A small-molecule dye for NIR-II imaging

Development of a high quantum yield dye for tumour imaging

A fluorescent dye, FEB, with high fluorescence quantum yield for tumour imaging is reported. FEB dyes can be efficiently synthesized in three steps and then easily modified with either PEG or PEG-iRGD to yield FEB-2000 or FEB-2000-iRGD, respectively. Both modified dyes showed negligible toxicity and were thus able to be adopted for in vivo tumour imaging. PEG modification endowed the dye FEB-2000 with both long circulating times and good tumour targeting properties in a MDA-MB-231 xenograft model. Further conjugation with iRGD to generate FEB-2000-iRGD showed minimal targeting enhancement. These results provide a template for the efficient preparation of FEB dyes for use in tumour imaging, thus providing a foundation for future modifications.

Amphiphilic semiconducting polymer as multifunctional nanocarrier for fluorescence/photoacoustic imaging guided chemo-photothermal therapy

Chemo-photothermal nanotheranostics has the advantage of synergistic therapeutic effect, providing opportunities for optimized cancer therapy. However, current chemo-photothermal nanotheranostic systems generally comprise more than three components, encountering the potential issues of unstable nanostructures and unexpected conflicts in optical and biophysical properties among different components. We herein synthesize an amphiphilic semiconducting polymer (PEG-PCB) and utilize it as a multifunctional nanocarrier to simplify chemo-photothermal nanotheranostics. PEG-PCB has a semiconducting backbone that not only serves as the diagnostic component for near-infrared (NIR) fluorescence and photoacoustic (PA) imaging, but also acts as the therapeutic agent for photothermal therapy. In addition, the hydrophobic backbone of PEG-PCB provides strong hydrophobic and π-π interactions with the aromatic anticancer drug such as doxorubicin for drug encapsulation and delivery. Such a trifunctionality of PEG-PCB eventually results in a greatly simplified nanotheranostic system with only two components but multimodal imaging and therapeutic capacities, permitting effective NIR fluorescence/PA imaging guided chemo-photothermal therapy of cancer in living mice. Our study thus provides a molecular engineering approach to integrate essential properties into one polymer for multimodal nanotheranostics.

UPAR targeted molecular imaging of cancers with small molecule-based probes

Molecular imaging can allow the non-invasive characterization and measurement of biological and biochemical processes at the molecular and cellular levels in living subjects. The imaging of specific molecular targets that are associated with cancers could allow for the earlier diagnosis and better treatment of diseases. Small molecule-based probes play prominent roles in biomedical research and have high clinical translation ability. Here, with an emphasis on small molecule-based probes, we review some recent developments in biomarkers, imaging techniques and multimodal imaging in molecular imaging and highlight the successful applications for molecular imaging of cancers.

Broadband Absorbing Semiconducting Polymer Nanoparticles for Photoacoustic Imaging in Second Near-Infrared Window

Photoacoustic (PA) imaging holds great promise for preclinical research and clinical practice. However, most studies rely on the laser wavelength in the first near-infrared (NIR) window (NIR-I, 650-950 nm), while few studies have been exploited in the second NIR window (NIR-II, 1000-1700 nm), mainly due to the lack of NIR-II absorbing contrast agents. We herein report the synthesis of a broadband absorbing PA contrast agent based on semiconducting polymer nanoparticles (SPN-II) and apply it for PA imaging in NIR-II window. SPN-II can absorb in both NIR-I and NIR-II regions, providing the feasibility to directly compare PA imaging at 750 nm with that at 1064 nm. Because of the weaker background PA signals from biological tissues in NIR-II window, the signal-to-noise ratio (SNR) of SPN-II resulted PA images at 1064 nm can be 1.4-times higher than that at 750 nm when comparing at the imaging depth of 3 cm. The proof-of-concept application of NIR-II PA imaging is demonstrated in in vivo imaging of brain vasculature in living rats, which showed 1.5-times higher SNR as compared with NIR-I PA imaging. Our study not only introduces the first broadband absorbing organic contrast agent that is applicable for PA imaging in both NIR-I and NIR-II windows but also reveals the advantages of NIR-II over NIR-I in PA imaging.

Multifunctional, Tunable Metal-Organic Framework Materials Platform for Bioimaging Applications

Herein, we describe a novel multifunctional metal-organic framework (MOF) materials platform that displays both porosity and tunable emission properties as a function of the metal identity (Eu, Nd, and tuned compositions of Nd/Yb). Their emission collectively spans the deep red to near-infrared (NIR) spectral region (∼614-1350 nm), which is highly relevant for in vivo bioimaging. These new materials meet important prerequisites as relevant to biological processes: they are minimally toxic to living cells and retain structural integrity in water and phosphate-buffered saline. To assess their viability as optical bioimaging agents, we successfully synthesized the nanoscale Eu analog as a proof-of-concept system in this series. In vitro studies show that it is cell-permeable in individual RAW 264.7 mouse macrophage and HeLa human cervical cancer tissue culture cells. The efficient discrimination between the Eu emission and cell autofluorescence was achieved with hyperspectral confocal fluorescence microscopy, used here for the first time to characterize MOF materials. Importantly, this is the first report that documents the long-term conservation of the intrinsic emission in live cells of a fluorophore-based MOF to date (up to 48 h). This finding, in conjunction with the materials' very low toxicity, validates the biocompatibility in these systems and qualifies them as promising for use in long-term tracking and biodistribution studies.

Emerging plasmonic nanostructures for controlling and enhancing photoluminescence

Localised surface plasmon resonance endows plasmonic nanostructures with unique, powerful properties such as photoluminescence enhancement, which is a phenomenon based on the interaction between light and a metal nanostructure. In particular, photoluminescence modulation and enhancement are of importance to many research fields such as photonics, plasmonics and biosensing. In this minireview, we introduce basic principles of plasmonic-nanostructure photoluminescence and recently reported plasmonic nanostructures exhibiting surface-enhanced fluorescence and direct photoluminescence, with one-photon photoluminescence being of particular interest. Gaining insights into these systems not only helps understand the fundamental concepts of plasmonic nanostructures but also advances and extends their applications.

Multifunctional biomedical imaging in physiological and pathological conditions using a NIR-II probe

Compared with imaging in the visible (400 - 650 nm) and near-infrared window I (NIR-I, 650 - 900 nm) regions, imaging in near-infrared window II (NIR-II, 1,000-1,700 nm) is a highly promising in vivo imaging modality with improved resolution and deeper tissue penetration. In this work, a small molecule NIR-II dye,5,5'-(1H,5H-benzo[1,2-c:4,5-c'] bis[1,2,5]thiadiazole)-4,8-diyl)bis(N,N-bis(4-(3-((tert-butyldimethylsilyl)oxy)propyl)phenyl) thiophen-2-amine), has been successfully encapsulated into phospholipid vesicles to prepare a probe CQS1000. Then this novel NIR-II probe has been studied for in vivo multifunctional biological imaging. Our results indicate that the NIR-II vesicle CQS1000 can noninvasively and dynamically visualize and monitor many physiological and pathological conditions of circulatory systems, including lymphatic drainage and routing, angiogenesis of tumor and vascular deformity such as arterial thrombus formation and ischemia with high spatial and temporal resolution. More importantly, by virtue of the favorable half-life of blood circulation of CQS1000, NIR-II imaging is capable of aiding us to accomplish precise resection of tumor such as osteosarcoma, and to accelerate the process of lymph nodes dissection to complete sentinel lymph node biopsy for better decision-making during the tumor surgery. Overall, CQS1000 is a highly promising NIR-II probe for multifunctional biomedical imaging in physiological and pathological conditions, surpassing traditional NIR-I imaging modality and pathologic assessments for clinical diagnosis and treatment.

Weight Multispectral Reconstruction Strategy for Enhanced Reconstruction Accuracy and Stability With Cerenkov Luminescence Tomography

Cerenkov luminescence tomography (CLT) provides a novel technique for 3-D noninvasive detection of radiopharmaceuticals in living subjects. However, because of the severe scattering of Cerenkov light, the reconstruction accuracy and stability of CLT is still unsatisfied. In this paper, a modified weight multispectral CLT (wmCLT) reconstruction strategy was developed which split the Cerenkov radiation spectrum into several sub-spectral bands and weighted the sub-spectral results to obtain the final result. To better evaluate the property of the wmCLT reconstruction strategy in terms of accuracy, stability and practicability, several numerical simulation experiments and in vivo experiments were conducted and the results obtained were compared with the traditional multispectral CLT (mCLT) and hybrid-spectral CLT (hCLT) reconstruction strategies. The numerical simulation results indicated that wmCLT strategy significantly improved the accuracy of Cerenkov source localization and intensity quantitation and exhibited good stability in suppressing noise in numerical simulation experiments. And the comparison of the results achieved from different in vivo experiments further indicated significant improvement of the wmCLT strategy in terms of the shape recovery of the bladder and the spatial resolution of imaging xenograft tumors. Overall the strategy reported here will facilitate the development of nuclear and optical molecular tomography in theoretical study.

Optical Surgical Navigation for Precision in Tumor Resections

Optical imaging methods have significant potential as effective intraoperative tools to visualize tissues, cells, and biochemical events aimed at objective assessment of the tumor margin and guiding the surgeon to adequately resect the tumor while sparing critical tissues. The wide variety of approaches to guide resection, the range of parameters that they detect, and the interdisciplinary nature involving biology, chemistry, engineering, and medicine suggested that there was a need for an organization that could review, discuss, refine, and help prioritize methods to optimize patient care and pharmaceutical and instrument development. To address these issues, the World Molecular Imaging Society created the Optical Surgical Navigation (OSN) interest group to bring together scientists, engineers, and surgeons to develop the field to benefit patients. Here, we provide an overview of approaches currently under clinical investigation for optical surgical navigation and offer our perspective on upcoming strategies.

Synthesis of Intrinsically Disordered Fluorinated Peptides for Modular Design of High-Signal 19 F MRI Agents

19 F MRI is valuable for in vivo imaging due to the only trace amounts of fluorine in biological systems. Because of the low sensitivity of MRI however, designing new fluorochemicals remains a significant challenge for achieving sufficient 19 F signal. Here, we describe a new class of high-signal, water-soluble fluorochemicals as 19 F MRI imaging agents. A polyamide backbone is used for tuning the proteolytic stability to avoid retention within the body, which is a limitation of current state-of-the-art perfluorochemicals. We show that unstructured peptides containing alternating N-ϵ-trifluoroacetyllysine and lysine provide a degenerate 19 F NMR signal. 19 F MRI phantom images provide sufficient contrast at micromolar concentrations, showing promise for eventual clinical applications. Finally, the degenerate high signal characteristics were retained when conjugated to a large protein, indicating potential for in vivo targeting applications, including molecular imaging and cell tracking.

DNA-Assembled Core-Satellite Upconverting-Metal-Organic Framework Nanoparticle Superstructures for Efficient Photodynamic Therapy

DNA-mediated assembly of core-satellite structures composed of Zr(IV)-based porphyrinic metal-organic framework (MOF) and NaYF4 ,Yb,Er upconverting nanoparticles (UCNPs) for photodynamic therapy (PDT) is reported. MOF NPs generate singlet oxygen (1 O2 ) upon photoirradiation with visible light without the need for additional small molecule, diffusional photosensitizers such as porphyrins. Using DNA as a templating agent, well-defined MOF-UCNP clusters are produced where UCNPs are spatially organized around a centrally located MOF NP. Under NIR irradiation, visible light emitted from the UCNPs is absorbed by the core MOF NP to produce 1 O2 at significantly greater amounts than what can be produced from simply mixing UCNPs and MOF NPs. The MOF-UCNP core-satellite superstructures also induce strong cell cytotoxicity against cancer cells, which are further enhanced by attaching epidermal growth factor receptor targeting affibodies to the PDT clusters, highlighting their promise as theranostic photodynamic agents.

Beyond the margins: real-time detection of cancer using targeted fluorophores

Over the past two decades, synergistic innovations in imaging technology have resulted in a revolution in which a range of biomedical applications are now benefiting from fluorescence imaging. Specifically, advances in fluorophore chemistry and imaging hardware, and the identification of targetable biomarkers have now positioned intraoperative fluorescence as a highly specific real-time detection modality for surgeons in oncology. In particular, the deeper tissue penetration and limited autofluorescence of near-infrared (NIR) fluorescence imaging improves the translational potential of this modality over visible-light fluorescence imaging. Rapid developments in fluorophores with improved characteristics, detection instrumentation, and targeting strategies led to the clinical testing in the early 2010s of the first targeted NIR fluorophores for intraoperative cancer detection. The foundations for the advances that underline this technology continue to be nurtured by the multidisciplinary collaboration of chemists, biologists, engineers, and clinicians. In this Review, we highlight the latest developments in NIR fluorophores, cancer-targeting strategies, and detection instrumentation for intraoperative cancer detection, and consider the unique challenges associated with their effective application in clinical settings.

Two-Photon Fluorescent Molybdenum Disulfide Dots for Targeted Prostate Cancer Imaging in the Biological II Window

Molybdenum disulfide (MoS2) quantum dots (QDs) derived from this two-dimensional (2D) transition metal dichalcogenide are emerging zero-dimensional materials that possess very good optical properties. Bioimaging using light in the biological II window (950-1350 nm) is a next-generation approach that will allow clinicians to achieve deeper tissue imaging with better image contrast and reduced phototoxicity and photobleaching. This article reports the development of a water-soluble, zero-dimensional antibody-conjugated transition metal dichalcogenide MoS2 QD-based two-photon luminescence (TPL) probe for the targeted bioimaging of cancer cells in the biological II window. The data indicates that MoS2 QDs exhibit an extremely high two-photon absorption cross-section (σ = 58960 GM) and two-photon brightness (4.7 × 103 GM) because of the quantum confinement and edge effects. Experimental data show that anti-PSMA antibody-attached MoS2 QDs can be used for selective two-photon imaging of live prostate cancer cells using 1064 nm light because of the high two-photon brightness, very good photostability, and very good biocompatibility of these MoS2 QDs. The data demonstrate that the bioconjugated MoS2 QDs can distinguish targeted and nontargeted cells. This study illuminates the high two-photon brightness mechanism of MoS2 QDs and provides a zero-dimensional transition metal dichalcogenide-based selective TPL agent for high-efficiency live cell imaging.

A high quantum yield molecule-protein complex fluorophore for near-infrared II imaging

Fluorescence imaging in the second near-infrared window (NIR-II) allows visualization of deep anatomical features with an unprecedented degree of clarity. NIR-II fluorophores draw from a broad spectrum of materials spanning semiconducting nanomaterials to organic molecular dyes, yet unfortunately all water-soluble organic molecules with >1,000 nm emission suffer from low quantum yields that have limited temporal resolution and penetration depth. Here, we report tailoring the supramolecular assemblies of protein complexes with a sulfonated NIR-II organic dye (CH-4T) to produce a brilliant 110-fold increase in fluorescence, resulting in the highest quantum yield molecular fluorophore thus far. The bright molecular complex allowed for the fastest video-rate imaging in the second NIR window with ∼50-fold reduced exposure times at a fast 50 frames-per-second (FPS) capable of resolving mouse cardiac cycles. In addition, we demonstrate that the NIR-II molecular complexes are superior to clinically approved ICG for lymph node imaging deep within the mouse body.

Near-infrared (NIR) fluorescence imaging >1,000 nm allows deep tissue imaging, but available organic dyes display poor brightness and temporal resolution. Here, the authors synthesize a NIR dye that, upon binding serum proteins, exhibits a 110-fold increase in intensity, giving an 11% quantum yield.

Affibody Molecules in Biotechnological and Medical Applications

Affibody molecules are small (6.5-kDa) affinity proteins based on a three-helix bundle domain framework. Since their introduction 20 years ago as an alternative to antibodies for biotechnological applications, the first therapeutic affibody molecules have now entered clinical development and more than 400 studies have been published in which affibody molecules have been developed and used in a variety of contexts. In this review, we focus primarily on efforts over the past 5 years to explore the potential of affibody molecules for medical applications in oncology, neurodegenerative, and inflammation disorders, including molecular imaging, receptor signal blocking, and delivery of toxic payloads. In addition, we describe recent examples of biotechnological applications, in which affibody molecules have been exploited as modular affinity fusion partners.

Live imaging of follicle stimulating hormone receptors in gonads and bones using near infrared II fluorophore

In vivo imaging of hormone receptors provides the opportunity to visualize target tissues under hormonal control in live animals. Detecting longer-wavelength photons in the second near-infrared window (NIR-II, 1000-1700 nm) region affords reduced photon scattering in tissues accompanied by lower autofluorescence, leading to higher spatial resolution at up to centimeter tissue penetration depths. Here, we report the conjugation of a small molecular NIR-II fluorophore CH1055 to a follicle stimulating hormone (FSH-CH) for imaging ovaries and testes in live mice. After exposure to FSH-CH, specific NIR-II signals were found in cultured ovarian granulosa cells containing FSH receptors. Injection of FSH-CH allowed live imaging of ovarian follicles and testicular seminiferous tubules in female and male adult mice, respectively. Using prepubertal mice, NIR-II signals were detected in ovaries containing only preantral follicles. Resolving earlier controversies regarding the expression of FSH receptors in cultured osteoclasts, we detected for the first time specific FSH receptor signals in bones in vivo. The present imaging of FSH receptors in live animals using a ligand-conjugated NIR-II fluorophore with low cell toxicity and rapid clearance allows the development of non-invasive molecular imaging of diverse hormonal target cells in vivo.

Novel bright-emission small-molecule NIR-II fluorophores for in vivo tumor imaging and image-guided surgery

Though high brightness and biocompatible small NIR-II dyes are highly desirable in clinical or translational cancer research, their fluorescent cores are relatively limited and their synthetic processes are somewhat complicated. Herein, we have explored the design and synthesis of novel NIR-II fluorescent materials (H1) without tedious chromatographic isolation with improved fluorescence performance (QY ≈ 2%) by introducing 2-amino 9,9-dialkyl-substituted fluorene as a donor into the backbone. Several types of water-soluble and biocompatible NIR-II probes: SXH, SDH, and H1 NPs were constructed via different chemical strategies based on H1, and then their potential to be used in in vivo tumor imaging and image-guided surgery in the NIR-II region was explored. High levels of uptake were obtained for both passive and active tumor targeting probes SXH and SDH. Furthermore, high resolution imaging of blood vessels on tumors and the whole body of living mice using H1 NPs for the first time has demonstrated precise NIR-II image-guided sentinel lymph node (SLN) surgery.

Gold and Hairpin DNA Functionalization of Upconversion Nanocrystals for Imaging and In Vivo Drug Delivery

Although multifunctional upconversion imaging probes have recently attracted considerable interest in biomedical research, there are currently few methods for stabilizing these luminescent nanoprobes with oligonucleotides in biological systems. Herein, a method to robustly disperse upconversion nanoprobes in physiological buffers based on rational design and synthesis of nanoconjugates comprising hairpin-DNA-modified gold nanoparticles is presented. This approach imparts the upconversion nanoprobes with excellent biocompatibility and circumvents the problem of particle agglomeration. By combining single-band anti-Stokes near-infrared emission and the photothermal effect mediated by the coupling of gold to upconversion nanoparticles, a simple, versatile nanoparticulate system for simultaneous deep-tissue imaging and drug molecule release in vivo is demonstrated.

Towards clinically translatable in vivo nanodiagnostics

Nanodiagnostics as a field makes use of fundamental advances in nanobiotechnology to diagnose, characterize and manage disease at the molecular scale. As these strategies move closer to routine clinical use, a proper understanding of different imaging modalities, relevant biological systems and physical properties governing nanoscale interactions is necessary to rationally engineer next-generation bionanomaterials. In this Review, we analyse the background physics of several clinically relevant imaging modalities and their associated sensitivity and specificity, provide an overview of the materials currently used for in vivo nanodiagnostics, and assess the progress made towards clinical translation. This work provides a framework for understanding both the impressive progress made thus far in the nanodiagnostics field as well as presenting challenges that must be overcome to obtain widespread clinical adoption.

Impact of Semiconducting Perylene Diimide Nanoparticle Size on Lymph Node Mapping and Cancer Imaging

Semiconducting molecules of perylene diimide (PDI) with strong light absorption properties in the near-infrared region and good biocompatibility have received increasing attention in the field of theranostics, especially as photoacoustic (PA) imaging agents. Herein, we report a series of [⁶⁴Cu]-labeled PDI nanoparticles (NPs) of different sizes (30, 60, 100, and 200 nm) as dual positron emission tomography (PET) and PA imaging probes and photothermal therapy agents. The precise size control of the PDI NPs can be achieved by adjusting the initial concentration of PDI molecules in the self-assembly process, and the photophysical property of different sized PDI NPs was studied in detail. Furthermore, we systematically investigated the size-dependent accumulation of the PDI NPs in the lymphatic system after local administration and in tumors after intravenous injection by PA and PET imaging. The results revealed that 100 nm is the best size for differentiating popliteal and sciatic LNs since the interval is around 60 min for the NPs to migrate from popliteal LNs to sciatic LNs, which is an ideal time window to facilitate surgical sentinel LN biopsy and pathological examination. Furthermore, different migration times of the different-sized PDI NPs will provide more choices for surgeons to map the specific tumor relevant LNs. PDI NP theranostics can also be applied to imaging-guided cancer therapy. The NPs with a size of 60 nm appear to be the best for tumor imaging and photothermal cancer therapy due to the maximum tumor accumulation efficiency. Thus, our study not only presents organic PDI NP theranostics but also introduces different-sized NPs for multiple bioapplications.

Ultralow-power near-infrared excited neodymium-doped nanoparticles for long-term in vivo bioimaging

Lanthanide-doped luminescent nanoparticles with both emission and excitation in the near-infrared (NIR-to-NIR) region hold great promise for bioimaging. Herein, core@shell structured LiLuF₄:Nd@LiLuF₄ (named as Nd@Lu) nanoparticles (NPs) with highly efficient NIR emission were developed for high-performance in vivo bioimaging. Strikingly, the absolute quantum yield of Nd@Lu NPs reached as high as 32%. After coating with polyethylene glycol (PEG), the water-dispersible Nd@Lu NPs showed good bio-compatibility and low toxicity. With efficient NIR emission, the Nd@Lu NPs were clearly detectable in tissues at depths of up to 20 mm. In addition, long-term in vivo biodistribution with a high signal-to-noise ratio of 25.1 was distinctly tracked upon an ultralow-power-density excitation (10 mW cm^-2) of 732 nm for the first time.

Long wavelength excitable near-infrared fluorescent nanoparticles with aggregation-induced emission characteristics for image-guided tumor resection

Near infrared (NIR) fluorescence imaging (700-900 nm) is a promising technology in preclinical and clinical tumor diagnosis and therapy. The availability of excellent NIR fluorescent contrast agents is still the main barrier to implementing this technology. Herein, we report the design and synthesis of two series of NIR fluorescent molecules with long wavelength excitation and aggregation-induced emission (AIE) characteristics by fine-tuning their molecular structures and substituents. Further self-assembly between an amphiphilic block co-polymer and the obtained AIE molecules leads to AIE nanoparticles (AIE NPs), which have absorption maxima at 635 nm and emission maxima between 800 and 815 nm with quantum yields of up to 4.8% in aggregated states. In vitro and in vivo toxicity results demonstrate that the synthesized AIE NPs are biocompatible. Finally, the synthesized AIE NPs have been successfully used for image-guided tumor resection with a high tumor-to-normal tissue signal ratio of 7.2.

Rational Design of Molecular Fluorophores for Biological Imaging in the NIR-II Window

A new design for second near-infrared window (NIR-II) molecular fluorophores based on a shielding unit-donor-acceptor-donor-shielding unit (S-D-A-D-S) structure is reported. With 3,4-ethylenedioxy thiophene as the donor and fluorene as the shielding unit, the best performance fluorophores IR-FE and IR-FEP exhibit an emission quantum yield of 31% in toluene and 2.0% in water, respectively, representing the brightest organic dyes in NIR-II region reported so far.

AIEgen-based theranostic system: targeted imaging of cancer cells and adjuvant amplification of antitumor efficacy of paclitaxel

Photosensitizers are generally treated as key components for photodynamic therapy. In contrast, we herein report an aggregation-induced emission luminogen (AIEgen)-based photosensitizer (TPE-Py-FFGYSA) that can serve as a non-toxic adjuvant to amplify the antitumor efficacy of paclitaxel, a well-known anticancer drug, with a synergistic effect of "0 + 1 > 1". Besides the adjuvant function, TPE-Py-FFGYSA can selectively light up EphA2 protein clusters overexpressed in cancer cells in a fluorescence turn-on mode, by taking advantage of the specific YSA peptide (YSAYPDSVPMMS)-EphA2 protein interaction. The simple incorporation of FFG as a self-assembly-aided unit between AIEgen (TPE-Py) and YSA significantly enhances the fluorescent signal output of TPE-Py when imaging EphA2 clusters in live cancer cells. Cytotoxicity and western blot studies reveal that the reactive oxygen species (ROS) generated by TPE-Py-FFGYSA upon exposure to light do not kill cancer cells, but instead provide an intracellular oxidative environment to help paclitaxel have much better efficacy. This study thus not only extends the application scope of photosensitizers, but also offers a unique theranostic system with the combination of diagnostic imaging and adjuvant antitumor therapy.

Next generation NIR fluorophores for tumor imaging and fluorescence-guided surgery: A review

Cancer is a group of diseases responsible for the major causes of mortality and morbidity among people of all ages. Even though medical sciences have made enormous growth, complete treatment of this deadly disease is still a challenging task. Last few decades witnessed an impressive growth in the design and development of near infrared (NIR) fluorophores with and without recognition moieties for molecular recognitions, imaging and image guided surgeries. The present article reviews recently reported NIR emitting organic/inorganic fluorophores that targets and accumulates in organelle/organs specifically for molecular imaging of cancerous cells. Near infrared (NIR probe) with or without a tumor-targeting warhead have been considered and discussed for their applications in the field of cancer imaging. In addition, challenges persist in this area are also delineated in this review.

Time resolved spectroscopy of infrared emitting Ag2S nanocrystals for subcutaneous thermometry

We report a systematic investigation on the temperature dependence of fluorescence decay dynamics of infrared emitting colloidal Ag₂S nanocrystals (NCs) with different surface coatings. The drastic lifetime reduction in the biological temperature range (20-50 °C) makes Ag₂S NCs outstanding candidates for high sensitivity subcutaneous lifetime-based thermal sensing in the second biological window (1000-1400 nm). Indeed, the lifetime thermal sensitivity of Ag₂S NCs has been found to be as large as 3-4% °C^-1 at an operating wavelength of 1250 nm. Their application for lifetime-based luminescence nanothermometry has been demonstrated through simple ex vivo experiments specially designed to elucidate the magnitude of subcutaneous thermal gradients. Experimental data were found to be in excellent agreement with numerical simulations.

Nanoparticle-mediated radiopharmaceutical-excited fluorescence molecular imaging allows precise image-guided tumor-removal surgery

Fluorescent molecular imaging technique has been actively explored for optical image-guided cancer surgery in pre-clinical and clinical research and has attracted many attentions. However, the efficacy of the fluorescent image-guided cancer surgery can be compromised by the low signal-to-noise ratio caused by the external light excitation. This study presents a novel nanoparticle-mediated radiopharmaceutical-excited fluorescent (REF) image-guided cancer surgery strategy, which employs the internal dual-excitation of europium oxide nanoparticles through both gamma rays and Cerenkov luminescence emitted from radiopharmaceuticals. The performance of the novel image-guided surgery technique was systematically evaluated using subcutaneous breast cancer 4 T1 tumor models, orthotropic and orthotropic-ectopic hepatocellular carcinoma tumor-bearing mice. The results reveal that the novel REF image-guided cancer surgery technique exhibits high performance of detecting invisible ultra-small size tumor (even less than 1 mm) and residual tumor tissue. Our study demonstrates the high potential of the novel image-guided cancer surgery for precise tumor resection.

Molecular imaging of biological systems with a clickable dye in the broad 800- to 1,700-nm near-infrared window

Fluorescence imaging multiplicity of biological systems is an area of intense focus, currently limited to fluorescence channels in the visible and first near-infrared (NIR-I; ∼700-900 nm) spectral regions. The development of conjugatable fluorophores with longer wavelength emission is highly desired to afford more targeting channels, reduce background autofluorescence, and achieve deeper tissue imaging depths. We have developed NIR-II (1,000-1,700 nm) molecular imaging agents with a bright NIR-II fluorophore through high-efficiency click chemistry to specific molecular antibodies. Relying on buoyant density differences during density gradient ultracentrifugation separations, highly pure NIR-II fluorophore-antibody conjugates emitting ∼1,100 nm were obtained for use as molecular-specific NIR-II probes. This facilitated 3D staining of ∼170-μm histological brain tissues sections on a home-built confocal microscope, demonstrating multicolor molecular imaging across both the NIR-I and NIR-II windows (800-1,700 nm).

Fluorescent chemical probes for accurate tumor diagnosis and targeting therapy

This review focuses on small molecular ligand-targeted fluorescent imaging probes and fluorescent theranostics, including their design strategies and applications in clinical tumor treatment.

Revealing the biodistribution and clearance of Ag2Se near-infrared quantum dots in mice

Ultra-small Ag₂Se QDs can be cleared from the mice body mostly by renal excretion without significant long-term organ accumulation.

Amorphous porphyrin glasses exhibit near-infrared excimer luminescence

The amorphous nature of a series of zinc–porphyrins bearing two 3,4,5-tri((S)-3,7-dimethyloctyloxy)phenyl groups at the meso-positions, named “porphyrin glass”, were tolerant of π-conjugation engineering in ethynylene-linked dimers.

New advances on the marrying of UCNPs and photothermal agents for imaging-guided diagnosis and the therapy of tumors

This review primarily focuses on the new advances in the design and theranostic applications of rare earth upconversion nanoparticles (UCNPs)–NIR photothermal absorbers multifunctional nanoplatforms.

Preparation of exciplex-based fluorescent organic nanoparticles and their application in cell imaging

Novel organic fluorescent nanoparticles based on exciplex were prepared and have been successfully applied in live cell imaging.

Emerging strategies in near-infrared light triggered drug delivery using organic nanomaterials

Near-infrared light has significant advantages for light-triggered drug delivery systems within deep tissues.

Agents for fluorescence-guided glioma surgery: a systematic review of preclinical and clinical results

BACKGROUND

Fluorescence-guided surgery (FGS) is a technique used to enhance visualization of tumor margins in order to increase the extent of tumor resection in glioma surgery. In this paper, we systematically review all clinically tested fluorescent agents for application in FGS for glioma and all preclinically tested agents with the potential for FGS for glioma.

METHODS

We searched the PubMed and Embase databases for all potentially relevant studies through March 2016. We assessed fluorescent agents by the following outcomes: rate of gross total resection (GTR), overall and progression-free survival, sensitivity and specificity in discriminating tumor and healthy brain tissue, tumor-to-normal ratio of fluorescent signal, and incidence of adverse events.

RESULTS

The search strategy resulted in 2155 articles that were screened by titles and abstracts. After full-text screening, 105 articles fulfilled the inclusion criteria evaluating the following fluorescent agents: 5-aminolevulinic acid (5-ALA) (44 studies, including three randomized control trials), fluorescein (11), indocyanine green (five), hypericin (two), 5-aminofluorescein-human serum albumin (one), endogenous fluorophores (nine) and fluorescent agents in a pre-clinical testing phase (30). Three meta-analyses were also identified.

CONCLUSIONS

5-ALA is the only fluorescent agent that has been tested in a randomized controlled trial and results in an improvement of GTR and progression-free survival in high-grade gliomas. Observational cohort studies and case series suggest similar outcomes for FGS using fluorescein. Molecular targeting agents (e.g., fluorophore/nanoparticle labeled with anti-EGFR antibodies) are still in the pre-clinical phase, but offer promising results and may be valuable future alternatives.

Tunable Narrow Band Emissions from Dye-Sensitized Core/Shell/Shell Nanocrystals in the Second Near-Infrared Biological Window

We introduce a hybrid organic-inorganic system consisting of epitaxial NaYF4:Yb3+/X3+@NaYbF4@NaYF4:Nd3+ (X = null, Er, Ho, Tm, or Pr) core/shell/shell (CSS) nanocrystal with organic dye, indocyanine green (ICG) on the nanocrystal surface. This system is able to produce a set of narrow band emissions with a large Stokes-shift (>200 nm) in the second biological window of optical transparency (NIR-II, 1000-1700 nm), by directional energy transfer from light-harvesting surface ICG, via lanthanide ions in the shells, to the emitter X3+ in the core. Surface ICG not only increases the NIR-II emission intensity of inorganic CSS nanocrystals by ∼4-fold but also provides a broadly excitable spectral range (700-860 nm) that facilitates their use in bioapplications. We show that the NIR-II emission from ICG-sensitized Er3+-doped CSS nanocrystals allows clear observation of a sharp image through 9 mm thick chicken breast tissue, and emission signal detection through 22 mm thick tissue yielding a better imaging profile than from typically used Yb/Tm-codoped upconverting nanocrystals imaged in the NIR-I region (700-950 nm). Our result on in vivo imaging suggests that these ICG-sensitized CSS nanocrystals are suitable for deep optical imaging in the NIR-II region.

Overcoming Autofluorescence: Long-Lifetime Infrared Nanoparticles for Time-Gated In Vivo Imaging

The always present and undesired contribution of autofluorescence is here completely avoided by combining a simple time gating technology with long lifetime neodymium doped infrared-emitting nanoparticles.

Penetration depth of photons in biological tissues from hyperspectral imaging in shortwave infrared in transmission and reflection geometries

Measurement of photon penetration in biological tissues is a central theme in optical imaging. A great number of endogenous tissue factors such as absorption, scattering, and anisotropy affect the path of photons in tissue, making it difficult to predict the penetration depth at different wavelengths. Traditional studies evaluating photon penetration at different wavelengths are focused on tissue spectroscopy that does not take into account the heterogeneity within the sample. This is especially critical in shortwave infrared where the individual vibration-based absorption properties of the tissue molecules are affected by nearby tissue components. We have explored the depth penetration in biological tissues from 900 to 1650 nm using Monte–Carlo simulation and a hyperspectral imaging system with Michelson spatial contrast as a metric of light penetration. Chromatic aberration-free hyperspectral images in transmission and reflection geometries were collected with a spectral resolution of 5.27 nm and a total acquisition time of 3 min. Relatively short recording time minimized artifacts from sample drying. Results from both transmission and reflection geometries consistently revealed that the highest spatial contrast in the wavelength range for deep tissue lies within 1300 to 1375 nm; however, in heavily pigmented tissue such as the liver, the range 1550 to 1600 nm is also prominent.

A Bright Future for Precision Medicine: Advances in Fluorescent Chemical Probe Design and Their Clinical Application

The Precision Medicine Initiative aims to use advances in basic and clinical research to develop therapeutics that selectively target and kill cancer cells. Under the same doctrine of precision medicine, there is an equally important need to visualize these diseased cells to enable diagnosis, facilitate surgical resection, and monitor therapeutic response. Therefore, there is a great opportunity for chemists to develop chemically tractable probes that can image cancer in vivo. This review focuses on recent advances in the development of optical probes, as well as their current and future applications in the clinical management of cancer. The progress in probe development described here suggests that optical imaging is an important and rapidly developing field of study that encourages continued collaboration among chemists, biologists, and clinicians to further refine these tools for interventional surgical imaging, as well as for diagnostic and therapeutic applications.

Visible and Near-Infrared Dual-Emission Carbogenic Small Molecular Complex with High RNA Selectivity and Renal Clearance for Nucleolus and Tumor Imaging

Fluorescence imaging requires bioselective, sensitive, nontoxic molecular probes to detect the precise location of lesions for fundamental research and clinical applications. Typical inorganic semiconductor nanomaterials with large sizes (>10 nm) can offer high-quality fluorescence imaging due to their fascinating optical properties but are limited to low selectivity as well as slow clearance pathway. We here report an N- and O-rich carbogenic small molecular complex (SMC, MW < 1000 Da) that exhibits high quantum yield (up to 80%), nucleic acid-binding enhanced excitation-dependent fluorescence (EDF), and a near-infrared (NIR) emission peaked at 850 nm with an ultralarge Stokes shift (∼500 nm). SMCs show strong rRNA affinity, and the resulting EDF enhancement allows multicolor visualization of nucleoli in cells for clear statistics. Furthermore, SMCs can be efficiently accumulated in tumor in vivo after injection into tumor-bearing mice. The NIR emission affords high signal/noise ratio imaging for delineating the true extent of tumor. Importantly, about 80% of injected SMCs can be rapidly excreted from the body in 24 h. No appreciable toxicological responses were observed up to 30 days by hematological, biochemical, and pathological examinations. SMCs have great potential as a promising nucleolus- and tumor-specific agent for medical diagnoses and biomedical research.