Evoking Photothermy by Capturing Intramolecular Bond Stretching Vibration-Induced Dark-State Energy

A planar electronic acceptor motif contributing to NIR-II AIEgen with combined imaging and therapeutic applications

Designing molecules with donor-acceptor-donor (D-A-D) architecture plays an important role in obtaining second near-infrared region (NIR-II, 1000-1700 nm) fluorescent dyes for biomedical applications; however, this always comes with a challenge due to very limited electronic acceptors. On the other hand, to endow NIR-II fluorescent dyes with combined therapeutic applications, trivial molecular design is indispensable. Herein, we propose a pyrazine-based planar electronic acceptor with a strong electron affinity, which can be used to develop NIR-II fluorescent dyes. By structurally attaching two classical triphenylamine electronic donors to it, a basic D-A-D module, namely Py-NIR, can be generated. The planarity of the electronic acceptor is crucial to induce a distinct NIR-II emission peaking at ∼1100 nm. The unique construction of the electronic acceptor can cause a twisted and flexible molecular conformation by the repulsive effect between the donors, which is essential to the aggregation-induced emission (AIE) property. The tuned intramolecular motions and twisted D-A pair brought by the electronic acceptor can lead to a remarkable photothermal conversion with an efficiency of 56.1% and induce a type I photosensitization with a favorable hydroxyl radical (OH˙) formation. Note that no additional measures are adopted in the molecular design, providing an ideal platform to realize NIR-II fluorescent probes with synergetic functions based on such an acceptor. Besides, the nanoparticles of Py-NIR can exhibit excellent NIR-II fluorescence imaging towards orthotopic 4T1 breast tumors in living mice with a high sensitivity and contrast. Combined with photothermal imaging and photoacoustic imaging caused by the thermal effect, the imaging-guided photoablation of tumors can be well performed. Our work has created a new opportunity to develop NIR-II fluorescent probes for accelerating biomedical applications.

Design of a two-degree-of-freedom magnetic levitation vibration energy harvester for bridge vibration response analysis

For bridges with high automobile traffic, a large amount of vibration is generated daily due to cars driving over imperfectly level roads, and a vibration energy harvester can convert this energy into electrical energy, thus providing energy for devices such as bridge health sensors. However, the traditional single degree of freedom magnetic levitation vibration energy harvester (SMEH) has the disadvantage of low output power, so this research designs an improved dual degree of freedom magnetic levitation vibration energy harvester (DMEH), and a mathematical model of the energy harvester is built for simulation tests and an optimization model based on NSGA-II algorithm is developed for optimizing the structural parameters of the energy harvester. The experimental results show that the maximum total output power of DMEH and SMEH on CSSBB1, CSSBB2 and CSSBB3 are 48.7 mW, 36.8 mW, 25.4 mW and 27.2 mW, 21.5 mW, 14.9 mW, respectively, and the minimum total magnet volumes of both on CSSBB1, CSSBB2 and CSSBB3 are 268 cm3, 132 cm3, 219 cm3, 214 cm3, 86.2 cm3, 156 cm3. Based on the experimental data, it is found that the maximum output power of the optimal solution of DMEH is larger than that of SMEH for the selected simply supported girder bridge project, and the volume of the former is also larger than that of the latter, but the degree of increase can still be adapted to the application environment. The research results have some reference significance for improving the energy harvesting efficiency of bridge vibration energy harvesters.

Pyrene-Based Deep-Blue Fluorophores with Narrow-Band Emission

High-efficiency narrow-band luminescent materials have attracted intense interest, resulting in their great colorimetric purity. This has led to a variety of high-tech applications in high-definition displays, spectral analysis, and biomedicine. In this study, a rigid pyrene core was employed as the molecular backbone, and four narrow-band pyrene-based blue emitters were synthesized using various synthetic methods (such as Lewis-acid catalyzed cyclization domino reactions, Pd-catalyzed coupling reactions like Suzuki-Miyaura and Sonogashira). Due to the steric effect of the hydroxy group at the 2-position, the target compounds exhibit deep blue emission (<429 nm, CIEy < 0.08) with full width at half-maximum (FWHM) less than 33 nm both in solution and when solidified. The experimental and theoretical results indicated that the substituents at the 1- and 3-positions afford a large dihedral angle with the pyrene core, and the molecular motion is almost fixed by multiple intra- and intermolecular hydrogen bonding interactions in the crystallized state, leading to a suppression of the vibrational relaxation of the molecular structure. Moreover, we observed that the suppression of the vibrational relaxation in the molecular structures and the construction of rigid conjugated structures can help develop narrow-band organic light-emitting materials.

Thiacalix[4]arene-Protected Silver Nanoclusters Encapsulating Different Two-Electron Superatom Oligomers

The subvalent silver kernel represents the nascent state of silver cluster formation, yet the growth mechanism has long been elusive. Herein, two silver nanoclusters (Ag30 and Ag34) coprotected by TC4A4- (H4TC4A = p-tert-butylthiacalix[4]arene) and TBPMT- (TBPMTH = 4-tert-butylbenzenemethanethiol) containing 6e and 4e silver kernels are synthesized and characterized. The trimer of the 2e superatom Ag14 kernel in Ag30 is built from a central Ag6 octahedron sandwiched by two orthogonally oriented Ag5 trigonal bipyramids through sharing vertexes, whereas a double-octahedral Ag10 kernel in Ag34 is a dimer of 2e superatoms. They manifest disparate polyhedron fusion growth patterns at the beginning of the silver cluster formation. Their excellent solution stabilities are contributed by the multisite and multidentate coordination fashion of TC4A4- and the special valence electron structures. This work demonstrates the precise control of silver kernel growth by the solvent strategy and lays a foundation for silver nanocluster application in photothermal conversion.

Assembly of fluorophore J-aggregates with nanospacer onto mesoporous nanoparticles for enhanced photoacoustic imaging

Many fluorophores, such as indocyanine green (ICG), have poor photostability and low photothermal efficiency hindering their wide application in photoacoustic (PA) tomography. In the present study, a supramolecular assembly approach was used to develop the hybrid nanoparticles (Hy NPs) of ICG and porous silicon (PSi) as a novel contrast agent for PA tomography. ICG was assembled on the PSi NPs to form J-aggregates within 30 min. The Hy NPs presented a red-shifted absorption, improved photothermal stability, and enhanced PA performance. Furthermore, 1-dodecene (DOC) was assembled into the NPs as a 'nanospacer', which enhanced non-radiative decay for increased thermal release. Compared to the Hy NPs, adding DOC into the Hy NPs (DOC-Hy) increased the PA signal by 83%. Finally, the DOC-Hy was detectable in PA tomography at 1.5 cm depth in tissue phantom even though its concentration was as low as 6.25 µg/mL, indicating the potential for deep tissue PA imaging.

Type I Photosensitization with Strong Hydroxyl Radical Generation in NIR Dye Boosted by Vigorous Intramolecular Motions for Synergistic Therapy

Development of type I photosensitizers (PSs) with strong hydroxyl radical (· OH) formation is particularly important in the anaerobic tumor treatment. On the other hand, it is challenging to obtain an efficient solid-state intramolecular motion to promote the development of molecular machine and molecular motor. However, the relationship between them is never revealed. In this work, a pyrazine-based near-infrared type I PS with remarkable donor-acceptor effect is developed. Notably, the intramolecular motions are almost maximized by the combination of intramolecular and intermolecular engineering to simultaneously introduce the unlimited bond stretching vibration and boost the group rotation. The photothermal conversion caused by the intramolecular motions is realized with efficiency as high as 86.8%. The D-A conformation of PS can also induce a very small singlet-triplet splitting of 0.07 eV, which is crucial to promote the intersystem crossing for the triplet sensitization. Interestingly, its photosensitization is closely related to the intramolecular motions, and a vigorous motion may give rise to a strong · OH generation. In view of its excellent photosensitization and photothermal behavior, the biocompatible PS exhibits a superior imaging-guided cancer synergistic therapy. This work stimulates the development of advanced PS for the biomedical application and solid-state intramolecular motions.

A tetraphenylethene-based Schiff base AIEgen with a large Stokes shift as probe for highly sensitive and selective detection of aqueous Cu2+ ions and its application in cell imaging

In this work, an AIE-active tetraphenylethene-based Schiff base fluorescent probe 3 with a large Stokes shift (247 nm) was designed and synthesized. It was found that the aggregated probe 3 exhibited very high selectivity and anti-interference ability for Cu²⁺ in PBS buffer (70% f_w) through a fluorescence "turn-off" strategy. Job's plot and NMR analysis indicated the two phenolic hydroxyl groups of the benzene ring and the N atom (-CH=N-) on probe 3 interacted with Cu²⁺ ions in a 1:1 stoichiometric ratio. A comprehensive analysis of the Stern-Volmer and binding constant indicated a rather strong interaction between probe 3 and Cu²⁺ ions. Probe 3 illustrated excellent sensitivity toward Cu²⁺ under ppb level (4.5 nM) and achieved more than 95% recovery in river, lake and tap water toward estimation of Cu²⁺ ions in the analytical applications. Moreover, probe 3 was able to realize bioimaging of HepG2 cells and be quenched by intracellular Cu²⁺ ions, making it promising as a sensitive Cu²⁺ sensor for organisms.

Pyroptosis-Mediated Synergistic Photodynamic and Photothermal Immunotherapy Enabled by a Tumor-Membrane-Targeted Photosensitive Dimer

Overcoming the resistance to apoptosis and immunosuppression of tumor cells is a significant challenge in augmenting the effect of cancer immunotherapy. Pyroptosis, a lytic programmed cell-death pathway unlike apoptosis, is considered a type of immunogenic cell death (ICD) that can intensify the ICD process in tumor cells, releasing dramatically increased tumor-associated antigens and damage-associated molecular patterns to promote cancer immunotherapy. Herein, a tumor cell membrane-targeted aggregation-induced emission photosensitive dimer is found to be able to achieve highly efficient ICD under the synergistic effect of photodynamic and photothermal therapy. The photosensitive dimer can efficiently produce type-I reactive oxygen species (ROS) by photodynamic therapy in hypoxic tumor tissue, leading to pyroptosis by direct cell membrane damage, which is further reinforced by its photothermal effect. Furthermore, the enhanced ICD effect based on the dimer can completely eliminate the primary tumor on the seventh day of treatment and can also boost systemic antitumor immunity by generating immune memory, which is demonstrated by the superior antitumor therapeutic effects on both solid tumors and metastatic tumors when healing 4T1 tumor mouse models with poor immunogenicity.

Advanced Peptide Nanomedicines for Bladder Cancer Theranostics

Cancer is still a global public health problem. Although remarkable success has been achieved in cancer diagnosis and treatment, the high recurrence and mortality rates remain severely threatening to human lives and health. In recent years, peptide nanomedicines with precise selectivity and high biocompatibility have attracted intense attention in biomedical applications. In particular, there has been a significant increase in the exploration of peptides and their derivatives for malignant tumor therapy and diagnosis. Herein, we review the applications of peptides and their derivatives in the diagnosis and treatment of bladder cancer, providing new insights for the design and development of novel peptide nanomedicines for the treatment of bladder cancer in the future.

Molecular Motion and Nonradiative Decay: Towards Efficient Photothermal and Photoacoustic Systems

Nonradiative decay invariably competes with radiative decay during the deexcitation process of matter. In the community of luminescence research, nonradiative decay has been deemed less attractive than radiative decay. However, all things in their being are good for something and so is nonradiative decay. As the molecular motion-facilitated nonradiative decay (MMFND) effect is inevitable in photophysical processes, it provides a new avenue to convert the harvested light energy into exploitable forms by harnessing molecular motion. In many cases, active molecular motion enables thermal deactivation from excited states. In this Minireview, recent advances in photothermal and photoacoustic systems with MMFND character are summarized. We believe that this presentation of the rational engineering of molecular motion for efficient photothermal generation will deepen the understanding of the relationship between molecular motion and nonradiative decay and navigate people to rethink the positive aspects of nonradiative decay for the establishment of new light-controllable techniques.

Photothermal agents based on small organic fluorophores with intramolecular motion

Photothermal therapy (PTT) has attracted great attention due to its noninvasive and low side effects. Photothermal agents (PTAs) which could convert absorbing light into heat play a critical role in PTT. For conventional small organic PTAs, the photothermal conversion ability is mainly achieved by intermolecular noncovalent interactions such as π-π interactions. However, in terms of organic fluorophores with rotator or vibrator segments, the balance between fluorescence emission and heat generation is mainly regulated by intramolecular motions which could be mediated by molecular engineering. Following this designing principle, various fluorophores with intramolecular motions for effective PTT have been reported. In this review, we highlight the recent progress of PTAs based on small organic fluorophores with intramolecular motions for enhanced PTT. Designing tactics of these fluorophores to afford long-wavelength absorption, high photothermal conversion ability, and effective accumulation capability are emphasized. Finally, one-for-all phototheranostics achieved by mediating intramolecular motions of these fluorophores are highlighted. We hope this review could pave a new avenue to developing fluorophores with intramolecular motion as PTAs to advance their clinical transition. STATEMENT OF SIGNIFICANCE: Recent progress of photothermal agents (PTAs) based on small organic fluorophores with intramolecular motion is summarized in this review. Molecular engineering of these small organic fluorophores to afford long-wavelength absorption, high photothermal conversion ability, and effective accumulation at tumor sites for enhanced photothermal therapy (PTT) is highlighted. Strategies to tune the intramolecular motions of these fluorophores to achieve multimodal phototherapy are emphasized as well.

Lighting up Self-Quenching Nanoaggregates with Protein Corona for Simultaneous Intraoperative Imaging and Photothermal Theranostics of Metastatic Cancer

Near-infrared (NIR) photothermal transduction agents (PTAs) with large rigid π-extended and planar structures are prone to aggregate in a physiological environment where their emission is often quenched due to the strong intermolecular dipole-dipole or π-π interactions. This aggregation-caused quenching effect greatly impedes their applications in image-guided photothermal theranostics. Herein, we made an interesting finding that engineering a bioinspired protein corona (PC), once thermodynamically stabilized in preferred orientations on PTA nanoaggregates, can produce brilliant NIR fluorescence with a high quantum yield (∼6.2%) without compromising their photothermal properties. Both experimental data and computational modeling suggest that the mechanism of fluorescence enhancement is due to the high-affinity binding of nano-sized PTA to albumin, which regulates the molecular conformation and aggregation state of PTA. High spatial and temporal resolution imaging of albumin PC-coated PTA aggregates enables image-guided photothermal therapy for cancer cells in sentinel lymph nodes to remarkably inhibit pulmonary metastasis. Such a treatment combined with the surgical removal of the primary tumor can prolong animal survival, which is a promising candidate for clinical applications in the treatment of advanced metastatic cancers.

Nonaromatic Organonickel(II) Phototheranostics

Earth-abundant metal-based theranostics, agents that integrate diagnostic and therapeutic functions within the same molecule, may hold the key to the development of low-cost personalized medicines. Here, we report a set of O-linked nonaromatic benzitripyrrin (C^N^N^N) macrocyclic organonickel(II) complexes, Ni-1-4, containing strong σ-donating M-C bonds. Complexes Ni-1-4 are characterized by a square-planar coordination geometry as inferred from the structural studies of Ni-1. They integrate photothermal therapy, photothermal imaging, and photoacoustic imaging (PAI) within one system. This makes them attractive as potential phototheranostics. Relative to traditional Ni(II) porphyrins, such as F₂₀TPP (tetrapentafluorophenylporphyrin), the lowest energy absorption of Ni-1 is shifted into the near infrared region, presumably as a consequence of Ni-C bonding. Ultrafast transient absorption spectroscopy combined with theoretical calculations revealed that, upon photoexcitation, a higher population of ligand-centered and ³MLCT states is seen in Ni-1 relative to NiTPBP (TPBP = 6,11,16,21-tetraphenylbenziporphyrin). Encapsulating Ni-1 in 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG₂₀₀₀) afforded nanoparticles, Ni-1@DSPE, displaying red-shifted absorption features, as well as good photothermal conversion efficiency (∼45%) in aqueous media. Proof-of-principle experiments involving thrombus treatment were carried out both in vitro and in vivo. It was found that Ni-1@DSPE in combination with 785 nm photo-irradiation for 3 min (0.3 W/cm²) proved successful in removing blood clots from a mouse thrombus model as monitored by photoacoustic imaging (PAI). The present work highlights the promise of organonickel(II) complexes as potential theranostics and the benefits that can accrue from manipulating the excited-state features of early transition-metal complexes via, for example, interrupting π-conjugation pathways.

Donor-Acceptor Molecule Based High-Performance Photothermal Organic Material for Efficient Water Purification and Electricity Generation

In this contribution, a unique donor-acceptor conjugated organic-small-molecule photothermal material, namely GDPA-QCN, is presented. Bulky dendritic triphenylamine (GDPA) was grafted onto quinoxaline-6,7-dicarbonitrile (QCN) with a phenyl ring as a bridge to form an "umbrella" architecture. Benefited from the particular molecular structure, in solid state, GDPA-QCN molecules adopted a loose packing mode due to the steric effect of "umbrella head" dendritic triphenylamine and flexible molecular structure feature, which allows efficient intramolecular motions and consequently elevates energy dissipation by taking the pathway of thermal deactivation within broad absorption range. The GDPA-QCN solid has high solar-thermal conversion efficiency with an absorption range from 300 to 1100 nm, which can promote superior water purification and electricity generation performance.

Reasonable design of NIR AIEgens for fluorescence imaging and effective photothermal/photodynamic cancer therapy

The development of a multifunctional single molecule phototherapeutic agent with excellent fluorescence imaging, photothermal therapy and photodynamic therapy at the same time is still a challenging task, which mainly arises from the low absorbance of the molecule, and the complexity of energy dissipation and molecular design. Herein, four donor-acceptor (D-A) compounds were synthesized by linking triphenylamine (TPA), thiophene/thieno[3,2-b]thiophene and different cyano acceptor structures. In this design, we propose a molecular design strategy to redshift absorption and increase the molar extinction coefficient (ε) by enhancing electron-withdrawing acceptors and enlarging the π-conjugation plane unit. Due to the twisted structure of TPA, these compounds exhibit aggregation-induced emission (AIE) characteristics. Notably, these AIEgens have long emission wavelengths, excellent photostability, biocompatibility, photothermal stability and singlet oxygen (¹O₂) generation performance. Among them, the photothermal conversion efficiency of a compound (named TCF-SS-TPA NPs) can reach 84.5%. Cellular internalization and therapy showed that TCF-SS-TPA NPs have good biocompatibility, excellent cell bioimaging and cancer phototherapy capabilities in vitro. This study will stimulate the molecular design of multifunctional phototherapeutics to realize effective synergistic cancer therapy.

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.

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.

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.

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.

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.

Practicable Applications of Aggregation-Induced Emission with Biomedical Perspective

Considerable efforts have been made into developing aggregation-induced emission fluorogens (AIEgens)-containing nano-therapeutic systems due to the excellent properties of AIEgens. Compared to other fluorescent molecules, AIEgens have advantages including low background, high signal-to-noise ratio, good sensitivity, and resistance to photobleaching, in addition to being exempt from concentration quenching or aggregation-caused quenching effects. The present review outlines the major developments in the biomedical applications of AIEgens-containing systems. From a literature survey, the recent AIE works are reviewed and the reasons why AIEgens are chosen in various biomedical applications are highlighted. The research activities on AIEgens-containing systems are increasing rapidly, therefore, the present review is timely.

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.

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.

A Simple Small Molecule with Synergistic Passive and Active Dual-Targeting Effects for Imaging-Guided Photothermal Cancer Therapy

Photothermal therapy allows spatiotemporal control of the treatment effect only at the site of the disease and provides promising opportunities for imaging-guided precision therapy. However, the development of photothermal transduction agents (PTAs) for tumor-specific accumulation and precision imaging, avoiding toxicity to the surrounding healthy tissue, is still challenging. Herein, a cyclooxygenase-2-specific small-organic-molecule-based PTA (Cy7-TCF-IMC) is developed, which can self-assemble into nanosaucers having unique photothermal and photoacoustic properties. Specifically, the self-assembling nature of Cy7-TCF-IMC affords preferential accumulation in tumors arising from synergistic passive enhanced permeability and retention effects and active targeting for precision theranostics. Antitumor therapy results show that these Cy7-TCF-IMC nanosaucers are highly photoacoustic imaging-guided PTAs for tumor ablation. These findings suggest the self-assembled Cy7-TCF-IMC nanosaucer represents a new paradigm as a single-component supramolecular medicine that can synergistically optimize passive and active targeting, thereby improving the therapeutic index of cancer and future clinical outcomes.

Charge Transfer Metal-Organic Framework Containing Redox-Active TTF/NDI Units for Highly Efficient Near-Infrared Photothermal Conversion

Metal-organic frameworks (MOFs), as a class of new inorganic-organic hybrid crystal materials, could have important applications in near-infrared (NIR) photothermal conversion. Herein, a new charge-transfer MOF (Co-MOF) with mixed ligands of H₄ TTFTB and bpmNDI incorporating redox-active tetrathiafulvalene/naphthalene diimide (TTF/NDI) units into one system is reported. Due to the presence of TTF/NDI oxidative and reductive couples, stable radicals can be observed in the MOF. In addition, charge transfer from the electron donor (TTF) to the acceptor (NDI) results in a broad absorption in the NIR region. The Co-MOF exhibited an efficient photothermal effect induced by irradiation with a NIR laser. Under the 808 nm laser (0.7 W cm^-2 ) illumination, the temperature of the Co-MOF increased from room temperature to 201 °C in only 10 s. Furthermore, a series of polydimethylsiloxane (PDMS) films doped with trace amounts of Co-MOF showed efficient NIR photothermal conversion. When a Co-MOF@PDMS (0.6 wt %) film is irradiated by 808 nm laser with power of 0.5 W cm^-2 , it's temperature can reach a plateau at 62 °C from 20 °C within 100 s. Our experimental results from the Co-MOF@PDMS film demonstrate that the effectiveness and feasibility of the material is promising for photothermal applications.

Precise Molecular Engineering of Small Organic Phototheranostic Agents toward Multimodal Imaging-Guided Synergistic Therapy

Precise molecular engineering is the most fundamental and even a great challenging task for the development of small organic fluorophores used as phototheranostic agents in multimodal imaging-guided synergistic therapy. To the best of our knowledge, there have been no previous reports regarding the fine fabrication of molecular structure from a proof-of-concept study, providing a single molecule with all phototheranostic modalities. Herein, an electron donating-accepting (D-A) system is constructed by using triphenylamine derivatives as donors and diverse electron-deficient partners as acceptors, yielding aggregation-induced emission luminogens with tunable emission wavelength (up to 933 nm) and light absorption capability (ε up to 6.9 × 10⁴ M^-1 cm^-1). Notably, by integrating the spin-orbit coupling-promoted carbonyl group and the strong stretching vibrations of -CN to the D-A systems, a highly performing phototheranostic agent, namely, MeTIC, is constructed. When encapsulating MeTIC into nanovehicles, the obtained MeTIC nanoparticles show excellent performance in multimodality theranostics for cancer treatment. This work is expected to provide an organic phototheranostic agent designing principle for potential clinical trials.

A Diradicaloid Small Molecular Nanotheranostic with Strong Near-Infrared Absorbance for Effective Cancer Photoacoustic Imaging and Photothermal Therapy

Organic small molecule-based phototheranostics hold great promise for clinical translation by virtue of their distinct chemical structure, easy reproducibility, and high purity. However, reported molecular agents typically have relatively low optical absorbances, particularly over the near-infrared (NIR) region, and this limits their phototheranostic performance. Herein, we first exploit a diradicaloid molecular structure for enhancing NIR absorption to facilitate efficient photoacoustic imaging (PAI)-guided photothermal therapy (PTT). The donor-acceptor interaction in the diradicaloid molecule (DRM) leads to strong charge transfer resulting on obvious diradical characteristics, which is beneficial for NIR absorption. The DRM possesses excellent light-harvesting ability, with a mass extinction coefficient of ∼220 L g^-1 cm^-1, which is much higher than those (∼5-100 L g^-1 cm^-1) of typical organic molecules. After assembling into nanoparticles, they show good water dispersibility, good photostability, and impressive performance for PAI-guided PTT in vitro and in vivo. The impressive in vitro and in vivo performances show that developing small molecules with diradicaloid structures can be an effective approach for enhancing NIR harvesting capability for biomedical applications.

An All-Round Athlete on the Track of Phototheranostics: Subtly Regulating the Balance between Radiative and Nonradiative Decays for Multimodal Imaging-Guided Synergistic Therapy

Aiming to achieve versatile phototheranostics with the integrated functionalities of multiple diagnostic imaging and synergistic therapy, the optimum use of dissipated energy through both radiative and nonradiative pathways is definitely appealing, yet a significantly challenging task. To the best of the knowledge, there have been no previous reports on a single molecular species effective at affording all phototheranostic modalities including fluorescence imaging (FLI), photoacoustic imaging (PAI), photothermal imaging (PTI), photodynamic therapy (PDT), and photothermal therapy (PTT). Herein, a simple and highly powerful one-for-all phototheranostics based on aggregation-induced emission (AIE)-active fluorophores is tactfully designed and constructed. Thanks to its strong electron donor-acceptor interaction and finely modulated intramolecular motion, the AIE fluorophore-based nanoparticles simultaneously exhibit bright near-infrared II (NIR-II) fluorescence emission, efficient reactive oxygen species generation, and high photothermal conversion efficiency upon NIR irradiation, indicating the actualization of a balance between radiative and nonradiative energy dissipations. Furthermore, the unprecedented performance on NIR-II FLI-PAI-PTI trimodal-imaging-guided PDT-PTT synergistic therapy is demonstrated by the precise tumor diagnosis and complete tumor elimination outcomes. This study thus brings a new insight into the development of superior versatile phototheranostics for practical cancer theranostics.

Energy-converting biomaterials for cancer therapy: Category, efficiency, and biosafety

Energy-converting biomaterials (ECBs)-mediated cancer-therapeutic modalities have been extensively explored, which have achieved remarkable benefits to overwhelm the obstacles of traditional cancer-treatment modalities. Energy-driven cancer-therapeutic modalities feature their distinctive merits, including noninvasiveness, low mammalian toxicity, adequate therapeutic outcome, and optimistical synergistic therapeutics. In this advanced review, the prevailing mainstream ECBs can be divided into two sections: Reactive oxygen species (ROS)-associated energy-converting biomaterials (ROS-ECBs) and hyperthermia-related energy-converting biomaterials (H-ECBs). On the one hand, ROS-ECBs can transfer exogenous or endogenous energy (such as light, radiation, ultrasound, or chemical) to generate and release highly toxic ROS for inducing tumor cell apoptosis/necrosis, including photo-driven ROS-ECBs for photodynamic therapy, radiation-driven ROS-ECBs for radiotherapy, ultrasound-driven ROS-ECBs for sonodynamic therapy, and chemical-driven ROS-ECBs for chemodynamic therapy. On the other hand, H-ECBs could translate the external energy (such as light and magnetic) into heat for killing tumor cells, including photo-converted H-ECBs for photothermal therapy and magnetic-converted H-ECBs for magnetic hyperthermia therapy. Additionally, the biosafety issues of ECBs are expounded preliminarily, guaranteeing the ever-stringent requirements of clinical translation. Finally, we discussed the prospects and facing challenges for constructing the new-generation ECBs for establishing intriguing energy-driven cancer-therapeutic modalities. This article is categorized under: Nanotechnology Approaches to Biology >Nanoscale Systems in Biology.