Fluorination Enhances NIR-II Fluorescence of Polymer Dots for Quantitative Brain Tumor Imaging

NIR-II Fluorescence Imaging for In Vivo Quantitative Analysis

In vivo real-time qualitative and quantitative analysis is essential for the diagnosis and treatment of diseases such as tumors. Near-infrared-II (NIR-II, 1000-1700 nm) bioimaging is an emerging visualization modality based on fluorescent materials. The advantages of NIR-II region fluorescent materials in terms of reduced photon scattering and low tissue autofluorescence enable NIR-II bioimaging with high resolution and increasing depth of tissue penetration, and thus have great potential for in vivo qualitative and quantitative analysis. In this review, we first summarize recent advances in NIR-II imaging, including fluorescent probe selection, quantitative analysis strategies, and imaging. Then, we describe in detail representative applications to illustrate how NIR-II fluorescence imaging has become an important tool for in vivo quantitative analysis. Finally, we describe the future possibilities and challenges of NIR-II fluorescence imaging.

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

The expansion applications of semiconducting polymer dots (Pdots) among optical nanomaterial field have long posed a challenge for researchers, promoting their intelligent application in multifunctional nano-imaging systems and integrated nanomedicine carriers for diagnosis and treatment. Despite notable progress, several inadequacies still persist in the field of Pdots, including the development of simplified near-infrared (NIR) optical nanoprobes, elucidation of their inherent biological behavior, and integration of information processing and nanotechnology into biomedical applications. This review aims to comprehensively elucidate the current status of Pdots as a classical nanophotonic material by discussing its advantages and limitations in terms of biocompatibility, adaptability to microenvironments in vivo, etc. Multifunctional integration and surface chemistry play crucial roles in realizing the intelligent application of Pdots. Information visualization based on their optical and physicochemical properties is pivotal for achieving detection, sensing, and labeling probes. Therefore, we have refined the underlying mechanisms and constructed multiple comprehensive original mechanism summaries to establish a benchmark. Additionally, we have explored the cross-linking interactions between Pdots and nanomedicine, potential yet complete biological metabolic pathways, future research directions, and innovative solutions for integrating diagnosis and treatment strategies. This review presents the possible expectations and valuable insights for advancing Pdots, specifically from chemical, medical, and photophysical practitioners' standpoints.

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.

NIR-II Absorption/Fluorescence of D-A π-Conjugated Polymers Composed of Strong Electron Acceptors Based on Boron-Fused Azobenzene Complexes

Luminescence in the second near-infrared (NIR-II, 1,000-1,700 nm) window is beneficial especially for deep tissue imaging and optical sensors because of intrinsic high permeability through various media. Strong electron-acceptors with low-lying lowest unoccupied molecular orbital (LUMO) energy levels are a crucial unit for donor-acceptor (D-A) π-conjugated polymers (CPs) with the NIR-II emission property, however, limited kinds of molecular skeletons are still available. Herein, D-A CPs involving fluorinated boron-fused azobenzene complexes (BAz) with enhanced electron-accepting properties are reported. Combination of fluorination at the azobenzene ligand and trifluoromethylation at the boron can effectively lower the LUMO energy level down to -4.42 eV, which is much lower than those of conventional strong electron-acceptors. The synthesized series of CPs showed excellent absorption/fluorescence property in solution over a wide NIR range including NIR-II. Furthermore, owing to the inherent solid-state emissive property of the BAz skeleton, obvious NIR-II fluorescence from the film (up to λFL=1213 nm) and the nanoparticle in water (λFL=1036 nm, brightness=up to 29 cm-1 M-1) were observed, proposing that our materials are applicable for developing next-generation of NIR-II luminescent materials.

Semiconducting Polymer Dots for Dual-Wavelength Differential Background-Suppressed Photoacoustic Imaging

Photoacoustic imaging (PAI) can sensitively detect regions and substances with strong optical absorption, which means that diseased tissue can be imaged with high contrast in the presence of surrounding healthy tissue through the photoacoustic effect. However, its signal intensity and resolution may be limited by background signals generated by endogenous chromophores such as melanin and hemoglobin. A feasible method for practical application of this so-called background-suppressed PAI is still lacking. In this work, a dual-wavelength differential background noise-suppressed photoacoustic tomography is developed based on organic semiconducting polymer dots (Pdots). The Pdots have a strong absorption peak at 945 nm, and then the absorption decreases sharply with the increase of wavelength, and the absorption intensity drops to only about a quarter of the original value at 1050 nm. The present system significantly suppresses the strong background noise of blood through dual-wavelength differential PAI, enabling precise monitoring of the distribution information of theranostic agents in diseased tissues. The signal-to-noise ratio of the theranostic agent distribution map is increased by about 20 dB. This work provides a platform for real-time and accurate monitoring of tumors and drugs, which helps avoid damage to healthy tissue during treatment and has clinical significance in cancer treatment.

Recent Progress on Second Near-Infrared Emitting Carbon Dots in Biomedicine

Second near-infrared (NIR-II) carbon dots, with absorption or emission between 1000 and 1700 nm, are gaining increasing attention in the biomaterial field due to their distinctive properties, which include straightforward preparation processes, stable photophysical characteristics, excellent biocompatibility, and low cost. As a result, there is a growing focus on the controlled synthesis and modulation of the photochemical and photophysical properties of NIR-II carbon dots, with the aim to further expand their biomedical applications, a current research hotspot. This account aims to provide a comprehensive overview of the recent advancements in NIR-II carbon dots within the biomedical field. The review will cover the following topics: (i) the design, synthesis, and purification of NIR-II carbon dots, (ii) the surface modification strategies, and (iii) the biomedical applications, particularly in the domain of cancer theranostics. Additionally, this account addresses the challenges encountered by NIR-II carbon dots and will outline future directions in the realm of cancer theranostics. By exploring carbon-based NIR-II biomaterials, we can anticipate that this contribution will garner increased attention and contribute to the development of next-generation advanced functional carbon dots, thereby offering enhanced tools and strategies in the biomedical field.

Polyvalent Aptamer-Functionalized NIR-II Quantum Dots for Targeted Theranostics in High PD-L1-Expressing Tumors

Ag2S quantum dots (QDs) show superior optical properties in the NIR-II region and display significant clinical potential with favorable biocompatibility. However, inherent defects of low targeting and poor solubility necessitate practical modification methods to achieve the theranostics of Ag2S QDs. Herein, we used rolling circle amplification (RCA) techniques to obtain long single-stranded DNA containing the PD-L1 aptamer and C-rich DNA palindromic sequence. The C-rich DNA palindromic sequences can specifically chelate Ag2+ and thus serve as a template to result in biomimetic mineralization and formation of pApt-Ag2S QDs. These QDs enable specific targeting and illuminate hot tumors with high PD-L1 expression effectively, serving as excellent molecular targeted probes. In addition, due to the high NIR-II absorption of Ag2S QDs, pApt-Ag2S QDs exhibit remarkable photothermal properties. And besides, polyvalent PD-L1 aptamers can recognize PD-L1 protein and effectively block the inhibitory signal of PD-L1 on T cells, enabling efficient theranostics through the synergistic effect of photothermal therapy and immune checkpoint blocking therapy. Summary, we enhance the biological stability and antibleaching ability of Ag2S QDs using long single-stranded DNA as a template, thereby establishing a theranostic platform that specifically targets PD-L1 high-expressing inflamed tumors and demonstrates excellent performance both in vitro and in vivo.

Organic Optoelectronic Materials: A Rising Star of Bioimaging and Phototherapy

Recently, many organic optoelectronic materials (OOMs), especially those used in organic light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic field-effect transistors (OFETs), are explored for biomedical applications including imaging and photoexcited therapies. In this review, recently developed OOMs for fluorescence imaging, photoacoustic imaging, photothermal therapy, and photodynamic therapy, are summarized. Relationships between their molecular structures, nanoaggregation structures, photophysical mechanisms, and properties for various biomedical applications are discussed. Mainly four kinds of OOMs are covered: thermally activated delayed fluorescence materials in OLEDs, conjugated small molecules and polymers in OSCs, and charge-transfer complexes in OFETs. Based on the OOMs unique optical properties, including excitation light wavelength and exciton dynamics, they are respectively exploited for suitable biomedical applications. This review is intended to serve as a bridge between researchers in the area of organic optoelectronic devices and those in the area of biomedical applications. Moreover, it provides guidance for selecting or modifying OOMs for high-performance biomedical uses. Current challenges and future perspectives of OOMs are also discussed with the hope of inspiring further development of OOMs for efficient biomedical applications.

Brightness Strategies toward NIR-II Emissive Conjugated Materials: Molecular Design, Application, and Future Prospects

Recent advances have been made in second near-infrared (NIR-II) fluorescence bioimaging and many related applications because of its advantages of deep penetration, high resolution, minimal invasiveness, and good dynamic visualization. To achieve high-performance NIR-II fluorescence bioimaging, various materials and probes with bright NIR-II emission have been extensively explored in the past few years. Among these NIR-II emissive materials, conjugated polymers and conjugated small molecules have attracted wide interest due to their native biosafety and tunable optical performance. This review summarizes the brightness strategies available for NIR-II emissive conjugated materials and highlights the recent developments in NIR-II fluorescence bioimaging. A concise, detailed overview of the molecular design and regulatory approaches is provided in terms of their high brightness, long wavelengths, and superior imaging performance. Then, various typical cases in which bright conjugated materials are used as NIR-II probes are introduced by providing step-by-step examples. Finally, the current problems and challenges associated with accessing NIR-II emissive conjugated materials for bright NIR-II fluorescence bioimaging are briefly discussed, and the significance and future prospects of these materials are proposed to offer helpful guidance for the development of NIR-II emissive materials.

X-ray Activated Nanoprodrug for Visualization of Cortical Microvascular Alterations and NIR-II Image-Guided Chemo-Radiotherapy of Glioblastoma

The permeability of the highly selective blood-brain barrier (BBB) to anticancer drugs and the difficulties in defining deep tumor boundaries often reduce the effectiveness of glioma treatment. Thus, exploring the combination of multiple treatment modalities under the guidance of second-generation near-infrared (NIR-II) window fluorescence (FL) imaging is considered a strategic approach in glioma theranostics. Herein, a hybrid X-ray-activated nanoprodrug was developed to precisely visualize the structural features of glioma microvasculature and delineate the boundary of glioma for synergistic chemo-radiotherapy. The nanoprodrug comprised down-converted nanoparticle (DCNP) coated with X-ray sensitive poly(Se-Se/DOX-co-acrylic acid) and targeted Angiopep-2 peptide (DCNP@P(Se-DOX)@ANG). Because of its ultrasmall size and the presence of DOX, the nanoprodrug could easily cross BBB to precisely monitor and localize glioblastoma via intracranial NIR-II FL imaging and synergistically administer antiglioblastoma chemo-radiotherapy through specific X-ray-induced DOX release and radiosensitization. This study provides a novel and effective strategy for glioblastoma imaging and chemo-radiotherapy.

The Balance Effect of π-π Electronic Coupling on NIR-II Emission and Photodynamic Properties of Highly Hydrophobic Conjugated Photosensitizers

Deep NIR organic phototheranostic molecules generally have large π-conjugation structures and show highly hydrophobic properties, thus, forming strong π-π stacking in the aqueous medium, which will affect the phototheranostic performance. Herein, an end-group strategy is developed to lift the performance of NIR-II emitting photosensitizers. Extensive characterizations reveal that the hydrogen-bonding interactions of the hydroxyl end group can induce a more intense π-π electronic coupling than the chlorination-mediated intermolecular forces. The results disclose that π-π stacking will lower fluorescence quantum yield but significantly benefit the photodynamic therapy (PDT) efficiency. Accordingly, an asymmetrically substituted derivative (BTIC-δOH-2Cl) is developed, which shows balanced phototheranostic properties with excellent PDT efficiency (14.6 folds of ICG) and high NIR-II fluorescence yield (2.27%). It proves the validity of the end-group strategy on controlling the π-π interactions and rational tuning the performance of NIR-II organic phototheranostic agents.

Nanocrystals for Deep-Tissue In Vivo Luminescence Imaging in the Near-Infrared Region

In vivo imaging technologies have emerged as a powerful tool for both fundamental research and clinical practice. In particular, luminescence imaging in the tissue-transparent near-infrared (NIR, 700-1700 nm) region offers tremendous potential for visualizing biological architectures and pathophysiological events in living subjects with deep tissue penetration and high imaging contrast owing to the reduced light-tissue interactions of absorption, scattering, and autofluorescence. The distinctive quantum effects of nanocrystals have been harnessed to achieve exceptional photophysical properties, establishing them as a promising category of luminescent probes. In this comprehensive review, the interactions between light and biological tissues, as well as the advantages of NIR light for in vivo luminescence imaging, are initially elaborated. Subsequently, we focus on achieving deep tissue penetration and improved imaging contrast by optimizing the performance of nanocrystal fluorophores. The ingenious design strategies of NIR nanocrystal probes are discussed, along with their respective biomedical applications in versatile in vivo luminescence imaging modalities. Finally, thought-provoking reflections on the challenges and prospects for future clinical translation of nanocrystal-based in vivo luminescence imaging in the NIR region are wisely provided.

Bromine Substitution Improves the Photothermal Performance of π-Conjugated Phototheranostic Molecules

NIR-II fluorescence imaging-guided photothermal therapy (PTT) has been widely investigated due to its great application potential in tumor theranostics. PTT is an effective and non-invasive tumor treatment method that can adapt to tumor hypoxia; nevertheless, simple and effective strategies are still desired to develop new materials with excellent PTT properties to meet clinical requirements. In this work, we developed a bromine-substitution strategy to enhance the PTT of A-D-A'-D-A π-conjugated molecules. The experimental results reveal that bromine substitution can notably enhance the absorptivity (ϵ) and photothermal conversion efficiency (PCE) of the π-conjugated molecules, resulting in the brominated molecules generating two times more heat (ϵ808 nm ×PCE) than their unsubstituted counterpart. We disclose that the enhanced photothermal properties of bromine-substituted π-conjugated molecules are a combined outcome of the heavy-atom effect, enhanced ICT effect, and more intense bromine-mediate intermolecular π-π stacking. Finally, the NIR-II tumor imaging capability and efficient PTT tumor ablation of the brominated π-conjugated materials demonstrate that bromine substitution is a promising strategy for developing future high-performance NIR-II imaging-guided PTT agents.

Oxyhaemoglobin saturation NIR-IIb imaging for assessing cancer metabolism and predicting the response to immunotherapy

In vivo quantitative assessment of oxyhaemoglobin saturation (sO2) status in tumour-associated vessels could provide insights into cancer metabolism and behaviour. Here we develop a non-invasive in vivo sO2 imaging technique to visualize the sO2 levels of healthy and tumour tissue based on photoluminescence bioimaging in the near-infrared IIb (NIR-IIb; 1,500-1,700 nm) window. Real-time dynamic sO2 imaging with a high frame rate (33 Hz) reveals the cerebral arteries and veins through intact mouse scalp/skull, and this imaging is consistent with the haemodynamic analysis results. Utilizing our non-invasive sO2 imaging, the tumour-associated-vessel sO2 levels of various cancer models are evaluated. A positive correlation between the tumour-associated-vessel sO2 levels and the basal oxygen consumption rate of corresponding cancer cells at the early stages of tumorigenesis suggests that cancer cells modulate the tumour metabolic microenvironment. We also find that a positive therapeutic response to the checkpoint blockade cancer immunotherapy could lead to a dramatic decrease of the tumour-associated-vessel sO2 levels. Two-plex dynamic NIR-IIb imaging can be used to simultaneously observe tumour-vessel sO2 and PD-L1, allowing a more accurate prediction of immunotherapy response.

Semiconducting Polymers for Cancer Immunotherapy

As a monumental breakthrough in cancer treatment, immunotherapy has attracted tremendous attention in recent years. However, one challenge faced by immunotherapy is the low response rate and the immune-related adverse events (irAEs). Therefore, it is important to explore new therapeutic strategies and platforms for boosting therapeutic benefits and decreasing the side effects of immunotherapy. In recent years, semiconducting polymer (SP), a category of organic materials with π-conjugated aromatic backbone, has been attracting considerable attention because of their outstanding characteristics such as excellent photophysical features, good biosafety, adjustable chemical flexibility, easy fabrication, and high stability. With these distinct advantages, SP is extensively explored for bioimaging and photo- or ultrasound-activated tumor therapy. Here, the recent advancements in SP-based nanomedicines are summarized for enhanced tumor immunotherapy. According to the photophysical properties of SPs, the cancer immunotherapies enabled by SPs with the photothermal, photodynamic, or sonodynamic functions are highlighted in detail, with a particular focus on the construction of combination immunotherapy and activatable nanoplatforms to maximize the benefits of cancer immunotherapy. Herein, new guidance and comprehensive insights are provided for the design of SPs with desired photophysical properties to realize maximized effectiveness of required biomedical applications.

pH-Responsive NIR-II phototheranostic agents for in situ tumor vascular monitoring and combined anti-vascular/photothermal therapy

Developing nanoplatforms integrating superior fluorescence imaging ability in second near-infrared (NIR-II) window and tumor microenvironment responsive multi-modal therapy holds great potential for real-time feedback of therapeutic efficacy and optimizing tumor inhibition. Herein, we developed a pH-sensitive pyrrolopyrrole aza-BODIPY-based amphiphilic molecule (PTG), which has a balanced NIR-II fluorescence brightness and photothermal effect. PTG is further co-assembled with a vascular disrupting agent (known as DMXAA) to prepare PTDG nanoparticles for combined anti-vascular/photothermal therapy and real-time monitoring of the tumor vascular disruption. Each PTG molecule has an active PT-3 core which is linked to two PEG chains via pH-sensitive ester bonds. The cleavage of ester bonds in the acidic tumor environment would tricker releases of DMXAA for anti-vascular therapy and further assemble PT-3 cores into micrometer particles for long term monitoring of the tumor progression. Furthermore, benefiting from the high brightness in the NIR-II region (119.61 M-1 cm-1) and long blood circulation time (t1/2 = 235.6 min) of PTDG nanoparticles, the tumor vascular disrupting process can be in situ visualized in real time during treatment. Overall, this study demonstrates a self-assembly strategy to build a pH-responsive NIR-II nanoplatform for real-time monitoring of tumor vascular disruption, long-term tracking tumor progression and combined anti-vascular/photothermal therapy.

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.

Near-infrared-II photoacoustic imaging and photo-triggered synergistic treatment of thrombosis via fibrin-specific homopolymer nanoparticles

The formation of an occlusive thrombus in the blood vessel is the main culprit for numerous life-threatening cardiovascular diseases that represent the leading cause of morbidity and mortality worldwide. Herein, we develop a polymer nanoplatform that integrates long-wavelength second near-infrared (NIR-II) photoacoustic imaging-based thrombosis detection and antithrombotic activity. We design and synthesize a semiconducting homopolymer with strong absorption in the NIR-II region and molecular motion that boosts photothermal conversion and photoacoustic signal. We dope the homopolymer with a thermosensitive nitric oxide donor to formulate a nanoplatform, on which a fibrin-specific ligand is functionalized to ensure selective thrombus targeting. We show that with strong NIR-II light harvesting capability, bright photoacoustic signal and active thrombus accumulation ability, the NIR-II photoacoustic nanoprobes are able to sensitively and selectively delineate thrombi. We find that the nanoplatform also displays rapid and efficient blood clot removal activity with nearly complete blood flow restoration in both carotid thrombosis models and low extremity arterial thrombosis models under NIR-II light trigger by integrating a thrombus-localized photothermal effect and on-demand nitric oxide release. This nanoplatform offers a versatile approach for the diagnosis and treatment of life-threatening diseases caused by various thrombotic disorders.

Space and Bond Synergistic Conjugation Controlling Multiple-Aniline NIR-II Absorption for Photoacoustic Imaging Guided Photothermal Therapy

Currently, clinical photothermal therapy (PTT) is greatly limited by the poor tissue penetration of the excitation light sources in visible (390-780 nm) and first near-infrared (NIR-I, 780-900 nm) window. Herein, based on space and bond synergistic conjugation, a multiple-aniline organic small molecule (TPD), is synthesized for high-efficiency second near-infrared (NIR-II, 900-1700 nm) photoacoustic imaging guided PTT. With the heterogeneity of six nitrogen atoms in TPD, the lone electrons on the nitrogen atom and the π bond orbital on the benzene ring form multielectron conjugations with highly delocalized state, which endowed TPD with strong NIR-II absorption (maximum peak at 925 nm). Besides, according to the single molecular reorganization, the alkyl side chains on TPD make more free space for intramolecular motion to enhance the photothermal conversion ability. Forming TPD nanoparticles (NPs) in J-aggregation, they show a further bathochromic-shifted absorbance (maximum peak at 976 nm) as well as a high photothermal conversion efficiency (66.7%) under NIR-II laser irradiation. In vitro and in vivo experiments demonstrate that TPD NPs can effectively inhibit the growth of tumors without palpable side effects. The study provides a novel NIR-II multiple-aniline structure based on multielectron hyperconjugation, and opens a new design thought for photothermal agents.

Near-Infrared II Semiconducting Polymer Dots: Chain Packing Modulation and High-Contrast Vascular Imaging in Deep Tissues

Fluorescence imaging in the second near-infrared (NIR-II) window has attracted considerable interest in investigations of vascular structure and angiogenesis, providing valuable information for the precise diagnosis of early stage diseases. However, it remains challenging to image small blood vessels in deep tissues because of the strong photon scattering and low fluorescence brightness of the fluorophores. Here, we describe our combined efforts in both fluorescent probe design and image algorithm development for high-contrast vascular imaging in deep turbid tissues such as mouse and rat brains with intact skull. First, we use a polymer blending strategy to modulate the chain packing behavior of the large, rigid, NIR-II semiconducting polymers to produce compact and bright polymer dots (Pdots), a prerequisite for in vivo fluorescence imaging of small blood vessels. We further developed a robust Hessian matrix method to enhance the image contrast of vascular structures, particularly the small and weakly fluorescent vessels. The enhanced vascular images obtained in whole-body mouse imaging exhibit more than an order of magnitude improvement in the signal-to-background ratio (SBR) as compared to the original images. Taking advantage of the bright Pdots and Hessian matrix method, we finally performed through-skull NIR-II fluorescence imaging and obtained a high-contrast cerebral vasculature in both mouse and rat models bearing brain tumors. This study in Pdot probe development and imaging algorithm enhancement provides a promising approach for NIR-II fluorescence vascular imaging of deep turbid tissues.

Carbonic anhydrase inhibitor-decorated semiconducting oligomer nanoparticles for active-targeting NIR-II fluorescence tumor imaging

Second near-infrared window (NIR-II) fluorescence imaging has shown great potential in the field of bioimaging. To achieve a better imaging effect, variety of NIR-II fluorescence probes have been designed and developed. Among them, semiconducting oligomers (SOs) have shown unique advantages including high photostability and quantum yield, making them promise in NIR-II fluorescence imaging. Herein, we design a SO nanoparticle (ASONi) for NIR-II fluorescence imaging of tumor. ASONi is composed of an azido-functionalized semiconducting oligomer as the NIR-II fluorescence emitter, and a benzene sulfonamide-ended DSPE-PEG (DSPE-PEG-CAi) as the stabilizer. Owing to the benzene sulfonamide groups on the surface, ASONi has the capability of targeting the carbonic anhydrase IX (CA IX) of MDA-MB-231 breast cancer cell. Compared with ASON without benzene sulfonamide groups on the surface, ASONi has a 1.4-fold higher uptake for MDA-MB-231 cells and 1.5-fold higher breast tumor accumulation after i.v. injection. The NIR-II fluorescence signal of ASONi can light the tumor up within 4 h, demonstrating its capability of active tumor targeting and NIR-II fluorescence imaging.

Engineered NIR-II fluorophores with ultralong-distance molecular packing for high-contrast deep lesion identification

The limited signal of long-wavelength near-infrared-II (NIR-II, 900-1880 nm) fluorophores and the strong background caused by the diffused photons make high-contrast fluorescence imaging in vivo with deep tissue disturbed still challenging. Here, we develop NIR-II fluorescent small molecules with aggregation-induced emission properties, high brightness, and maximal emission beyond 1200 nm by enhancing electron-donating ability and reducing the donor-acceptor (D-A) distance, to complement the scarce bright long-wavelength emissive organic dyes. The convincing single-crystal evidence of D-A-D molecular structure reveals the strong inhibition of the π-π stacking with ultralong molecular packing distance exceeding 8 Å. The delicately-designed nanofluorophores with bright fluorescent signals extending to 1900 nm match the background-suppressed imaging window, enabling the signal-to-background ratio of the tissue image to reach over 100 with the tissue thickness of ~4-6 mm. In addition, the intraluminal lesions with strong negatively stained can be identified with almost zero background. This method can provide new avenues for future long-wavelength NIR-II molecular design and biomedical imaging of deep and highly scattering tissues.

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.

Pyrrolopyrrole aza-BODIPY-based NIR-II fluorophores for in vivo dynamic vascular dysfunction visualization of vascular-targeted photodynamic therapy

Real-time monitoring vascular responses is crucial for evaluating the therapeutic effects of vascular-targeted photodynamic therapy (V-PDT). Herein, we developed a highly-stable and bright aggregation induced emission (AIE) fluorophore (PTPE3 NP) for dynamic fluorescence (FL) imaging of vascular dysfunction beyond 1300 nm window during V-PDT. The superior brightness (ϵ_maxΦ_{f>1000 nm} ≈ 180.05 M^-1 cm^-1) and high resolution of PTPE3 NP affords not only high-clarity images of whole-body and local vasculature (hindlimbs, mesentery, and tumor) but also high-speed video imaging for tracking blood circulation process. By virtue of the NPs' prolonged blood circulation time (t_1/2 ≈ 86.5 min) and excellent photo/chemical (pH, RONS) stability, mesenteric and tumor vascular dysfunction (thrombosis formation, vessel occlusion, and hemorrhage) can be successfully visualized during V-PDT by FL imaging for the first time. Furthermore, the reduction of blood flow velocity (BFV) can be monitored in real time for precisely evaluating efficacy of V-PDT. These provide a powerful approach for assessing vascular responses during V-PDT and promote the development of advanced fluorophores for biological imaging.

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.

Tracking tumor heterogeneity and progression with near-infrared II fluorophores

Heterogeneous cells are the main feature of tumors with unique genetic and phenotypic characteristics, which can stimulate differentially the progression, metastasis, and drug resistance. Importantly, heterogeneity is pervasive in human malignant tumors, and identification of the degree of tumor heterogeneity in individual tumors and progression is a critical task for tumor treatment. However, current medical tests cannot meet these needs; in particular, the need for noninvasive visualization of single-cell heterogeneity. Near-infrared II (NIR-II, 1000-1700 nm) imaging exhibits an exciting prospect for non-invasive monitoring due to the high temporal-spatial resolution. More importantly, NIR-II imaging displays more extended tissue penetration depths and reduced tissue backgrounds because of the significantly lower photon scattering and tissue autofluorescence than traditional the near-infrared I (NIR-I) imaging. In this review, we summarize systematically the advances made in NIR-II in tumor imaging, especially in the detection of tumor heterogeneity and progression as well as in tumor treatment. As a non-invasive visual inspection modality, NIR-II imaging shows promising prospects for understanding the differences in tumor heterogeneity and progression and is envisioned to have the potential to be used clinically.

Second Near-Infrared (NIR-II) Window for Imaging-Navigated Modulation of Brain Structure and Function

For a long time, optical imaging of the deep brain with high resolution has been a challenge. Recently, with the advance in second near-infrared (NIR-II) bioimaging techniques and imaging contrast agents, NIR-II window bioimaging has attracted great attention to monitoring deeper biological or pathophysiological processes with high signal-to-noise ratio (SNR) and spatiotemporal resolution. Assisted with NIR-II bioimaging, the modulation of structure and function of brain is promising to be noninvasive and more precise. Herein, in this review, first the advantage of NIR-II light in brain imaging from the interaction between NIR-II and tissue is elaborated. Then, several specific NIR-II bioimaging technologies are introduced, including NIR-II fluorescence imaging, multiphoton fluorescence imaging, and photoacoustic imaging. Furthermore, the corresponding contrast agents are summarized. Next, the application of various NIR-II bioimaging technologies in visualizing the characteristics of cerebrovascular network and monitoring the changes of the pathology signals will be presented. After that, the modulation of brain structure and function based on NIR-II bioimaging will be discussed, including treatment of glioblastoma, guidance of cell transplantation, and neuromodulation. In the end, future perspectives that would help improve the clinical translation of NIR-II light are proposed.

NIR-II Luminescent and Multi-Responsive Rare Earth Nanocrystals for Improved Chemodynamic Therapy

Chemodynamic therapy (CDT) based on the Fe²⁺-mediated Fenton reaction can amplify intracellular oxidative stress by producing toxic •OH. However, the high-dose need for Fe²⁺ delivery in tumors and its significant cytotoxicity to normal tissues set a challenge. Therefore, a controllable delivery to activate the Fenton reaction and enhance Fe²⁺ tumor accumulation has become an approach to solve this conflict. Herein, we report a rare-earth-nanocrystal (RENC)-based Fe²⁺ delivery system using light-control techniques and DNA nanotechnology to realize programmable Fe²⁺ delivery. Ferrocenes, the source of Fe²⁺, are modified on the surface of RENCs through pH-responsive DNAs, which are further shielded by a PEG layer to elongate blood circulation and "turn off" the cytotoxicity of ferrocene. The up-/down-conversion dual-mode emissions of RENCs endow the delivery system with both capabilities of diagnosis and delivery control. The down-conversion NIR-II fluorescence can locate tumors. Consequently, up-conversion UV light spatiotemporally activates the catalytic activity of Fe²⁺ by shedding off the protective PEG layer. The exposed ferrocene-DNAs not only can "turn on" Fenton catalytic activity but also respond to tumor acidity, driving cross-linking and enhanced Fe²⁺ enrichment in tumors by 4.5-fold. Accordingly, this novel design concept will be inspiring for developing CDT nanomedicines in the future.

Single-Excitation Triple-Emission Down-/Up-Conversion Nanoassemblies for Tumor Microenvironment-Enhanced Ratiometric NIR-II Fluorescence Imaging and Chemo-/Photodynamic Combination Therapy

Tumor microenvironment-mediated ratiometric second near-infrared (NIR-II) fluorescence imaging and photodynamic therapy contribute to accurate diagnosis and highly efficient therapy of deep tumors. However, it is challenging to integrate these functions into one nanodrug due to the difficulty in preparing triple-emission nanoprobes. In this work, single-excitation triple-emission (wavelength at 660, 1060, and 1550 nm) down-/up-conversion nanoassemblies were prepared by conjugating dual-ligands-stabilized gold nanoclusters (_cgAuNCs) into down-/up-conversion nanoparticles (D/UCNPs), which simultaneously realized ratiometric NIR-II fluorescence imaging and chemo-/photodynamic combination therapy toward tumors upon exposure to an 808 nm laser. The presence of dual ligands endowed _cgAuNCs with an enhanced NIR-II fluorescence response to endogenous glutathione, allowing in situ ratiometric NIR-II fluorescence imaging of tumors using the prepared nanoassemblies. Additionally, the stabilizing ligand cyclodextrin of _cgAuNCs facilitated the loading of the antitumor drug doxorubicin, and D/UCNPs could be modified with the photosensitizer methylene blue. Such a spatially separated functionalization method enabled chemo-/photodynamic combination therapy. This study provides new insights into the design of multifunctional nanoplatforms for tumor diagnosis and treatment.

Increasing Molecular Planarity through Donor/Side-Chain Engineering for Improved NIR-IIa Fluorescence Imaging and NIR-II Photothermal Therapy under 1064 nm

Developing conjugated small molecules (CSM) with intense NIR-II (1000-1700 nm) absorption for phototheranostic is highly desirable but remains a tremendous challenge due to a lack of reliable design guidelines. This study reports a high-performance NIR-II CSM for phototheranostic by tailoring molecular planarity. A series of CSM show bathochromic absorption extended to the NIR-II region upon the increasing thiophene number, but an excessive number of thiophene results in decreased NIR-IIa (1300-1400 nm) brightness and photothermal effects. Further introduction of terminal nonconjugated alkyl chain can enhance NIR-II absorption coefficient, NIR-IIa brightness, and photothermal effects. Mechanism studies ascribe this overall enhancement to molecular planarity stemming from the collective contribution of donor/side-chain engineering. This finding directs the design of NIR-II CSM by rational manipulating molecular planarity to perform 1064 nm mediated phototheranostic at high efficiency.

Nano-inspired smart medicines targeting brain cancer: diagnosis and treatment

Cancer, despite being the bull's eye for the research community, accounts for a large number of morbidity and mortality. Cancer of the brain is considered the most intractable, with the least diagnosis rates, hence treatment and survival. Despite the extensive development of therapeutic molecules, their targeting to the diseased site is a challenge. Specially tailored nanoparticles can efficiently deliver drugs and genes to the brain to treat tumours and diseases. These nanotechnology-based strategies target the blood-brain barrier, the local space, or a specific cell type. These nanoparticles are preferred over other forms of targeted drug delivery due to the chances for controlled delivery of therapeutic cargo to the intended receptor. Targeted cancer therapy involves using specific receptor-blocking compounds that block the spreading or growth of cancerous cells. This review presents an account of the recent applications of nano-based cancer theragnostic, which deal in conjunct functionalities of nanoparticles for effective diagnosis and treatment of cancer. It commences with an introduction to tumours of the brain and their grades, followed by hurdles in its conventional diagnosis and treatment. The characteristic mechanism of nanoparticles for efficiently tracing brain tumour grade and delivery of therapeutic genes or drugs has been summarised. Nanocarriers like liposomes have been widely used and commercialized for human brain cancer treatment. However, nano-inspired structures await their translational recognition. The green synthesis of nanomaterials and their advantages have been discussed. The article highlights the challenges in the nano-modulation of brain cancer and its future outlook.

The Current Status of Photodynamic Therapy in Cancer Treatment

Although we have made great strides in treating deadly diseases over the years, cancer therapy still remains a daunting challenge. Among numerous anticancer methods, photodynamic therapy (PDT), a non-invasive therapeutic approach, has attracted much attention. PDT exhibits outstanding performance in cancer therapy, but some unavoidable disadvantages, including limited light penetration depth, poor tumor selectivity, as well as oxygen dependence, largely limit its therapeutic efficiency for solid tumors treatment. Thus, numerous strategies have gone into overcoming these obstacles, such as exploring new photosensitizers with higher photodynamic conversion efficiency, alleviating tumor hypoxia to fuel the generation of reactive oxygen species (ROS), designing tumor-targeted PS, and applying PDT-based combination strategies. In this review, we briefly summarized the PDT related tumor therapeutic approaches, which are mainly characterized by advanced PSs, these PSs have excellent conversion efficiency and additional refreshing features. We also briefly summarize PDT-based combination therapies with excellent therapeutic effects.

Semiconducting Polymer Dots for Point-of-Care Biosensing and In Vivo Bioimaging: A Concise Review

In recent years, semiconducting polymer dots (Pdots) have attracted much attention due to their excellent photophysical properties and applicability, such as large absorption cross section, high brightness, tunable fluorescence emission, excellent photostability, good biocompatibility, facile modification and regulation. Therefore, Pdots have been widely used in various types of sensing and imaging in biological medicine. More importantly, the recent development of Pdots for point-of-care biosensing and in vivo imaging has emerged as a promising class of optical diagnostic technologies for clinical applications. In this review, we briefly outline strategies for the preparation and modification of Pdots and summarize the recent progress in the development of Pdots-based optical probes for analytical detection and biomedical imaging. Finally, challenges and future developments of Pdots for biomedical applications are given.

Albumin-Consolidated AIEgens for Boosting Glioma and Cerebrovascular NIR-II Fluorescence Imaging

The application of an exogenous polymer matrix to construct aggregation-induced emission (AIE) nanoprobes promotes the utility of AIE luminogens (AIEgens) in diagnosing brain diseases. However, the limited fluorescence (FL) and low active-targeting abilities of AIE-based nanoprobes impede their imaging application. Here, we employed endogenous albumin as an effective matrix to encapsulate AIEgens to enhance FL quantum yield (QY) and active-targeting ability. The albumin-consolidated strategy effectively inhibited the intramolecular vibration of AIEgens and enhanced endocytosis mediated by the gp60 receptor. The QYs of three kinds of albumin-based AIE nanoprobes with FL emissions ranging from the visible (400-650 nm) to the second near-infrared (NIR-II, 1000-1700 nm) region was at least 10% higher, and the tumor-targeting efficiency was ∼25% higher, compared with those of nanoprobes constructed by the exogenous polymer. Albumin-based AIE nanoprobes have achieved active-targeting NIR-II imaging of brain tumors and cerebrovascular imaging with a high signal-to-background ratio (SBR, ∼90) and high resolution (∼70 μm) in mouse models. Therefore, the albumin-based AIE nanoprobes will enable FL imaging-guided surgery of brain tumors and cerebral ischemia, which will improve surgical efficacy to prevent recurrence and side effects.

Fluorination Enhances NIR-II Emission and Photothermal Conversion Efficiency of Phototheranostic Agents for Imaging-Guided Cancer Therapy

Phototheranostics with second near-infrared (NIR-II) imaging and photothermal effect have become a burgeoning biotechnology for tumor diagnosis and precise treatment. As important parameters of phototheranostic agents (PTAs), fluorescence quantum yield (QY) and photothermal conversion efficiency (PCE) are usually considered as a pair of contradictions that is difficult to be simultaneously enhanced. Herein, a fluorination strategy for designing A-D-A type PTAs with synchronously improved QY and PCE is proposed. Experimental results show that the molar extinction coefficient (ε), NIR-II QY, and PCE of all fluorinated PTAs nanoparticles (NPs) are definitely improved compared with the chlorinated counterparts. Theoretical calculation results demonstrate that fluorination can maximize the electrostatic potential difference by virtue of the high electronegativity of fluorine, which may increase intra/intermolecular D-A interactions, tighten molecule packing, and further promote the increase of ε, ultimately leading to simultaneously enhanced QY and PCE. In these PTA NPs, FY6-NPs display NIR-II emission extended to 1400 nm with the highest NIR-II QY (4.2%) and PCE (80%). These features make FY6-NPs perform well in high-resolution imaging of vasculature and NIR-II imaging-guided photothermal therapy (PTT) of tumors. This study develops a valuable guideline for constructing NIR-II organic PTAs with high performance.

Structural and functional imaging of brains

Analyzing the complex structures and functions of brain is the key issue to understanding the physiological and pathological processes. Although neuronal morphology and local distribution of neurons/blood vessels in the brain have been known, the subcellular structures of cells remain challenging, especially in the live brain. In addition, the complicated brain functions involve numerous functional molecules, but the concentrations, distributions and interactions of these molecules in the brain are still poorly understood. In this review, frontier techniques available for multiscale structure imaging from organelles to the whole brain are first overviewed, including magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), serial-section electron microscopy (ssEM), light microscopy (LM) and synchrotron-based X-ray microscopy (XRM). Specially, XRM for three-dimensional (3D) imaging of large-scale brain tissue with high resolution and fast imaging speed is highlighted. Additionally, the development of elegant methods for acquisition of brain functions from electrical/chemical signals in the brain is outlined. In particular, the new electrophysiology technologies for neural recordings at the single-neuron level and in the brain are also summarized. We also focus on the construction of electrochemical probes based on dual-recognition strategy and surface/interface chemistry for determination of chemical species in the brain with high selectivity and long-term stability, as well as electrochemophysiological microarray for simultaneously recording of electrochemical and electrophysiological signals in the brain. Moreover, the recent development of brain MRI probes with high contrast-to-noise ratio (CNR) and sensitivity based on hyperpolarized techniques and multi-nuclear chemistry is introduced. Furthermore, multiple optical probes and instruments, especially the optophysiological Raman probes and fiber Raman photometry, for imaging and biosensing in live brain are emphasized. Finally, a brief perspective on existing challenges and further research development is provided.

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.

Surface Plasmon-Enhanced NIR-II Fluorescence in a Multilayer Nanoprobe for Through-Skull Mouse Brain Imaging

Fluorescence imaging in the second near-infrared window (NIR-II, 1000-1700 nm) holds great potential for the accurate visualization of deeply located biological structures in vivo. However, the weak fluorescence of current NIR-II fluorophores remains a long-standing challenge for the ever-growing imaging demand. Here, we describe a surface plasmon-enhanced NIR-II fluorescence strategy by incorporating silica-coated gold nanorods (GNRs) and polymer dots (Pdots) into a multilayer nanostructure. Precise manipulation of the silica spacing layer thickness signifies an optimum distance of 8.6 nm, where an enhancement factor of up to 6.4 is achieved in the NIR-II imaging window. The surface plasmon enhancement approach is successfully extended to several types of Pdots fluorophores with NIR-II emission. We finally perform outer-layer encapsulation and PEGylation for the multilayer probes and demonstrate surface plasmon-enhanced NIR-II fluorescence for mouse brain imaging through the skull, which exhibits a refined signal-to-background ratio and penetration depth as compared to the clinically approved ICG dye.

The Pursuit of Shortwave Infrared-Emitting Nanoparticles with Bright Fluorescence through Molecular Design and Excited-State Engineering of Molecular Aggregates

Shortwave infrared (SWIR) fluorescence detection gradually becomes a pivotal real-time imaging modality, allowing one to elucidate biological complexity in deep tissues with subcellular resolution. The key challenge for the further growth of this imaging modality is the design of new brighter biocompatible fluorescent probes. This review summarizes the recent progress in the development of organic-based nanomaterials with an emphasis on new strategies that extend the fluorescence wavelength from the near-infrared to the SWIR spectral range and amplify the fluorescence brightness. We first introduce the most representative molecular design strategies to obtain near-infrared-SWIR wavelength fluorescence emission from small organic molecules. We then discuss how the formation of nanoparticles based on small organic molecules contributes to the improvement of fluorescence brightness and the shift of fluorescence to SWIR, with a special emphasis on the excited-state engineering of molecular probes in an aggregate state and spatial packing of the molecules in nanoparticles. We build our discussion based on a historical perspective on the photophysics of molecular aggregates. We extend this discussion to nanoparticles made of conjugated polymers and discuss how fluorescence characteristics could be improved by molecular design and chain conformation of the polymer molecules in nanoparticles. We conclude the article with future directions necessary to expand this imaging modality to wider bioimaging applications including single-particle deep tissue imaging. Issues related to the characterization of SWIR fluorophores, including fluorescence quantum yield unification, are also mentioned.

Semiconducting Polymer Nanoparticles with Surface-Mimicking Protein Secondary Structure as Lysosome-Targeting Chimaeras for Self-Synergistic Cancer Immunotherapy

Immunotherapy has received tremendous attention for tumor treatment, but the efficacy is greatly hindered by insufficient tumor-infiltration of immune cells and immunosuppressive tumor microenvironment. The strategy that can efficiently activate cytotoxic T lymphocytes and inhibit negative immune regulators will greatly amplify immunotherapy outcome, which is however very rare. Herein, a new kind of semiconducting polymer (SP) nanoparticles is developed, featured with surface-mimicking protein secondary structure (SPSS NPs) for self-synergistic cancer immunotherapy by combining immunogenic cell death (ICD) and immune checkpoint blockade therapy. The SPs with excellent photodynamic property are synthesized by rational fluorination, which can massively induce ICD. Additionally, the peptide antagonists are introduced and self-assembled into β-sheet protein secondary structures on the photodynamic NP surface via preparation process optimization, which function as efficient lysosome-targeting chimaeras (LYTACs) to mediate the degradation of programmed cell death ligand-1 (PD-L1) in lysosome. In vivo experiments demonstrate that SPSS NPs can not only elicit strong antitumor immunity to suppress both primary tumor and distant tumor, but also evoke long-term immunological memory against tumor rechallenge. This work introduces a new kind of robust immunotherapy agents by combining well-designed photosensitizer-based ICD induction and protein secondary structures-mediated LYTAC-like multivalence PD-L1 blockade, rendering great promise for synergistic immunotherapy.

Recent Advances in Near-Infrared-II Fluorescence Imaging for Deep-Tissue Molecular Analysis and Cancer Diagnosis

Fluorescence imaging with high sensitivity and minimal invasiveness has received tremendous attention, which can accomplish visualized monitoring and evaluation of cancer progression. Compared with the conventional first near-infrared (NIR-I) optical window (650-950 nm), fluorescence imaging in the second NIR optical window (NIR-II, 950-1700 nm) exhibits deeper tissue penetration capability and higher temporal-spatial resolution with lower background interference for achieving deep-tissue in vivo imaging and real-time monitoring of cancer development. Encouraged by the significant preponderances, a variety of multifunctional NIR-II fluorophores have been designed and fabricated for sensitively imaging biomarkers in vivo and visualizing the treatment procedure of cancers. In this review, the differences between NIR-I and NIR-II fluorescence imaging are briefly introduced, especially the advantages of NIR-II fluorescence imaging for the real-time visualization of tumors in vivo and cancer diagnosis. An important focus is to summarize the NIR-II fluorescence imaging for deep-tissue biomarker analysis in vivo and tumor tissue visualization, and a brief introduction of NIR-II fluorescence imaging-guided cancer therapy is also presented. Finally, the significant challenges and reasonable prospects of NIR-II fluorescence imaging for cancer diagnosis in clinical applications are outlined.

Biomimetic semiconducting polymer dots for highly specific NIR-II fluorescence imaging of glioma

Glioma with very short medium survival time consists of 80% of primary malignant types of brain tumors. The unique microenvironment such as the existence of the blood-brain barrier (BBB) makes the glioma theranostics exhibit low sensitivity in diagnosis, a poor prognosis and low treatment efficacy. Therefore, the development of multifunctional nanoplatform that can cross BBB and target the glioma is essential for the high-sensitivity detection and ablation of cancer cells. In this study, C6 cell membrane-coated conjugated polymer dots (Pdots-C6) were constructed for targeted glioma tumor detection. As a new kind of biomimetic and biocompatible nanoprobes, Pdots-C6 preserve the complex biological functions of natural cell membranes while possessing physicochemical properties for NIR-II fluorescence imaging of glioma. After encapsulating C6 cell membrane on the surface of conjugated Pdots, Pdots-C6 exhibited the most favorable specific targeting capabilities in vitro and in vivo. In particular, this pilot study demonstrates that biomimetic nanoparticles offer a potential tool to enhance specific targeting to the brain, hence improving glioma tumor detection accuracy.

Acceptor engineering for NIR-II dyes with high photochemical and biomedical performance

It is highly important and challenging to develop donor-acceptor-donor structured small-molecule second near-infrared window (NIR-II) dyes with excellent properties such as water-solubility and chem/photostability. Here, we discovery an electron acceptor, 6,7-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline (TQT) with highest stability in alkaline conditions, compared with conventional NIR-II building block benzobisthiadiazole (BBT) and 6,7-diphenyl-[1,2,5] thiadiazolo[3,4-g]quinoxaline (PTQ). The sulfonated hydrophilic dye, FT-TQT, is further synthesized with 2.13-fold increased quantum yield than its counterpart FT-BBT with BBT as acceptor. FT-TQT complexed with FBS is also prepared and displays a 16-fold increase in fluorescence intensity compared to FT-TQT alone. It demonstrates real-time cerebral and tumor vessel imaging capability with µm-scale resolution. Dynamic monitoring of tumor vascular disruption after drug treatment is achieved by NIR-II fluorescent imaging. Overall, TQT is an efficient electron acceptor for designing innovative NIR-II dyes. The acceptor engineering strategy provides a promising approach to design next generation of NIR-II fluorophores which open new biomedical applications.

Small molecule NIR-II fluorophores are of interest for a range of applications but can suffer from chemical and photostability issues. Here, the authors report on the development of an acceptor molecule with improved stability in alkaline conditions expanding the range of possible applications.

Chiral NIR-II fluorescent Ag2S quantum dots with stereospecific biological interactions and tumor accumulation behaviors

Near-infrared II (NIR-II) fluorescent nanoprobes hold great potential for biomedical applications. Elucidating the relationship between surface properties of NIR-II nanoprobes and their biological behaviors is particularly important for future probe design and their performance optimization. Despite the rapid development of NIR-II nanoprobes, the distinct role of surface chirality on their biological fates has rarely been exploited. Herein, chiral NIR-II fluorescent Ag₂S quantum dots (QDs) are synthesized to investigate the relationship between their chirality and biological functions at both in vitro and in vivo levels. D-/L-Ag₂S QDs exhibit significant differences on their interactions with serum proteins, which further affect the cellular uptake. As a result, D-Ag₂S QDs can be internalized with higher efficiency (over 2-fold) than that of L-Ag₂S QDs. Moreover, in vivo studies reveal that the chirality determines the primary localization of these chiral QDs, where a more efficient renal elimination of D-Ag₂S QDs was observed than that of L-Ag₂S QDs. Importantly, D-Ag₂S QDs show preferential accumulation in tumor region than that of L-Ag₂S QDs in orthotopic kidney tumor model, which points out a new avenue of enhancing targeting capabilities of nanoprobes by engineering their surface chirality.

Capillaries segmentation of NIR-II images and its application in ischemic stroke

Fluorescence imaging in the second near-infrared window (NIR-II) offers μm resolution blood vessel information noninvasively, which is crucial for the diagnosis and surgery treatment of some blood vessel-related diseases. However, only a few blood vessel segmentation algorithms have been done for the NIR-II images so far. Here, we proposed a vessel segmentation algorithm that used multi-scale enhancement and fractional differential to enhance capillaries, and then segmented vessels based on the blood vessels' tubular characteristics. Experimental results showed that this method could effectively suppress the point and lump tissue noise influence during vascular segmentation. The accuracy of vessel identification by other algorithms dropped below 30%, while our algorithm still achieved an accuracy of around 50% in deep vessel segmentation experiments with the 6.5 mm Intralipid. So it had the advantage of accurately detecting deep and dim blood capillaries. Meanwhile, the vascular density quantization algorithm had been successfully applied to the mice's ischemic stroke evaluations for the first time. In addition, this algorithm can provide the quantified vessel features under physiological or pathological conditions, which could be used to accurately evaluate the stroke drugs' therapeutic effect in the future.