Noninvasive In Vivo Imaging in the Second Near-Infrared Window by Inorganic Nanoparticle-Based Fluorescent Probes

A high-performance organic fluorescent probe with aggregation-induced emission properties for long-term tumor monitoring

Near-infrared organic fluorescent probes have great need in biological sciences and medicine but most of them are still largely unable to meet demand. In this work, a delicate multipurpose organic fluorescent probe (DPPM-TPA) with aggregation-induced emission performances is designed and prepared by facile method to reflect fluorescence labeling, two-photon imaging, and long-term fluorescent tracking. Specifically, DPPM-TPA NPs was constructed from 4-(diphenylamino)phenylboronic acid and DPPM-Br by classical Suzuki coupling reaction and then coated with F127. Such nanoprobe possessed high stability in diverse medium under ambient temperatures, low cytotoxicity, and brilliant fluorescence performance. More importantly, DPPM-TPA NPs showed excellent two-photon imaging and extraordinary long-term fluorescence tracing capacity to malignant tumor, and it can last up to 9 days. These results indicated that DPPM-TPA NPs is expected to serve as a fluorescent probe for photodiagnostic and providing a new idea for the development of long-term fluorescent tracker.

Application of Photoactive Compounds in Cancer Theranostics: Review on Recent Trends from Photoactive Chemistry to Artificial Intelligence

According to the World Health Organization (WHO) and the International Agency for Research on Cancer (IARC), the number of cancer cases and deaths worldwide is predicted to nearly double by 2030, reaching 21.7 million cases and 13 million fatalities. The increase in cancer mortality is due to limitations in the diagnosis and treatment options that are currently available. The close relationship between diagnostics and medicine has made it possible for cancer patients to receive precise diagnoses and individualized care. This article discusses newly developed compounds with potential for photodynamic therapy and diagnostic applications, as well as those already in use. In addition, it discusses the use of artificial intelligence in the analysis of diagnostic images obtained using, among other things, theranostic agents.

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

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

Roadmap on multifunctional materials for drug delivery

This Roadmap on drug delivery aims to cover some of the most recent advances in the field of materials for drug delivery systems (DDSs) and emphasizes the role that multifunctional materials play in advancing the performance of modern DDSs in the context of the most current challenges presented. The Roadmap is comprised of multiple sections, each of which introduces the status of the field, the current and future challenges faced, and a perspective of the required advances necessary for biomaterial science to tackle these challenges. It is our hope that this collective vision will contribute to the initiation of conversation and collaboration across all areas of multifunctional materials for DDSs. We stress that this article is not meant to be a fully comprehensive review but rather an up-to-date snapshot of different areas of research, with a minimal number of references that focus upon the very latest research developments.

Preparation of thrombin-loaded calcium alginate microspheres with dual-mode imaging and study on their embolic properties in vivo

Transcatheter arterial embolization (TAE) has played a huge role in the interventional treatment of organ bleeding and accidental bleeding. Choosing bio-embolization materials with good biocompatibility is an important part of TAE. In this work, we prepared a calcium alginate embolic microsphere using high-voltage electrostatic droplet technology. The microsphere simultaneously encapsulated silver sulfide quantum dots (Ag2S QDs) and barium sulfate (BaSO4), and fixed thrombin on its surface. Thrombin can achieve an embolic effect while stopping bleeding. The embolic microsphere has good near-infrared two-zone (NIR-II) imaging and X-ray imaging effects, and the luminous effect of NIR-II is better than that of X-rays. This breaks the limitations of traditional embolic microspheres that only have X-ray imaging. And the microspheres have good biocompatibility and blood compatibility. Preliminary application results show that the microspheres can achieve a good embolization effect in the ear arteries of New Zealand white rabbits, and can be used as an effective material for arterial embolization and hemostasis. This work realizes the clinical embolization application of NIR-II combined with X-ray multimodal imaging technology in biomedical imaging, achieving complementary advantages and excellent results, more suitable for studying biological changes and clinical applications.

Band Gap Engineering Improves Three-Photon Luminescence of Quantum Dots for Deep Brain Imaging

Three-photon fluorescence microscopy (3PFM) has emerged as a promising tool in monitoring the structures and functions of the brain. Compared to the various imaging technologies, 3PFM enables a deep-penetrating depth attributed to tighter excitation confinement and suppressed photon scattering. However, the shortage of three-photon probes with a large absorption cross section (σ₃) substantially limits its uses. Herein, CdSe/CdS/ZnS quantum dots (QDs) with enhanced 3PF performance were synthesized via the band gap engineering strategy. The introduction of a CdS interlayer with optimized thickness between the emitting CdSe core and the ZnS shell significantly enhanced the 3P absorption cross section of QDs, which originated from the intrinsic piezoelectric polarization effect and the change of the core/shell structure from type-I to quasi-type-II. In addition, the outer ZnS layer compensated the poor electronic passivation of CdS, providing a high level of passivation for the improvement of quantum yield as well as the 3P action cross section of QDs. Under the excitation of a 1600 nm femtosecond laser, PEGylated CdSe/CdS/ZnS QDs were used for in vivo 3PFM imaging of cerebral vessels with high resolution. A tiny capillary with a diameter of 0.8 μm could be resolved at the imaging depth of 1550 μm in a mouse brain with an opened skull. A penetration depth of 850 μm beneath the skull was also achieved using a mouse model with an intact skull.

Artificial Intelligence-Aided Optical Imaging for Cancer Theranostics

The use of artificial intelligence (AI) to assist biomedical imaging have demonstrated its high accuracy and high efficiency in medical decision-making for individualized cancer medicine. In particular, optical imaging methods are able to visualize both the structural and functional information of tumors tissues with high contrast, low cost, and noninvasive property. However, no systematic work has been performed to inspect the recent advances on AI-aided optical imaging for cancer theranostics. In this review, we demonstrated how AI can guide optical imaging methods to improve the accuracy on tumor detection, automated analysis and prediction of its histopathological section, its monitoring during treatment, and its prognosis by using computer vision, deep learning and natural language processing. By contrast, the optical imaging techniques involved mainly consisted of various tomography and microscopy imaging methods such as optical endoscopy imaging, optical coherence tomography, photoacoustic imaging, diffuse optical tomography, optical microscopy imaging, Raman imaging, and fluorescent imaging. Meanwhile, existing problems, possible challenges and future prospects for AI-aided optical imaging protocol for cancer theranostics were also discussed. It is expected that the present work can open a new avenue for precision oncology by using AI and optical imaging tools.

Esterase-Activated, pH-Responsive, and Genetically Targetable Nano-Prodrug for Cancer Cell Photo-Ablation

Activatable prodrugs have drawn considerable attention for cancer cell ablation owing to their high specificity in drug delivery systems. However, phototheranostic prodrugs with dual organelle-targeting and synergistic effects are still rare due to low intelligence of their structures. Besides, the cell membrane, exocytosis, and diffusional hindrance by the extracellular matrix reduce drug uptake. Moreover, the up-regulation of heat shock protein and short singlet-oxygen lifetime in cancer cells hamper photo-ablation efficacy, especially in the mono-therapeutic model. To overcome those obstacles, we prepare an esterase-activated DM nano-prodrug, which is conjugated by diiodine-substituted fluorogenic malachite green derivative (MG-2I) and phototherapeutic agent DPP-OH via hydrolyzable ester linkage, having pH-responsiveness and genetically targetable activity for dual organelles-targeting to optimize photo-ablation efficacy. The DM nanoparticles (NPs) present improved pH-responsive photothermal/photodynamic property by the protonation of diethylaminophenyl units in acidic environment. More importantly, the MG-2I and DPP-OH moieties can be released from DM nano-prodrug through overexpressed esterase; then specifically target lysosomes and mitochondria in CT-26 Mito-FAP cells. Hence, near-infrared DM NPs can trigger parallel damage in dual-organelles with strong fluorescence and effective phototoxicity, thus inducing serious mitochondrial dysfunction and apoptotic death, showing excellent photo-ablation effect based on esterase-activated, pH-responsive, and genetically targetable activities.

Near-infrared fluorescence imaging of hepatocellular carcinoma cells regulated by β-catenin signaling pathway

Background

Near-infrared fluorescence (NIRF) imaging has recently emerged as a promising tool for noninvasive cancer imaging. However, lack of tumor sensitivity and specificity restricts the application of NIRF dyes in surgical navigation.

Methods

Herein, we investigated the imaging features of NIRF dye MHI-148 and indocyanine green (ICG) in live cell imaging and xenograft nude mice models. TCGA dataset analysis and immunohistochemistry were conducted to investigate the expression of OATPs or ABCGs in hepatocellular carcinoma (HCC) tissues. OATPs or ABCGs were knocked down and overexpressed in HCC cells using transient transfection by siRNA and plasmids or stable transfection by lentivirus. Further, qRT-PCR ,Western blotting and the use of agonists or inhibitors targeting β-catenin signaling pathway were applied to explore its important role in regulation of OATP2B1 and ABCG2 expression.

Results

Here we demonstrated that NIRF dye MHI-148 was biocompatible as indocyanine green (ICG) but with higher imaging intensity and preferential uptake and retention in hepatocellular carcinoma (HCC) cells and tissues. Moreover, our data indicated that membrane transporters OATP2B1 and ABCG2, which regulated by β-catenin signaling pathway, mediated tumor-specific accumulation and retention of MHI-148 in HCC cells. In addition, the treatment with β-catenin inhibitor significantly enhanced the accumulation of MHI-148 in HCC tissues and improved the efficacy of tumor imaging with MHI-148 in vivo.

Conclusions

Our study uncovers a mechanism that links the distribution and expression of the membrane transporters OATP2B1 and ABCG2 to the tumor-specific accumulation of MHI-148, and provides evidence supporting a regulating role of the β-catenin signaling pathway in OATP2B1 and ABCG2- induced retention of MHI-148 inHCC tissues, and strategy targeting key components of MHI-148 transport machinery may be a potential approach to improve HCC imaging.

A rational design of polymers through donor modulation to weaken the aggregation-caused quenching effect for NIR-II fluorescence imaging

The great tissue penetration depth and low tissue autofluorescence of NIR-II fluorescence imaging make it attractive for in vivo diagnosis. However, the aggregation-caused quenching (ACQ) effect is among the dominant obstacles that weaken NIR-II imaging and restrict its application. Herein, the donor unit, 2,8-dibromo-6H,12H-5,11-methanodibenzo[b,f] [1,5]diazocine with a V-configuration, was introduced to prepare the donor-acceptor (D-A) polymer P-TB with a twisted backbone, while the planar D-A polymer P-TP was used as a control. P-TB and P-TP were prepared by Stille Coupling with DPP as the acceptor. The main absorption peaks of P-TB and P-TP are located at 610 nm and 640 nm, and the emission peaks of P-TB and P-TP are 1060 nm and 930 nm, respectively. Significantly, the V-shaped P-TB showed no obvious ACQ effect within 600 μM, and the same phenomenon was demonstrated during in vivo NIR-II imaging in mice, which proves that the introduction of V-configuration donor units is beneficial for weakening the ACQ effect. This work outlines a prospective tactic for the design of conventional NIR-II fluorescent polymers by modulating the configuration of the donor units.

Recent advances in plasmon-enhanced luminescence for biosensing and bioimaging

Plasmon-enhanced luminescence (PEL) is a unique photophysical phenomenon in which the interaction between luminescent moieties and metal nanostructures results in a marked luminescence enhancement. PEL offers several advantages and has been extensively used to design robust biosensing platforms for luminescence-based detection and diagnostics applications, as well as for the development of many efficient bioimaging platforms, enabling high-contrast non-invasive real-time optical imaging of biological tissues, cells, and organelles with high spatial and temporal resolution. This review summarizes recent progress in the development of various PEL-based biosensors and bioimaging platforms for diverse biological and biomedical applications. Specifically, we comprehensively assessed rationally designed PEL-based biosensors that can efficiently detect biomarkers (proteins and nucleic acids) in point-of-care tests, highlighting significant improvements in the sensing performance upon the integration of PEL. In addition to discussing the merits and demerits of recently developed PEL-based biosensors on substrates or in solutions, we include a brief discussion on integrating PEL-based biosensing platforms into microfluidic devices as a promising multi-responsive detection method. The review also presents comprehensive details about the recent advances in the development of various PEL-based multi-functional (passive targeting, active targeting, and stimuli-responsive) bioimaging probes, highlighting the scope of future improvements in devising robust PEL-based nanosystems to achieve more effective diagnostic and therapeutic insights by enabling imaging-guided therapy.

Near-Infrared Ratiometric Hemicyanine-Based pH Fluorescence Probe with Bone Targetability for Monitoring Bone Resorption

Accurate detection of bone resorption is extremely important in the orthodontic treatment process as it can provide a basis for clinical treatment strategies. Recently, pH-responsive fluorescence probes have received tremendous attention in bone resorption monitoring owing to their high sensitivity, good specificity, and in situ and real-time detection capabilities, but there are still some shortcomings like the increase in the risk of osteonecrosis of the jaw by use of bisphosphonate as the bone-targeting moiety and the insufficient monitoring accuracy due to susceptibility to interference. Herein, we designed and synthesized a near-infrared ratiometric hemicyanine-based pH fluorescence probe (Hcy-Asp6) with fluorescence-imaging and pH-determining capabilities, and bone targetability for more reliably and safely monitoring the bone resorption in orthodontic treatment. In vitro optical performance tests of Hcy-Asp6 revealed that the probe had high sensitivity, excellent photostability, reversibility, and strong resistance to interference, and the probe suggested excellent bone-binding ability and biocompatibility in the bone-targeting evaluation and the cytotoxicity test. Furthermore, in vitro and in vivo bone resorption monitoring assays demonstrated that this probe can detect bone resorption by fluorescence imaging and quantitative monitoring of pH associated with the bone resorption. Thus, the results indicated that this probe possessing bone targetability and accurate bone resorption-monitoring capability has an extraordinarily great clinical potential to be employed for real-time monitoring of bone resorption in orthodontic treatment and could also serve as a reference in bone resorption monitoring for other bone resorption-related diseases.

Cell membrane-targeting NIR fluorescent probes with large Stokes shifts for ultralong-term transplanted neural stem cell tracking

There is an emerging therapeutic strategy to transplant stem cells into diseased host tissue for various neurodegenerative diseases, owing to their self-renewal ability and pluripotency. However, the traceability of long-term transplanted cells limits the further understanding of the mechanism of the therapy. Herein, we designed and synthesized a quinoxalinone scaffold-based near-infrared (NIR) fluorescent probe named QSN, which exhibits ultra-strong photostability, large Stokes shift, and cell membrane-targeting capacity. It could be found that QSN-labeled human embryonic stem cells showed strong fluorescent emission and photostability both in vitro and in vivo. Additionally, QSN would not impair the pluripotency of embryonic stem cells, indicating that QSN did not perform cytotoxicity. Moreover, it is worth mentioning that QSN-labeled human neural stem cells held cellular retention for at least 6 weeks in the mouse brain striatum post transplantation. All these findings highlight the potential application of QSN for ultralong-term transplanted cell tracking.

A rationally designed cancer vaccine based on NIR-II fluorescence image-guided light-triggered remote control of antigen cross-presentation and autophagy

Cancer vaccines represent a promising immunotherapeutic treatment modality. The promotion of cross-presentation of extracellular tumor-associated antigens on the major histocompatibility complex (MHC) class I molecules and dendritic cell maturation at the appropriate time and place is crucial for cancer vaccines to prime cytolytic T cell response with reduced side effects. Current vaccination strategies, however, are not able to achieve the spatiotemporal control of antigen cross-presentation. Here, we report a liposomal vaccine loading the second near-infrared window (NIR-II, 1000-1700 nm) fluorophore BPBBT with an efficient photothermal conversion effect that offers an NIR-light-triggered endolysosomal escape under the imaging guidance. The NIR-II image-guided vaccination strategy specifically controls the cytosolic delivery of antigens for cross-presentation in the draining lymph nodes (DLNs). Moreover, the photothermally induced endolysosomal rupture initiates autophagy. We also find that the adjuvant simvastatin acts as an autophagy activator through inhibiting the PI3K/AKT/mTOR pathway. The light-induced autophagy in the DLNs together with simvastatin treatment cooperatively increase MHC class II expression by activating autophagy machinery for dendritic cell maturation. This study presents a paradigm of NIR-II image-guided light-triggered vaccination. The approach for remote control of antigen cross-presentation and autophagy represents a new strategy for vaccine development.

Tumor microenvironment enhanced NIR II fluorescence imaging for tumor precise surgery navigation via tetrasulfide mesoporous silica-coated Nd-based rare-earth nanocrystals

In vivo fluorescent imaging by using the new contrast agents emitted at short-wavelength infrared region (NIR II, 1000–1700 ​nm) presents an unprecedent advantages in imaging sensitivity and spatial resolution over traditional near-infrared (NIR) light. Recently, Nd-based rare-earth nanocrystals have attracted considerable attention due to the high quantum yield (∼40%) of their emission at NIR II. However, undesirable capture by reticuloendothelial system to bring strong background signal is unsatisfying for tumor discrimination. Here, GSH-sensitive tetrasulfide bond incorporated mesoporous silica shell has entrusted onto Nd-based down-conversion nanocrystals (DCNPs) surface to totally quench the fluorescence of DCNPs. After RGD conjugation on the silica surface, the NIR II contrast agents could actively target to liver tumors. Then tetrasulfide bonds can be broken during the silica framework decomposing in cytoplasm under high GSH concentration to result in NIR II fluorescence explosive recover. Benefiting from this specific response under tumor microenvironment, the NIR II signal in other organs was markedly reduced, while the signal-to-background ratio is prominently enhanced in tumors. Then, solid liver tumors were successfully resected under the guidance of our GSH responsive NIR II fluorescent imaging with no recurrence after 20-day of surgery. Meanwhile, by combining with the ignorable side effects, the Nd-based nanoprobes vastly improved the imaging resolution of tumor margin, opening a paradigm of NIR II fluorescent imaging-guided surgery.

Quantum Dot-Based Micromotors with NIR-I Light Photocatalytic Propulsion and NIR-II Fluorescence

Here, we report the first PbS quantum dot (QD)-based micromotors with NIR-I light-driven photocatalytic propulsion and NIR-II fluorescence. Under the irradiation of NIR-I light (808 nm), PbS QD-doped cuprous oxide (Cu₂O@PbS) micromotors can display efficient propulsion in a variety of biocompatible fuels such as malic acid, glucose, and urea. Among them, the Cu₂O@PbS micromotors exhibit the best propulsion performance in a very low concentration of malic acid, with an average speed as high as 11.86 μm/s. The enhanced NIR-I photocatalytic activity of Cu₂O@PbS micromotors benefits from the doping of NIR-I PbS QDs that can be excited by NIR-I light and exhibit high electron transport efficiency. The doped PbS QDs can effectively increase the absorption efficiency of the micromotors in the NIR-I region while also inhibiting the recombination of photogenerated electron-hole pairs. Interestingly, due to the presence of NIR PbS QDs, the Cu₂O@PbS micromotors demonstrate prominent and stable NIR-II fluorescence (emission wavelength: 1100 nm), which offer promising potential for visualization of their position in vivo. In comparison to other photocatalytic micromotors, the simple fabrication strategy, excellent NIR-II fluorescence, together with the NIR-I light-dependent propulsion behavior of the current Cu₂O@PbS micromotors, thus pave the way for further development of advanced smart "robots" for intelligent biomedical applications.

A lanthanide nanocomposite with cross-relaxation enhanced near-infrared emissions as a ratiometric nanothermometer

Lanthanide luminescence nanothermometers (LNTs) provide microscopic, highly sensitive, and visualizable optical signals for reporting temperature information, which is particularly useful in biomedicine to achieve precise diagnosis and therapy. However, LNTs with efficient emissions at the long-wavelength region of the second and the third near-infrared (NIR-II/III) biological window, which is more favourable for in vivo thermometry, are still limited. Herein, we present a lanthanide-doped nanocomposite with Tm³⁺ and Nd³⁺ ions as emitters working beyond 1200 nm to construct a dual ratiometric LNT. The cross-relaxation processes among lanthanide ions are employed to establish a strategy to enhance the NIR emissions of Tm³⁺ for bioimaging-based temperature detection in vivo. The dual ratiometric probes included in the nanocomposite have potential in monitoring the temperature difference and heat transfer at the nanoscale, which would be useful in modulating the heating operation more precisely during thermal therapy and other biomedical applications. This work not only provides a powerful tool for temperature sensing in vivo but also proposes a method to build high-efficiency NIR-II/III lanthanide luminescent nanomaterials for broader bio-applications.

The Role of Optical Imaging in Translational Nanomedicine

Nanomedicines have been a major research focus in the past two decades and are increasingly emerging in a broad range of clinical applications. However, a proper understanding of their biodistribution is required to further progress the field of nanomedicine. For this, imaging methods to monitor the delivery and therapeutic efficacy of nanoparticles are urgently needed. At present, optical imaging is the most common method used to study the biodistribution of nanomaterials, where the unique properties of nanomaterials and advances in optical imaging can jointly result in novel methods for optimal monitoring of nanomaterials in preclinical animal models. This review article aims to give an introduction to nanomedicines and their translational impact to highlight the potential of optical imaging to study the biodistribution of nanoparticles and to monitor the delivery and therapeutic efficacy at the preclinical level. After introducing both domains, the review focuses on different techniques that can be used to overcome some intrinsic limitations of optical imaging and how this can specifically benefit nanoparticle studies. Finally, we point out some important key features of nanoparticles that currently hinder their full potential in the clinic and how the advances in optical imaging can help to provide us with the information needed to further boost the clinical translation and expand the field of nanomedicines.

Organic fluorescent nanoprobes with NIR-IIb characteristics for deep learning

Illumination of biological events with near-infrared II sub-channel (NIR-IIb, 1500-1700 nm) enhances the transparency of biological tissues, which is very attractive for deep imaging. Due to the long-wavelength, which reduces optical damage, suppresses autofluorescence, and obviates light scattering, NIR-IIb nanoprobes afford deep tissue penetration with unprecedented spatiotemporal resolution. Hence, NIR-IIb imaging facilitates deep learning and decipherment of biological proceedings in living organisms with astounding high clarity. In comparison to its predecessors in the visible-near-infrared spectrum, imaging in the NIR-IIb has shown great potential for tissue imaging and extrapolating imaging applications for clinical studies. However, the use of organic fluorescent nanoprobes (OFNPs) in the NIR-IIb region is still rare since it is in its early stages. Thus, herein we aim to survey the recent development of different organic fluorescent nanomaterials with NIR-IIb characteristics, their unique photophysical properties, and their utilization in deep imaging in animal models. Further, practical researches on organic fluorescent nanoprobes with NIR-IIb emission and their transition to clinical applications are highlighted.

Near-infrared excitation/emission microscopy with lanthanide-based nanoparticles

Near-infrared optical imaging offers some advantages over conventional imaging, such as deeper tissue penetration, low or no autofluorescence, and reduced tissue scattering. Lanthanide-doped nanoparticles (LnNPs) have become a trend in the field of photoactive nanomaterials for optical imaging due to their unique optical features and because they can use NIR light as excitation and/or emission light. This review is focused on NaREF₄ NPs and offers an overview of the state-of-the-art investigation in their use as luminophores in optical microscopy, time-resolved imaging, and super-resolution nanoscopy based on, or applied to, LnNPs. Secondly, whenever LnNPs are combined with other nanomaterial or nanoparticle to afford nanohybrids, the characterization of their physical and chemical properties is of current interest. In this context, the latest trends in optical microscopy and their future perspectives are discussed.

Streptavidin-Conjugated Oxygen-Doped Single-Walled Carbon Nanotubes as Near-Infrared Labels for Immunoassays

Single-walled carbon nanotubes (CNTs) are promising candidates for near-infrared (NIR) fluorescent labels in diagnostic fields. We report a complex of oxygen-doped CNT (o-CNT) and streptavidin (SA) for preparing CNT-based NIR labels with a high reaction efficiency in immunoassays. This complex specifically binds to biotin molecules by conjugating a linker molecule of phospholipid polyethylene glycol (PL-PEG) to SA (o-CNT-SA). The immunoprecipitation reaction efficiency between o-CNT-SA and biotin reaches 79.3% when the surface of o-CNTs is uniformly covered with SA-conjugated PL-PEG. The strong affinity between SA and biotin is useful for preparing CNT-based sensitive NIR fluorescent labels.

Brain-Targeted Aggregation-Induced-Emission Nanoparticles with Near-Infrared Imaging at 1550 nm Boosts Orthotopic Glioblastoma Theranostics

A remaining challenge in the treatment of glioblastoma multiforme (GBM) is surmounting the blood-brain barrier (BBB). Such a challenge prevents the development of efficient theranostic approaches that combine reliable diagnosis with targeted therapy. In this study, brain-targeted near-infrared IIb (NIR-IIb) aggregation-induced-emission (AIE) nanoparticles are developed via rational design, which involves twisting the planar molecular backbone with steric hindrance. The resulting nanoparticles can balance competing responsiveness demands for radiation-mediated NIR fluorescence imaging at 1550 nm and non-radiation NIR photothermal therapy (NIR-PTT). The brain-targeting peptide apolipoprotein E peptide (ApoE) is grafted onto these nanoparticles (termed as ApoE-Ph NPs) to target glioma and promote efficient BBB traversal. A long imaging wavelength 1550 nm band-pass filter is utilized to monitor the in vivo biodistribution and accumulation of the nanoparticles in a model of orthotopic glioma, which overcomes previous limitations in wavelength range and equipment. The results demonstrate that the ApoE-Ph NPs have a higher PTT efficiency and significantly enhanced survival of mice bearing orthotopic GBM with moderate irradiation (0.5 W cm^-2 ). Collectively, the work highlights the smart design of a brain-targeted NIR-II AIE theranostic approach that opens new diagnosis and treatment options in the photonic therapy of GBM.

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

In situ Injection of pH- and Temperature-Sensitive Nanomaterials Increases Chemo-Photothermal Efficacy by Alleviating the Tumor Immunosuppressive Microenvironment

Purpose

Triple-negative breast cancer (TNBC) is challenging to treat with traditional "standard of care" therapy due to the lack of targetable biomarkers and rapid progression to distant metastasis.

Methods

We synthesized a novel combination regimen that included chemotherapy and photothermal therapy (PTT) to address this problem. Here, we tested a magnetic nanosystem (MNs-PEG/IR780-DOX micelles) loaded with the near-infrared (NIR) photothermal agent IR780 and doxorubicin (DOX) to achieve chemo-photothermal and boost antitumor immunity. Intraductal (i.duc) administration of MNs-PEG/IR780-DOX could increase the concentration of the drug in the tumor while reducing systemic side effects.

Results

We showed more uptake of MNs-PEG/IR780-DOX by 4T1-luc cells and higher penetration in the tumor. MNs-PEG/IR780-DOX exhibited excellent photothermal conversion in vivo and in vitro. The release of DOX from MNs-PEG/IR780-DOX is pH- and temperature-sensitive. Facilitated by i.duc administration, MNs-PEG/IR780-DOX displayed antitumor effects and prevented distant organs metastasis under NIR laser (L) irradiation and magnetic field (MF)while avoiding DOX-induced toxicity. More importantly, MNs-PEG/IR780-DOX alleviated tumor immunosuppressive microenvironment by increasing tumor CD8⁺ T cells infiltration and reducing the proportion of myeloid-derived suppressor cells (MDSCs) and Tregs.

Conclusion

Intraductal administration of pH- and temperature-sensitive MNs-PEG/IR780-DOX with L and MF had the potential for achieving minimally invasive, targeted, and accurate treatment of TNBC.

Synergistic strategy of rare-earth doped nanoparticles for NIR-II biomedical imaging

Featuring simultaneous multicolor imaging for multiple targets, a synergistic strategy has become promising for fluorescence imaging applications. Visible and first near infrared (NIR-I, 700-900 nm) fluorophores have been explored for multicolor imaging to achieve good multi-target capacity, but they are largely hampered by the narrow imaging bands available (400-900 nm, bandwidth 500 nm), the broad emission spectra of many fluorophores, shallow tissue penetration and scattering loss. With attractive characteristic emission peaks in the second NIR window (NIR-II, 1000-1700 nm), a narrow emission spectrum, and deeper tissue penetration capability, rare-earth doped nanoparticles (RENPs) have been considered by us to be outstanding candidates for multicolor bioimaging. Herein, two RENPs, NaYF4:Yb20Er2@NaYF4 and NaYF4:Nd5@NaYF4, were prepared and modified with polyethylene glycol (PEG) to explore simultaneous imaging in the NIR-IIb (1530 nm, under 980 nm laser excitation) and the NIR-II (1060 nm, under 808 nm laser excitation) windows. The PEGylated-RENPs (RENPs@PEG) were able to simultaneously visualize the circulatory system, trace the lymphatic system, and evaluate the skeletal system. Our study demonstrates that RENPs have high synergistic imaging capability in multifunctional biomedical applications using their NIR-II fluorescence. Importantly, the two RENPs@PEG are complementary to each other for higher temporal resolution in NaYF4:Nd5@NaYF4@PEG and higher spatial resolution in NaYF4:Yb20Er2@NaYF4@PEG, which may provide more comprehensive and accurate imaging diagnosis. In conclusion, RENPs are highly promising nanomaterials for multicolor imaging in the NIR-II window.

Enzyme-activated probes in optical imaging: a focus on atherosclerosis

Enzyme-activated probes enable complex biological processes to be studied in real-time. A wide range of enzymes are modulated in diseases, including cancer, inflammatory diseases and cardiovascular disease, and have the potential to act as vital diagnostic and prognostic biomarkers to monitor and report on disease progression. In this perspective article, we discuss suitable design characteristics of enzyme-activated fluorescent probes for ex vivo and in vivo optical imaging applications. With a particular focus on atherosclerosis imaging, we highlight recent approaches to report on the activity of cathepsins (K and B), matrix metalloproteinases (MMP-2 and MMP-9), thrombin, heme oxygenase-1 (HO-1) and myeloperoxidase (MPO).

Versatile Types of Inorganic/Organic NIR-IIa/IIb Fluorophores: From Strategic Design toward Molecular Imaging and Theranostics

In vivo imaging in the second near-infrared window (NIR-II, 1000-1700 nm), which enables us to look deeply into living subjects, is producing marvelous opportunities for biomedical research and clinical applications. Very recently, there has been an upsurge of interdisciplinary studies focusing on developing versatile types of inorganic/organic fluorophores that can be used for noninvasive NIR-IIa/IIb imaging (NIR-IIa, 1300-1400 nm; NIR-IIb, 1500-1700 nm) with near-zero tissue autofluorescence and deeper tissue penetration. This review provides an overview of the reports published to date on the design, properties, molecular imaging, and theranostics of inorganic/organic NIR-IIa/IIb fluorophores. First, we summarize the design concepts of the up-to-date functional NIR-IIa/IIb biomaterials, in the order of single-walled carbon nanotubes (SWCNTs), quantum dots (QDs), rare-earth-doped nanoparticles (RENPs), and organic fluorophores (OFs). Then, these novel imaging modalities and versatile biomedical applications brought by these superior fluorescent properties are reviewed. Finally, challenges and perspectives for future clinical translation, aiming at boosting the clinical application progress of NIR-IIa and NIR-IIb imaging technology are highlighted.

Second near-infrared (NIR-II) imaging: a novel diagnostic technique for brain diseases

Imaging in the second near-infrared II (NIR-II) window, a kind of biomedical imaging technology with characteristics of high sensitivity, high resolution, and real-time imaging, is commonly used in the diagnosis of brain diseases. Compared with the conventional visible light (400-750 nm) and NIR-I (750-900 nm) imaging, the NIR-II has a longer wavelength of 1000-1700 nm. Notably, the superiorities of NIR-II can minimize the light scattering and autofluorescence of biological tissue with the depth of brain tissue penetration up to 7.4 mm. Herein, we summarized the main principles of NIR-II in animal models of traumatic brain injury, cerebrovascular visualization, brain tumor, inflammation, and stroke. Simultaneously, we encapsulated the in vivo process of NIR-II probes and their in vivo and in vitro toxic effects. We further dissected its limitations and following optimization measures.

Recent advances in near infrared light responsive multi-functional nanostructures for phototheranostic applications

Light-based theranostics have become indispensable tools in the field of cancer nanomedicine. Specifically, near infrared (NIR) light mediated imaging and therapy of deeply seated tumors using a single multi-functional nanoplatform have gained significant attention. To this end, several multi-functional nanomaterials have been utilized to tackle cancer and thereby achieve significant outcomes. The present review mainly focuses on the recent advances in the development of NIR light activatable multi-functional materials such as small molecules, quantum dots, and metallic nanostructures for the diagnosis and treatment of deeply seated tumors. The need for improved disease detection and enhanced treatment options, together with realistic considerations for clinically translatable nanomaterials will be the key driving factors for theranostic agent research in the near future. NIR-light mediated cancer imaging and therapeutic approaches offer several advantages in terms of minimal invasiveness, deeper tissue penetration, spatiotemporal resolution, and molecular specificities. Herein, we have reviewed the recent developments in NIR light responsive multi-functional nanostructures for phototheranostic applications in cancer therapy.

Recent Progress of Near-Infrared Fluorescence in vivo Bioimaging in the Second and Third Biological Window

Near-infrared (NIR) fluorescence bioimaging using above to 1000 nm wavelength region is a promising analytical method on visualizing deep tissues. As compared to the short-wavelength ultraviolet (UV: < 400 nm) or visible (VIS: 400 - 700 nm) region, which results in an extremely low absorption or scattering of biomolecules and water in the body, NIR light passes through the tissues. Various fluorescent probes that emit NIR emission in the second (1100 - 1400 nm) or third (1550 - 1800 nm) biological windows have been developed and used for NIR in vivo imaging. Single-walled carbon nanotubes (SWCNTs), quantum dots (QDs), rare-earth doped ceramic nanoparticles (RED-CNPs), and organic dye-based probes have been proposed by many researchers, and are used to successfully visualize the bloodstream, organs, and disease-affected regions, such as cancer. NIR imaging in the second and third biological windows is an effective analytical method on visualizing deep tissues.

Recent Developments in Semiconducting Polymer Dots for Analytical Detection and NIR-II Fluorescence Imaging

In recent years, semiconducting polymer dots (Pdots) have attracted enormous attention in applications from fundamental analytical detection to advanced deep-tissue bioimaging due to their ultrahigh fluorescence brightness with excellent photostability and minimal cytotoxicity. Pdots have therefore been widely adopted for a variety types of molecular sensing for analytical detection. More importantly, the recent development of Pdots for use in the optical window between 1000 and 1700 nm, popularly known as the "second near-infrared window" (NIR-II), has emerged as a class of optical transparent imaging technology in the living body. The advantages of the NIR-II region over the traditional NIR-I (700-900 nm) window in fluorescence imaging originate from the reduced autofluorescence, minimal absorption and scattering of light, and improved penetration depths to yield high spatiotemporal images for biological tissues. Herein, we discuss and summarize the recent developments of Pdots employed for analytical detection and NIR-II fluorescence imaging. Starting with their preparation, the recent developments for targeting various analytes are then highlighted. After that, the importance of and latest progress in NIR-II fluorescence imaging using Pdots are reported. Finally, perspectives and challenges associated with the emergence of Pdots in different fields are given.

Surgical Navigation for Malignancies Guided by Near-Infrared-II Fluorescence Imaging

Near-infrared (NIR) fluorescence imaging is an emerging noninvasive imaging modality, with unique advantages in guiding tumor resection surgery, thanks to its high sensitivity and instantaneity. In the past decade, studies on the conventional NIR window (NIR-I, 750-900 nm) have gradually focused on the second NIR window (NIR-II, 1000-1700 nm). With its reduced light scattering, photon absorption, and auto-fluorescence qualities, NIR-II fluorescence imaging significantly improves penetration depths and signal-to-noise ratios in bio-imaging. Recently, several studies have applied NIR-II imaging to navigating cancer surgery, including localizing cancers, assessing surgical margins, tracing lymph nodes, and mapping important anatomical structures. These studies have exemplified the significant prospects of this new approach. In this review, several NIR-II fluorescence agents and some of the complex applications for guiding cancer surgeries are summarized. Future prospects and the challenges of clinical translation are also discussed.

Optimization of spatial resolution and scattering effects for biomedical fluorescence imaging by using sub-regions of the shortwave infrared spectrum

We evaluated the impact of light-scattering effects on spatial resolution in different shortwave infrared (SWIR) sub-regions by analyzing two SWIR emissive phantoms made of polydimethylsiloxane (PDMS)-gold nanoclusters (Au NCs) composite covered with mice skin, or capillary tubes filled with Au NCs or IRDye 800CW at different depth in intralipids and finally, after administration of the Au NCs intravenously in mice. Our findings highlighted the benefit of working at the highest tested spectral range of the SWIR region with a 50% enhancement of spatial resolution measured in artificial model when moving from NIR-II (1000-1300 nm) to NIR-IIa (1300-1450 nm) region, and a 25% reduction of the scattering from the skin determined by point spread function analysis from the NIR-II to NIR-IIb region (1500-1700 nm). We also confirmed that a series of Monte Carlo restoration of images significantly improved the spatial resolution in vivo in mice in deep tissues both in the NIR-II and NIR-IIa spectral windows.

Polymethine-Based Semiconducting Polymer Dots with Narrow-Band Emission and Absorption/Emission Maxima at NIR-II for Bioimaging

Deep-penetration fluorescence imaging in the second near-infrared (NIR-II) window heralds a new era of clinical surgery, in which high-resolution vascular/lymphatic anatomy and detailed cancerous tissues can be visualized in real time. Described here is a series of polymethine-based semiconducting polymers with intrinsic emission maxima in the NIR-IIa (1300-1400 nm) window and absorption maxima ranging from 1082 to 1290 nm. These polymers were prepared as semiconducting polymer dots (Pdots) in aqueous solutions with fluorescence quantum yields of 0.05-0.18 %, and they demonstrate promising applications in noninvasive through-skull brain imaging in live mice with remarkable spatial resolution as well as signal-to-background contrast. This study offers a platform for future design of NIR-IIa or even NIR-IIb emitting Pdots.

A chalcone-based fluorescent responsive probe for selective detection of nitroreductase activity in bacteria

A new chalcone-based fluorescent turn-on probe (3c) responsive to nitroreductase (NTR) activity and its application toward the detection of bacteria are presented.

Activatable Molecular Probes for Second Near-Infrared Fluorescence, Chemiluminescence, and Photoacoustic Imaging

Optical imaging plays a crucial role in biomedicine. However, due to strong light scattering and autofluorescence in biological tissue between 650-900 nm, conventional optical imaging often has a poor signal-to-background ratio and shallow penetration depth, which limits its ability in deep-tissue in vivo imaging. Second near-infrared fluorescence, chemiluminescence, and photoacoustic imaging modalities mitigate these issues by their respective advantages of minimized light scattering, eliminated external excitation, and ultrasound detection. To enable disease detection, activatable molecular probes (AMPs) with the ability to change their second near-infrared fluorescence, chemiluminescence, or photoacoustic signals in response to a biomarker have been developed. This Minireview summarizes the molecular design strategies, sensing mechanisms, and imaging applications of AMPs. The potential challenges and perspectives of AMPs in deep-tissue imaging are also discussed.