Lifetime-engineered NIR-II nanoparticles unlock multiplexed in vivo imaging

Three-Dimensional Visualization of Breast Cancer Pathology Evolution in Clinical Patient Tissues with NIR-II Imaging

Breast cancer (BC) is the most common tumor worldwide and requires crucial molecular typing for treatment and prognosis assessment. Currently, approaches like pathological staining, immunohistochemistry (IHC), and immunofluorescence (IF) face limitations due to the low signal-to-background ratio (SBR) and high tumor heterogeneity, resulting in a high misdiagnosis rate. Fluorescent assay in the second near-infrared region (NIR-II, 1000-1700 nm) exhibits ultrahigh SBR owing to diminished scattering and tissue autofluorescence. Here, we present a NIR-II strategy for accurate BC molecular typing and three-dimensional (3D) visualization based on the atomically precise fluorescent Au24Pr1 clusters. Single-atom Pr doping results in 3.9-fold fluorescence enhancement and long-term photostability. The Au24Pr1 clusters possess high fluorescence centered at ∼1100 nm and the SBR on pathological section diagnosis was 4 times higher than that of NIR-I imaging. This enables high spatial resolution 3D visualization of biopsy specimens, which can surmount tissue heterogeneity for clinical diagnosis of BC.

Fourier Raman light field microscopy based on surface-enhanced Raman scattering

Raman scattering, as a vibrational spectrum that carries material information, has no photobleaching that enables long-duration imaging. Raman spectra have very narrow emission peaks, and multiplex Raman imaging can be achieved by using different Raman scattering peak signals. These advantages make Raman imaging widely used in biology, cytology, and medicine, which has a wider range of application scenarios. However, obtaining a three-dimensional (3D) Raman image requires scanning for tens of minutes to several hours at present. Therefore, a fast non-scanning 3D Raman imaging method is greatly needed. In this article, we propose a Fourier Raman light field microscopy based on surface-enhanced Raman scattering (sers-FRLFM). Using flower-like gap-enhanced Raman nanoparticles (F-GERNs) to enhance Raman scattering signals, a Fourier-configured light field microscope (LFM) is capable of recording complete four-dimensional Raman field information in a single frame, facilitating the 3D reconstruction of the Raman image without generating reconstruction artifacts at the native object plan. Moreover, F-GERNs can mark specific locations and have the potential to become a new tracing method to achieve specific imaging. This imaging method has great potential in the 3D real-time Raman imaging of cells, microorganisms, and tissues with the lateral resolution of 2.40 µm and an axial resolution of 4.02 µm.

Noninvasive in vivo microscopy of single neutrophils in the mouse brain via NIR-II fluorescent nanomaterials

In vivo microscopy of single cells enables following pathological changes in tissues, revealing signaling networks and cell interactions critical to disease progression. However, conventional intravital microscopy at visible and near-infrared wavelengths <900 nm (NIR-I) suffers from attenuation and is typically performed following the surgical creation of an imaging window. Such surgical procedures cause the alteration of the local vasculature and induce inflammation in skin, muscle and skull, inevitably altering the microenvironment in the imaging area. Here, we detail the use of near-infrared fluorescence (NIR-II, 1,000-1,700 nm) for in vivo microscopy to circumvent attenuation in living tissues. This approach enables the noninvasive visualization of cell migration in deep tissues by labeling specific cells with NIR-II lanthanide downshifting nanoparticles exhibiting high physicochemical stability and photostability. We further developed a NIR-II fluorescence microscopy setup for in vivo imaging through the intact skull with high spatiotemporal resolution, which we use for the real-time dynamic visualization of single-neutrophil behavior in the deep brain of a mouse model of ischemic stroke. The labeled downshifting nanoparticle synthesis takes 5-6 d, the imaging system setup takes 1-2 h, the in vivo cell labeling takes 1-3 h, the in vivo NIR-II microscopic imaging takes 3-5 h and the data analysis takes 3-8 h. The procedures can be performed by users with standard laboratory training in nanomaterials research and appropriate animal handling.

An ultra-small organic dye nanocluster for enhancing NIR-II imaging-guided surgery outcomes

PURPOSE

The accuracy of surgery for patients with solid tumors can be greatly improved through fluorescence-guided surgery (FGS). However, existing FGS technologies have limitations due to their low penetration depth and sensitivity/selectivity, which are particularly prevalent in the relatively short imaging window (< 900 nm). A solution to these issues is near-infrared-II (NIR-II) FGS, which benefits from low autofluorescence and scattering under the long imaging window (> 900 nm). However, the inherent self-assembly of organic dyes has led to high accumulation in main organs, resulting in significant background signals and potential long-term toxicity.

METHODS

We rationalize the donor structure of donor-acceptor-donor-based dyes to control the self-assembly process to form an ultra-small dye nanocluster, thus facilitating renal excretion and minimizing background signals.

RESULTS

Our dye nanocluster can not only show clear vessel imaging, tumor and tumor sentinel lymph nodes definition, but also achieve high-performance NIR-II imaging-guided surgery of tumor-positive sentinel lymph nodes.

CONCLUSION

In summary, our study demonstrates that the dye nanocluster-based NIR-II FGS has substantially improved outcomes for radical lymphadenectomy.

Modulating Visible-Light Driven NIR Lanthanide Polymer Photocatalysis for Amplification Detection of Exosomal Proteins and Cancer Diagnosis

Near-infrared (NIR) luminescent lanthanide materials hold great promise for bioanalysis, as they have anti-interference properties. The approach of efficient luminescence is sensitization through a reasonable chromophore to overcome the obstacle of the aqueous phase. The involvement of the surfactant motif is an innovative strategy to arrange the amphiphilic groups to be regularly distributed near the polymer to form a closed sensitized space. Herein, a lanthanide polymer (TCPP-PEI70K-FITC@Yb/SDBS) is designed in which the meso-tetra(4-carboxyphenyl)porphine (TCPP) ligand serves as both a sensitizer and photocatalytic switch. The surfactant sodium dodecyl benzenesulfonate (SDBS) wraps the photosensitive polymers to form a hydrophobic layer, which augments the light-harvesting ability and expedites its photocatalysis. TCPP-PEI70K-FITC@Yb/SDBS is subsequently applied as an amplified photocatalysis toolbox for universally regulating the generation of reactive oxygen species (ROS). Boosting 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to produce blue products, a dual-mode biosensor is fabricated for improving the diagnosis of programmed death ligand-1-positive (PDL1) cancer exosomes. Exosomes were captured by Fe3O4 modified by the PDL1 aptamer, enabling replacement of alkaline phosphatase (ALP)-labeled multiple hybridized chains; then, the isolated ALP triggered a hydrolysis reaction to block the generation of oxTMB. Detection sensitivity improves by 1 order of magnitude through SDBS modulation, down to 104 particles/mL. The sensor performed well clinically in distinguishing cancer patients from healthy individuals, expanding physiological applications of near-infrared lanthanide luminescence.

Time Division Colorful Multiplexing Based on Carbon Nanodots with Modifiable Colors and Lifetimes

Optical multiplexing technology plays a crucial role in various fields such as data storage, anti-counterfeiting, and time-resolved biological imaging. Nevertheless, employing single-wavelength phosphorescence for multiplexing often results in spectral overlap among the emission peaks of various channels, which can precipitate crosstalk and misinterpretation in the information-decoding process, thereby compromising the integrity and precision of the encrypted data. This paper proposes a time-divided colorful multiplexing technology based on phosphorescent carbon nanodots with different colors and lifetimes. Using different luminescence colors to symbolize varying information levels helps achieve multitiered information encryption and storage. By modulation of the lifetime and the emission wavelength, intricate information can be encoded, thereby enhancing the intricacy and security of the encryption mechanism. By assigning different data bits to each color, more information can be encoded in the same physical space. This method enables higher-density information storage and fortifies encryption, ensuring the compactness and security of information.

Targeting macrophages with multifunctional nanoparticles to detect and prevent atherosclerotic cardiovascular disease

Despite the emergence of novel diagnostic, pharmacological, interventional, and prevention strategies, atherosclerotic cardiovascular disease remains a significant cause of morbidity and mortality. Nanoparticle (NP)-based platforms encompass diverse imaging, delivery, and pharmacological properties that provide novel opportunities for refining diagnostic and therapeutic interventions for atherosclerosis at the cellular and molecular levels. Macrophages play a critical role in atherosclerosis and therefore represent an important disease-related diagnostic and therapeutic target, especially given their inherent ability for passive and active NP uptake. In this review, we discuss an array of inorganic, carbon-based, and lipid-based NPs that provide magnetic, radiographic, and fluorescent imaging capabilities for a range of highly promising research and clinical applications in atherosclerosis. We discuss the design of NPs that target a range of macrophage-related functions such as lipoprotein oxidation, cholesterol efflux, vascular inflammation, and defective efferocytosis. We also provide examples of NP systems that were developed for other pathologies such as cancer and highlight their potential for repurposing in cardiovascular disease. Finally, we discuss the current state of play and the future of theranostic NPs. Whilst this is not without its challenges, the array of multifunctional capabilities that are possible in NP design ensures they will be part of the next frontier of exciting new therapies that simultaneously improve the accuracy of plaque diagnosis and more effectively reduce atherosclerosis with limited side effects.

Understanding of Lanthanide-Doped Core-Shell Structure at the Nanoscale Level

The groundbreaking development of lanthanide-doped core-shell nanostructures have successfully achieved precise optical tuning of rare-earth nanocrystals, leading to significant improvements in energy transfer efficiency and facilitating multifunctional integration. Exploring the atomic-level structural, physical, and optical properties of rare-earth core-shell nanocrystals is essential for advancing our understanding of their fundamental principles and driving the development of emerging applications. However, our knowledge of the atomic-level structural details of rare-earth nanocrystal core-shell structures remains limited. This review provides a comprehensive discussion of synthesis strategies, characterization techniques, interfacial ion-mixing phenomena, strain effects, and spectral modulation in core-shell structures of rare-earth-doped nanocrystals. Additionally, we prospectively discuss the challenges encountered in studying the fine structures of rare-earth-doped core-shell nanocrystals, particularly the increasing demand for researchers to integrate interdisciplinary knowledge and utilize high-end precision instruments.

Immunological nanomaterials to combat cancer metastasis

Metastasis causes greater than 90% of cancer-associated deaths, presenting huge challenges for detection and efficient treatment of cancer due to its high heterogeneity and widespread dissemination to various organs. Therefore, it is imperative to combat cancer metastasis, which is the key to achieving complete cancer eradication. Immunotherapy as a systemic approach has shown promising potential to combat metastasis. However, current clinical immunotherapies are not effective for all patients or all types of cancer metastases owing to insufficient immune responses. In recent years, immunological nanomaterials with intrinsic immunogenicity or immunomodulatory agents with efficient loading have been shown to enhance immune responses to eliminate metastasis. In this review, we would like to summarize various types of immunological nanomaterials against metastasis. Moreover, this review will summarize a series of immunological nanomaterial-mediated immunotherapy strategies to combat metastasis, including immunogenic cell death, regulation of chemokines and cytokines, improving the immunosuppressive tumour microenvironment, activation of the STING pathway, enhancing cytotoxic natural killer cell activity, enhancing antigen presentation of dendritic cells, and enhancing chimeric antigen receptor T cell therapy. Furthermore, the synergistic anti-metastasis strategies based on the combinational use of immunotherapy and other therapeutic modalities will also be introduced. In addition, the nanomaterial-mediated imaging techniques (e.g., optical imaging, magnetic resonance imaging, computed tomography, photoacoustic imaging, surface-enhanced Raman scattering, radionuclide imaging, etc.) for detecting metastasis and monitoring anti-metastasis efficacy are also summarized. Finally, the current challenges and future prospects of immunological nanomaterial-based anti-metastasis are also elucidated with the intention to accelerate its clinical translation.

Rational Design of Activatable Lanthanide NIR-IIb Emissive Nanoprobe for In Situ Specific Imaging of HOCl In Vivo

Hypochlorous acid (HOCl), as an indispensable signaling molecule in organisms, is one of the key members of reactive oxygen species (ROS). However, in vivo, real-time dynamic near-infrared fluorescence imaging of HOCl levels in the 1400-1700 nm sub-window (NIR-IIb) remains a major challenge due to the lack of suitable detection methods. Herein, a general design of HOCl-responsive NIR-IIb fluorescence nanoprobe is proposed by integrating NaLuF4Yb/Er@NaLuF4 downshift nanoparticles (DSNPs) and HOCl recognition/NIR-IIb emissive modulation unit of M2-xS (M = Cu, Co, Pb) nanodots for real-time monitoring of HOCl levels. The fluorescence modulation unit of M2-xS nanodots presents remarkably enhanced absorption than Yb sensitizer at 980 nm and greatly inhibits the NIR-IIb fluorescence emission via competitive absorption mechanism. While, the M2-xS nanodots are easily degraded after triggering by HOCl, resulting in HOCl responsive turn-on (≈ten folds) NIR-IIb emission at 1532 nm. More importantly, in vivo highly precise and specific monitoring of inflammatory with abnormal HOCl expression is successfully achieved. Thus, the explored competitive absorption mediated quenching-activation mechanism provides a new general strategy of designing HOCl-responsive NIR-IIb fluorescence nanoprobe for highly specific and sensitive HOCl detection.

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.

Development of Polymethine Dyes for NIR-II Fluorescence Imaging and Therapy

Fluorescence imaging in the second near-infrared window (NIR-II) is burgeoning because of its higher imaging fidelity in monitoring physiological and pathological processes than clinical visible/the second near-infrared window fluorescence imaging. Notably, the imaging fidelity is heavily dependent on fluorescence agents. So far, indocyanine green, one of the polymethine dyes, with good biocompatibility and renal clearance is the only dye approved by the Food and Drug Administration, but it shows relatively low NIR-II brightness. Importantly, tremendous efforts are devoted to synthesizing polymethine dyes for imaging preclinically and clinically. They have shown feasibility in the customization of structure and properties to fulfill various needs in imaging and therapy. Herein, a timely update on NIR-II polymethine dyes, with a special focus on molecular design strategies for fluorescent, photoacoustic, and multimodal imaging, is offered. Furthermore, the progress of polymethine dyes in sensing pathological biomarkers and even reporting drug release is illustrated. Moreover, the NIR-II fluorescence imaging-guided therapies with polymethine dyes are summarized regarding chemo-, photothermal, photodynamic, and multimodal approaches. In addition, artificial intelligence is pointed out for its potential to expedite dye development. This comprehensive review will inspire interest among a wide audience and offer a handbook for people with an interest in NIR-II polymethine dyes.

Shortwave-infrared-light-emitting probes for the in vivo tracking of cancer vaccines and the elicited immune responses

Tracking and imaging immune cells in vivo non-invasively would offer insights into the immune responses induced by vaccination. Here we report a cancer vaccine consisting of polymer-coated NaErF4/NaYF4 core-shell down-conversion nanoparticles emitting luminescence in the near-infrared spectral window IIb (1,500-1,700 nm in wavelength) and with surface-conjugated antigen (ovalbumin) and electrostatically complexed adjuvant (class-B cytosine-phosphate-guanine). Whole-body wide-field imaging of the subcutaneously injected vaccine in tumour-bearing mice revealed rapid migration of the nanoparticles to lymph nodes through lymphatic vessels, with two doses of the vaccine leading to the complete eradication of pre-existing tumours and to the prophylactic inhibition of tumour growth. The abundance of antigen-specific CD8+ T lymphocytes in the tumour microenvironment correlated with vaccine efficacy, as we show via continuous-wave imaging and lifetime imaging of two intravenously injected near-infrared-emitting probes (CD8+-T-cell-targeted NaYbF4/NaYF4 nanoparticles and H-2Kb/ovalbumin257-264 tetramer/PbS/CdS quantum dots) excited at different wavelengths, and by volumetrically visualizing the three nanoparticles via light-sheet microscopy with structured illumination. Nanoparticle-based vaccines and imaging probes emitting infrared light may facilitate the design and optimization of immunotherapies.

Lanthanide-dye hybrid luminophores for advanced NIR-II bioimaging

In vivo luminescence imaging in the second near-infrared window (NIR-II, 1000-2000 nm) is a potent technique for observing deep-tissue life activities, leveraging reduced light scattering, minimized autofluorescence, and moderate absorption attenuation to substantially enhance image contrast. Pushing the frontiers of NIR-II luminescence imaging forward, moving from static to dynamic event visualization, monochromatic to multicolor images, and fundamental research to clinical applications, necessitates the development of novel luminophores featuring bright emission, extendable wavelength, and optimal biocompatibility. Recently, lanthanide-dye hybrid luminophores (LDHLs) are gaining increasing attention for their wavelength extensibility, molecular size, narrowband emission, mega stokes shift, long lifetime, and high photostability. In this review, we will summarize the recent advances of NIR-II LDHLs and their applications in imaging and analysis of living mammals, and discuss future challenges in designing new LDHLs for deep-tissue imaging.

NIR-II light in clinical oncology: opportunities and challenges

Novel strategies utilizing light in the second near-infrared region (NIR-II; 900-1,880 nm wavelengths) offer the potential to visualize and treat solid tumours with enhanced precision. Over the past few decades, numerous techniques leveraging NIR-II light have been developed with the aim of precisely eliminating tumours while maximally preserving organ function. During cancer surgery, NIR-II optical imaging enables the visualization of clinically occult lesions and surrounding vital structures with increased sensitivity and resolution, thereby enhancing surgical quality and improving patient prognosis. Furthermore, the use of NIR-II light promises to improve cancer phototherapy by enabling the selective delivery of increased therapeutic energy to tissues at greater depths. Initial clinical studies of NIR-II-based imaging and phototherapy have indicated impressive potential to decrease cancer recurrence, reduce complications and prolong survival. Despite the encouraging results achieved, clinical translation of innovative NIR-II techniques remains challenging and inefficient; multidisciplinary cooperation is necessary to bridge the gap between preclinical research and clinical practice, and thus accelerate the translation of technical advances into clinical benefits. In this Review, we summarize the available clinical data on NIR-II-based imaging and phototherapy, demonstrating the feasibility and utility of integrating these technologies into the treatment of cancer. We also introduce emerging NIR-II-based approaches with substantial potential to further enhance patient outcomes, while also highlighting the challenges associated with imminent clinical studies of these modalities.

Fluorescence Multi-Detection Device Using a Lensless Matrix Addressable microLED Array

A Point-of-Care system for molecular diagnosis (PoC-MD) is described, combining GaN and CMOS chips. The device is a micro-system for fluorescence measurements, capable of analyzing both intensity and lifetime. It consists of a hybrid micro-structure based on a 32 × 32 matrix addressable GaN microLED array, with square LEDs of 50 µm edge length and 100 µm pitch, with an underneath wire bonded custom chip integrating their drivers and placed face-to-face to an array of 16 × 16 single-photon avalanche diodes (SPADs) CMOS. This approach replaces instrumentation based on lasers, bulky optical components, and discrete electronics with a full hybrid micro-system, enabling measurements on 32 × 32 spots. The reported system is suitable for long lifetime (>10 ns) fluorophores with a limit of detection ~1/4 µM. Proof-of-concept measurements of streptavidin conjugate Qdot™ 605 and Amino PEG Qdot™ 705 are demonstrated, along with the device ability to detect both fluorophores in the same measurement.

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.

Persistent Luminescence Lifetime-Based Near-Infrared Nanoplatform via Deep Learning for High-Fidelity Biosensing of Hypochlorite

In light of deep tissue penetration and ultralow background, near-infrared (NIR) persistent luminescence (PersL) bioprobes have become powerful tools for bioapplications. However, the inhomogeneous signal attenuation may significantly limit its application for precise biosensing owing to tissue absorption and scattering. In this work, a PersL lifetime-based nanoplatform via deep learning was proposed for high-fidelity bioimaging and biosensing in vivo. The persistent luminescence imaging network (PLI-Net), which consisted of a 3D-deep convolutional neural network (3D-CNN) and the PersL imaging system, was logically constructed to accurately extract the lifetime feature from the profile of PersL intensity-based decay images. Significantly, the NIR PersL nanomaterials represented by Zn1+xGa2-2xSnxO4: 0.4 % Cr (ZGSO) were precisely adjusted over their lifetime, enabling the PersL lifetime-based imaging with high-contrast signals. Inspired by the adjustable and reliable PersL lifetime imaging of ZGSO NPs, a proof-of-concept PersL nanoplatform was further developed and showed exceptional analytical performance for hypochlorite detection via a luminescence resonance energy transfer process. Remarkably, on the merits of the dependable and anti-interference PersL lifetimes, this PersL lifetime-based nanoprobe provided highly sensitive and accurate imaging of both endogenous and exogenous hypochlorite. This breakthrough opened up a new way for the development of high-fidelity biosensing in complex matrix systems.

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.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

Short-wave Infrared Photoluminescence Lifetime Mapping of Rare-Earth Doped Nanoparticles Using All-Optical Streak Imaging

The short-wave infrared (SWIR) photoluminescence lifetimes of rare-earth doped nanoparticles (RENPs) have found diverse applications in fundamental and applied research. Despite dazzling progress in the novel design and synthesis of RENPs with attractive optical properties, existing optical systems for SWIR photoluminescence lifetime imaging are still considerably restricted by inefficient photon detection, limited imaging speed, and low sensitivity. To overcome these challenges, SWIR photoluminescence lifetime imaging microscopy using an all-optical streak camera (PLIMASC) is developed. Synergizing scanning optics and a high-sensitivity InGaAs CMOS camera, SWIR-PLIMASC has a 1D imaging speed of up to 138.9 kHz in the spectral range of 900-1700 nm, which quantifies the photoluminescence lifetime of RENPs in a single shot. A 2D photoluminescence lifetime map can be acquired by 1D scanning of the sample. To showcase the power of SWIR-PLIMASC, a series of core-shell RENPs with distinct SWIR photoluminescence lifetimes is synthesized. In particular, using Er3+ -doped RENPs, SWIR-PLIMASC enables multiplexed anti-counterfeiting. Leveraging Ho3+ -doped RENPs as temperature indicators, this system is applied to SWIR photoluminescence lifetime-based thermometry. Opening up a new avenue for efficient SWIR photoluminescence lifetime mapping, this work is envisaged to contribute to advanced materials characterization, information science, and biomedicine.

White light and near-infrared emissions of Pr3+ ions in SiO2-LaF3 sol-gel nano-glass-ceramics

In this work, we report the results of our investigations on the structural and luminescence properties of SiO2-LaF3:Pr3+ nano-glass-ceramics synthesized using the sol-gel method. Based on XRD, microscopic (TEM), and ATR-IR measurements, the crystallization of LaF3 nanocrystals favorably occupied by Pr3+ ions and overall transformations within the silicate sol-gel hosts dependent on heat-treatment conditions of the as-prepared amorphous xerogels were characterized. The fabricated oxyfluoride nano-glass-ceramics revealed the emissions within the greenish-blue (3P0,1 → 3H4, 3P0,1 → 3H5), reddish-orange (3P0,1 → 3H6, 1D2 → 3H4, 3P0 → 3F2,3), and NIR spectral scopes (1D2 → 3F4,1G4, 1G4 → 3H5, 3F3,4 → 3H4). Based on the luminescence spectra in the VIS range, the CIE chromaticity coordinates, correlated color temperatures (CCT), and color purities (CP) were calculated. The obtained results clearly indicate that the prepared Pr3+-doped sol-gel nano-glass-ceramics exhibit warm or neutral white light emissions with CCT values in the range from 2567 K to 3962 K. The lowest CP value was estimated at 12.8%, indicating that the fabricated samples are able to emit bright white light. Additionally, the NIR emissions cover E, S, C, and L bands, which are important for devices applicable in telecommunication technologies. For further characterization, the τ(3P0) and τ(1D2) decay times were estimated. It was established that the emissions from the 3P0 and the 1D2 excited states of Pr3+ ions, as well as the participation of cross-relaxation (CR) processes, are dependent on the size of crystallized LaF3 phase, distribution of optically active Pr3+ ions between amorphous and crystalline phase (determining the Pr3+-Pr3+ inter-ionic distances), and relative content of OH groups in the prepared sol-gel hosts.

Preparation of rare earth-doped nano-fluorescent materials in the second near-infrared region and their application in biological imaging

Second near-infrared (NIR-II) fluorescence imaging (FLI) has gained widespread interest in the biomedical field because of its advantages of high sensitivity and high penetration depth. In particular, rare earth-doped nanoprobes (RENPs) have shown completely different physical and chemical properties from macroscopic substances owing to their unique size and structure. This paper reviews the synthesis methods and types of RENPs for NIR-II imaging, focusing on new methods to enhance the luminous intensity of RENPs and multi-band imaging and multi-mode imaging of RENPs in biological applications. This review also presents an overview of the challenges and future development prospects based on RENPs in NIR-II regional bioimaging.

An Intelligent DNA Nanoreactor for Easy-to-Read In Vivo Tumor Imaging and Precise Therapy

Nanomaterial-based in vivo tumor imaging and therapy have attracted extensive attention; however, they suffer from the unintelligent "always ON" or single-parameter responsive signal output, substantial off-target effects, and high cost. Therefore, achieving in vivo easy-to-read tumor imaging and precise therapy in a multi-parameter responsive and intelligent manner remains challenging. Herein, an intelligent DNA nanoreactor (iDNR) was constructed following the "AND" Boolean logic algorithm to address these issues. iDNR-mediated in situ deposition of photothermal substance polydopamine (PDA) can only be satisfied in tumor tissues with abundant membrane protein biomarkers "AND" hydrogen peroxide (H2 O2 ). Therefore, intelligent temperature-based in vivo easy-to-read tumor imaging is realized without expensive instrumentation, and its diagnostic performance matches with that of flow cytometry, and photoacoustic imaging. Moreover, precise photothermal therapy (PTT) of tumors could be achieved via intelligent heating of tumor tissues. The precise PTT of primary tumors in combination with immune checkpoint blockade (ICB) therapy suppresses the growth of distant tumors and inhibits tumor recurrence. Therefore, highly programmable iDNR is a powerful tool for intelligent biomedical applications.

Photophysics and its application in photon upconversion

Photoluminescence (PL) upconversion is a phenomenon involving light-matter interaction, where the energy of the emitted photons is higher than that of the incident photons. PL upconversion has promising applications in optoelectronic devices, displays, photovoltaics, imaging, diagnosis and treatment. In this review, we summarize the mechanism of PL upconversion and ultrafast PL physical processes. In particular, we highlight the advances in laser cooling, biological imaging, volumetric displays and photonics.

Directive giant upconversion by supercritical bound states in the continuum

Photonic bound states in the continuum (BICs), embedded in the spectrum of free-space waves1,2 with diverging radiative quality factor, are topologically non-trivial dark modes in open-cavity resonators that have enabled important advances in photonics3,4. However, it is particularly challenging to achieve maximum near-field enhancement, as this requires matching radiative and non-radiative losses. Here we propose the concept of supercritical coupling, drawing inspiration from electromagnetically induced transparency in near-field coupled resonances close to the Friedrich-Wintgen condition2. Supercritical coupling occurs when the near-field coupling between dark and bright modes compensates for the negligible direct far-field coupling with the dark mode. This enables a quasi-BIC field to reach maximum enhancement imposed by non-radiative loss, even when the radiative quality factor is divergent. Our experimental design consists of a photonic-crystal nanoslab covered with upconversion nanoparticles. Near-field coupling is finely tuned at the nanostructure edge, in which a coherent upconversion luminescence enhanced by eight orders of magnitude is observed. The emission shows negligible divergence, narrow width at the microscale and controllable directivity through input focusing and polarization. This approach is relevant to various physical processes, with potential applications for light-source development, energy harvesting and photochemical catalysis.

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.

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.

Ultrastrong Infrared Emission at 1460 nm from Lanthanide-Doped Nanoparticles with Interfacial Sensitization

Fluorescent imaging in the second near-infrared window (NIR-II; 1000-1700 nm) has recently received tremendous attention due to its excellent tissue probing depths and high resolution. Under NIR pumping, lanthanide-doped nanoparticles can emit infrared light covering a wide range of 800-3000 nm which has good potential for NIR-II imaging and detection. However, the low efficiency hinders their application. Here, we report intense infrared emission at 1460 nm from lanthanide-doped core/shell nanoparticles with efficient interfacial sensitization. The emitter Tm3+ ion and the sensitizer Yb3+ and Nd3+ ions are spatially separated in core and shells so that the efficient interfacial energy transfer is established between Tm3+ and Yb3+/Nd3+ ions, while thermal vibration spread of high concentration of Yb3+ ions and cross-relaxation among Tm3+, Yb3+, and Nd3+ ions are suppressed. As a result, the ultrastrong NIR-II emission at 1460 nm is achieved, which is more than 100-times that in classic core/shell nanoparticles doped with Tm3+ (NaYF4:20%Yb,0.5%Tm@ NaYF4).

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.

NIR-II organic small molecule probe for labeling lymph nodes and guiding tumor imaging

Organic small molecule fluorescent groups have injected new material support into the field of medical imaging due to their unique luminescence mechanism and easy tuning of structure. The great potential of NIR-II window imaging forces us to continuously optimize the structure of organic fluorophores to design better fluorescent molecules for fluorescence imaging-guided surgery. An ideal organic small molecule fluorescent group: it can penetrate into the inside of the organism, clearly present the internal structure and the edge contour of different tissues, so as to perfectly achieve internal imaging and accurately guide external surgery. In vivo, fluorescent groups do not damage normal tissues and organs. However, problems such as low quantum yield and poor biocompatibility greatly limit the clinical transformation of NIR-II fluorescent small molecules. To avoid the shortcomings of NIR-II fluorescent probes as much as possible and better realize image-guided surgery, in this experiment, the biplane donor unit was incorporated into the twisted D-π-A-π-D structure to expand the conjugated structure of the fluorescent group, which not only realized NIR-II emission, but also had high quantum yield and biosafety.

A FRET-Based Ratiometric H2S Sensor for Sensitive Optical Molecular Imaging in Second Near-Infrared Window

Second near-infrared (NIR-II) window optical molecular imaging kicks off a new revolution in high-quality imaging in vivo, but always suffers from the hurdles of inevitable tissue autofluorescence background and NIR-II probe development. Here, we prepare a Förster resonance energy transfer-based ratiometric NIR-II window hydrogen sulfide (H2S) sensor through the combination of an H2S-responsive NIR-II cyanine dye (acceptor, LET-1055) and an H2S-inert rhodamine hybrid polymethine dye (donor, Rh930). This sensor not only exhibits high sensitivity and selectivity, but also shows rapid reaction kinetics (~20 min) and relatively low limit of detection (~96 nM) toward H2S, allowing in vivo ratiometric NIR-II fluorescence imaging of orthotopic liver and colon tumors and visualization of the drug-induced hepatic H2S fluctuations. Our findings provide the potential for advancing the feasibility of NIR-II activity-based sensing for in vivo clinical diagnosis.

Luminescent Gold Nanoparticles with Discrete DNA Valences for Precisely Controlled Transport at the Subcellular Level

Ultrasmall luminescent gold nanoparticles (AuNPs) with excellent capabilities to cross biological barriers offer great promise in designing intelligent model nanomedicines for investigating structure-property relationships at the subcellular level. However, the strict surface controllability of ultrasmall AuNPs is challenging because of their small size. Herein, we report a facile in situ method for precisely controlling DNA aptamer valences on the surface of luminescent AuNPs with emission in the second near-infrared window using a phosphorothioate-modified DNA aptamer, AS1411, as a template. The discrete DNA aptamer number of AS1411-functionalized AuNPs (AS1411-AuNPs, ≈1.8 nm) with emission at 1030 nm was controlled in one aptamer (V1), two aptamers (V2), and four aptamers (V4). It was then discovered that not only the tumor-targeting efficiencies but also the subcellular transport of AS1411-AuNPs were precisely dependent on valences. A slight increase in valence from V1 to V2 increased tumor-targeting efficiencies and resulted in higher nucleus accumulation, whereas a further increase in valence (e.g., V4) significantly increased tumor-targeting efficiencies and led to higher cytomembrane accumulation. These results provide a basis for the strict surface control of nanomedicines in the precise regulation of in vivo transport at the subcellular level and their translation into clinical practice in the future.

An Extended NIR-II Superior Imaging Window from 1500 to 1900 nm for High-Resolution In Vivo Multiplexed Imaging Based on Lanthanide Nanocrystals

High-resolution in vivo optical multiplexing in second near-infrared window (NIR-II, 1000-1700 nm) is vital to biomedical research. Presently, limited by bio-tissue scattering, only luminescent probes located at NIR-IIb (1500-1700 nm) window can provide high-resolution in vivo multiplexed imaging. However, the number of available luminescent probes in this narrow NIR-IIb region is limited, which hampers the available multiplexed channels of in vivo imaging. To overcome the above challenges, through theoretical simulation we expanded the conventional NIR-IIb window to NIR-II long-wavelength (NIR-II-L, 1500-1900 nm) window on the basis of photon-scattering and water-absorption. We developed a series of novel lanthanide luminescent nanoprobes with emission wavelengths from 1852 nm to 2842 nm. NIR-II-L nanoprobes enabled high-resolution in vivo dynamic multiplexed imaging on blood vessels and intestines, and provided multi-channels imaging on lymph tubes, tumors and intestines. The proposed NIR-II-L probes without mutual interference are powerful tools for high-contrast in vivo multiplexed detection, which holds promise for revealing physiological process in living body.

Tailoring Near-Infrared-IIb Fluorescence of Thulium(III) by Nanocrystal Structure Engineering

Currently, mainstream lanthanide probes with fluorescence located in the second near-infrared subwindow of 1500-1700 nm (NIR-IIb) are predominantly Er(III)-based nanoparticles (NPs). Here we report a newly developed NIR-IIb fluorescent nanoprobe, α-Tm NP (cubic-phase NaYF4@NaYF4:Tm@NaYF4), with an emission at 1630 nm. We activate the 1630 nm emission of Tm(III) in α-Tm NP through the large spread of the Stark split sublevels induced by the crystal-field effect of the α-NaYF4 host. Further, we systematically investigated the effect of crystalline structure of the host NaYF4 NP (cubic phase (α) or hexagonal phase (β)), the type and concentrations of dopants (Yb(III), Tm(III), and Ca(II) ions) in the α-phase host, and the thicknesses of the interlayer and inert shell on the NIR-IIb fluorescence of Tm(III). The ultimate nanostructure presents a significant enhancement factor of the NIR-IIb photoluminescence intensity of Tm(III) up to ∼315. With this bright NIR-IIb fluorescent nanoprobe, we demonstrate high-spatial-resolution time-coursing imaging of breast cancer bone metastasis.

Subnano Te Cluster in Glass for Efficient Full-Spectrum Conversion

Broadband near-infrared (NIR) photonic materials have wide applications. Although extensive studies on rare-earth, transition-metal, and even semiconductor-activated materials have enabled the development of a rich NIR material pool, developing broadband and efficient photonic candidates covering the NIR I and II regions from 750 to 1500 nm has been met with limited success. Here, it is reported that a subnano Te cluster with a characteristic configuration different from that of the ion state may fill the aforementioned gap. Further, a strategy is proposed for the in situ generation and stabilization of Te clusters by tuning the cluster evolution in glass. A novel active photonic glass embedded with a Te cluster is fabricated; it exhibits intense and broadband short-wave NIR luminescence with a central wavelength at 1030 nm and a bandwidth exceeding 330 nm. Interestingly, the glass exhibited a full visible-spectrum conversion ability from 300 to 800 nm. The application of this unique broadband excitation feature for night vision and tissue penetration is demonstrated using a smartphone as the excitation source. These findings demonstrate a fundamental principle of cluster design in glass for creating new properties and provide a new direction for developing novel cluster-derived functional composite materials.

Engineering of cyanine-based nanoplatform with tunable response toward reactive species for ratiometric NIR-II fluorescent imaging in mice

High-quality second near-infrared (NIR-II) nanoprobes are of great significance for real-time bioimaging and medical diagnosis. Cyanine is an important class of fluorophores to construct activatable probes; however, there are still significant challenges hindering their biological applications, including weak fluorescence in aqueous solution, instability, and insufficient specificity. Herein, an integrated engineering strategy is conducted to develop the cyanine-based activatable NIR-II nanoplatforms with bright, stable emission and high specificity. Specifically, poly(styrene-co-maleic anhydride) (PSMA) is employed to encapsulate NIR-II fluorescent molecules (IR1048) to render the stable and bright NIR-II nanoparticles (PSMA@IR1048 NPs). By charge-modulated strategy, a series of cyanine-fluorophores are loaded on the surface of PSMA@IR1048 NPs and exhibit tunable response toward reactive species. Combing those two strategies, NIR-II ratiometric fluorescent nanoprobes (RNPs, including RNP1, RNP2, and RNP3) are constructed; among them, RNP2 displays hypochlorous acid (HClO) responsive performance and generates a higher NIR-II fluorescent ratio (FL2/FL1) signal. Such nanoprobe can reliably report the pathological HClO level in models of diabetic liver injury and lower limb ischemia-reperfusion (I/R) injury mice. Our study paves an engineering strategy to construct cyanine-based stable, bright, and specific NIR-II probes for bioimaging.

Bone disease imaging through the near-infrared-II window

Skeletal disorders are commonly diagnosed by X-ray imaging, but the radiation limits its use. Optical imaging through the near-infrared-II window (NIR-II, 1000-1700 nm) can penetrate deep tissues without radiation risk, but the targeting of contrast agent is non-specific. Here, we report that lanthanide-doped nanocrystals can passively target the bone marrow, which can be effective for over two months. We therefore develop the high-resolution NIR-II imaging method for bone disease diagnosis, including the 3D bone imaging instrumentation to show the intravital bone morphology. We demonstrate the monitoring of 1 mm bone defects with spatial resolution comparable to the X-ray imaging result. Moreover, NIR-II imaging can reveal the early onset inflammation as the synovitis in the early stage of rheumatoid arthritis, comparable to micro computed tomography (μCT) in diagnosis of osteoarthritis, including the symptoms of osteophyte and hyperostosis in the knee joint.

Low-rate smartphone videoscopy for microsecond luminescence lifetime imaging with machine learning

Time-resolved techniques have been widely used in time-gated and luminescence lifetime imaging. However, traditional time-resolved systems require expensive lab equipment such as high-speed excitation sources and detectors or complicated mechanical choppers to achieve high repetition rates. Here, we present a cost-effective and miniaturized smartphone lifetime imaging system integrated with a pulsed ultraviolet (UV) light-emitting diode (LED) for 2D luminescence lifetime imaging using a videoscopy-based virtual chopper (V-chopper) mechanism combined with machine learning. The V-chopper method generates a series of time-delayed images between excitation pulses and smartphone gating so that the luminescence lifetime can be measured at each pixel using a relatively low acquisition frame rate (e.g. 30 frames per second [fps]) without the need for excitation synchronization. Europium (Eu) complex dyes with different luminescent lifetimes ranging from microseconds to seconds were used to demonstrate and evaluate the principle of V-chopper on a 3D-printed smartphone microscopy platform. A convolutional neural network (CNN) model was developed to automatically distinguish the gated images in different decay cycles with an accuracy of >99.5%. The current smartphone V-chopper system can detect lifetime down to ∼75 µs utilizing the default phase shift between the smartphone video rate and excitation pulses and in principle can detect much shorter lifetimes by accurately programming the time delay. This V-chopper methodology has eliminated the need for the expensive and complicated instruments used in traditional time-resolved detection and can greatly expand the applications of time-resolved lifetime technologies.

Recent advances in fluorescence imaging-guided photothermal therapy and photodynamic therapy for cancer: From near-infrared-I to near-infrared-II

Phototherapy (including photothermal therapy, PTT; and photodynamic therapy, PDT) has been widely used for cancer treatment, but conventional PTT/PDT show limited therapeutic effects due to the lack of disease recognition ability. The integration of fluorescence imaging with PTT/PDT can reveal tumor locations in a real-time manner, holding great potential in early diagnosis and precision treatment of cancers. However, the traditional fluorescence imaging in the visible and near-infrared-I regions (VIS/NIR-I, 400-900 nm) might be interfered by the scattering and autofluorescence from tissues, leading to a low imaging resolution and high false positive rate. The deeper near-infrared-II (NIR-II, 1000-1700 nm) fluorescence imaging can address these interferences. Combining NIR-II fluorescence imaging with PTT/PDT can significantly improve the accuracy of tumor theranostics and minimize damages to normal tissues. This review summarized recent advances in tumor PTT/PDT and NIR-II fluorophores, especially discussed achievements, challenges and prospects around NIR-II fluorescence imaging-guided PTT/PDT for cancers.

Suppressed Concentration Quenching Brightens Short-Wave Infrared Emitters

The brightness of doped luminescent materials is usually limited by the ubiquitous concentration quenching phenomenon resulting in an intractable tradeoff between internal quantum efficiency and excitation efficiency. Here, an intrinsic suppression of concentration quenching in sensitized luminescent systems, by exploiting the competitive relationship between light emitters and quenchers in trapping excitation energies from sensitizers, is reported. Although Cr3+ sensitizers and trivalent lanthanide (Ln3+ , Ln = Yb, Nd, and Er) emitters themselves are highly susceptible to concentration quenching, the unprecedentedly high-brightness luminescence of Cr3+ -Ln3+ systems is demonstrated in the short-wave infrared (SWIR) range employing high concentrations of Cr3+ , whereby a record photoelectric efficiency of 23% is achieved for SWIR phosphor-converted light-emitting diodes, which is about twice as high as those previously reported. The results underscore the beneficial role of emitters in terminating excitation energies, opening up a new dimension for developing efficient sensitized luminescent materials.

Fluorescence-amplified nanocrystals in the second near-infrared window for in vivo real-time dynamic multiplexed imaging

Optical imaging in the second near-infrared window (NIR-II, 1,000-1,700 nm) holds great promise for non-invasive in vivo detection. However, real-time dynamic multiplexed imaging remains challenging due to the lack of available fluorescence probes and multiplexing techniques in the ideal NIR-IIb (1,500-1,700 nm) 'deep-tissue-transparent' sub-window. Here we report on thulium-based cubic-phase downshifting nanoparticles (α-TmNPs) with 1,632 nm fluorescence amplification. This strategy was also validated for the fluorescence enhancement of nanoparticles doped with NIR-II Er3+ (α-ErNPs) or Ho3+ (α-HoNPs). In parallel, we developed a simultaneous dual-channel imaging system with high spatiotemporal synchronization and accuracy. The NIR-IIb α-TmNPs and α-ErNPs facilitated the non-invasive real-time dynamic multiplexed imaging of cerebrovascular vasomotion activity and the single-cell-level neutrophil behaviour in mouse subcutaneous tissue and ischaemic stroke model.

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.

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.

Narrowband Organic Afterglow via Phosphorescence Förster Resonance Energy Transfer for Multifunctional Applications

Achieving multicolor organic afterglow materials with narrowband emission and high color purity is important in various optoelectronic fields but remains a great challenge. Here, an efficient strategy is presented to obtain narrowband organic afterglow materials via Förster resonance energy transfer from long-lived phosphorescence donors to narrowband fluorescence acceptors in a polyvinyl alcohol matrix. The resulting materials exhibit narrowband emission with a full width at half maximum (FWHM) as small as 23 nm and the longest lifetime of 721.22 ms. Meanwhile, by pairing the appropriate donors and acceptors, multicolor and high color purity afterglow ranging from green to red with the maximum photoluminescence quantum yield of 67.1% are achieved. Moreover, given their long luminescence lifetime, high color purity, and flexibility, the potential applications are demonstrated in high-resolution afterglow displays and dynamic and quick information identification in low-light conditions. This work provides a facile approach for developing multicolor and narrowband afterglow materials as well as expands the features of organic afterglow.

Design and Synthesis of CdHgSe/HgS/CdZnS Core/Multi-Shell Quantum Dots Exhibiting High-Quantum-Yield Tissue-Penetrating Shortwave Infrared Luminescence

Cdx Hg1- x Se/HgS/Cdy Zn1- y S core/multi-shell quantum dots (QDs) exhibiting bright tissue-penetrating shortwave infrared (SWIR; 1000-1700 nm) photoluminescence (PL) are engineered. The new structure consists of a quasi-type-II Cdx Hg1- x Se/HgS core/inner shell domain creating luminescent bandgap tunable across SWIR window and a wide-bandgap Cdy Zn1- y S outer shell boosting the PL quantum yield (QY). This compositional sequence also facilitates uniform and coherent shell growth by minimizing interfacial lattice mismatches, resulting in high QYs in both organic (40-80%) and aqueous (20-70%) solvents with maximum QYs of 87 and 73%, respectively, which are comparable to those of brightest visible-to-near infrared QDs. Moreover, they maintain bright PL in a photocurable resin (QY 40%, peak wavelength ≈ 1300 nm), enabling the fabrication of SWIR-luminescent composites of diverse morphology and concentration. These composites are used to localize controlled amounts of SWIR QDs inside artificial (Intralipid) and porcine tissues and quantitatively evaluate the applicability as luminescent probes for deep-tissue imaging.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Recent advances of nanocrystals in cancer theranostics

Emerging cancer cases across the globe and treating them with conventional therapies with multiple limitations have been challenging for decades. Novel drug delivery systems and alternative theranostics are required for efficient detection and treatment. Nanocrystals (NCs) have been established as a significant cancer diagnosis and therapeutic tool due to their ability to deliver poorly water-soluble drugs with sustained release, low toxicity, and flexibility in the route of administration, long-term sustainable drug release, and noncomplicated excretion. This review summarizes several therapies of NCs, including anticancer, immunotherapy, radiotherapy, biotheranostics, targeted therapy, photothermal, and photodynamic. Further, different imaging and diagnostics using NCs are mentioned, including imaging, diagnosis through magnetic resonance imaging (MRI), computed tomography (CT), biosensing, and luminescence. In addition, the limitations and potential solutions of NCs in the field of cancer theranostics are discussed. Preclinical and clinical data depicting the importance of NCs in the spotlight of cancer, its current status, future aspects, and challenges are covered in detail.

Intraoperative diagnosis of early lymphatic metastasis using neodymium-based rare-earth NIR-II fluorescence nanoprobe

The high mortality of breast cancer is closely related to lymph node (LN) metastasis. Sentinel LNs (SLNs) are the first station where tumor cells metastasize through the lymphatic system. As such, achieving precise diagnosis of the early metastatic status of SLNs during surgery is of paramount importance for precision therapy of breast cancer. While invasive SLNs biopsy is the gold standard for evaluating the status of SLNs, its use is often time-consuming and may increase the risk of operation. It is still challenging to develop a means for rapid SLN metastasis diagnosis. Herein, NaGdF4:5%Nd@NaLuF4 rare earth nanoparticles (Gd:Nd-RENPs) with near-infrared-II (NIR-II) fluorescence and magnetic resonance imaging (MRI) properties were fabricated. With the nanoprobe, metastatic SLNs and lymph vessels (LVs) rapidly brighten and can be observed by the NIR-II imaging system, which is totally different from normal LNs and LVs. The remarkable contrast observed via NIR-II imaging serves to swiftly delineate metastatic SLNs from normal ones, subsequently guiding precise surgical resection of metastatic LNs in just 10 minutes. Furthermore, the consistency between the results obtained via MRI and NIR-II imaging further validates the dependability of this nanoprobe as a diagnostic tool for metastatic SLNs. Additionally, the Gd:Nd-RENPs exhibited good biocompatibility in vitro and in vivo. In this study, we demonstrated the advantages and prospects of NIR-II imaging for intraoperative early SLN metastasis assessment and shed light on the potential of the dual-modal Gd:Nd-RENPs as a nanoprobe.