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

A novel NIR-II fluorescent probe for hydrogen peroxide detection in drug-induced liver injury

The synthesis of H2O2-activatable small molecules in the second near-infrared (NIR-II) window remains challenging. We present the NIR-II probe Z-1065 for real-time detection of H2O2. Z-1065 demonstrates high sensitivity and selectivity towards H2O2in vitro and effectively monitors H2O2 generation in drug-induced liver injury (DILI) mouse models.

Near-Infrared II Agent with Excellent Overall Performance for Imaging-Guided Photothermal Thrombolysis

Near-infrared II (NIR-II) imaging and photothermal therapy hold tremendous potential in precision diagnosis and treatment within biological organisms. However, a significant challenge is the shortage of NIR-II fluorescent probes with both high photothermal conversion coefficient (PCE) and fluorescence quantum yield (ΦF). Herein, we address this issue by integrating a large conjugated electron-withdrawing core, multiple rotors, and multiple alkyl chains into a molecule to successfully generate a NIR-II agent 4THTPB with excellent PCE (87.6%) and high ΦF (3.2%). 4THTPB shows a maximum emission peak at 1058 nm, and the emission tail could extend to as long as 1700 nm. These characteristics make its nanoparticles (NPs) perform well in NIR-II high-resolution angiography, thereby allowing for precise diagnosis of thrombus through NIR-II imaging and enabling efficient photothermal thrombolysis. This work not only furnishes a NIR-II agent with excellent overall performance but also provides valuable guidance for the design of high-performance NIR-II agents.

Thiophene assisted cellular uptake enhancement for highly efficient NIR-II cancer phototheranostics

We designed two series of NIR-II PTAs with D-A or D-A-D structures, in which the introduction of thiophene promotes a bathochromic shift of emission into the NIR-II region, helps to improve the cellular uptake of the PTAs and facilitates NIR-II imaging-guided PDT/PTT cancer phototherapy.

BF2-Bridged Azafulvene Dimer-Based 1064 nm Laser-Driven Superior Photothermal Agent for Deep-Seated Tumor Therapy

Small organic photothermal agents (PTAs) with absorption bands located in the second near-infrared (NIR-II, 1000-1700 nm) window are highly desirable for effectively combating deep-seated tumors. However, the rarely reported NIR-II absorbing PTAs still suffer from a low molar extinction coefficient (MEC, ϵ), inadequate chemostability and photostability, as well as the high light power density required during the therapeutic process. Herein, we developed a series of boron difluoride bridged azafulvene dimer acceptor-integrated small organic PTAs. The B-N coordination bonds in the π-conjugated azafulvene dimer backbone endow it the strong electron-withdrawing ability, facilitating the vigorous donor-acceptor-donor (D-A-D) structure PTAs with NIR-II absorption. Notably, the PTA namely OTTBF shows high MEC (7.21×104 M-1 cm-1), ultrahigh chemo- and photo-stability. After encapsulated into water-dispersible nanoparticles, OTTBF NPs can achieve remarkable photothermal conversion effect under 1064 nm irradiation with a light density as low as 0.7 W cm-2, which is the lowest reported NIR-II light power used in PTT process as we know. Furthermore, OTTBF NPs have been successfully applied for in vitro and in vivo deep-seated cancer treatments under 1064 nm laser. This study provides an insight into the future exploration of versatile D-A-D structured NIR-II absorption organic PTAs for biomedical applications.

Sulfur oxidation states manipulate excited state electronic configurations for constructing highly efficient organic type I photosensitizers

The multiple relaxation processes of excited states are a bridge connecting molecular structures and properties, providing enormous application potential for organic luminogens. However, a systematic understanding and manipulation of the relationship between the molecular structure, excited state relaxation processes, and properties of organic luminogens is still lacking. Herein, we report a strategy for manipulating excited state electronic configurations through the regulation of the sulfur oxidation state to construct eminent organic type I PSs. Combined with the experimental results and theoretical calculations, we have successfully revealed the decisive role of high sulfur oxidation states in promoting ROS production capacity. Impressively, a higher sulfur oxidation state can reduce the singlet-triplet energy gap (ΔE ST), increase the matching degree of transition configurations, promote the changes of the excited state electronic configurations, and boost the effective ISC proportion by enhancing intramolecular interactions. Therefore, DBTS2O with the highest sulfur oxidation state exhibits the strongest type I ROS generation ability. Additionally, guided by our strategy, a water-soluble PS (2OA) is designed and synthesized, showing selective imaging capacity and photokilling ability against Gram-positive bacteria. This study broadens the horizons for both molecular design and mechanism study of high-performance organic type I PSs.

Interstitial Optical Fiber-Mediated Multimodal Phototheranostics Based on an Aggregation-Induced NIR-II Emission Luminogen for Orthotopic Breast Cancer Treatment

One-for-all phototheranostics based on a single molecule is recognized as a convenient approach for cancer treatment, whose efficacy relies on precise lesion localization through multimodal imaging, coupled with the efficient exertion of phototherapy. To unleash the full potential of phototheranostics, advancement in both phototheranostic agents and light delivery methods is essential. Herein, an integrated strategy combining a versatile molecule featuring aggregation-induced emission, namely tBuTTBD, with a modified optical fiber to realize comprehensive tumor diagnosis and "inside-out" irradiation in the orthotopic breast tumor, is proposed for the first time. Attributed to the intense donor-acceptor interaction, highly distorted conformation, abundant molecular rotors, and loose intermolecular packing upon aggregation, tBuTTBD can synchronously undergo second near-infrared (NIR-II) fluorescence emission, photothermal and photodynamic generation under laser irradiation, contributing to a trimodal NIR-II fluorescence-photoacoustic (PA)-photothermal imaging-guided phototherapy. The tumor treatment is further carried out following the insertion of a modified optical fiber, which is fabricated by splicing a flat-end fiber with an air-core fiber. This configuration aims to enable effective in situ phototherapy by maximizing energy utilization for therapeutic benefits. This work not only enriches the palette of NIR-II phototheranostic agents but also provides valuable insight for exploring an integrated phototheranostic protocol for practical cancer treatment.

Homo-Dyad with Outer Hydration Layer Approach for Developing NIR-II Chromophore of High Stability and Water-Solubility as Injectable and Sprayable Optical Probe

Dyes with extended conjugate structures are the focus of extensive design and synthesis efforts, aiming to confer unique and improved optical and electronic properties. Such advancements render these dyes applicable across a wide spectrum of uses, ranging from second-window near-infrared (NIR-II) bioimaging to organic photovoltaics. Nevertheless, the inherent benefits of long conjugation are often accompanied by persistent challenges like aggregation, fluorescence quenching, absorption blueshift, and low stability and poor water solubility. Herein, a unique structural design strategy termed "homo-dyad with outer hydration layer" is introduced to address these inherent problems, tailored for the development of imaging probes exhibiting long absorption/emission wavelengths. This approach involves bringing two heptamethine cyanines together through a flexible linker, forming a homo-dyad structure, while strategically attaching four polyethylene glycol (PEG9) chains to the terminal heterocycles. This approach imparts excellent water solubility, biocompatibility, and enhanced chemical, photo-, and spectral stability for the dyes. Utilizing this strategy, a biomarker-activatable probe (HD-FL-4PEG9-N) for NIR-II fluorescent and 3D multispectral optoacoustic tomography imaging is developed, and its effectiveness in disease visualization. It can not only serve as an injectable probe for acute kidney injury imaging due to its high water solubility, but also a sprayable probe for imaging bacterial-infected wounds.

Systematic Structural Modification of Squaraine Dye for Near-Infrared Window One and Two Multiplexed In Vivo Imaging and Photothermal Therapy

Due to the wide application of reporter gene-related visible/NIR-I bioluminescent imaging, multiplexed fluorescence imaging across visible/NIR-I/NIR-II has excellent potential in biomedical research. However, in vivo multiplexed imaging applications across those regions have rarely been reported due to the lack of proper fluorophores. Herein, nine squaraine dyes, which exhibit diverse adsorption and emission wavelengths, were synthesized. Among them, water-soluble SQ 710-5k and SQ 905 were found to have significant absorption differences, which allowed the tumor and lymph nodes to be identified. Then, for the first time, six-channel multiplexed fluorescence imaging across visible/NIR-I/II was achieved by coordination with reporter gene-related bioluminescent phosphors. Additional research revealed that SQ 710-5k exhibited higher-quality blood vessels and tumor imaging in NIR-II. H-aggregates SQ 905 demonstrated a high photothermal conversion efficiency for photothermal therapy. This study proposed an approach to creating small molecular dyes that coordinate with reporter gene-related bioluminescent phosphors for six-color fluorescence imaging.

A firm-push-to-open and light-push-to-lock strategy for a general chemical platform to develop activatable dual-modality NIR-II probes

Activatable near-infrared (NIR) imaging in the NIR-II range is crucial for deep tissue bioanalyte tracking. However, designing such probes remains challenging due to the limited availability of general chemical strategies. Here, we introduced a foundational platform for activatable probes, using analyte-triggered smart modulation of the π-conjugation system of a NIR-II-emitting rhodamine hybrid. By tuning the nucleophilicity of the ortho-carboxy moiety, we achieved an electronic effect termed "firm-push-to-open and light-push-to-lock," which enables complete spirocyclization of the probe before sensing and allows for efficient zwitterion formation when the light-pushing aniline carbamate trigger is transformed into a firm-pushing aniline. This platform produces dual-modality NIR-II imaging probes with ~50-fold fluorogenic and activatable photoacoustic signals in live mice, surpassing reported probes with generally below 10-fold activatable signals. Demonstrating generality, we successfully designed probes for hydrogen peroxide (H2O2) and hydrogen sulfide (H2S). We envision a widespread adoption of the chemical platform for designing activatable NIR-II probes across diverse applications.

Two-Photon Absorption Aggregation-Induced Emission Luminogen/Paclitaxel Nanoparticles for Cancer Theranostics

Multifaceted nanoplatforms integrating fluorescence imaging and chemotherapy have garnered acknowledgment for their potential potency in cancer diagnosis and simultaneous in situ therapy. However, some drawbacks remain for traditional organic photosensitizers, such as poor photostability, short excitation wavelength, and shallow penetration depth, which will greatly lower the chemotherapy treatment efficiency. Herein, we present lipid-encapsulated two-photon active aggregation-induced emission (AIE) luminogen and paclitaxel (PTX) nanoparticles (AIE@PTX NPs) with bright red fluorescence emission, excellent photostability, and good biocompatibility. The AIE@PTX NPs exhibit dual functionality as two-photon probes for visualizing blood vessels and tumor structures, achieving penetration depth up to 186 and 120 μm, respectively. Furthermore, the tumor growth of the HeLa-xenograft model can be effectively prohibited after the fluorescence imaging-guided and PTX-induced chemotherapy, which shows great potential in the clinical application of two-photon cell and tumor fluorescence imaging and cancer treatment.

An NIR-II-emitting type-I photosensitizer for efficient hypoxic tumor phototheranostics

A small molecule-based NIR-II type-I photosensitizer (IT-IC) with a strong push-pull effect and good planar π-conjugated structure was synthesized. The IT-IC NPs exhibited strong light absorption, outstanding NIR-II fluorescence emission, excellent photothermal conversion and efficient type-I/II ROS generation, showing encouraging therapeutic outcomes for hypoxic tumors.

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.

Preparation of NIR-II Polymer Nanoprobe Through Twisted Intramolecular Charge Transfer and Förster Resonance Energy Transfer of NIR-I Dye

Near-infrared-II (NIR-II) fluorescence imaging is pivotal in biomedical research. Organic probes exhibit high potential in clinical translation, due to advantages such as precise structure design, low toxicity, and post-modifications convenience. In related preparation, enhancement of NIR-II tail emission from NIR-I dyes is an efficient method. In particular, the promotion of twisted intramolecular charge transfer (TICT) of relevant NIR-I dyes is a convenient protocol. However, present TICT-type probes still show disadvantages in relatively low emission, large particle sizes, or limited choice of NIR-I dyes, etc. Herein, the synthesis of stable small-sized polymer NIR-II fluoroprobes (e.g., 7.2 nm), integrating TICT and Förster resonance energy transfer process to synergistically enhance the NIR-II emission is reported. Strong enhanced emissions can be obtained from various NIR-I dyes and lanthanide elements (e.g., twelvefold at 1250 nm from Nd-DTPA/IR-808 sample). The fluorophore provides high-resolution angiography, with high-contrast imaging on middle cerebral artery occlusion model mice for distinguishing occlusion. The fluorophore can be rapidly excreted from the kidney (urine ≈65% within 4 h) in normal mice and exhibits long-term renal retention on acute kidney injury mice, showing potential applications in the prognosis of kidney diseases. This development provides an effective strategy to design and synthesize effective NIR-II fluoroprobes.

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.

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.

NIR-II fluorescence imaging without intended excitation light

Nowadays, second near-infrared window (NIR-II) dyes are almost excited by laser diodes, but none of the white light (400-700 nm) excited NIR-II imaging has been studied because of the lack of suitable optical probes. Herein, a novel blue-shifted NIR-II dye, TPA-TQT, has been selected for use in multi-wavelength white light emitting diode (LED) excited NIR-II imaging. This white LED barely caused photo-quenching of the dyes, especially indocyanine green (ICG), whereas the ICG's brightness decreased by 90% under continuous 808 nm laser irradiation. Compared to single-wavelength LED, multi-wavelength LED showed a lower background and similar signal-to-background ratios. This system provided high image resolution to identify blood vessels (103 μm), lymphatic capillaries (129.8 μm), and to monitor hindlimb ischemia-reperfusion and lymphatic inflammation. Furthermore, white LED excited NIR-II fluorescence imaging-guided surgery (FIGS) was successfully performed in 4T1 tumor-bearing mice. Impressively, the lighting LED-based NIR-II FIGS was found to clearly delineate small lesions of metastatic tumors of about ∼350 μm diameter and further was able to guide surgical removal. Overall, multi-wavelength LED-based NIR-II imaging is a promising imaging strategy for tumor delineation and other biomedical applications.

Molecular Engineering of Bright NIR-I/NIR-II Nanofluorophores for High-Resolution Bioimaging and Tumor Detection in Vivo

A comprehensive approach for the construction of NIR-I/NIR-II nanofluorophores with exceptional brightness and excellent chemo- and photostability has been developed. This study first confirmed that the amphiphilic molecules with stronger hydrophobic moieties and weaker hydrophilic moieties are superior candidates for constructing brighter nanofluorophores, which are attributed to its higher efficiency in suppressing the intramolecular charge transfer/aggregation-caused fluorescence quenching of donor-acceptor-donor type fluorophores. The prepared nanofluorophore demonstrates a fluorescence quantum yield exceeding 4.5% in aqueous solution and exhibits a strong NIR-II tail emission up to 1300 nm. The superior performance of the nanofluorophore enabled the achievement of high-resolution whole-body vessel imaging and brain vessel imaging, as well as high-contrast fluorescence imaging of the lymphatic system in vivo. Furthermore, their potential for highly sensitive fluorescence detection of tiny tumors in vivo has been successfully confirmed, thus supporting their future applications in precise fluorescence imaging-guided surgery in the early stages of cancer.

Multiplexed Short-wave Infrared Imaging Highlights Anatomical Structures in Mice

While multiplexed fluorescence imaging is frequently used for in vitro microscopy, extending the technique to whole animal imaging in vivo has remained challenging due to the attenuation and scattering of visible and traditional near infrared (NIR-I) wavelengths. Fluorescence imaging using short-wave infrared (SWIR, 1000 - 1700 nm, a.k.a. NIR-II) light enables deeper tissue penetration for preclinical imaging compared to previous methods due to reduced tissue scattering and minimal background autofluorescence in this optical window. Combining NIR-I excitation wavelengths with multiple distinct SWIR emission peaks presents a tremendous opportunity to distinguish multiple fluorophores with high precision for non-invasive, multiplexed anatomical imaging in small animal models. SWIR-emitting semiconductor quantum dots (QDs) with tunable emission peaks and optical stability have emerged as powerful contrast agents, but SWIR imaging demonstrations have yet to move beyond two-color imaging schemes. In this study, we engineered a set of three high quantum yield lead sulfide/cadmium sulfide (PbS/CdS) core/shell QDs with distinct SWIR emissions ranging from 1100 - 1550 nm and utilize these for simultaneous three-color imaging in mice. We first use QDs to non-invasively track lymphatic drainage, highlighting the detailed network of lymphatic vessels with high-resolution with a widefield imaging over a 2 hr period. We then perform multiplexed imaging with all three QDs to distinctly visualize the lymphatic system and spatially overlapping vasculature network. This work establishes optimized SWIR QDs for next-generation multiplexed preclinical imaging, moving beyond the capability of previous dual-labeling techniques. The capacity to discriminate several fluorescent labels through non-invasive NIR-I excitation and SWIR detection unlocks numerous opportunities for studies of disease progression, drug biodistribution, and cell trafficking dynamics in living organisms.

A selenium-based NIR-II photosensitizer for a highly effective and safe phototherapy plan

High efficiency, stability, long emission wavelength (NIR-II), and good biocompatibility are crucial for photosensitizers in phototherapy. However, current Food and Drug Administration (FDA)-approved organic fluorophores exhibit poor chemical stability and photostability as well as short emission wavelength, limiting their clinical usage. To address this, we developed Se-IR1100, a novel organic photosensitizer with a photostable and thermostable benzobisthiadiazole (BBTD) backbone. By incorporating selenium as a heavy atom and constructing a D-A-D structure, Se-IR1100 exhibits a maximum fluorescence emission wavelength of 1100 nm. Compared with FDA-approved indocyanine green (ICG), DSPE-PEGylated Se-IR1100 nanoparticles exhibit prominent photostability and long-lasting photothermal effects. Upon 808 nm laser irradiation, Se-IR1100 NPs efficiently convert light energy into heat and reactive oxygen species (ROS), inducing cancer cell death in cellular studies and living organisms while maintaining biocompatibility. With salient photostability and a photothermal conversion rate of 55.37%, Se-IR1100 NPs hold promise as a superior photosensitizer for diagnostic and therapeutic agents in oncology. Overall, we have designed and optimized a multifunctional photosensitizer Se-IR1100 with good biocompatibility that performs NIR-II fluorescence imaging and phototherapy. This dual-strategy method may offer novel approaches for the development of multifunctional probes using dual-strategy or even multi-strategy methods in bioimaging, disease diagnosis, and therapy.

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.

Multi-Stimuli-Responsive and Cell Membrane Camouflaged Aggregation-Induced Emission Nanogels for Precise Chemo-photothermal Synergistic Therapy of Tumors

Targeted and controllable drug release at lesion sites with the aid of visual navigation in real-time is of great significance for precise theranostics of cancers. Benefiting from the marvelous features (e.g., bright emission and phototheranostic effects in aggregates) of aggregation-induced emission (AIE) materials, constructing AIE-based multifunctional nanocarriers that act as all-arounders to integrate multimodalities for precise theranostics is highly desirable. Here, an intelligent nanoplatform (P-TN-Dox@CM) with homologous targeting, controllable drug release, and in vivo dual-modal imaging for precise chemo-photothermal synergistic therapy is proposed. AIE photothermic agent (TN) and anticancer drug (Dox) are encapsulated in thermo-/pH-responsive nanogels (PNA), and the tumor cell membranes are camouflaged onto the surface of nanogels. Active targeting can be realized through homologous effects derived from source tumor cell membranes, which advantageously elevates the specific drug delivery to tumor sites. After being engulfed into tumor cells, the nanogels exhibit a burst drug release at low pH. The near-infrared (NIR) photoinduced local hyperthermia can activate severe cytotoxicity and further accelerate drug release, thus generating enhanced synergistic chemo-photothermal therapy to thoroughly eradicate tumors. Moreover, P-TN-Dox@CM nanogels could achieve NIR-fluorescence/photothermal dual-modal imaging to monitor the dynamic distribution of therapeutics in real-time. This work highlights the great potential of smart P-TN-Dox@CM nanogels as a versatile nanoplatform to integrate multimodalities for precise chemo-photothermal synergistic therapy in combating cancers.

Polymeric engineering of AIEgens for NIR-II fluorescence imaging and detection of abdominal metastases of ovarian cancer in vivo

A polymeric engineering design principle is proposed for the construction of small-sized (∼20 nm) NIR-II AIEgen-doped nanodots (AIEdots) with high brightness and prolonged circulation time in blood vessels. With the utilization of the as-designed NIR-II AIEdots, the successful achievement of high-resolution NIR-II fluorescence imaging of tumor vessels and precise detection of abdominal metastases of ovarian cancer has been attained.

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.

More Is Better: Dual-Acceptor Engineering for Constructing Second Near-Infrared Aggregation-Induced Emission Luminogens to Boost Multimodal Phototheranostics

The manipulation of electron donor/acceptor (D/A) shows an endless impetus for innovating optical materials. Currently, there is booming development in electron donor design, while research on electron acceptor engineering has received limited attention. Inspired by the philosophical idea of "more is different", two systems with D'-D-A-D-D' (1A system) and D'-D-A-A-D-D' (2A system) structures based on acceptor engineering were designed and studied. It was demonstrated that the 1A system presented a weak aggregation-induced emission (AIE) to aggregation-caused quenching (ACQ) phenomenon, along with the increased acceptor electrophilicity and planarity. In sharp contrast, the 2A system with one more acceptor exhibited an opposite ACQ-to-AIE transformation. Interestingly, the fluorophore with a more electron-deficient A-A moiety in the 2A system displayed superior AIE activity. More importantly, all compounds in the 2A system showed significantly higher molar absorptivity (ε) in comparison to their counterparts in the 1A system. Thanks to the highest ε, near-infrared-II (NIR-II, 1000-1700 nm) emission, desirable AIE property, favorable reactive oxygen species (ROS) generation, and high photothermal conversion efficiency, a representative member of the 2A system handily performed in fluorescence-photoacoustic-photothermal multimodal imaging-guided photodynamic-photothermal collaborative therapy for efficient tumor elimination. Meanwhile, the NIR-II fluorescence imaging of blood vessels and lymph nodes in living mice was also accomplished. This study provides the first evidence that the dual-connected acceptor tactic could be a new molecular design direction for the AIE effect, resulting in high ε, aggregation-intensified NIR-II fluorescence emission, and improved ROS and heat generation capacities of phototheranostic agents.

Acceptor engineering-facilitated versatile AIEgen for mitochondria-targeted multimodal imaging-guided cancer photoimmunotherapy

Photoimmunotherapy has been acknowledged to be an unprecedented strategy to obtain significantly improved cancer treatment efficacy. In this regard, the exploitation of high-performance multimodal phototheranostic agents is highly desired. Apart from tailoring electron donors, acceptor engineering is gradually rising as a deliberate approach in this field. Herein, we rationally designed a family of aggregation-induced emission (AIE)-active compounds with the same donors but different acceptors based on the acceptor engineering. Through finely adjusting the functional groups on electron acceptors, the electron affinity of electron acceptors and the conformation of the compounds were simultaneously modulated. It was found that one of the molecules (named DCTIC), bearing a moderately electrophilic electron acceptor and the best planarity, exhibited optimal phototheranostic properties in terms of light-harvesting ability, fluorescence emission, reactive oxygen species (ROS) production, and photothermal performance. For the purpose of amplified therapeutic outcomes, DCTIC was fabricated into tumor and mitochondria dual-targeted DCTIC nanoparticles (NPs), which afforded good performance in the fluorescence/photoacoustic/photothermal trimodal imaging-guided photodynamic/photothermal-synergized cancer immunotherapy with the combination of programmed cell death protein-1 (PD-1) antibody. Not only the primary tumors were totally eradicated, but efficient growth inhibition of distant tumors was also realized.

Hyperbranched Polymer Dots with Strong Absorption and High Fluorescence Quantum Yield for In Vivo NIR-II Imaging

In order to improve the fluorescence quantum yield (QY) of NIR-II-emitting nanoparticles, D-A-D fluorophores are typically linked to intramolecular rotatable units to reduce aggregation-induced quenching. However, incorporating such units often leads to a twisted molecular backbone, which affects the coupling within the D-A-D unit and, as a result, lowers the absorption. Here, we overcome this limitation by cross-linking the NIR-II fluorophores to form a 2D polymer network, which simultaneously achieves a high QY by well-controlled fluorophore separation and strong absorption by restricting intramolecular distortion. Using the strategy, we developed polymer dots with the highest NIR-II single-particle brightness among reported D-A-D-based nanoparticles and applied them for imaging of hindlimb vasculatures and tumors as well as fluorescence-guided tumor resection. The high brightness of the polymer dots offered exceptional image quality and excellent surgical results, showing a promising performance for these applications.

Synthesis, Optical Properties and Cellular Toxicity of Water-Soluble near Infrared-II Fluorescent Assemblies Based on Pillar[5]arene

The main challenges in second near-infrared region molecular fluorophores are poor water solubility and unknown long-term toxicity at present. Herein, new NIR-II molecular fluorophores have been designed and employed to integrate biocompatible pillar[5]arene with 10 outer triethylene oxide groups for the synthesis of rotaxane IRCR. In addition, PEGylated pillar[5]arenes have been combined for the self-assembly of two supramolecular vesicular systems, i.e., PP5-IR1 and PP5-IR2, affording aqueous solubility and lowered cellular toxicity. In aqueous solution, all these fluorophores displayed room-temperature emission with λmax at 986-1013 nm and quantum yields of 0.54-1.45%. They also exhibited good chemical stability and reasonable self-assembled sizes, which may find potential applications in NIR-II imaging. In addition, PP5-IR1 can be used as a fluorescent chemosensor for selective recognition of glutathione through the cleavage of dinitrophenyl ether and release the fluorescent dye.

Revisiting molecularly conformation-planarized organic dyes for NIR-II fluorescence imaging

Fluorescence imaging in the second window (NIR-II, 1000-1700 nm) provides deeper penetration depth and higher resolution, but there is still a dilemma for designing NIR-II dyes for simultaneously enhancing fluorescence efficiency and prolonging excitation wavelength. Herein, a molecular conformation planarization strategy has been revisited to guide the synthesis of two donor-acceptor-donor dyes (named T-BBT and BT-BBT). On the one hand, conformational planarization can extend the absorption peaks of T-BBT and BT-BBT to the NIR region with high molar extinction coefficients of 30.5 × 103 and 16.4 × 103 L (mol-1 cm-1) at 1064 nm, respectively. On the other hand, structural rigidity can weaken electronic vibration coupling-related non-radiative decay pathways, whereby both T-BBT and BT-BBT display rather high fluorescence efficiencies of 3.6% and 13.5% in solution. Furthermore, a molecular doping strategy is adopted to alleviate fluorescence quenching in the aggregated state by suppressing long-distance energy migration, and 2.5 wt% doped BT-BBT nanoparticles show a high fluorescence efficiency of 2.0%, which enables the application of in vivo deep NIR-II fluorescence imaging for vessels and tumors with high resolution under 980 nm excitation. This work demonstrates that organic dyes with structural planarization can bridge the gap between NIR-II absorption and fluorescence efficiency.

Orchestrated Strategies for Developing Fluorophores for NIR-II Imaging

Fluorescence imaging (FLI), a non-invasive, real-time, and highly sensitive imaging modality, allows for investigating the molecular/cellular level activities to understand physiological functions and diseases. The emergence of the second near-infrared window (NIR-II, 1000-1700 nm) has endowed fluorescence imaging with deeper tissue penetration and unprecedented clarity. Among the various NIR-II imaging fluorophores, the organic fluorescent probes have occupied a pivotal position in bioimaging due to their higher biocompatibility, safety, and potential for clinical applications compared with those of the inorganic probes. To obtain high-quality organic dyes, diverse strategies have been taken. In this review, different strategies for optimizing NIR-II organic fluorophores are summarized, including traditional chemical modifications, and emerging bioengineering operations, which have not previously been elaborated on and summarized. Moreover, the bioengineering strategies are highlighted using endogenous serum proteins and even exogenous gene-editing proteins, which would provide fresh insights to design good-performance dyes and help develop NIR-II probes with clinical translation potential in the future. A critical perspective on the direction of the design strategies of NIR-II dyes for disease imaging is also proposed.

The Application of Bio-orthogonality for In Vivo Animal Imaging

The application of bio-orthogonality has greatly facilitated numerous aspects of biological studies in recent years. In particular, bio-orthogonal chemistry has transformed biological research, including in vitro conjugate chemistry, target identification, and biomedical imaging. In this review, we highlighted examples of bio-orthogonal in vivo imaging published in recent years. We grouped the references into two major categories: bio-orthogonal chemistry-related imaging and in vivo imaging with bio-orthogonal nonconjugated pairing. Lastly, we discussed the challenges and opportunities of bio-orthogonality for in vivo imaging.

A Highly Water-Soluble Aggregation-Induced Emission Luminogen with Anion-π+ Interactions for Targeted NIR Imaging of Cancer Cells and Type I Photodynamic Therapy

The low oxygen dependence of type I photosensitizers (PSs) has made them a popular choice for treating solid tumors. However, the drawbacks of poor water solubility, short emission wavelength, poor stability, and inability to distinguish cancer cells from normal cells limit the application of most type I PSs in clinical therapy. Thereby, developing novel type I PSs for overcoming these problems is an urgent but challenging task. Herein, by utilizing the distinctive structural characteristics of anion-π+ interactions, a highly water-soluble type I PS (DPBC-Br) with aggregation-induced emission (AIE) characteristic and near-infrared (NIR) emission is fabricated for the first time. DPBC-Br displays remarkable water solubility (7.3 mM) and outstanding photobleaching resistance, enabling efficient and precise differentiation between tumor cells and normal cells in a wash-free and long-term tracking manner via NIR-I imaging. Additionally, the superior type I reactive oxygen species (ROS) produced by DPBC-Br provide both specific killing of cancer cells in vitro and inhibition of tumor growth in vivo, with negligible systemic toxicity. This study rationally constructs a highly water-soluble type I PS, which has higher reliability and controllability compared with conventional nanoparticle formulating procedures, offering great potential for clinical cancer treatment.

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.

Addressing the in vivo delivery of nucleic-acid nanostructure therapeutics

DNA and RNA nanostructures are being investigated as therapeutics, vaccines, and drug delivery systems. These nanostructures can be functionalized with guests ranging from small molecules to proteins with precise spatial and stoichiometric control. This has enabled new strategies to manipulate drug activity and to engineer devices with novel therapeutic functionalities. Although existing studies have offered encouraging in vitro or pre-clinical proof-of-concepts, establishing mechanisms of in vivo delivery is the new frontier for nucleic-acid nanotechnologies. In this review, we first provide a summary of existing literature on the in vivo uses of DNA and RNA nanostructures. Based on their application areas, we discuss current models of nanoparticle delivery, and thereby highlight knowledge gaps on the in vivo interactions of nucleic-acid nanostructures. Finally, we describe techniques and strategies for investigating and engineering these interactions. Together, we propose a framework to establish in vivo design principles and advance the in vivo translation of nucleic-acid nanotechnologies.

Acceptor Engineering Produces Ultrafast Nonradiative Decay in NIR-II Aza-BODIPY Nanoparticles for Efficient Osteosarcoma Photothermal Therapy via Concurrent Apoptosis and Pyroptosis

Small-molecule photothermal agents (PTAs) with intense second near-infrared (NIR-II, 1,000 to 1,700 nm) absorption and high photothermal conversion efficiencies (PCEs) are promising candidates for treating deep-seated tumors such as osteosarcoma. To date, the development of small-molecule NIR-II PTAs has largely relied on fabricating donor-acceptor-donor (D-A-D/D') structures and limited success has been achieved. Herein, through acceptor engineering, a donor-acceptor-acceptor (D-A-A')-structured NIR-II aza-boron-dipyrromethene (aza-BODIPY) PTA (SW8) was readily developed for the 1,064-nm laser-mediated phototheranostic treatment of osteosarcoma. Changing the donor groups to acceptor groups produced remarkable red-shifts of absorption maximums from first near-infrared (NIR-I) regions (~808 nm) to NIR-II ones (~1,064 nm) for aza-BODIPYs (SW1 to SW8). Furthermore, SW8 self-assembled into nanoparticles (SW8@NPs) with intense NIR-II absorption and an ultrahigh PCE (75%, 1,064 nm). This ultrahigh PCE primarily originated from an additional nonradiative decay pathway, which showed a 100-fold enhanced decay rate compared to that shown by conventional pathways such as internal conversion and vibrational relaxation. Eventually, SW8@NPs performed highly efficient 1,064-nm laser-mediated NIR-II photothermal therapy of osteosarcoma via concurrent apoptosis and pyroptosis. This work not only illustrates a remote approach for treating deep-seated tumors with high spatiotemporal control but also provides a new strategy for building high-performance small-molecule NIR-II PTAs.

Hypsochromic Shift Donor-Acceptor NIR-II Dye for High-Efficiency Tumor Imaging

Nowadays, second near-infrared window (NIR-II) dyes' development focuses on pursuing a longer absorption/emission wavelength and higher quantum yield, which usually means an extended π conjugation system, resulting in an enormous molecular weight and poor druggability. Most researchers thought that the reduced π conjugation system would bring on a blueshift spectrum that causes dim imaging qualities. Little efforts have been made to study smaller NIR-II dyes with a reduced π conjugation system. Herein, we synthesized a reduced π conjugation system donor-acceptor (D-A) probe TQ-1006 (Em = 1006 nm). Compared with its counterpart donor-acceptor-donor (D-A-D) structure TQT-1048 (Em = 1048 nm), TQ-1006 exhibited comparable excellent blood vessels, lymphatic drainage imaging performance, and a higher tumor-to-normal tissue (T/N) ratio. An RGD conjugated probe TQ-RGD showed an extra high contrast tumor imaging (T/N ≥ 10), further proving D-A dyes' excellent NIR-II biomedical imaging applications. Overall, the D-A framework provides a promising approach to designing next-generation NIR-II fluorophores.

Fluorescence attenuated by a thick scattering medium: Theory, simulations and experiments

Fluorescence-based imaging has an enormous impact on our understanding of biological systems. However, in vivo fluorescence imaging is greatly influenced by tissue scattering. A better understanding of this dependence can improve the potential of noninvasive in vivo fluorescence imaging. In this article, we present a diffusion model, based on an existing master-slave model, of isotropic point sources imbedded in a scattering slab, representing fluorophores within a tissue. The model was compared with Monte Carlo simulations and measurements of a fluorescent slide measured through tissue-like phantoms with different reduced scattering coefficients (0.5-2.5 mm^-1 ) and thicknesses (0.5-5 mm). Results show a good correlation between our suggested theory, simulations and experiments; while the fluorescence intensity decays as the slab's scattering and thickness increase, the decay rate decreases as the reduced scattering coefficient increases in a counterintuitive manner, suggesting fewer fluorescence artifacts from deep within the tissue in highly scattering media.

THQ-Xanthene: An Emerging Strategy to Create Next-Generation NIR-I/II Fluorophores

Near-infrared fluorescence imaging is vital for exploring the biological world. The short emissions (<650 nm) and small Stokes shifts (<30 nm) of current xanthene dyes obstruct their biological applications since a long time. Recently, a potent and universal THQ structural modification technique that shifts emission to the NIR-I/II range and enables a substantial Stokes shift (>100 nm) for THQ-modified xanthene dyes is established. Thus, a timely discussion of THQ-xanthene and its applications is extensive. Hence, the advent, working principles, development trajectory, and biological applications of THQ-xanthene dyes, especially in the fields of fluorescence probe-based sensing and imaging, cancer theranostics, and super-resolution imaging, are introduced. It is envisioned that the THQ modification tactic is a simple yet exceptional approach to upgrade the performance of conventional xanthene dyes. THQ-xanthene will advance the strides of xanthene-based potentials in early fluorescent diagnosis of diseases, cancer theranostics, and imaging-guided surgery.

Anti-Quenching NIR-II J-Aggregates of Benzo[c]thiophene Fluorophore for Highly Efficient Bioimaging and Phototheranostics

Molecular fluorophores with the second near-infrared (NIR-II) emission hold great potential for deep-tissue bioimaging owing to their excellent biocompatibility and high resolution. Recently, J-aggregates are used to construct long-wavelength NIR-II emitters as their optical bands show remarkable red shifts upon forming water-dispersible nano-aggregates. However, their wide applications in the NIR-II fluorescence imaging are impeded by the limited varieties of J-type backbone and serious fluorescence quenching. Herein, a bright benzo[c]thiophene (BT) J-aggregate fluorophore (BT6) with anti-quenching effect is reported for highly efficient NIR-II bioimaging and phototheranostics. The BT fluorophores are manipulated to have Stokes shift over 400 nm and aggregation-induced emission (AIE) property for conquering the self-quenching issue of the J-type fluorophores. Upon forming BT6 assemblies in an aqueous environment, the absorption over 800 nm and NIR-II emission over 1000 nm are boosted for more than 41 and 26 folds, respectively. In vivo visualization of the whole-body blood vessel and imaging-guided phototherapy results verify that BT6 NPs are excellent agent for NIR-II fluorescence imaging and cancer phototheranostics. This work develops a strategy to construct bright NIR-II J-aggregates with precisely manipulated anti-quenching properties for highly efficient biomedical applications.

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.

1,4-Bisvinylbenzene-Bridged BODIPY Dimers for Fluorescence Imaging in the Second Near-Infrared Window

Herein, we report a class of 1,4-bisvinylbenzene-bridged BODIPY dimers with fluorescence emission in the second near-infrared window (NIR-II, 1000-1700 nm). These dyes show excellent NIR-II fluorescence properties and can be easily functionalized to achieve good water-solubility or tumor-targeting ability. In vivo imaging results demonstrate that these dyes have high resolution and deep-penetration NIR-II imaging ability, which enable them to be used as promising NIR-II imaging agents.

NIR-II fluorescence imaging-guided colorectal cancer surgery targeting CEACAM5 by a nanobody

BACKGROUND

Surgery is the cornerstone of colorectal cancer (CRC) treatment, yet complete removal of the tumour remains a challenge. The second near-infrared window (NIR-II, 1000-1700 nm) fluorescent molecular imaging is a novel technique, which has broad application prospects in tumour surgical navigation. We aimed to evaluate the ability of CEACAM5-targeted probe for CRC recognition and the value of NIR-II imaging-guided CRC resection.

METHODS

We constructed the probe 2D5-IRDye800CW by conjugated anti-CEACAM5 nanobody (2D5) with near-infrared fluorescent dye IRDye800CW. The performance and benefits of 2D5-IRDye800CW at NIR-II were confirmed by imaging experiments in mouse vascular and capillary phantom. Then mouse colorectal cancer subcutaneous tumour model (n = 15), orthotopic model (n = 15), and peritoneal metastasis model (n = 10) were constructed to investigate biodistribution of probe and imaging differences between NIR-I and NIR-II in vivo, and then tumour resection was guided by NIR-II fluorescence. Fresh human colorectal cancer specimens were incubated with 2D5-IRDye800CW to verify its specific targeting ability.

FINDINGS

2D5-IRDye800CW had an NIR-II fluorescence signal extending to 1600 nm and bound specifically to CEACAM5 with an affinity of 2.29 nM. In vivo imaging, 2D5-IRDye800CW accumulated rapidly in tumour (15 min) and could specifically identify orthotopic colorectal cancer and peritoneal metastases. All tumours were resected under NIR-II fluorescence guidance, even smaller than 2 mm tumours were detected, and NIR-II had a higher tumour-to-background ratio than NIR-I (2.55 ± 0.38, 1.94 ± 0.20, respectively). 2D5-IRDye800CW could precisely identify CEACAM5-positive human colorectal cancer tissue.

INTERPRETATION

2D5-IRDye800CW combined with NIR-II fluorescence has translational potential as an aid to improve R0 surgery of colorectal cancer.

FUNDINGS

This study was supported by Beijing Natural Science Foundation (JQ19027), the National Key Research and Development Program of China (2017YFA0205200), National Natural Science Foundation of China (NSFC) (61971442, 62027901, 81930053, 92059207, 81227901, 82102236), Beijing Natural Science Foundation (L222054), CAS Youth Interdisciplinary Team (JCTD-2021-08), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA16021200), the Zhuhai High-level Health Personnel Team Project (Zhuhai HLHPTP201703), the Fundamental Research Funds for the Central Universities (JKF-YG-22-B005) and Capital Clinical Characteristic Application Research (Z181100001718178). The authors would like to acknowledge the instrumental and technical support of the multi-modal biomedical imaging experimental platform, Institute of Automation, Chinese Academy of Sciences.

NIR-II Responsive Upconversion Nanoprobe with Simultaneously Enhanced Single-Band Red Luminescence and Phase/Size Control for Bioimaging and Photodynamic Therapy

Lanthanide based upconversion (UC) nanoprobes have emerged as promising agents for biological applications. Extending the excitation light to the second near-infrared (NIR-II), instead of the traditional 980/808 nm light, and realizing NIR-II responsive single-band red UC emission is highly demanded for bioimaging application, which has not yet been explored. Here, a new type of NIR-II (1532 nm) light responsive UC nanoparticles (UCNPs) with enhanced single-band red UC emission and controllable phase and size is designed by introducing Er³⁺ as sensitizer and utilizing Mn²⁺ as energy manipulator. Through tuning the content of Mn²⁺ in NaLnF₄ :Er/Mn, the crystal phase, size, and emitting color are readily controlled, and the red-to-green (R/G) ratio is significantly increased from ≈20 to ≈300, leading to NIR-II responsive single band red emission via efficient energy transfer between Er³⁺ and Mn²⁺ . In addition, the single band red emitting intensity can be further improved by coating shell to avoid the surface quenching effect. More importantly, NIR-II light activated red UC bioimaging and photodynamic therapy through loading photosensitizer of zinc phthalocyanine are successfully achieved for the first time. These findings provide a new strategy of designing NIR-II light responsive single-band red emissive UCNPs for biomedical applications.

A Water-Soluble AIEgen for Noninvasive Diagnosis of Kidney Fibrosis via SWIR Fluorescence and Photoacoustic Imaging

Early diagnosis of renal fibrosis is crucially significant on account of its worldwide prevalent tendency. Optical imaging in the near-infrared window has been recognized as an appealing technique for the timely detection of renal dysfunction. However, formulating a contrast agent that allows early monitoring of renal fibrosis and concurrently renally clearable in a normal group is still challenging. Herein, a nanosized fluorophore with aggregation-induced emission (AIE) features, namely AIE-4PEG550 NPs, is well-tailored and amenable to longitudinal visualization of the fibrosis progression specifically in the early-stage via short-wave infrared (SWIR, 900-1700 nm) fluorescence and photoacoustic bimodal imaging. The small size (≈26 nm), renally filtrable molecular weight (3.3 kDa), high renal clearance efficiency (93.1 ± 1.7% excretion through the kidneys within 24 h), outstanding imaging performance, and good biocompatibility, together make AIE-4PEG550 NPs remarkably impressive and far superior to clinical diagnostic assays. The finding in this study would provide a blueprint for the next generation of diagnostic agents for the extent of renal fibrosis.

Water-Dispersible Activatable Nanoprobe for Detecting Cadmium-Ion-Induced Oxidative Stress in Edible Crops via Near-Infrared Second-Window Fluorescence Imaging

Edible crops are important in terms of food security and sustainable agriculture. Heavy-metal-ion contamination of water/soil has deleterious impacts on the growth of edible crops. Among the heavy metals, cadmium (Cd) is toxic to plants, people, and animals, as it is widely used in industry; it has become the most important metal ion in the soil/water pollution. Once the toxic Cd ion enters edible crops via the water/soil in which the crops grow, it will induce oxidative stress (overproduction of reactive oxygen species with H₂O₂ being the most abundant) in the crops, and strong oxidative stress leads to the crops' growth depression or inhibition. Hence, it is of great significance to accurately monitor the oxidative stress induced by Cd ions in edible crops, as the monitoring results could be employed for the early warning of Cd-ion pollution in water/soil. Herein, we design an activatable nanoprobe that can detect Cd-ion-induced oxidative stress in edible crops via near-infrared second-window (NIR-II) fluorescence imaging. The molecular probe IXD-B contains the diphenylamine-modified xanthene group acting as the electron-donating unit, bis(methylenemalononitrile)indan as the electron-accepting unit, and the methenephenylboronic acid group as the recognition moiety for H₂O₂ and the fluorescence quencher. The probe molecules being encapsulated by the amphiphilic DSPE-PEG2000 render the water-dispersible nanoprobe (IXD-B@DSPE-PEG2000). When the nanoprobe enters the edible crops, it can be activated by the overexpressed H₂O₂ therein and consequently emit strong NIR-II fluorescence signals for visualizing and tracking the oxidative stress in edible crops induced by Cd ions.

J-aggregates albumin-based NIR-II fluorescent dye nanoparticles for cancer phototheranostics

Phototheranostics, relying on energy conversions of fluorophores upon excitation, integrating diagnostic fluorescence imaging and photo-driven therapy, represents a promising strategy for cancer precision medicine. Compared with the first near-infrared biological window (NIR-I), fluorophores imaged in the second window (NIR-II, 1000–1700 ​nm) exhibit a higher temporal and spatial resolution and tissue penetration depth. Polymethine cyanine-based dye IR1061 is a typical NIR-II small-molecule organic fluorophore, but its low water solubility and short circulation time limiting its biological applications. Therefore, human serum albumin (HSA) nanoparticles with great biocompatibility and biosafety were employed to fabricate hydrophobic IR1061, which exhibited red-shifted absorption band as typical for J-aggregates. Moreover, IR1061@HSA nanoparticles can be successfully used for NIR-II imaging to noninvasively visualize the tumor vascular networks, as well as real-time intraoperative image-guided tumor resection. Interestingly, benefiting from the high photothermal conversion efficiency brought by J-aggregates, IR1061@HSA nanoparticles were also explored for photothermal therapy (PTT) and cause efficient thermal ablation of tumors. Overall, IR1061@HSA, as a novel J-aggregates albumin-based NIR II dye nanoparticle with high biocompatibility, provides an integrated versatile platform for cancer phototheranostics with promising clinical translation prospects.