Non-Invasive Optical Guided Tumor Metastasis/Vessel Imaging by Using Lanthanide Nanoprobe with Enhanced Down-Shifting Emission beyond 1500 nm

Aggregation-Induced Emission Luminogens with Photoresponsive Behaviors for Biomedical Applications

Fluorescent biomedical materials can visualize subcellular structures and therapy processes in vivo. The aggregation-induced emission (AIE) phenomenon helps suppress the quenching effect in the aggregated state suffered by conventional fluorescent materials, thereby contributing to design strategies for fluorescent biomedical materials. Photoresponsive biomedical materials have attracted attention because of the inherent advantages of light; i.e., remote control, high spatial and temporal resolution, and environmentally friendly characteristics, and their combination with AIE facilitates development of fluorescent molecules with efficient photochemical reactions upon light irradiation. In this review, organic compounds with AIE features for biomedical applications and design strategies for photoresponsive AIE luminogens (AIEgens) are first summarized briefly. Applications are then reviewed, with the employment of photoresponsive and AIE-active molecules for photoactivation imaging, super-resolution imaging, light-induced drug delivery, photodynamic therapy with photochromic behavior, and bacterial targeting and killing being discussed at length. Finally, the future outlook for AIEgens is considered with the aim of stimulating innovative work for further development of this field.

High-Specificity In Vivo Tumor Imaging Using Bioorthogonal NIR-IIb Nanoparticles

Lanthanide-based NIR-IIb nanoprobes are ideal for in vivo imaging. However, existing NIR-IIb nanoprobes often suffer from low tumor-targeting specificity, limiting their widespread use. Here the application of bioorthogonal nanoprobes with high tumor-targeting specificity for in vivo NIR-IIb luminescence imaging and magnetic resonance imaging (MRI) is reported. These dual-modality nanoprobes can enhance NIR-IIb emission by 20-fold and MRI signal by twofold, compared with non-bioorthogonal nanoprobes in murine subcutaneous tumors. Moreover, these bioorthogonal probes enable orthotopic brain tumor imaging. Implementation of bio-orthogonal chemistry significantly reduces the nanoprobe dose and hence cytotoxicity, providing a paradigm for real-time in vivo visualization of tumors.

Estimating dynamic vascular perfusion based on Er-based lanthanide nanoprobes with enhanced down-conversion emission beyond 1500 nm

Peripheral artery disease (PAD) is a common, yet serious, circulatory condition that can increase the risk of amputation, heart attack or stroke. Accurate identification of PAD and dynamic monitoring of the treatment efficacy of PAD in real time are crucial for optimizing therapeutic outcomes. However, current imaging techniques do not enable these requirements.

Methods: A lanthanide-based nanoprobe with emission in the second near-infrared window b (NIR-IIb, 1500-1700 nm), Er-DCNPs, was utilized for continuous imaging of dynamic vascular structures and hemodynamic alterations in real time using PAD-related mouse models. The NIR-IIb imaging capability, stability, and biocompatibility of Er-DCNPs were evaluated in vitro and in vivo.

Results: Owing to their high temporal-spatial resolution in the NIR-IIb imaging window, Er-DCNPs not only exhibited superior capability in visualizing anatomical and pathophysiological features of the vasculature of mice but also provided dynamic information on blood perfusion for quantitative assessment of blood recovery, thereby achieving the synergistic integration of diagnostic and therapeutic imaging functions, which is very meaningful for the successful management of PAD.

Conclusion: Our findings indicate that Er-DCNPs can serve as a promising system to facilitate the diagnosis and treatment of PAD as well as other vasculature-related diseases.

Artificial exosomes mediated spatiotemporal-resolved and targeted delivery of epigenetic inhibitors

BACKGROUND

Malignant tumor is usually associated with epigenetic dysregulation, such as overexpression of histone deacetylase (HDAC), thus HDAC has emerged as a therapeutic target for cancer. Histone deacetylase inhibitor has been approved for clinical use to treat hematological cancers. However, the low solubility, short circulation lifetime, and high cytotoxicity partially limited their applications in solid tumor.

METHODS

The upconversion nanoparticles (UC) modified with mesoporous silica (SUC) was used to load an HDACI, suberoylanilide hydroxamic acid (SAHA), and further camouflaged with M1 macrophage-derived exosome membranes (EMS). EMS was characterized in size and compositions. We also analyzed the epigenetic regulation induced by EMS. Furthermore, we evaluate the biodistribution and in vivo tumor inhibition after the systemic administration of EMS.

RESULTS

This novel style spatiotemporal-resolved drug delivery system, EMS showed a high loading efficiency of SAHA. EMS could be taken up by lung cancer cells and lead to efficient epigenetic inhibition. We found that the integrin α4β1 on M1-EM, was crucial for the homing of EMS to tumor tissues for the first time. In tumor-bearing mice, EMS showed spatiotemporal-resolved properties and facilitated the drug accumulation in the tumors, which induced superior anti-tumor effects.

CONCLUSION

This novel style of spatiotemporal-resolved nanoparticles can be used as a theranostic platform for lung cancer therapy.

A CORM loaded nanoplatform for single NIR light-activated bioimaging, gas therapy, and photothermal therapy in vitro

Carbon monoxide (CO) can cause mitochondrial dysfunction, inducing apoptosis of cancer cells, which sheds light on a potential alternative for cancer treatment. However, the existing CO-based compounds are inherently limited by their chemical nature, such as high biological toxicity and uncontrolled CO release. Therefore, a nanoplatform - UmPF - that addresses such pain points is urgently in demand. In this study, we have proposed a nanoplatform irradiated by near-infrared (NIR) light to release CO. Iron pentacarbonyl (Fe(CO)₅) was loaded in the mesoporous polydopamine layer that was coated on rare-earth upconverting nanoparticles (UCNPs). The absorption wavelength of Fe(CO)₅ overlaps with the emission bands of the UCNPs in the UV-visible light range, and therefore the emissions from the UCNPs can be used to incite Fe(CO)₅ to control the release of CO. Besides, the catechol groups, which are abundant in the polydopamine structure, serve as an ideal locating spot to chelate with Fe(CO)₅; in the meantime, the mesoporous structure of the polydopamine layer improves the loading efficiency of Fe(CO)₅ and reduces its biological toxicity. The photothermal effect (PTT) of the polydopamine layer is highly controllable by adjusting the external laser intensity, irradiation time and the thickness of the polydopamine layer. The results illustrate that the combination of CO gas therapy (GT) and polydopamine PTT brought by the final nanoplatform can be synergistic in killing cancer cells in vitro. More importantly, the possible toxic side effects can be effectively prevented from affecting the organism, since CO will not be released in this system without near-infrared light radiation.

Energy Migration Control of Multimodal Emissions in an Er3+ -Doped Nanostructure for Information Encryption and Deep-Learning Decoding

Modulating the emission wavelengths of materials has always been a primary focus of fluorescence technology. Nanocrystals (NCs) doped with lanthanide ions with rich energy levels can produce a variety of emissions at different excitation wavelengths. However, the control of multimodal emissions of these ions has remained a challenge. Herein, we present a new composition of Er³⁺ -based lanthanide NCs with color-switchable output under irradiation with 980, 808, or 1535 nm light for information security. The variation of excitation wavelengths changes the intensity ratio of visible (Vis)/near-infrared (NIR-II) emissions. Taking advantage of the Vis/NIR-II multimodal emissions of NCs and deep learning, we successfully demonstrated the storage and decoding of visible light information in pork tissue.

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.

A H2S-Triggered Dual-Modal Second Near-Infrared/Photoacoustic Intelligent Nanoprobe for Highly Specific Imaging of Colorectal Cancer

An endogenous H₂S-triggered intelligent optical nanoprobe combining second near-infrared (NIR-II) fluorescence with photoacoustic (PA) imaging can provide more comprehensive information to further improve the sensitivity and reliability of diagnosis for colorectal tumor, which is rarely explored. Herein, an endogenous H₂S-triggered SiO₂@Ag nanoprobe was designed for in situ dual-modal NIR-II/PA imaging of colorectal cancer. The designed dual-modal nanoprobe can be converted to SiO₂@Ag₂S after in situ biosynthesis via a sulfuration reaction with the over-expressed endogenous H₂S in the colorectal tumor. More importantly, the designed SiO₂@Ag nanoprobe exhibits high sensitivity and specificity for diagnosing colorectal cancer in vivo via dual-modal NIR-II/PA imaging. These results provide a new NIR-II/PA dual-modal imaging strategy for noninvasive intelligent detection of colorectal cancer.

Optical Imaging in the Second Near Infrared Window for Vascular Bioimaging

Optical imaging in the second near infrared region (NIR-II, 1000-1700 nm) provides higher resolution and deeper penetration depth for accurate and real-time vascular anatomy, blood dynamics, and function information, effectively contributing to the early diagnosis and curative effect assessment of vascular anomalies. Currently, NIR-II optical imaging demonstrates encouraging results including long-term monitoring of vascular injury and regeneration, real-time feedback of blood perfusion, tracking of lymphatic metastases, and imaging-guided surgery. This review summarizes the latest progresses of NIR-II optical imaging for angiography including fluorescence imaging, photoacoustic (PA) imaging, and optical coherence tomography (OCT). The development of current NIR-II fluorescence, PA, and OCT probes (i.e., single-walled carbon nanotubes, quantum dots, rare earth doped nanoparticles, noble metal-based nanostructures, organic dye-based probes, and semiconductor polymer nanoparticles), highlighting probe optimization regarding high brightness, longwave emission, and biocompatibility through chemical modification or nanotechnology, is first introduced. The application of NIR-II probes in angiography based on the classification of peripheral vascular, cerebrovascular, tumor vessel, and cardiovascular, is then reviewed. Major challenges and opportunities in the NIR-II optical imaging for vascular imaging are finally discussed.

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.

NIR II Luminescence Imaging for Sentinel Lymph Node and Enhanced Chemo-/Photothermal Therapy for Breast Cancer

In this research, a NIR II luminescence imaging and enhanced chemo-/photothermal therapy system of CuS-DOX-Nd/FA NPs for breast cancer and lymph node tracing under single 808 nm irradiation is proposed. Nd-DTPA molecular cluster with the NIR II imaging effect as the carrier was designed to load the ultrasmall CuS nanoparticles and chemotherapeutic drug doxorubicin hydrochloride (DOX). The composite probe is used for tumor lesion imaging and tracking the breast cancer sentinel lymph nodes with simultaneous chemo-/photothermal therapy (PTT) for breast cancer under the single 808 nm laser. This designed probe not only has high permeability and retention (EPR) targeting effect but also can respond to the tumor microenvironment (TME), realizing more precise and efficient release of DOX at the cancer focus. At the same time, CuS as a drug carrier has a good photothermal therapy effect (photothermal conversion efficiency: 27.9%). The serialized released chemotherapy DOX and synergistic PTT effect can be used to the treat the in situ breast cancer land and simultaneously kill the metastasis cancer. The system made the combined molecular clusters Nd-DTPA achieve NIR II imaging of tumor lesions of breast cancer and lymph node to obtain the integration of diagnosis of the transferred disease for better prognosis. The feasibility of the system had obvious tumor growth inhibition effect with NIR II imaging guided is verified by a series of in vitro and in vivo experiments.

Visualizing Oxidative Stress Level for Timely Assessment of Ischemic Stroke via a Ratiometric Near-Infrared-II Luminescent Nanoprobe

Ischemic stroke (IS) characterized with high morbidity and mortality rates is considered as one of the most dangerous brain diseases. The timely assessment of IS is crucial for making a clinical decision due to the severity of IS featured with time-dependence. Herein, we develop a highly reactive oxygen species (HROS)-responsive ratiometric near-infrared-II (NIR-II) nanoprobe based on a dye-sensitized system between IR-783 dye and lanthanide-doped nanoparticles. Once intravenously injected into the mice, the probe is rapidly accumulated at a lesion site by recognizing the activated endothelial cell or impaired blood-brain barrier (BBB) in the ischemic area and further responds to HROS, thereby allowing in vivo imaging of the oxidative stress level. The probe is not only able to discriminate the salvageable ischemic tissue from infarcted stroke core by visualizing the enriched degree of the probe at the lesion site but also can grade the salvageable ischemic tissue by analyzing the oxidative stress level. In addition, the ischemia area was clearly delineated by NIR-II luminescence imaging after cerebral ischemia for 30 min, which is significantly earlier than with the magnetic resonance imaging (MRI) method, thereby providing a practical tool for the timely assessing of IS.

Gram-scale synthesis of a neodymium chelate as a spectral CT and second near-infrared window imaging agent for visualizing the gastrointestinal tract in vivo

The diagnosis of gastrointestinal (GI) tract diseases is frequently performed in the clinic, so it is crucial to develop high-performance contrast agents for real-time and non-invasive imaging examination of the GI tract. Herein, we show a novel method to synthesize a neodymium (Nd) chelate, Nd-diethylenetriaminepentaacetic acid (Nd-DTPA), on a large scale without byproducts for spectral computed tomography (CT) and second near-infrared window imaging of the GI tract in vivo. The Nd-DTPA was simply generated by heating the mixture of Nd2O3 and DTPA in water at 85 °C for 2 h. This dual-modal imaging agent has the advantages of a simple and green synthesis route, no need of purification process, high yield (86.24%), large-scale production capability (>10 g in lab synthesis), good chemical stability and excellent water solubility (≈2 g mL-1). Moreover, the Nd-DTPA emitted strong near-infrared fluorescence at 1308 nm, and exhibited superior X-ray attenuation ability compared to clinical iohexol. The proposed Nd-DTPA can integrate the complementary merits of dual-modal imaging to realize spatial-temporal and highly sensitive imaging of the GI tract in vivo, and accurate diagnosis of the location of intestinal obstruction and monitor its recovery after surgery. The developed highly efficient method for the gram-scale synthesis of Nd-DTPA and the proposed spectral CT and second near-infrared window dual-modal imaging strategy provide a promising route for accurate visualization of the GI tract in vivo.

Advanced Devices for Tumor Diagnosis and Therapy

At present, tumor diagnosis is performed using common procedures, which are slow, costly, and still presenting difficulties in diagnosing tumors at their early stage. Tumor therapeutic methods also mainly rely on large-scale equipment or non-intelligent treatment approaches. Thus, an early and accurate tumor diagnosis and personalized treatment may represent the best treatment option for a successful result, and the efforts in finding them are still in progress and mainly focusing on non-destructive, integrated, and multiple technologies. These objectives can be achieved with the development of advanced devices and smart technology that represent the topic of the current investigations. Therefore, this review summarizes the progress in tumor diagnosis and therapy and briefly explains the advantages and disadvantages of the described microdevices, finally proposing advanced micro smart devices as the future development trend for tumor diagnosis and therapy.

Dye-Sensitized Rare Earth-Doped Nanoparticles with Boosted NIR-IIb Emission for Dynamic Imaging of Vascular Network-Related Disorders

Real-time dynamic vascular network imaging can provide accurate hemodynamic and anatomical information, facilitating the diagnosis of blood circulatory system-related diseases and achieving precise evaluation of therapeutic effects. In vivo luminescence imaging in the NIR-IIb biological window (1500-1700 nm) has developed into a next generation of optical imaging method with significantly improved temporal-spatial resolution and penetration depth. Unfortunately, an imaging contrast agent capable of emitting NIR-IIb luminescence with sufficient brightness in this region is lacking. Herein, we designed and proposed a type of dye-sensitized rare earth-doped nanoparticle (RENPs@Alk-pi) with obviously boosted NIR-IIb emission and high biocompatibility, which can be used to realize the real-time NIR-IIb luminescence imaging with high temporal-spatial resolution and contrast. The dye sensitization process provides a 40-fold enhanced brightness of the NIR-IIb emission at 1525 nm of Er3+. Consequently, the RENPs@Alk-pi was not only able to depict a vascular network but also applicable in noninvasively monitoring the dynamic vascular processes and changes in the vascular anatomy of two blood circulatory system-related disorders, including hindlimbs ischemia and atherosclerosis. Our research provides a powerful tool for evaluating vascular network-related dysfunction and physiological processes.

Real-Time Imaging of Hepatic Inflammation Using Hydrogen Sulfide-Activatable Second Near-Infrared Luminescent Nanoprobes

The sensing and visualized monitoring of hydrogen sulfide (H₂S) in vivo is crucial to understand its physiological and pathological roles in human health and diseases. Common methods for H₂S detection require the destruction of the biosamples and are not suitable to be applied in vivo. In this Communication, we report a "turn-on" second near-infrared (NIR-II) luminescent approach for sensitive, real-time, and in situ H₂S detection, which is based on the absorption competition between the H₂S-responsive chromophores (compound 1) and the NIR-II luminescent lanthanide nanoparticles. Specifically, the luminescence was suppressed by compound 1 due to the competitive absorption of the incident light. In the presence of H₂S, the compound 1 was bleached to recover the luminescence. Thanks to the deep tissue penetration depth and the low absorbance/scattering on biological samples of the NIR-II nanoprobes, the monitoring of the endogenous H₂S in lipopolysaccharide-induced liver inflammation was achieved, which is unattainable by the conventional histopathological and serological approaches.

Sensitizing the Luminescence of Lanthanide-Doped Nanoparticles over 1500 nm for High-Contrast and Deep Imaging of Brain Injury

Real-time and in situ visualization of cerebrovascular dysfunction is significant for studying brain injury, which however, is restricted by the complex brain structure and limited imaging strategies. Luminescence imaging in NIR-IIb region (1500-1700 nm) is a promising tool owing to its merits including deep penetration, high resolution, and fast data acquisition. Unfortunately, a luminescent material in this region with sufficient brightness and biocompatibility is scarce. Herein, Ag₂Se quantum dot-sensitized lanthanide-doped nanocrystals (QDs-LnNCs) with emission beyond 1500 nm were fabricated to image the cerebrovascular structure and hemodynamics in ischemic stroke and traumatic brain injury. The sensitization by QDs provided an over 100-fold enhanced brightness of LnNCs and a remarkable penetration depth of 11 mm. Dynamic information of blood perfusion and flow rates were acquired and the damage of the blood-brain barrier in the two injury models was investigated. Our results proved QDs-LnNCs as a kind of competent nanomaterial for noninvasive brain imaging.

Lanthanide ion (Ln3+ )-based upconversion sensor for quantification of food contaminants: A review

The food safety issue has gradually become the focus of attention in modern society. The presence of food contaminants poses a threat to human health and there are a number of interesting researches on the detection of food contaminants. Upconversion nanoparticles (UCNPs) are superior to other fluorescence materials, considering the benefits of large anti-Stokes shifts, high chemical stability, non-autofluorescence, good light penetration ability, and low toxicity. These properties render UCNPs promising candidates as luminescent labels in biodetection, which provides opportunities as a sensitive, accurate, and rapid detection method. This paper intended to review the research progress of food contaminants detection by UCNPs-based sensors. We have proposed the key criteria for UCNPs in the detection of food contaminants. Additionally, it highlighted the construction process of the UCNPs-based sensors, which includes the synthesis and modification of UCNPs, selection of the recognition elements, and consideration of the detection principle. Moreover, six kinds of food contaminants detected by UCNPs technology in the past 5 years have been summarized and discussed fairly. Last but not least, it is outlined that UCNPs have great potential to be applied in food safety detection and threw new insight into the challenges ahead.

Low Dose Soft X-Ray Remotely Triggered Lanthanide Nanovaccine for Deep Tissue CO Gas Release and Activation of Systemic Anti-Tumor Immunoresponse

Gas-based therapy has emerged as a new green therapy strategy for anti-tumor treatment. However, the therapeutic efficacy is still restricted by the deep tissue controlled release, poor lymphocytic infiltration, and inherent immunosuppressive tumor microenvironment (TME). Herein, a new type of nanovaccine is designed by integrating low dose soft X-ray-triggered CO releasing lanthanide scintillator nanoparticles (ScNPs: NaLuF4 :Gd,Tb@NaLuF4 ) with photo-responsive CO releasing moiety (PhotoCORM) for synergistic CO gas/immuno-therapy of tumors. The designed nanovaccine presents significantly boosted radioluminescence and enables deep tissue CO generation at unprecedented tissue depths of 5 cm under soft X-ray irradiation. Intriguingly, CO as a superior immunogenic cell death (ICD) inducer further reverses the deep tissue immunosuppressive TME and concurrently activates adaptive anti-tumor immunity through efficient reactive oxygen species (ROS) generation. More importantly, the designed nanovaccine presents efficient growth inhibition of both local and distant tumors via a soft X-ray activated systemic anti-tumor immunoresponse. This work provides a new strategy of designing anti-tumor nanovaccines for synergistic deep tissue gas-therapy and remote soft X-ray photoactivation of the immune response.

Exploiting a New Approach to Destroy the Barrier of Tumor Microenvironment: Nano-Architecture Delivery Systems

Recent findings suggest that tumor microenvironment (TME) plays an important regulatory role in the occurrence, proliferation, and metastasis of tumors. Different from normal tissue, the condition around tumor significantly altered, including immune infiltration, compact extracellular matrix, new vasculatures, abundant enzyme, acidic pH value, and hypoxia. Increasingly, researchers focused on targeting TME to prevent tumor development and metastasis. With the development of nanotechnology and the deep research on the tumor environment, stimulation-responsive intelligent nanostructures designed based on TME have attracted much attention in the anti-tumor drug delivery system. TME-targeted nano therapeutics can regulate the distribution of drugs in the body, specifically increase the concentration of drugs in the tumor site, so as to enhance the efficacy and reduce adverse reactions, can utilize particular conditions of TME to improve the effect of tumor therapy. This paper summarizes the major components and characteristics of TME, discusses the principles and strategies of relevant nano-architectures targeting TME for the treatment and diagnosis systematically.

Janus Nanoparticles: From Fabrication to (Bio)Applications

Janus nanoparticles (JNPs) refer to the integration of two or more chemically discrepant composites into one structure system. Studies into JNPs have been of significant interest due to their interesting characteristics stemming from their asymmetric structures, which can integrate different functional properties and perform more synergetic functions simultaneously. Herein, we present recent progress of Janus particles, comprehensively detailing fabrication strategies and applications. First, the classification of JNPs is divided into three blocks, consisting of polymeric composites, inorganic composites, and hybrid polymeric/inorganic JNPs composites. Then, the fabrication strategies are alternately summarized, examining self-assembly strategy, phase separation strategy, seed-mediated polymerization, microfluidic preparation strategy, nucleation growth methods, and masking methods. Finally, various intriguing applications of JNPs are presented, including solid surfactants agents, micro/nanomotors, and biomedical applications such as biosensing, controlled drug delivery, bioimaging, cancer therapy, and combined theranostics. Furthermore, challenges and future works in this field are provided.

Er3+ self-sensitized nanoprobes with enhanced 1525 nm downshifting emission for NIR-IIb in vivo bio-imaging

Traditional sensitizer (Yb³⁺ or Nd³⁺) and activator (Er³⁺) co-doped lanthanide-based nanoprobes possessing emission of Er³⁺ at 1525 nm have attracted much attention in NIR-IIb bio-imaging. However, the 1525 nm fluorescence efficiency was not high enough in such co-doped systems due to the serious back energy transfer from the activator to the sensitizer, resulting in a lot of excitation energy loss. Herein, we have designed an efficient NIR-IIb nanoprobe Er³⁺ self-sensitized NaErF₄:0.5%Tm³⁺@NaLuF₄, where substantially all the excitation energy could contribute to Er³⁺ ions and most energy transfer processes were confined among Er³⁺ ions, avoiding the energy dissipation by heterogeneous sensitizer ions. The influence of the types of epitaxial heterogeneous shells, the doping effect and optimal doping concentration of Tm³⁺ ions, as well as the critical shell thickness for obtaining the surface quenching-assisted downshifting emission are systematically investigated to acquire the most efficient 1525 nm luminescence under 800 nm excitation. The quantum yield in the 1500-1700 nm region reached 13.92%, enabling high-resolution through-skull cerebrovascular microscopy imaging and large-depth in vivo physiological dynamic imaging with an extremely low excitation powder density of 35 mW cm^-2. The designed nanoprobe can be potentially used for brain science research and clinical diagnosis.

Organic Dots with Large π-Conjugated Planar for Cholangiography beyond 1500 nm in Rabbits: A Non-Radioactive Strategy

Iatrogenic extrahepatic bile duct injury remains a dreaded complication while performing cholecystectomy. Although X-ray based cholangiography could reduce the incidence of biliary tract injuries, the deficiencies including radiation damage and expertise dependence hamper its further clinical application. The effective strategy for intraoperative cholangiography is still urgently required. Herein, a fluorescence-based imaging approach for cholangiography in the near-infrared IIb window (1500-1700 nm) using TT3-oCB, a bright aggregation-induced emission luminogen with large π-conjugated planar unit, is reported. In phantom studies, TT3-oCB nanoparticles exhibit high near-infrared IIb emission and show better image clarity at varying penetrating depths. When intrabiliary injected into the gallbladder or the common bile duct of the rabbit, TT3-oCB nanoparticles enable the real-time imaging of the biliary structure with deep penetrating capability and high signal-to-background ratio. Moreover, the tiny iatrogenic biliary injuries and the gallstones in established disease models could be precisely diagnosed by TT3-oCB nanoparticle assisted near-infrared IIb imaging. In summary, we reported a feasible application for aggregation-induced emission dots as biliary contrast agent and realized high-quality cholangiography in the near-infrared IIb window with precise diagnostic ability and nonradioactive damage, which could possibly be applied for intraoperative diagnosis.

Highly NIR-emitting ytterbium complexes containing 2-(tosylaminobenzylidene)-N-benzoylhydrazone anions: structure in solution and use for bioimaging

Solution behaviour in DMSO using 1D and 2D NMR spectroscopy was performed for lanthanide complexes Ln(L)(HL) and Ln(HL)₂Cl, containing non-macrocyclic 2-(tosylamino)-benzylidene-N-benzoylhydrazone (H₂L), and the structure of [Yb(L)]⁺ cation in solution was determined. Based on the NMR data, the possibility to obtain novel complexes containing [Ln(L)₂]^- was predicted, which was successfully synthesized, and the crystal structure of K(C₂H₅OH)₃[Yb(L)₂] was determined. Thanks to its high quantum yield of NIR luminescence (1.3 ± 0.2%), high absorption, low toxicity, and the stability of its anion against dissociation in DMSO, K(H₂O)₃[Yb(L)₂] was successfully used for bioimaging.

Bi2O3 boosts brightness, biocompatibility and stability of Mn-doped Ba3(VO4)2 as NIR-II contrast agent

Deep-tissue fluorescence imaging remains a major challenge as there is limited availability of bright biocompatible materials with high photo- and chemical stability. Contrast agents with emission wavelengths above 1000 nm are most favorable for deep tissue imaging, offering deeper penetration and less scattering than those operating at shorter wavelengths. Organic fluorophores suffer from low stability while inorganic nanomaterials (e.g. quantum dots) are based typically on heavy metals raising toxicity concerns. Here, we report scalable flame aerosol synthesis of water-dispersible Ba₃(VO₄)₂ nanoparticles doped with Mn⁵⁺ which exhibit a narrow emission band at 1180 nm upon near-infrared excitation. Their co-synthesis with Bi₂O₃ results in even higher absorption and ten-fold increased emission intensity. The addition of Bi₂O₃ also improved both chemical stability and cytocompatibility by an order of magnitude enabling imaging deep within tissue. Taken together, these bright particles offer excellent photo-, chemical and colloidal stability in various media with cytocompatibility to HeLa cells superior to existing commercial contrast agents.

Tunable upconversion of holmium sublattice through interfacial energy transfer for anti-counterfeiting

Photon upconversion is a fascinating phenomenon that can convert low-energy photons to high-energy photons efficiently. However, most previous relevant research has been focused on upconversion systems with a sufficiently low lanthanide emitter concentration, such as 2 mol% for Er3+ in an Er-Yb coupled system. Realizing the upconversion from lanthanide heavily doped systems in particular, the emitter sublattice is still a challenge. Here, we report a mechanistic strategy to achieve the intense upconversion of the holmium sublattice in a core-shell-based nanostructure design through interfacial energy transfer channels. This design allowed a spatial separation of Ho3+ and sensitizers (e.g., Yb3+) into different regions and unwanted back energy transfers between them could then be minimized. By taking advantage of the dual roles of Yb3+ as both a migrator and energy trapper, a gradual color change from red to yellowish green was achievable upon 808 nm excitation, which could be further markedly enhanced by surface attaching indocyanine green dyes to facilitate the harvesting of the incident excitation energy. Moreover, emission colors could be tuned by applying non-steady state excitation. Such a fine-tunable color behavior holds great promise in anti-counterfeiting. Our results present a facile but effective conceptual model for the upconversion of the holmuim sublattice, which is helpful for the development of a new class of luminescent materials toward frontier applications.

Luminescence approaches for the rapid detection of disease-related receptor proteins using transition metal-based probes

Protein biomarkers, particularly abnormally expressed receptor proteins, have been proved to be one of the crucial biomarkers for the rapid assessment, diagnosis, prognosis and prediction of specific human diseases. Transition metal based strategies in particular possess delightful strengths in the in-field and real-time visualization of receptor proteins owing to their unique photophysical properties. In this review, we highlight recent advances in the development of detection methods for receptor protein biomarkers using transition metal based approaches, particularly those employing transition metal complexes. We first discuss the strengths and weaknesses of various strategies used for protein biomarker monitoring in live cells. We then describe the principles of the various sensing platforms and their application for receptor protein detection. Finally, we discuss the challenges and future inspirations in this specific field.

Endogenous H2S-Activated Orthogonal Second Near-Infrared Emissive Nanoprobe for In Situ Ratiometric Fluorescence Imaging of Metformin-Induced Liver Injury

Metformin as a hypoglycemic drug for antidiabetic treatment has emerged as a multipotential drug for many disease treatments such as cognitive disorders, cancers, promoting weight loss. However, overdose uptake may upregulate the hepatic H₂S level, subsequently leading to serious liver injury and toxicity. Therefore, developing intelligent second near-infrared (NIR-II) emitting nanoprobes by using endogenous H₂S as a smart trigger for noninvasive highly specific in situ monitoring of the metformin-induced hepatotoxicity is highly desirable, which is rarely explored. Herein, an endogenous H₂S activated orthogonal NIR-II emitting myrica rubra-like nanoprobe based on NaYF₄:Gd/Yb/Er@NaYF₄:Yb@SiO₂ coated with Ag nanodots was explored for highly specific in vivo ratiometrically monitoring of hepatotoxicity. The designed nanoprobes were mainly uptaken by the liver and subsequently converted to NaYF₄:Gd/Yb/Er@NaYF₄:Yb@SiO₂@Ag₂S via in situ sulfuration reaction triggered by the overexpressed endogenous H₂S in the injured liver tissues, finally leading to a turn-on orthogonal emission centered at 1053 nm (irradiation by 808 nm laser) and 1525 nm (irradiation by 980 nm laser). The designed nanoprobe presents a high detection limit down to 0.7 nM of H₂S. More importantly, the in situ highly specific ratiometric imaging of the metformin-induced hepatotoxicity was successfully achieved by using the activatable orthogonal NIR-II emitting probe. Our results provide an NIR-II ratiometric fluorescence imaging strategy for highly sensitive/specific diagnosis of hepatotoxicity levels induced by metformin.

Pathogenic Virus Detection by Optical Nanobiosensors

The novel coronavirus pandemic is sweeping the world and causing global crises. The lack of effective methods of early diagnosis and accurate detection may result in severe infection as well as mortality. Therefore, it is urgently required that rapid, selective, and accurate techniques for detecting pathogenic viruses are developed. Nanotechnology-based biosensors are finding many applications in biological detection, which may address these issues and realize direct detection of molecular targets in real time. Among various nanoplatforms, optical nanobiosensors have aroused much interest due to their inherent advantages of high sensitivity and direct readout. In this review, a summary of recent progress on the optical biosensors based on nanotechnology for pathogenic virus detection is provided, with focus on quantum dots (QDs), upconversion nanoparticles (UCNPs), noble metal nanoparticles, and organic fluorescent molecules-based nanoprobes and chemiluminescence assays. These representative studies demonstrate appealing performance as biosensors and hold great promise for clinical diagnosis.

"One stone, two birds": engineering 2-D ultrathin heterostructure nanosheet BiNS@NaLnF4 for dual-modal computed tomography/magnetic resonance imaging guided, photonic synergetic theranostics

It is interesting yet challenging to design theranostic nanoplatforms for the accurate diagnosis and therapy of diseases; these nanoplatforms consist of single contrast-enhanced imaging or therapeutic agents, and they possess their own unique shortcomings that limit their widespread bio-medical applications. Therefore, designing a potential theranostic agent is an emerging approach for the synergistic diagnosis and therapeutics in bio-medical applications. Herein, a lanthanide-loaded (NaLnF₄) heterostructure BiOCl ultrathin nanosheet (BiNS@NaLnF₄) as a theranostic agent was synthesized facilely by a solvothermal protocol. BiNS@NaLnF₄ was employed as a multi-modal contrast agent for computed tomography (CT) and magnetic resonance imaging (MRI), showing a high-performance X-ray absorption contrast effect, an outstanding T₁-weighted imaging function result, good cytocompatibility and favorable in vivo effective imaging for CT. Notably, BiNS@NaLnF₄ was applied to achieve a satisfactory photon-thermal conversion efficiency (35.3%). Moreover, the special heterostructure barrier achieved increased utilization of electrons/holes, enhancing the generation of reactive oxygen species (ROS) under visible-light irradiation to further expand the therapeutic effect. Dramatically, visible light emission with the up-conversion law was employed to stimulate ROS after irradiation with a 980 nm laser. Simultaneously, the as-prepared BiNS@NaLnF₄ can be applied in photothermal/photodynamic therapy (PTT/PDT) investigation for tumor ablation. In summary, the results reveal that BiNS@NaLnF₄ is a potential multi-modal theranostic candidate, providing new insights for synergistic theranostics of tumors.

In Situ Synthesis of FeOCl in Hollow Dendritic Mesoporous Organosilicon for Ascorbic Acid-Enhanced and MR Imaging-Guided Chemodynamic Therapy in Neutral pH Conditions

Chemodynamic therapy (CDT) based on the Fenton reaction is a promising strategy for nonlight cancer treatment. However, the traditional Fenton reaction is only efficient in strongly acidic conditions (pH = 2-4), resulting in the limited curative effect in a weakly acidic tumor microenvironment (TME). Herein, we first developed a simple in situ growth method to confine FeOCl nanosheets into hollow dendritic mesoporous organosilicon (H-DMOS) nanoparticles to obtain FeOCl@H-DMOS nanospheres. Ascorbic acid (AA) was then absorbed on the nanosystem as a H₂O₂ prodrug and, meanwhile, was used for the regeneration of Fentons reagent for Fe²⁺. Finally, poly(ethylene glycol) (PEG) was coated on FeOCl@H-DMOS-AA to enhance the permeability and retention (EPR) effect in tumor tissue. The as-fabricated FeOCl@H-DMOS-AA/PEG can generate a large amount of highly toxic hydroxyl radicals (^•OH) by catalyzing H₂O₂ even in neutral pH conditions with the help of AA. As a result, the effect of CDT has been markedly enhanced by the increased amount of H₂O₂ and the efficient Fenton reaction in mild acidic TME, which can remove almost all of the tumors in mice. In addition, FeOCl also endows the nanosystem with T₂-weighted MR imaging capability (r₂ = 34.08 mM^-1 s^-1), thus realizing the imaging-guided cancer therapy. All in all, our study may contribute a new direction and may have a bright future for enhanced CDT with a neutral pH range.

Metal Ions Doping for Boosting Luminescence of Lanthanide-Doped Nanocrystals

With the developing need for luminous materials with better performance, lanthanide-doped nanocrystals have been widely studied for their unique luminescence properties such as their narrow bandwidth emission, excellent chemical stability, and photostability, adjustable emission color, high signal-to-background ratio, deeper tissue penetration with less photo-damage, and low toxicity, etc., which triggered enthusiasm for research on the broad applications of lanthanide-doped nanocrystals in bioimaging, anti-counterfeiting, biosensing, and cancer diagnosis and treatment. Considerable progress has been made in the past few decades, but low upconversion luminescence efficiency has been a hindrance in achieving further progress. It is necessary to summarize the recently relevant literature and find solutions to improve the efficiency. The latest experimental and theoretical studies related to the deliberate design of rare earth luminescent nanocrystals have, however, shown the development of metal ion-doped approaches to enhance the luminescent intensity. Host lattice manipulation can enhance the luminescence through increasing the asymmetry, which improves the probability of electric dipole transition; and the energy transfer modulation offers a reduced cross-relaxation pathway to improve the efficiency of the energy transfer. Based on the mechanisms of host lattice manipulation and energy transfer modulation, a wide range of enhancements at all wavelengths or even within a particular wavelength have been accomplished with an enhancement of up to a hundred times. In this mini review, we present the strategy of metal ion-doped lanthanide nanocrystals to cope with the issue of enhancing luminescence, overview the advantages and tricky challenges in boosting the luminescence, and provide a potential trend of future study in this field.

Fluoride-Free 2D Niobium Carbide MXenes as Stable and Biocompatible Nanoplatforms for Electrochemical Biosensors with Ultrahigh Sensitivity

Recently, 2D niobium carbide MXene has drawn vast attention due to its merits of large surface area, good metallic conductivity, and tunable band gap, making it desirable for various applications. However, the usage of highly toxic fluoride-containing etchant and quite long etching time in the conventional synthesis route has greatly hindered further exploration of MXene, especially restricting its biomedical application. Herein, novel fluoride-free Nb2CT x nanosheets are prepared by a facile strategy of electrochemical etching (E-etching) exfoliation. Taking advantage of rapid aluminum clearance, excellent chemical stability, and biocompatibility from the MXene by E-etching, fluoride-free Nb2CT x /acetylcholinesterase-based biosensors are constructed for phosmet detection with the limit of detection down to 0.046 ng mL-1. The fabricated Nb2CT x -based biosensor is superior to the counterpart from hydrofluoric acid-etched Nb2CT x , indicating that fluoride-free MXene can enhance the enzyme activity and electron transfer in the biosensor. The results prove that the fluorine-free MXene shows promise for developing biosensors with high performance of ultrahigh sensitivity and selectivity. It is highly expected that the fluoride-free MXene as a stable and biocompatible nanoplatform has great potential to be expanded to many other biomedical fields.

Nanoparticle Surface Functionalization: How to Improve Biocompatibility and Cellular Internalization

The use of nanoparticles (NP) in diagnosis and treatment of many human diseases, including cancer, is of increasing interest. However, cytotoxic effects of NPs on cells and the uptake efficiency significantly limit their use in clinical practice. The physico-chemical properties of NPs including surface composition, superficial charge, size and shape are considered the key factors that affect the biocompatibility and uptake efficiency of these nanoplatforms. Thanks to the possibility of modifying physico-chemical properties of NPs, it is possible to improve their biocompatibility and uptake efficiency through the functionalization of the NP surface. In this review, we summarize some of the most recent studies in which NP surface modification enhances biocompatibility and uptake. Furthermore, the most used techniques used to assess biocompatibility and uptake are also reported.

Multimode Imaging-Guided Photothermal/Chemodynamic Synergistic Therapy Nanoagent with a Tumor Microenvironment Responded Effect

The development of near-infrared (NIR) laser triggered phototheranostics for multimodal imaging-guided combination therapy is highly desirable. However, multiple laser sources, as well as inadequate therapeutic efficacy, impede the application of phototheranostics. Here, we develop an all-in-one theranostic nanoagent PEGylated DCNP@DMSN-MoO_x NPs (DCDMs) with a flower-like structure fabricated by coating uniformly sized down-conversion nanoparticles (DCNPs) with dendritic mesoporous silica (DMSN) and then loading the ultrasmall oxygen-deficient molybdenum oxide nanoparticles (MoO_x NPs) inside through an electrostatic interaction. Owing to the doping of Nd ions, when excited by an 808 nm laser, DCNPs emit bright NIR-II emissions (1060 and 1300 nm), which have characteristic high spatial resolution and deep tissue penetration. In terms of treatment, MoO_x NPs could be specifically activated by excessive hydrogen peroxide (H₂O₂) in the tumor microenvironment, thus generating ¹O₂ via the Russell mechanism. In addition, the excessive glutathione (GSH) in the tumor cells could be depleted through the Mo-mediated redox reaction, thus effectively decreasing the antioxidant capacity of tumor cells. Importantly, the excellent photothermal properties (photothermal conversion efficiency of 51.5% under an 808 nm laser) synergistically accelerate the generation of ¹O₂. This cyclic redox reaction of molybdenum indeed ensured the high efficacy of tumor-specific therapy, leaving the normal tissues unharmed. MoO_x NPs could also efficiently catalyze tumor endogenous H₂O₂ into a considerable amount of O₂ in an acidic tumor microenvironment, thus relieving hypoxia in tumor tissues. Moreover, the computed tomography (CT) and T₁-weighted magnetic resonance imaging (MRI) effect from Gd³⁺ and Y³⁺ ions make DCNPs act as a hybrid imaging agent, allowing comprehensive analysis of tumor lesions. Both in vitro and in vivo experiments validate that such an "all-in-one" nanoplatform possesses desirable anticancer abilities under single laser source irradiation, benefiting from the NIR-II fluorescence/CT/MR multimodal imaging-guided photothermal/chemodynamic synergistic therapy. Overall, our strategy paves the way to explore other noninvasive cancer phototheranostics.

Lanthanide-Activated Nanoparticles: A Toolbox for Bioimaging, Therapeutics, and Neuromodulation

Owing to their unique features, the past decade has witnessed rapid developments of lanthanide-activated nanoparticles for biological applications. These include highly tunable upconverting and downshifting photoluminescence when illuminated in deep tissue, excellent photostability against blinking and bleaching effects, biocompatibility through versatile surface modification, and ease of achieving multifunctionality, as well as satisfactory signal output. These attributes make lanthanide-doped nanoparticles an ideal toolbox for advanced bioimaging and next-generation therapeutics.The interest in lanthanide-doped nanoparticles for biomedical research arises from their unique optical properties in response to deep-tissue-penetrable light sources. Upon near-infrared irradiation, these nanoparticles with properly doped emitters display photon upconversion with large anti-Stokes shifts and broad-spectrum tunability from the ultraviolet to the visible. It is also possible to achieve orthogonal photoluminescence with variations in wavelength and lifetime. Coupled with surface ligands, dyes, biomolecules, or other types of functional nanomaterials, lanthanide-doped nanoparticles offer new opportunities for applications in bioimaging, advanced oncotherapy, and neuromodulation. Given the possibility of locating downshifting luminescence at "biological transmission windows", exquisite design of lanthanide-doped nanoparticles also enables deep-tissue imaging with high spatial resolution. In addition, these nanoparticles can respond to high-energy photons, such as X-rays, to trigger nonradioactive and radiative pathways, making it possible to develop high-sensitivity X-ray detectors. Precise control of paramagnetic lanthanide ions in nanocrystal lattices also provides advanced materials for high-performance magnetic resonance imaging in medical diagnostics and biomedical research. Full consideration of fundamental attributes of lanthanide-doped nanoparticles will facilitate the design of multifunctional and sensitive probes and improve diagnostic and therapeutic outcomes.In this Account, we categorize various lanthanide-activation strategies into three modes: near-infrared excitation, X-ray irradiation, and magnetic field stimulation. We introduce energy manipulations in upconverting, downshifting, and persistence luminescence in spectral and time domains and discuss how they can be applied in biological practices. We assess general design principles for lanthanide-activated nanosystems with multiple modalities of bioimaging, oncotherapy, and neuromodulation. We also review the current state-of-the-art in the field of lanthanide-based theranostic nanoplatforms, with particular emphasis on energy conversion and nano-/biointerfacing as well as emerging bioapplications. In this context, we also highlight recent advances in controlling optical properties of nanoplatforms for single- or multimodal bioimaging, stimulus-responsive phototherapy, and optogenetics. Finally, we discuss future opportunities and challenges of this exciting research field.

A Dual-Excitation Decoding Strategy Based on NIR Hybrid Nanocomposites for High-Accuracy Thermal Sensing

Optical thermal sensing holds great promise for disease theranostics. However, traditional ratiometric thermometry methods, in which intensity ratio of two nonoverlapping emissions is defined as the thermosensitive parameter, may have a limited accuracy in temperature read-out due to the deleterious interference from wavelength- and temperature-dependent photon attenuation in tissue. To overcome this limitation, a dual-excitation decoding strategy based on NIR hybrid nanocomposites comprising self-assembled quantum dots (QDs) and Nd3+ doped fluoride nanocrystals (NCs) is proposed for thermal sensing. Upon excitation at 808 nm, the intensity ratio of two emissions at identical wavelength (1057 nm) from QDs and NCs, respectively, is defined as the thermometric parameter R. By employing another 830 nm laser beam following the same optical path as 808 nm laser to exclusively excite QDs, the two overlapping emissions can be easily decoded. The acquired R proves to be inert to the detection depth in tissue, with a minimized temperature reading error of ≈2.3 °C at 35 °C (at a depth of ≈1.1 mm), while the traditional thermometry mode based on the nonoverlapping 1025 and 863 nm emissions may exhibit a large error of ≈43.0 °C. The insights provided by this work pave the way toward high-accuracy deep-tissue biosensing.

Insight into the Luminescence Alternation of Sub-30 nm Upconversion Nanoparticles with a Small NaHoF4 Core and Multi-Gd3+ /Yb3+ Coexisting Shells

It is absolutely imperative for development of material science to adjust upconversion luminescence (UCL) properties of highly doped upconversion nanoparticles (UCNPs) with special optical properties and prominent application prospects. In this work, featuring NaHoF₄ @NaYbF₄ (Ho@Yb) structures, sub-30 nm core-multishell UCNPs are synthesized with a small NaHoF₄ core and varied Gd³⁺ /Yb³⁺ coexisting shells. X-ray diffraction, transmission electron microscopy, UCL spectrum, UCL lifetime, and pump power dependence are adhibited for characterization. Compared with the former work, except for a smaller total size, tunable emission in color from red to yellow to green, and intensity from low to stronger than that of traditional UCNPs is achieved for ≈10 nm NaHoF₄ core size by means of changing number of layers and Gd³⁺ /Yb³⁺ concentration ratios in different layers. Besides, simultaneously doping Ho³⁺ into the shells will result in lowered UCL intensity and lifted green/red ratio. Surface energy loss and sensitizing energy supply, which can be modulated with inert shielding of Gd³⁺ and sensitization of Yb³⁺ , are proved to be the essential determinant. More UCL properties of these peculiar Ho@Yb UCNPs are uncovered and detailedly summarized, and the findings can help to expand the application scope of NaHoF₄ into photoinduced therapy.

Novel small-molecule fluorophores for in vivo NIR-IIa and NIR-IIb imaging

Near-infrared fluorescence imaging in the 1000-1700 nm-wavelength window (NIR-II) has exhibited great potential for deep-tissue bioimaging due to its diminished auto-fluorescence, suppressed photo-scattering, deep penetration, and high spatial and temporal resolutions. Various kinds of inorganic nanomaterials have been extensively developed for NIR-IIa (1300-1400 nm) and NIR-IIb (1500-1700 nm) bioimaging. However, the development of small-molecule NIR-IIa and NIR-IIb fluorophores is still in its infancy. Herein, we designed and synthesized a novel NIR-II organic aggregation-induced emission (AIE) fluorophore (HQL2) with a fluorescence tail extending into the NIR-IIa and NIR-IIb region based on our previous reported skeleton Q4. The encapsulated NIR-II AIE nanoparticles (HQL2 dots) exhibited water solubility and biocompatibility, and high brightness for NIR-IIa and NIR-IIb vascular imaging in vivo, a first for NIR-II AIE dots.

All-in-One Theranostic Nanomedicine with Ultrabright Second Near-Infrared Emission for Tumor-Modulated Bioimaging and Chemodynamic/Photodynamic Therapy

Reactive oxygen species (ROS)-based therapeutic modalities including chemodynamic therapy (CDT) and photodynamic therapy (PDT) hold great promise for conquering malignant tumors. However, these two methods tend to be restricted by the overexpressed glutathione (GSH) and hypoxia in the tumor microenvironment (TME). Here, we develop biodegradable copper/manganese silicate nanosphere (CMSN)-coated lanthanide-doped nanoparticles (LDNPs) for trimodal imaging-guided CDT/PDT synergistic therapy. The tridoped Yb³⁺/Er³⁺/Tm³⁺ in the ultrasmall core and the optimal Yb³⁺/Ce³⁺ doping in the shell enable the ultrabright dual-mode upconversion (UC) and downconversion (DC) emissions of LDNPs under near-infrared (NIR) laser excitation. The luminescence in the second near-infrared (NIR-II, 1000-1700 nm) window offers deep-tissue penetration, high spatial resolution, and reduced autofluorescence when used for optical imaging. Significantly, the CMSNs are capable of relieving the hypoxic TME through decomposing H₂O₂ to produce O₂, which can react with the sample to generate ¹O₂ upon excitation of UC photons (PDT). The GSH-triggered degradation of CMSNs results in the release of Fenton-like Mn²⁺ and Cu⁺ ions for ^•OH generation (CDT); simultaneously, the released Mn²⁺ ions couple with NIR-II luminescence imaging, computed tomography (CT) imaging, and magnetic resonance (MR) imaging of LDNPs, performing a TME-amplified trimodal effect. In such a nanomedicine, the TME modulation, bimetallic silicate photosensitizer, Fenton-like nanocatalyst, and NIR-II/MR/CT contrast agent were achieved "one for all", thereby realizing highly efficient tumor theranostics.

Near-Infrared Multipurpose Lanthanide-Imaging Nanoprobes

Optical imaging plays a growing role in modern biomedical research and clinical applications due to its high sensitivity, superb spatiotemporal resolution and minimal hazards. Lanthanide-doped nanoparticles (LDNPs), as a classical category of luminescent materials, exhibit promising photostability, near-infrared (NIR)-excited frequency up-/down-converting capabilities, emission fine-tuning and multispectral features, which have greatly promoted the endeavors of deeper and clearer diagnostics in complex living conditions. This review focuses on the recent advances of LDNP-based multipurpose imaging studies using upconversion, downshifting, lifetime, photoacoustic and multimodal nanoprobes in the NIR (650-1000 nm) and the second near-infrared window (NIR-II, 1000-1700 nm). The principle and design of various functional, activatable, multiplexing or multimodal lanthanide-imaging nanoprobes (LINPs) as well as representative biophotonic applications are summarized in detail. In addition, the future perspectives and challenges for facilitating LINPs to clinical translations are discussed.

Ultrafast photochemistry produces superbright short-wave infrared dots for low-dose in vivo imaging

Optical probes operating in the second near-infrared window (NIR-II, 1,000-1,700 nm), where tissues are highly transparent, have expanded the applicability of fluorescence in the biomedical field. NIR-II fluorescence enables deep-tissue imaging with micrometric resolution in animal models, but is limited by the low brightness of NIR-II probes, which prevents imaging at low excitation intensities and fluorophore concentrations. Here, we present a new generation of probes (Ag₂S superdots) derived from chemically synthesized Ag₂S dots, on which a protective shell is grown by femtosecond laser irradiation. This shell reduces the structural defects, causing an 80-fold enhancement of the quantum yield. PEGylated Ag₂S superdots enable deep-tissue in vivo imaging at low excitation intensities (<10 mW cm⁻²) and doses (<0.5 mg kg⁻¹), emerging as unrivaled contrast agents for NIR-II preclinical bioimaging. These results establish an approach for developing superbright NIR-II contrast agents based on the synergy between chemical synthesis and ultrafast laser processing.

Deep tissue imaging has been limited by the low brightness of probes emitting in the second near-infrared window. Here, the authors use femtosecond laser irradiation to grow a protective shell on Ag₂S nanoparticles, achieving 80-fold quantum yield enhancement and imaging with low excitation intensities.