Near‐Infrared Fluorescent Ag2Se–Cetuximab Nanoprobes for Targeted Imaging and Therapy of Cancer

Theranostic nanoprobes integrated with diagnostic imaging and therapy capabilities have shown great potential for highly effective tumor therapy by realizing imaging‐guided drug delivery and tumor treatment. Developing novel high‐performance nanoprobes is an important basis for tumor theranostic application. Here, near‐infrared (NIR) fluorescent and low‐biotoxicity Ag₂Se quantum dots (QDs) have been coupled with cetuximab, a clinical antiepidermal growth factor receptor antibody drug for tumor therapy, via a facile bioconjugation strategy to prepare multifunctional Ag₂Se–cetuximab nanoprobes. Compared with the Ag₂Se QDs alone, the Ag₂Se–cetuximab nanoprobes display faster and more enrichment at the site of orthotopic tongue cancer, and thus present better NIR fluorescence contrast between the tumor and the surrounding regions. At 24 h postinjection, the NIR fluorescence of Ag₂Se–cetuximab nanoprobes at the tumor site is still easily detectable, whereas no fluorescence is observed for the Ag₂Se QDs. Moreover, the Ag₂Se–cetuximab nanoprobes have also significantly inhibited the tumor growth and improved the survival rate of orthotopic tongue cancer‐bearing nude mice from 0% to 57.1%. Taken together, the constructed multifunctional Ag₂Se–cetuximab nanoprobes have achieved combined targeted imaging and therapy of orthotopic tongue cancer, which may greatly contribute to the development of nanotheranostics.     

Controlled Synthesis of Ag2Te@Ag2S Core–Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near‐Infrared Window

Fluorescence in the second near‐infrared window (NIR‐II, 900–1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR‐II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag‐rich Ag₂Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag₂S shell to passivate the Ag₂Te core via a facile colloidal route, which greatly enhances the PLQY of Ag₂Te QDs and significantly improves the stability of Ag₂Te QDs. This strategy works well with different sized core Ag₂Te QDs so that the NIR‐II PL can be tuned in a wide range. In vivo imaging using the as‐prepared Ag₂Te@Ag₂S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag₂Te nanoprobes administrated, suggesting the success of the core–shell synthetic strategy and the potential biomedical applications of core–shell NIR‐II nanoprobes.     

Hyperbranched Conjugated Polyelectrolyte for Dual‐modality Fluorescence and Magnetic Resonance Cancer Imaging

Herein is reported the synthesis of gadolinium ion (Gd(III))‐chelated hyperbranched conjugated polyelectrolyte (HCPE‐Gd) and its application in fluorescence and magnetic resonance (MR) dual imaging in live animals. The synthesized HCPE‐Gd forms nanospheres with an average diameter of ～42 nm measured by laser light scattering and a quantum yield of 10% in aqueous solution. The absorption spectrum of HCPE‐Gd has two maxima at 318 and 417 nm, and its photoluminescence maximum centers at 591 nm. Confocal laser scanning microscopy studies indicate that the HCPE‐Gd is internalized in MCF‐7 cancer cell cytoplasm with good photostability and low cytotoxicity. Further fluorescence and MR imaging studies on hepatoma H₂₂ tumor‐bearing mouse model reveal that HCPE‐Gd can serve as an efficient optical/MR dual‐modal imaging nanoprobe for in vivo cancer diagnosis.     

Hierarchically Nanostructured Hybrid Platform for Tumor Delineation and Image‐Guided Surgery via NIR‐II Fluorescence and PET Bimodal Imaging

Bimodal imaging with fluorescence in the second near infrared window (NIR‐II) and positron emission tomography (PET) has important significance for tumor diagnosis and management because of complementary advantages. It remains challenging to develop NIR‐II/PET bimodal probes with high fluorescent brightness. Herein, bioinspired nanomaterials (melanin dot, mesoporous silica nanoparticle, and supported lipid bilayer), NIR‐II dye CH‐4T, and PET radionuclide ⁶⁴Cu are integrated into a hybrid NIR‐II/PET bimodal nanoprobe. The resultant nanoprobe exhibits attractive properties such as highly uniform tunable size, effective payload encapsulation, high stability, dispersibility, and biocompatibility. Interestingly, the incorporation of CH‐4T into the nanoparticle leads to 4.27‐fold fluorescence enhancement, resulting in brighter NIR‐II imaging for phantoms in vitro and in situ. Benefiting from the fluorescence enhancement, NIR‐II imaging with the nanoprobe is carried out to precisely delineate and resect tumors. Additionally, the nanoprobe is successfully applied in tumor PET imaging, showing the accumulation of the nanoprobe in a tumor with a clear contrast from 2 to 24 h postinjection. Overall, this hierarchically nanostructured platform is able to dramatically enhance fluorescent brightness of NIR‐II dye, detect tumors with NIR‐II/PET imaging, and guide intraoperative resection. The NIR‐II/PET bimodal nanoprobe has high potential for sensitive preoperative tumor diagnosis and precise intraoperative image‐guided surgery.     

Ultrasmall Pb:Ag2S Quantum Dots with Uniform Particle Size and Bright Tunable Fluorescence in the NIR‐II Window

Ag₂S quantum dots (QDs) are well‐known near‐infrared fluorophores and have attracted great interest in biomedical labeling and imaging in the past years. However, their photoluminescence efficiency is hard to compete with Cd‐, Pb‐based QDs. The high Ag⁺ mobility in Ag₂S crystal, which causes plenty of cation deficiency and crystal defects, may be responsible mainly for the low photoluminescence quantum yield (PLQY) of Ag₂S QDs. Herein, a cation‐doping strategy is presented via introducing a certain dosage of transition metal Pb²⁺ ions into Ag₂S nanocrystals to mitigate this intrinsic shortcoming. The Pb‐doped Ag₂S QDs (designated as Pb:Ag₂S QDs) present a renovated crystal structure and significantly enhanced optical performance. Moreover, by simply adjusting the levels of Pb doping in the doped nanocrystals, Pb:Ag₂S QDs with bright emission (PLQY up to 30.2%) from 975 to 1242 nm can be prepared without altering the ultrasmall particle size (≈2.7–2.8 nm). Evidently, this cation‐doping strategy facilitates both the renovation of crystal structure of Ag₂S QDs and modulation of their optical properties.     

Core–Satellite Polydopamine–Gadolinium‐Metallofullerene Nanotheranostics for Multimodal Imaging Guided Combination Cancer Therapy

Integration of magnetic resonance imaging (MRI) and other imaging modalities is promising to furnish complementary information for accurate cancer diagnosis and imaging‐guided therapy. However, most gadolinium (Gd)–chelator MR contrast agents are limited by their relatively low relaxivity and high risk of released‐Gd‐ions‐associated toxicity. Herein, a radionuclide‐⁶⁴Cu‐labeled doxorubicin‐loaded polydopamine (PDA)–gadolinium‐metallofullerene core–satellite nanotheranostic agent (denoted as CDPGM) is developed for MR/photoacoustic (PA)/positron emission tomography (PET) multimodal imaging‐guided combination cancer therapy. In this system, the near‐infrared (NIR)‐absorbing PDA acts as a platform for the assembly of different moieties; Gd₃N@C₈₀, a kind of gadolinium metallofullerene with three Gd ions in one carbon cage, acts as a satellite anchoring on the surface of PDA. The as‐prepared CDPGM NPs show good biocompatibility, strong NIR absorption, high relaxivity (r ₁ = 14.06 mM^?1 s^?1), low risk of release of Gd ions, and NIR‐triggered drug release. In vivo MR/PA/PET multimodal imaging confirms effective tumor accumulation of the CDPGM NPs. Moreover, upon NIR laser irradiation, the tumor is completely eliminated with combined chemo‐photothermal therapy. These results suggest that the CDPGM NPs hold great promise for cancer theranostics.     

Facile Aqueous‐Phase Synthesis of Biocompatible and Fluorescent Ag2S Nanoclusters for Bioimaging: Tunable Photoluminescence from Red to Near Infrared

Low toxicity and fluorescent nanomaterials have many advantages in biological imaging. Herein, a novel and facile aqueous‐phase approach to prepare biocompatible and fluorescent Ag₂S nanoclusters (NCs) is designed and investigated. The resultant Ag₂S NCs show tunable luminescence from the visible red (624 nm) to the near infrared (NIR; 724 nm) corresponding to the increasing size of the NCs. The key for preparing tunable fluorescent Ag₂S NCs is the proper choice of capping reagent, glutathione (GSH), and the novel sulfur‐hydrazine hydrate complex as the S^2? source. As a naturally occurring and readily available tripeptide, GSH functions as an important scaffold to prevent NCs from growing large nanoparticles. Additionally, GSH is a small biomolecule with several functional groups, including carboxyl and amino groups, which suggests the resultant Ag₂S NCs are well‐dispersed in aqueous solution. These advantages make the as‐prepared Ag₂S NCs potentially applicable to biological labeling as well. For example, the resultant Ag₂S NCs are used as a probe for MC3T3‐EI cellular imaging.     

Controllable preparation of Ag2S quantum dots with size-dependent fluorescence and cancer photothermal therapy

Although Ag₂S quantum dots (QDs) have attracted extensive attention in the fields of diagnosis and therapy, it is still a challenge to prepare Ag₂S QDs with well-controlled size distribution. Herein, size-tunable Ag₂S QDs with glutathione (GSH) as ligands were prepared via a facile aqueous precipitation method. The QDs are precisely prepared through carefully controlled growth of Ag2S QDs by varying the heating time. Morphology and structure characterization verify that Ag₂S QDs with 2.0–5.8 nm in diameter are coordinated with GSH through thiol group. The as-prepared Ag₂S QDs exhibit broad absorption spectra and narrow fluorescence emission spectra in the near-infrared region. Meanwhile, the QDs perform excellent and stable photothermal effect with a photothermal conversion efficiency up to 58.6%. More importantly, it is found that the size of Ag₂S QDs has a significant influence on the fluorescence intensity and photothermal effect. The cell viability evaluation in vitro demonstrates that Ag₂S QDs have low cytotoxicity to 293 T cells and Hela cells by methyl thiazolyl tetrazolium test. This paper proposes a convenient route to prepare unique Ag₂S QDs, which are capable to act as ideal theranostics probes for photothermal therapy and simultaneously monitoring the therapeutic effect for effective cancer treatment.     

Responsive Upconversion Nanoprobe for Background‐Free Hypochlorous Acid Detection and Bioimaging

Responsive nanoprobes play an important role in bioassay and bioimaging, early diagnosis of diseases and treatment monitoring. Herein, a upconversional nanoparticle (UCNP)‐based nanoprobe, Ru@UCNPs, for specific sensing and imaging of hypochlorous acid (HOCl) is reported. This Ru@UCNP nanoprobe consists of two functional components,, i.e., NaYF₄:Yb, Tm UCNPs that can convert near infrared light‐to‐visible light as the energy donor, and a HOCl‐responsive ruthenium(II) complex [Ru(bpy)₂(DNCH‐bpy)](PF₆)₂ (Ru‐DNPH) as the energy acceptor and also the upconversion luminescence (UCL) quencher. Within this luminescence resonance energy transfer nanoprobe system, the UCL OFF–ON emission is triggered specifically by HOCl. This triggering reaction enables the detection of HOCl in aqueous solution and biological systems. As an example of applications, the Ru@UCNPs nanoprobe is loaded onto test papers for semiquantitative HOCl detection without any interference from the background fluorescence. The application of Ru@UCNPs for background‐free detection and visualization of HOCl in cells and mice is successfully demonstrated. This research has thus shown that Ru@UCNPs is a selective HOCl‐responsive nanoprobe, providing a new way to detect HOCl and a new strategy to develop novel nanoprobes for in situ detection of various biomarkers in cells and early disgnosis of animal diseases.     

Near-infrared-emitting colloidal Ag<Subscript>2</Subscript>S quantum dots excited by an 808 nm diode laser

Thioglycolic acid (TGA)-coated colloidal Ag₂S quantum dots (QDs) emitting in the near-infrared (NIR) region upon excitation by an 808 nm diode laser were synthesized. The observed photoluminescence (PL) was attributed to the presence of ligand-modified Ag₂S on the QD surfaces and could be easily controlled by a simple dilution process due to the concentration-dependent surface structure of the colloidal QDs. Upon dilution of the solution, the PL intensity initially increased before later decreasing, with a blueshift being observed in the PL spectra. These phenomena can be accounted for by the aggregation of QDs due to a decrease in the content of ligand-modified Ag₂S on the QD surfaces upon dilution, which in turn affected the fluorescence resonance energy transfer (FRET), and re-emission of the surface energy level.     

A Non-Invasive Nanoprobe for In Vivo Photoacoustic Imaging of Vulnerable Atherosclerotic Plaque

Vulnerable atherosclerotic (AS) plaque is the major cause of cardiovascular death. However, clinical methods cannot directly identify the vulnerable AS plaque at molecule level. Herein, osteopontin antibody (OPN Ab) and NIR fluorescence molecules of ICG co-assembled Ti₃C₂ nanosheets are reported as an advanced nanoprobe (OPN Ab/Ti₃C₂/ICG) with enhanced photoacoustic (PA) performance for direct and non-invasive in vivo visual imaging of vulnerable AS plaque. The designed OPN Ab/Ti₃C₂/ICG nanoprobes successfully realize obvious NIR fluorescence imaging toward foam cells as well as the vulnerable AS plaque slices. After intravenous injection of OPN Ab/Ti₃C₂/ICG nanoprobes into AS model mice, in vivo imaging results show a significantly enhanced PA signal in the aortic arch accumulated with vulnerable plaque, well indicating the remarkable feasibility of OPN Ab/Ti₃C₂/ICG nanoprobes to distinguish the vulnerable AS plaque. The proposed OPN Ab/Ti₃C₂/ICG nanoprobes not only overcome the clinical difficulty to differentiate vulnerable plaque, but also achieve the non-invasively specific in vivo imaging of vulnerable AS plaque at molecule level, greatly promoting the innovation of cardiovascular diagnosis technology.     

NIR‐II‐Excited Intravital Two‐Photon Microscopy Distinguishes Deep Cerebral and Tumor Vasculatures with an Ultrabright NIR‐I AIE Luminogen

Intravital fluorescence imaging of vasculature morphology and dynamics in the brain and in tumors with large penetration depth and high signal‐to‐background ratio (SBR) is highly desirable for the study and theranostics of vascular‐related diseases and cancers. Herein, a highly bright fluorophore (BTPETQ) with long‐wavelength absorption and aggregation‐induced near‐infrared (NIR) emission (maximum at ≈700 nm) is designed for intravital two‐photon fluorescence (2PF) imaging of a mouse brain and tumor vasculatures under NIR‐II light (1200 nm) excitation. BTPETQ dots fabricated via nanoprecipitation show uniform size of around 42 nm and a high quantum yield of 19 ± 1% in aqueous media. The 2PF imaging of the mouse brain vasculatures labeled by BTPETQ dots reveals a 3D blood vessel network with an ultradeep depth of 924 µm. In addition, BTPETQ dots show enhanced 2PF in tumor vasculatures due to their unique leaky structures, which facilitates the differentiation of normal blood vessels from tumor vessels with high SBR in deep tumor tissues. Moreover, the extravasation and accumulation of BTPETQ dots in deep tumor (more than 900 µm) is visualized under NIR‐II excitation. This study highlights the importance of developing NIR‐II light excitable efficient NIR fluorophores for in vivo deep tissue and high contrast tumor imaging.     

Revealing the Fate of Transplanted Stem Cells In Vivo with a Novel Optical Imaging Strategy

Stem‐cell‐based regenerative medicine holds great promise in clinical practices. However, the fate of stem cells after transplantation, including the distribution, viability, and the cell clearance, is not fully understood, which is critical to understand the process and the underlying mechanism of regeneration for better therapeutic effects. Herein, we develop a dual‐labeling strategy to in situ visualize the fate of transplanted stem cells in vivo by combining the exogenous near‐infrared fluorescence imaging in the second window (NIR‐II) and endogenous red bioluminescence imaging (BLI). The NIR‐II fluorescence of Ag₂S quantum dots is employed to dynamically monitor the trafficking and distribution of all transplanted stem cells in vivo due to its deep tissue penetration and high spatiotemporal resolution, while BLI of red‐emitting firefly luciferase (RfLuc) identifies the living stem cells after transplantation in vivo because only the living stem cells express RfLuc. This facile strategy allows for in situ visualization of the dynamic trafficking of stem cells in vivo and the quantitative evaluation of cell translocation and viability with high temporal and spatial resolution, and thus reports the fate of transplanted stem cells and how the living stem cells help, regeneration, for an instance, of a mouse with acute liver failure.     

In Vivo Dynamic Monitoring of Bacterial Infection by NIR‐II Fluorescence Imaging

Time window of antibiotic administration is a critical but long‐neglected point in the treatment of bacterial infection, as unnecessary prolonged antibiotics are increasingly causing catastrophic drug‐resistance. Here, a second near‐infrared (NIR‐II) fluorescence imaging strategy based on lead sulfide quantum dots (PbS QDs) is presented to dynamically monitor bacterial infection in vivo in a real‐time manner. The prepared PbS QDs not only provide a low detection limit (10⁴ CFU mL^?1) of four typical bacteria strains in vitro but also show a particularly high labeling efficiency with Escherichia coli (E. coli). The NIR‐II in vivo imaging results reveal that the number of invading bacteria first decreases after post‐injection, then increases from 1 d to 1 week and drop again over time in infected mouse models. Meanwhile, there is a simultaneous variation of dendritic cells, neutrophils, macrophages, and CD8+ T lymphocytes against bacterial infection at the same time points. Notably, the infected mouse self‐heals eventually without antibiotic treatment, as a robust immune system can successfully prevent further health deterioration. The NIR‐II imaging approach enables real‐time monitoring of bacterial infection in vivo, thus facilitating spatiotemporal deciphering of time window for antibiotic treatment.     

An Activatable Phototheranostic Nanoplatform for Tumor Specific NIR-II Fluorescence Imaging and Synergistic NIR-II Photothermal-Chemodynamic Therapy

The phototheranostics in the second near-infrared window (NIR-II) have proven to be promising for the precise cancer theranostics. However, the non-responsive and “always on” imaging mode lacks the selectivity, leading to the poor diagnosis specificity. Herein, a tumor microenvironment (TME) activated NIR-II phototheranostic nanoplatform (Ag₂S-Fe(III)-DBZ Pdots, AFD NPs) is designed based on the principle of Förster resonance energy transfer (FRET). The AFD NPs are fabricated through self-assembly of Ag₂S QDs (NIR-II fluorescence probe) and ultra-small semiconductor polymer dots (DBZ Pdots, NIR-II fluorescence quencher) utilizing Fe(III) as coordination nodes. In normal tissues, the AFD NPs maintain in “off” state, due to the FRET between Ag₂S QDs and DBZ Pdots. However, the NIR-II fluorescence signal of AFD NPs can be rapidly “turn on” by the overexpressed GSH in tumor tissues, achieving a superior tumor-to-normal tissue (T/NT) signal ratio. Moreover, the released Pdots and reduced Fe(II) ions provide NIR-II photothermal therapy (PTT) and chemodynamic therapy (CDT), respectively. The GSH depletion and NIR-II PTT effect further aggravate CDT mediated oxidative damage toward tumors, achieving the synergistic anti-tumor therapeutic effect. The work provides a promising strategy for the development of TME activated NIR-II phototheranostic nanoprobes.     

Color‐Convertible,Unimolecular, Micelle‐Based,Activatable Fluorescent Probe for Tumor‐Specific Detection and Imaging In Vitro and In Vivo

Recent years have witnessed significant progress in molecular probes for cancer diagnosis. However, the conventional molecular probes are designed to be “always‐on” by attachment of tumor‐targeting ligands, which limits their abilities to diagnose tumors universally due to the variations of targeting efficiency and complex environment in different cancers. Here, it is proposed that a color‐convertible, activatable probe is responding to a universal tumor microenvironment for tumor‐specific diagnosis without targeting ligands. Based on the significant hallmark of up‐regulated hydrogen peroxide (H₂O₂) in various tumors, a novel unimolecular micelle constructed by boronate coupling of a hydrophobic hyperbranched poly(fluorene‐co‐2,1,3‐benzothiadiazole) core and many hydrophilic poly(ethylene glycol) arms is built as an H₂O₂‐activatable fluorescent nanoprobe to delineate tumors from normal tissues through an aggregation‐enhanced fluorescence resonance energy transfer strategy. This color‐convertible, activatable nanoprobe is obviously blue‐fluorescent in various normal cells, but becomes highly green‐emissive in various cancer cells. After intravenous injection to tumor‐bearing mice, green fluorescent signals are only detected in tumor tissue. These observations are further confirmed by direct in vivo and ex vivo tumor imaging and immunofluorescence analysis. Such a facile and simple methodology without targeting ligands for tumor‐specific detection and imaging is worthwhile to further development.     

Bright Aggregation‐Induced‐Emission Dots for Targeted Synergetic NIR‐II Fluorescence and NIR‐I Photoacoustic Imaging of Orthotopic Brain Tumors

Precise diagnostics are of significant importance to the optimal treatment outcomes of patients bearing brain tumors. NIR‐II fluorescence imaging holds great promise for brain‐tumor diagnostics with deep penetration and high sensitivity. This requires the development of organic NIR‐II fluorescent agents with high quantum yield (QY), which is difficult to achieve. Herein, the design and synthesis of a new NIR‐II fluorescent molecule with aggregation‐induced‐emission (AIE) characteristics is reported for orthotopic brain‐tumor imaging. Encapsulation of the molecule in a polymer matrix yields AIE dots showing a very high QY of 6.2% with a large absorptivity of 10.2 L g^?1 cm^?1 at 740 nm and an emission maximum near 1000 nm. Further decoration of the AIE dots with c‐RGD yields targeted AIE dots, which afford specific and selective tumor uptake, with a high signal/background ratio of 4.4 and resolution up to 38 µm. The large NIR absorptivity of the AIE dots facilitates NIR‐I photoacoustic imaging with intrinsically deeper penetration than NIR‐II fluorescence imaging and, more importantly, precise tumor‐depth detection through intact scalp and skull. This research demonstrates the promise of NIR‐II AIE molecules and their dots in dual NIR‐II fluorescence and NIR‐I photoacoustic imaging for precise brain cancer diagnostics.     

A GSH‐Gated DNA Nanodevice for Tumor‐Specific Signal Amplification of microRNA and MR Imaging–Guided Theranostics

Developing tumor‐responsive diagnosis and therapy strategies for tumor theranostics is still a challenge owing to their high accuracy and specificity. Herein, an AND logic gated–DNA nanodevice, based on the fluorescence nucleic acid probe and polymer‐modified MnO₂ nanosheets, for glutathione (GSH)‐gated miRNA‐21 signal amplification and GSH‐activated magnetic resonance (MR) imaging–guided chemodynamic therapy (CDT) is reported. In the presence of overexpressed miRNA and GSH (tumor cells), the nanodevice can be in situ activated and release significantly amplified fluorescence signals and MR signals. Conversely, the fluorescence signal is quenched and MR signal remains at the background level with low miRNA and GSH (normal cells), efficiently reducing the false‐positive signals by more than 50%. Under the guide of miRNA profiling and MR imaging, the tumor‐responsive hydroxyl radical ( · OH) can effectively kill tumor cells. Furthermore, the nanodevice shows catalase‐like activity and glucose oxidase–like activity with the performance of O₂ production and glucose consumption. This is the first time to fabricate a tumor‐responsive theranostic DNA nanodevice with tumor‐specific signal amplification of microRNA and GSH‐activated MR imaging for CDT, potential hypoxia relief and starvation therapy, which provides a new insight for designing smart theranostic strategies.     

“Dual Lock‐and‐Key”‐Controlled Nanoprobes for Ultrahigh Specific Fluorescence Imaging in the Second Near‐Infrared Window

Fluorescence imaging in the second near‐infrared window (NIR‐II) is a new technique that permits visualization of deep anatomical features with unprecedented spatial resolution. Although attractive, effectively suppressing the interference signal of the background is still an enormous challenge for obtaining target‐specific NIR‐II imaging in the complex and dynamic physiological environment. Herein, dual‐pathological‐parameter cooperatively activatable NIR‐II fluorescence nanoprobes (HISSNPs) are developed whereby hyaluronic acid chains and disulfide bonds act as the “double locks” to lock the fluorescence‐quenched aggregation state of the NIR‐II fluorescence dyes for performing ultrahigh specific imaging of tumors in vivo. The fluorescence can be lit up only when the “double locks” are opened by reacting with the “dual smart keys” (overexpressed hyaluronidase and thiols in tumor) simultaneously. In vivo NIR‐II imaging shows that they reduce nonspecific activitation and achieve ultralow background fluorescence, which is 10.6‐fold lower than single‐parameter activatable probes (HINPs) in the liver at 15 h postinjection. Consequently, these “dual lock‐and‐key”‐controlled HISSNPs exhibit fivefold higher tumor‐to‐normal tissue ratio than “single lock‐and‐key”‐controlled HINPs at 24 h postinjection, attractively realizing ultrahigh specificity of tumor imaging. This is thought to be the first attempt at implementing ultralow background interference with the participation of multiple pathological parameters in NIR‐II fluorescence imaging.     

Atomic‐Precision Gold Clusters for NIR‐II Imaging

Near‐infrared II (NIR‐II) imaging at 1100–1700 nm shows great promise for medical diagnosis related to blood vessels because it possesses deep penetration and high resolution in biological tissue. Unfortunately, currently available NIR‐II fluorophores exhibit slow excretion and low brightness, which prevents their potential medical applications. An atomic‐precision gold (Au) cluster with 25 gold atoms and 18 peptide ligands is presented. The Au₂₅ clusters show emission at 1100–1350 nm and the fluorescence quantum yield is significantly increased by metal‐atom doping. Bright gold clusters can penetrate deep tissue and can be applied in in vivo brain vessel imaging and tumor metastasis. Time‐resolved brain blood‐flow imaging shows significant differences between healthy and injured mice with different brain diseases in vivo. High‐resolution imaging of cancer metastasis allows for the identification of the primary tumor, blood vessel, and lymphatic metastasis. In addition, gold clusters with NIR‐II fluorescence are used to monitor high‐resolution imaging of kidney at a depth of 0.61 cm, and the quantitative measurement shows 86% of the gold clusters are cleared from body without any acute or long‐term toxicity at a dose of 100 mg kg^?1.