fused-ring electron acceptor-donator-acceptor (A-D-A) type molecule (IDT) with aggregation-caused quenching (ACQ) properties, molecular engineering smoothly proceeds and successfully yields a novel AIE luminogen (IDT-TPE) via simply modifying tetraphenylethene (TPE) moieties on the sides of IDT backbone. The AIE tendency endows IDT-TPE nanoparticles with enhanced fluorescence brightness and far superior fluorescence imaging performance to IDT nanoparticles for mice tumors. Moreover, IDT-TPE nanoparticles exhibit near-infrared light-excitable features with a high ε of 8.9 × 10⁴ m^-1 cm^-1 , which is roughly an order of magnitude higher than that of most previously reported AIE luminogens. Combining with their reactive oxygen species generation capability and extremely high photothermal conversion efficiency (59.7%), IDT-TPE nanoparticles actualize unprecedented performance in multimodal phototheranostics. This study thus brings useful insights into the development of versatile phototheranostic materials with great potential for practical cancer theranostics.

Ultrathin Two-Dimensional Plasmonic PtAg Nanosheets for Broadband Phototheranostics in Both NIR-I and NIR-II Biowindows

Broadband near-infrared (NIR) photothermal and photoacoustic agents covering from the first NIR (NIR-I) to the second NIR (NIR-II) biowindow are of great significance for imaging and therapy of cancers. In this work, ultrathin two-dimensional plasmonic PtAg nanosheets are discovered with strong broadband light absorption from NIR-I to NIR-II biowindow, which exhibit outstanding photothermal and photoacoustic effects under both 785 and 1064 nm lasers. Photothermal conversion efficiencies (PCEs) of PtAg nanosheets reach 19.2% under 785 nm laser and 45.7% under 1064 nm laser. The PCE under 1064 nm laser is higher than those of most reported inorganic NIR-II photothermal nanoagents. After functionalization with folic acid modified thiol-poly(ethylene glycol) (SH-PEG-FA), PtAg nanosheets endowed with good biocompatibility and 4T1 tumor-targeted function give high performances for photoacoustic imaging (PAI) and photothermal therapy (PTT) in vivo under both 785 and 1064 nm lasers. The effective ablation of tumors in mice can be realized without side effects and tumor metastasis by PAI-guided PTT of PtAg nanosheets under 785 or 1064 nm laser. The results demonstrate that the prepared PtAg nanosheets with ultrathin thickness and small size can serve as a promising phototheranostic nanoplatform for PAI-guided PTT of tumors in both NIR-I and NIR-II biowindows.

Biomimetic Polydopamine-Modified Silk Fibroin/Curcumin Nanofibrous Scaffolds for Chemo-photothermal Therapy of Bone Tumor

The simultaneous therapy of tumor recurrence and bone defects resulting from surgical resection of osteosarcoma is still a challenge in the clinic. Combination therapy based on a localized drug-delivery system shows great promise in the treatment of osteosarcoma. Herein, bifunctional polydopamine (PDA)-modified curcumin (CM)-loaded silk fibroin (SF) composite (SF/CM-PDA) nanofibrous scaffolds, which combined photothermal therapy with chemotherapy to synergistically enhance osteosarcoma therapy, were prepared by PDA coating of the SF/CM nanofibrous scaffolds fabricated by supercritical carbon dioxide (SC-CO₂) technology. The PDA coating improved hydrophilicity and mechanical strength of the SF/CM scaffolds. The SF/CM-PDA scaffolds present good photothermal conversion capacity and excellent photostability. The low pH and near-infrared (NIR) irradiation could effectively accelerate release of CM in the SF/CM-PDA scaffolds. The in vitro anticancer results indicated that the biocompatible SF/CM-PDA scaffolds had a long-term, stable, and superior anticancer effect compared to pure CM. Furthermore, the SF/CM-PDA scaffolds significantly increased the growth inhibition of osteosarcoma MG-63 cells under NIR irradiation (808 nm and 1.3 W/cm²). Besides, the SF/CM-PDA scaffolds could enhance osteoblast MC3T3-E1 cell proliferation in vitro when the mass ratio of CM was 0.05-0.5%. This work has therefore demonstrated that the bifunctional SF/CM-PDA scaffolds provide a competitive strategy for local osteosarcoma therapy and bone regeneration.

Highly efficient photothermal nanoparticles for the rapid eradication of bacterial biofilms

Biofilm-related infections, such as dental plaque, chronic sinusitis, native valve endocarditis, and chronic airway infections in cystic fibrosis have brought serious suffering to patients and financial burden to society. Materials that can eliminate mature biofilms without developing drug resistance are promising tools to treat biofilm-related infections, and thus they are in urgent demand. Herein, we designed and readily prepared organic nanoparticles (NPs) with highly efficient photothermal conversion by harvesting energy via excited-state intramolecular motions and enlarging molar absorptivity. The photothermal NPs can sufficiently eliminate mature bacterial biofilms upon low-power near-infrared laser irradiation. NPs hold great promise for the rapid eradication of bacterial biofilms by photothermal therapy.

Boosting Photoacoustic Effect via Intramolecular Motions Amplifying Thermal-to-Acoustic Conversion Efficiency for Adaptive Image-Guided Cancer Surgery

Photoacoustic (PA) imaging emerges as a promising technique for biomedical applications. The development of new strategies to boost PA conversion without depressing other properties (e.g., fluorescence) is highly desirable for multifunctional imaging but difficult to realize. Here, we report a new phenomenon that active intramolecular motions could promote PA signal by specifically increasing thermal-to-acoustic conversion efficiency. The compound with intense intramolecular motion exhibits amplified PA signal by elevating thermal-to-acoustic conversion, and the fluorescence also increases due to aggregation-induced emission signature. The simultaneously high PA and fluorescence brightness of TPA-TQ3 NPs enable precise image-guided surgery. The preoperative fluorescence and PA imaging are capable of locating orthotopic breast tumor in a high-contrast manner, and the intraoperative fluorescence imaging delineates tiny residual tumors. This study highlights a new design guideline of intramolecular motion amplifying PA effect.

Competition between the Photothermal Effect and Emission in Potential Phototherapy Agents

Planar donor-acceptor-donor (D-A-D) organic molecules have been highlighted as promising photothermal agents due to their good light-to-heat conversion ratio, easy degradation, and chemical tunability. Very recently, it has been demonstrated that their photothermal conversion can be boosted by appending rather long alkyl chains. Despite this behavior being tentatively associated with the population of a nonradiative twisted intramolecular charge transfer (TICT) state driven by an intramolecular motion, the precise mechanisms and the role played by the environment, and most notably aggregation, still remain elusive. In this context, we carried out a series of time-dependent density functional theory (TD-DFT) calculations combined with molecular dynamics (MD) simulations to achieve a realistic description of the isolated and aggregated systems. Our theoretical models unambiguously evidence that the population of CT states is very unlikely in both cases, whereas the light-triggered heat dissipation can be ascribed to the activation of specific vibrational degrees of freedom related to the relative motion of the peripheral chains. Overall, our results clearly corroborate the active role played by the alkyl substituents in the photothermal conversion through vibrational motion, while breaking from the conventional picture, which invokes the formation of dark TICT states in loosely packed aggregates.

Leveraging BODIPY nanomaterials for enhanced tumor photothermal therapy

In the past ten years, photothermal therapy (PTT) has attracted widespread attention in tumor treatment due to its non-invasiveness and little side effects. PTT utilizes heat produced by photothermal agents under the irradiation of near-infrared light to kill tumor cells. Boron-dipyrromethene (BODIPY), an organic phototherapy agent, has been widely used in tumor phototherapy due to its higher molar extinction coefficient, robust photostability and good phototherapy effect. However, there are some issues in the application of BODIPY for tumor PTT, such as low photothermal conversion efficiency and short absorption wavelength. In this review, we focus on the latest development of BODIPY nanomaterials for overcoming the above problems and enhancing the PTT effect.

Biomimetic Glucan Particles with Aggregation-Induced Emission Characteristics for Noninvasive Monitoring of Transplant Immune Response

Real-time monitoring of post-transplant immune response is critical to prolong the survival of grafts. The current gold standard for assessing the immune response to graft is biopsy. However, such a method is invasive and prone to false negative results due to limited tissue size available and the heterogeneity of the rejection site. Herein, we report biomimetic glucan particles with aggregation-induced emission (AIE) characteristics (HBTTPEP/GPs) for real-time noninvasive monitoring of post-transplant immune response. We have found that the positively charged near-infrared AIEgens can effectively aggregate in the confined space of glucan particles (GPs), thereby turning on the fluorescence emission. HBTTPEP/GPs can track macrophages for 7 days without hampering the bioactivity. Oral administration of HBTTPEP/GPs can specially target macrophages by mimicking yeast, which then migrate to the transplant rejection site. The fluorescence emitted from HBTTPEP/GPs correlated well with the infiltration of macrophages and the degree of allograft rejection. Furthermore, a single oral HBTTPEP/GPs dose can dynamically evaluate the therapeutic response to immunosuppressive therapy. Consequently, the biomimetic AIE-active glucan particles can be developed as a promising probe for immune-monitoring in solid organ transplantation.

Emerging contrast agents for multispectral optoacoustic imaging and their biomedical applications

Optoacoustic imaging is a hybrid biomedical imaging modality which collects ultrasound waves generated via photoexciting contrast agents in tissues and produces images of high resolution and penetration depth. As a functional optoacoustic imaging technique, multispectral optoacoustic imaging, which can discriminate optoacoustic signals from different contrast agents by illuminating samples with multi-wavelength lasers and then processing the collected data with specific algorithms, assists in the identification of a specific contrast agent in target tissues and enables simultaneous molecular and physiological imaging. Moreover, multispectral optoacoustic imaging can also generate three-dimensional images for biological tissues/samples with high resolution and thus holds great potential in biomedical applications. Contrast agents play essential roles in optoacoustic imaging, and they have been widely explored and applied as probes and sensors in recent years, leading to the emergence of a variety of new contrast agents. In this review, we aim to summarize the latest advances in emerging contrast agents, especially the activatable ones which can respond to specific biological stimuli, as well as their preclinical and clinical applications. We highlight their design strategies, discuss the challenges and prospects in multispectral optoacoustic imaging, and outline the possibility of applying it in clinical translation and public health services using synthetic contrast agents.

Improving Image-Guided Surgical and Immunological Tumor Treatment Efficacy by Photothermal and Photodynamic Therapies Based on a Multifunctional NIR AIEgen

Multimodal therapy is attracting increasing attention to improve tumor treatment efficacy, but generally requires various complicated ingredients combined within one theranostic system to achieve multiple functions. Herein, a multifunctional theranostic nanoplatform based on a single aggregation-induced-emission luminogen (AIEgen), DDTB, is designed to integrate near-infrared (NIR) fluorescence, photothermal, photodynamic, and immunological effects. Intravenously injected AIEgen-based nanoparticles can efficiently accumulate in tumors with NIR fluorescence to provide preoperative diagnosis. Most of the tumors are excised under intraoperative fluorescence navigation, whereafter, some microscopic residual tumors are completely ablated by photodynamic and photothermal therapies for maximally killing the tumor cells and tissues. Up to 90% of the survival rate can be achieved by this synergistic image-guided surgery and photodynamic and photothermal therapies. Importantly, the nanoparticles-mediated photothermal/photodynamic therapy plus programmed death-ligand 1 antibody significantly induce tumor elimination by enhancing the effect of immunotherapy. This theranostic strategy on the basis of a single AIEgen significantly improves the survival of cancer mice with maximized therapeutic outcomes, and holds great promise for clinical cancer treatment.

Antiviral and Anti‐Inflammatory Treatment with Multifunctional Alveolar Macrophage‐Like Nanoparticles in a Surrogate Mouse Model of COVID‐19

The pandemic of coronavirus disease 2019 (COVID‐19) is continually worsening. Clinical treatment for COVID‐19 remains primarily supportive with no specific medicines or regimens. Here, the development of multifunctional alveolar macrophage (AM)‐like nanoparticles (NPs) with photothermal inactivation capability for COVID‐19 treatment is reported. The NPs, made by wrapping polymeric cores with AM membranes, display the same surface receptors as AMs, including the coronavirus receptor and multiple cytokine receptors. By acting as AM decoys, the NPs block coronavirus from host cell entry and absorb various proinflammatory cytokines, thus achieving combined antiviral and anti‐inflammatory treatment. To enhance the antiviral efficiency, an efficient photothermal material based on aggregation‐induced emission luminogens is doped into the NPs for virus photothermal disruption under near‐infrared (NIR) irradiation. In a surrogate mouse model of COVID‐19 caused by murine coronavirus, treatment with multifunctional AM‐like NPs with NIR irradiation decreases virus burden and cytokine levels, reduces lung damage and inflammation, and confers a significant survival advantage to the infected mice. Crucially, this therapeutic strategy may be clinically applied for the treatment of COVID‐19 at early stage through atomization inhalation of the NPs followed by NIR irradiation of the respiratory tract, thus alleviating infection progression and reducing transmission risk.