Simultaneous Enhancement of the Long-Wavelength NIR-II Brightness and Photothermal Performance of Semiconducting Polymer Nanoparticles

Achieving Ultrabright NIR-II Nanofluorophore for In Vivo Imaging by Inhibiting H-Aggregates Formation

Small molecules with an acceptor-donor-acceptor (A-D-A) structure, featuring a fused-ring core as the donor and two electron-withdrawing end groups as acceptor units, represent a potential option for NIR-II fluorophores, benefiting from their narrow bandgaps, superior light-harvesting capabilities, and exceptional photostabilities. However, their planar conformations predispose them to forming H-aggregates during self-assembly, leading to significantly reduced fluorescence quantum yield (QY) of the resulting nanofluorophores. Herein, we report a small molecule, PF8CN, with a terminal unit-A-D-A-terminal unit structure. The terminal units of 3,5-bis(octyloxy)phenyl group result in a twisted conformation for PF8CN, preventing face-to-face stacking and thereby inhibiting the formation of H-aggregates. Consequently, the NIR-II fluorescence QY of PF8CN NPs is 3.8 times that of the model nanofluorophore (F8CN NPs), which contains a substantial amount of H-aggregates. The NIR-II brightness of PF8CN NPs is 5.3- and 14.9-times that of F8CN NPs and ICG/FBS, respectively, at an equal molar concentration. Such ultrahigh NIR-II brightness of PF8CN NPs allows us to perform long-term and real-time NIR-II fluorescence imaging of cerebral and hindlimb vessels, as well as the thrombolytic process. This work provides an effective method for producing nanofluorophores with ultrahigh NIR-II brightness, positioning PF8CN NPs as a strong contender in the field of NIR-II nanofluorophores.

Recent advances of versatile fluorophores for multifunctional biomedical imaging in the NIR-II region

Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) enables high-resolution visualization of deep-tissue biological architecture and physiopathological events, due to the reduced light absorption, scattering and tissue autofluorescence. Numerous versatile NIR-II fluorescent probes have been reported over the past decades. In this review, we first provide a detailed account of the advantages of fluorescence imaging in the NIR-II region. Following this, the classification, design and performance optimization strategies of NIR-II fluorescent probes are systematically discussed, along with a broad range of biomedical applications in vivo. Finally, the discussion extends to the next generation of fluorescent probes for in vivo imaging and the challenges and perspectives for the clinical translation of fluorescence imaging technology in the NIR-II region.

Rational Design of NIR-II Emitting Conjugated Polymer Derived Nanoparticles for Image-Guided Cancer Interventions

Due to the reduced absorption, light scattering, and tissue autofluorescence in the NIR-II (1000-1700 nm) region, significant efforts are underway to explore diverse material platforms for in vivo fluorescence imaging, particularly for cancer diagnostics and image-guided interventions. Of the reported imaging agents, nanoparticles derived from conjugated polymers (CPNs) offer unique advantages to alternative materials including biocompatibility, remarkable absorption cross-sections, exceptional photostability, and tunable emission behavior independent of cell labeling functionalities. Herein, the current state of NIR-II emitting CPNs are summarized and structure-function-property relationships are highlighted that can be used to elevate the performance of next-generation CPNs. Methods for particle processing and incorporating cancer targeting modalities are discussed, as well as detailed characterization methods to improve interlaboratory comparisons of novel materials. Contemporary methods to specifically apply CPNs for cancer diagnostics and therapies are then highlighted. This review not only summarizes the current state of the field, but offers future directions and provides clarity to the advantages of CPNs over other classes of imaging agents.

High-Performance NIR-II Fluorescent Type I/II Photosensitizer Enabling Augmented Mild Photothermal Therapy of Tumors by Disrupting Heat Shock Proteins

NIR-II fluorescent photosensitizers as phototheranostic agents hold considerable promise in the application of mild photothermal therapy (MPTT) for tumors, as the reactive oxygen species generated during photodynamic therapy can effectively disrupt heat shock proteins. Nevertheless, the exclusive utilization of these photosensitizers to significantly augment the MPTT efficacy has rarely been substantiated, primarily due to their insufficient photodynamic performance. Herein, the utilization of high-performance NIR-II fluorescent type I/II photosensitizer (AS21:4) is presented as a simple but effective nanoplatform derived from molecule AS2 to enhance the MPTT efficacy of tumors without any additional therapeutic components. By taking advantage of heavy atom effect, AS21:4 as a type I/II photosensitizer demonstrates superior efficacy in producing 1O2 (1O2 quantum yield = 12.4%) and O2 •- among currently available NIR-II fluorescent photosensitizers with absorption exceeding 800 nm. In vitro and in vivo findings demonstrate that the 1O2 and O2 •- generated from AS21:4 induce a substantial reduction in the expression of HSP90, thereby improving the MPTT efficacy. The remarkable phototheranostic performance, substantial tumor accumulation, and prolonged tumor retention of AS21:4, establish it as a simple but superior phototheranostic agent for NIR-II fluorescence imaging-guided MPTT of tumors.

Planar-structured thiadiazoloquinoxaline-based NIR-II dye for tumor phototheranostics

Second near-infrared (NIR-II) fluorescence imaging shows huge application prospects in clinical disease diagnosis and surgical navigation, while it is still a big challenge to exploit high performance NIR-II dyes with long-wavelength absorption and high fluorescence quantum yield. Herein, based on planar π-conjugated donor-acceptor-donor systems, three NIR-II dyes (TP-DBBT, TP-TQ1, and TP-TQ2) were synthesized with bulk steric hindrance, and the influence of acceptor engineering on absorption/emission wavelengths, fluorescence efficiency and photothermal properties was systematically investigated. Compared with TP-DBBT and TP-TQ2, the TP-TQ1 based on 6,7-diphenyl-[1,2,5]thiadiazoloquinoxaline can well balance absorption/emission wavelengths, NIR-II fluorescence brightness and photothermal effects. And the TP-TQ1 nanoparticles (NPs) possess high absorption ability at a peak absorption of 877 nm, with a high relative quantum yield of 0.69% for large steric hindrance hampering the close π-π stacking interactions. Furthermore, the TP-TQ1 NPs show a desirable photothermal conversion efficiency of 48% and good compatibility. In vivo experiments demonstrate that the TP-TQ1 NPs can serve as a versatile theranostic agent for NIR-II fluorescence/photoacoustic imaging-guided tumor phototherapy. The molecular planarization strategy provides an approach for designing efficient NIR-II fluorophores with extending absorption/emission wavelength, high fluorescence brightness, and outstanding phototheranostic performance.

Gene and Photothermal Combination Therapy: Principle, Materials, and Amplified Anticancer Intervention

Gene therapy (GT) and photothermal therapy (PTT) have emerged as promising alternatives to chemotherapy and radiotherapy for cancer treatment, offering noninvasiveness and reduced side effects. However, their efficacy as standalone treatments is limited. GT exhibits slow response rates, while PTT is confined to local tumor ablation. The convergence of GT and PTT, known as GT-PTT, facilitated by photothermal gene nanocarriers, has attracted considerable attention across various disciplines. In this integrated approach, GT reciprocates PTT by sensitizing cellular response to heat, while PTT benefits GT by improving gene translocation, unpacking, and expression. Consequently, this integration presents a unique opportunity for cancer therapy with rapid response and improved effectiveness. Extensive efforts over the past few years have been dedicated to the development of GT-PTT, resulting in notable achievements and rapid progress from the laboratory to potential clinical applications. This comprehensive review outlines recent advances in GT-PTT, including synergistic mechanisms, material systems, imaging-guided therapy, and anticancer applications. It also explores the challenges and future prospects in this nascent field. By presenting innovative ideas and insights into the implementation of GT-PTT for enhanced cancer therapy, this review aims to inspire further progress in this promising area of research.

Self-assembly of three-dimensional liver organoids: virtual reconstruction via endocytosed polymer dots for refactoring the fine structure

In vitro culture of organoids holds considerable promise for the treatment of diseases or the provision of artificial organs. Traditional 2D differentiation from mesenchymal stem cells (MSCs) faces challenges in replicating the development of embryonic organs at the cellular level; conversely, the cultivation of 3D organoids exhibits potential for application. It is crucial for clinicians and technology researchers to acquire insights into organoid tissue differentiation, autonomous morphogenesis, as well as 3D assembly processes in vitro. In this investigation, novel 3D organoids capable of engendering complex liver-like tissues in vitro were cultured, and a class of high-luminance semiconductor polymer dots (Pdots) was employed to monitor the self-assembly process of 3D liver organoid tissues and cellular interaction and migration dynamics. Three-dimensional liver-bud (3D-LB) organoid tissues were derived through the interplay of induced MSCs, Wharton's Jelly, and human umbilical vein endothelial cells (HUVECs), and their structural characteristics were determined during the liver-bud organoid development; ultimately, the co-cultured organoid spatial cellular clusters resembling a truffle were successfully replicated. Utilizing R8-Pdots with remarkable resolution and biocompatibility, the structural elements of functional and vascularized organs derived from liver organoid tissues were adeptly reconstituted, and this investigation shall contribute to a further understanding of human hepato-developmental physiology and liver-disease modeling.

Near-Infrared-II Fluorophore with Inverted Dependence of Fluorescence Quantum Yield on Polarity as Potent Phototheranostics for Fluorescence-Image-Guided Phototherapy of Tumors

Organic phototheranostics simultaneously having fluorescence in the second near-infrared (NIR-II, 1000-1700 nm) window, and photothermal and photodynamic functions possess great prospects in tumor diagnosis and therapy. However, such phototheranostics generally suffer from low brightness and poor photodynamic performance due to severe solvatochromism. Herein, an organic NIR-II fluorophore AS1, which possesses an inverted dependence of fluorescence quantum yield on polarity, is reported to serve as potent phototheranostics for tumor diagnosis and therapy. After encapsulation of AS1 into nanostructures, the obtained phototheranostics (AS1R ) exhibit high extinction coefficients (e.g., 68200 L mol-1  cm-1 at 808 nm), NIR-II emission with high fluorescence quantum yield up to 4.7% beyond 1000 nm, photothermal conversion efficiency of ≈65%, and 1 O2 quantum yield up to 4.1%. The characterization of photophysical properties demonstrates that AS1R is superior to other types of organic phototheranostics in brightness, photothermal effect, and photodynamic performance at the same mass concentration. The excellent phototheranostic performance of AS1R enables clear visualization and complete elimination of tumors using a single and low injection dose. This study demonstrates the merits and prospects of NIR-II fluorophore with inverted polarity dependence of fluorescence quantum yield as high-performance phototheranostic agents for fluorescence imaging and phototherapy of tumors.

Photoactive oligomer with D-D'-A-D'-D''-D'-A-D'-D scaffold for high-efficiency NIR-II phototheranostics

A D-D'-A-D'-D''-D'-A-D'-D type photoactive oligomer (O-BT) based nanoparticles (NPs) were prepared for biomedical application. The O-BT NPs possessed a high extinction coefficient, excellent hyperthermia generation ability, satisfactory NIR-II fluorescence emission, and good batch-to-batch reproducibility, and could be used as high-efficiency phototheranostics for photothermal therapy and NIR-II fluorescence imaging.

Precise Planar-Twisted Molecular Engineering to Construct Semiconducting Polymers with Balanced Absorption and Quantum Yield for Efficient Phototheranostics

Semiconducting polymers (SPs) have shown great feasibility as candidates for near-infrared-II (NIR-II) fluorescence imaging-navigated photothermal therapy due to their strong light-harvesting ability and flexible tunability. However, the fluorescence signal of traditional SPs tends to quench in their aggregate states owing to the strong π-π stacking, which can lead to the radiative decay pathway shutting down. To address this issue, aggregation-induced emission effect has been used as a rational tactic to boost the aggregate-state fluorescence of NIR-II emitters. In this contribution, we developed a precise molecular engineering tactic based on the block copolymerizations that integrate planar and twisted segments into one conjugated polymer backbone, providing great flexibility in tuning the photophysical properties and photothermal conversion capacity of SPs. Two monomers featured with twisted and planar architectures, respectively, were tactfully incorporated via a ternary copolymerization approach to produce a series of new SPs. The optimal copolymer (SP2) synchronously shows desirable absorption ability and good NIR-II quantum yield on the premise of maintaining typical aggregation-induced emission characteristics, resulting in balanced NIR-II fluorescence brightness and photothermal property. Water-dispersible nanoparticles fabricated from the optimal SP2 show efficient photothermal therapeutic effects both in vitro and in vivo. The in vivo investigation reveals the distinguished NIR-II fluorescence imaging performance of SP2 nanoparticles and their photothermal ablation toward tumor with prominent tumor accumulation ability and excellent biocompatibility.

Conjugated Polymer Nanoparticles for Tumor Theranostics

Water-dispersible conjugated polymer nanoparticles (CPNs) have demonstrated great capabilities in biological applications, such as in vitro cell/subcellular imaging and biosensing, or in vivo tissue imaging and disease treatment. In this review, we summarized the recent advances of CPNs used for tumor imaging and treatment during the past five years. CPNs with different structures, which have been applied to in vivo solid tumor imaging (fluorescence, photoacoustic, and dual-modal) and treatment (phototherapy, drug carriers, and synergistic therapy), are discussed in detail. We also demonstrated the potential of CPNs as cancer theranostic nanoplatforms. Finally, we discussed current challenges and outlooks in this field.

Incorporation of Robust NIR-II Fluorescence Brightness and Photothermal Performance in a Single Large π-Conjugated Molecule for Phototheranostics

Second near-infrared (NIR-II, 1000-1700 nm) window fluorescence imaging-guided photothermal therapy probes are promising for precise cancer phototheranostics. However, most of the currently reported probes do not demonstrate high NIR-II fluorescent brightness (molar absorption coefficient (ε) × quantum yield (QY)) and photothermal performance (ε × photothermal conversion efficiency (PCE)) in a single molecule. Herein, a versatile strategy to solve this challenge is reported by fabricating a large π-conjugated molecule (BNDI-Me) with a rigid molecular skeleton and flexible side groups. The proposed BNDI-Me nanoprobe boosts the ε and simultaneously optimizes its QY and PCE. Therefore, high NIR-II fluorescent brightness (ε × QY = 2296 m^-1 cm^-1 ) and strong photothermal performance (ε × PCE = 82 000) are successfully incorporated in a single small molecule, and, to the best of knowledge, either of these two parameters is better than the best currently available fluorescent or photothermal probes. Thus, superior NIR-II imaging effect in vivo and high photothermal tumor inhibition rate (81.2%) at low systemic injection doses are obtained. The work provides further insights into the relationship of photophysical mechanisms and structures, and presents promising molecular design guidelines for the integration of more efficient multiple theranostic functions in a single molecule.

Molecular Oligomerization and Donor Engineering Strategies for Achieving Superior NIR-II Fluorescence Imaging and Thermotherapy under 1064 nm Laser Irradiation

An enormous challenge still exists for designing molecules with the second near-infrared (NIR-II, 1000-1700 nm) window absorption, NIR-II fluorescence emission, and batch-to-batch reproducibility, which is the premise for high-performance NIR-II phototheranostics. Although organic small molecules and polymers have been largely explored for phototheranostics, it is difficult to satisfy the above three elements simultaneously. In this work, molecular oligomerization (the general structure is S-D-A-D'-A-D-S) and donor engineering (changing the donor linker D') strategies are applied to design phototheranostic agents. Such strategies are proved to be efficient in adjusting molecular configuration and energy level, affecting the optical and thermal properties. Three oligomers (O-T, O-DT, and O-Q) are further prepared into water-soluble nanoparticles (NPs). Particularly, the O-T NPs exhibit a higher molar extinction coefficient at 1064 nm (≈4.3-fold of O-DT NPs and ≈4.8-fold of O-Q NPs). Furthermore, the O-T NPs show the highest NIR-II fluorescence brightness and heating capacity (PCE = 73%) among the three NPs under 1064 nm laser irradiation and served as agents for NIR-II imaging guided in vivo photothermal therapy. Overall, by using molecular oligomerization and donor engineering strategies, a powerful example of constructing high-performance NIR-II phototheranostics for clinical translation is given.

Effective design of organic luminogens for near-infrared-II fluorescence imaging and photo-mediated therapy

Due to their electron coupling capability, organic luminescent materials exhibit powerful optoelectronic features that are responsible for their light-harvesting and light-amplification properties. The extensive modification of conjugated systems has shown significant improvement in their photonic properties thus broadening their applicability in photo-mediated imaging and photo-based treatment. Organic luminogens with emission in the near-infrared second region are found attractive not only for their deeper penetrating power but also for accurate visual imaging superiority with higher temporal resolution and spatial resolution suitable for tumor precision treatment. In this review, we underscore the latest development in organic luminogens (conjugated polymers and small molecules), focusing on chemical design, molecular engineering, and their applications in the scope of bioimaging followed by photo-assisted treatment, including photodynamic therapy (PDT), photothermal therapy (PTT), and immunotherapy ablation. Organic luminogens integrated with an aggregation-induced emission feature significantly optimize their physicochemical properties to act as quintessential nanoplatforms for controllable image-guided therapy. In conclusion, we clarify the limitations and challenges and provide insights into how to design organic dyes with improved safety for potential clinical applications.

Recent Advances of NIR-II Emissive Semiconducting Polymer Dots for In Vivo Tumor Fluorescence Imaging and Theranostics

Accurate diagnosis and treatment of tumors, one of the top global health problems, has always been the research focus of scientists and doctors. Near-infrared (NIR) emissive semiconducting polymers dots (Pdots) have demonstrated bright prospects in field of in vivo tumor fluorescence imaging owing to some of their intrinsic advantages, including good water-dispersibility, facile surface-functionalization, easily tunable optical properties, and good biocompatibility. During recent years, much effort has been devoted to developing Pdots with emission bands located in the second near-infrared (NIR-II, 1000-1700 nm) region, which hold great advantages of higher spatial resolution, better signal-to-background ratios (SBR), and deeper tissue penetration for solid-tumor imaging in comparison with the visible region (400-680 nm) and the first near-infrared (NIR-I, 680-900 nm) window, by virtue of the reduced tissue autofluorescence, minimal photon scattering, and low photon absorption. In this review, we mainly summarize the latest advances of NIR-II emissive semiconducting Pdots for in vivo tumor fluorescence imaging, including molecular engineering to improve the fluorescence quantum yields and surface functionalization to elevate the tumor-targeting capability. We also present several NIR-II theranostic Pdots used for integrated tumor fluorescence diagnosis and photothermal/photodynamic therapy. Finally, we give our perspectives on future developments in this field.

D-A Type NIR-II Organic Molecules: Strategies for the Enhancement Fluorescence Brightness and Applications in NIR-II Fluorescence Imaging-Navigated Photothermal Therapy

NIR-II fluorescence imaging (NIR-II FI) and photothermal therapy (PTT) have received broad attentions in precise tumor diagnosis and effective treatment attributed to high-resolution and deep tissue imaging, negligible invasivity, and high-efficiency treatment. Although many fluorescent molecules have been designed and conducted for NIR-II FI and PTT, it is still an enormous challenge for researchers to pioneer some rational design guidelines to improve fluorescence brightness. Organic D-A-type molecules, including small molecules and conjugated polymers, can be designed and developed to improve fluorescence brightness due to their tunable and easy functionalized chemical structures, allowing molecules tailored photophysical properties. In this review, some approaches to the development and design strategies of D-A type small molecules and conjugated polymers for the enhancement of fluorescence brightness are systemically introduced. Meanwhile, some applications of PTT and PTT-based combination therapy (such as PDT, chemotherapy, or gas therapy) assisted by NIR-II FI-based single or multiimaging technologies are classified and represented in detail as well. Finally, the current issues and challenges of NIR-II organic molecules in NIR-II FI-navigated PTT are summarized and discussed, which gives some guidelines for the future development direction of NIR-II organic molecules for NIR-II FI-navigated PTT.

Chiral nanomaterials for biosensing, bioimaging, and disease therapies

Chiral plasmonic nanomaterials for biosensing, bioimaging and disease therapy.

Thiadiazoloquinoxaline derivatives-based NIR-II organic molecules for NIR-II fluorescence imaging and photothermal therapy

NIR-II FI have emerged as a promising imaging tool for in vivo precise diagnosis and visualization towards various diseases, ascribed to its merits of attenuated light scattering and tissue absorption...