Comparative Study of Indocyanine Green Fluorescence Imaging in Lung Cancer with Near-Infrared-I/II Windows.

BACKGROUND: We compare the application of intravenous indocyanine green (ICG) fluorescence imaging in lung cancer with near-infrared-I (NIR-I) and near-infrared-II (NIR-II) windows. METHODS: From March to December 2022, we enrolled patients who received an intravenous injection of ICG (5 mg/kg) 1 day before the planned lung cancer surgery. The lung cancer nodules were imaged by NIR-I/II fluorescence imaging systems, and the tumor-to-normal-tissue ratio (TNR) was calculated. In addition, the fluorescence intensity and signal-to-background ratio (SBR) of capillary glass tubes containing ICG covered with different thicknesses of lung tissue were measured by NIR-I/II fluorescence imaging systems. RESULTS: In this study, 102 patients were enrolled, and the mean age was 59.9 ± 9.2 years. A total of 96 (94.1%) and 98 (96.1%) lung nodules were successfully imaged with NIR-I and NIR-II fluorescence, and the TNR of NIR-II was significantly higher than that of NIR-I (3.9 ± 1.3 versus 2.4 ± 0.6, P < 0.001). In multiple linear regression, solid nodules (P < 0.001) and squamous cell carcinoma (P < 0.001) were independent predictors of a higher TNR of NIR-I/II. When capillary glass tubes were covered with lung tissue whose thickness was more than 2 mm, the fluorescence intensity and the SBR of NIR-II were significantly higher than those of NIR-I. CONCLUSIONS: We verified the feasibility of NIR-II fluorescence imaging in intravenous ICG lung cancer imaging for the first time. NIR-II fluorescence can improve the TNR and penetration depth of lung cancer with promising clinical prospects.

Focused Ultrasound-Responsive Nanocomposite with Near-Infrared II Mechanoluminescence for Spatiotemporally Selective Immune Activation in Lymph Nodes.

The immune regulation of the lymphatic system, especially the lymph node (LN), is of great significance for the treatment of diseases and the inhibition of pathogenic organisms spreading in the body. However, achieving precise spatiotemporal control of immune cell activation in LN in vivo remains a challenge due to tissue depth and off-target effects. Furthermore, minimally invasive and real-time feedback methods to monitor the regulation of the immune system in LN are lacking. Here, focused ultrasound responsive immunomodulator loaded nanoplatform (FURIN) with near-infrared II (NIR-II) luminescence is designed to achieve spatiotemporally controllable immune activation in LN in vivo. The NIR-II persistent luminescence of FURIN can track its delivery in LN through bioimaging. Under focused ultrasound (FUS) stimulation, the immunomodulator encapsulated in FURIN can be released locally in the LN to activate immune cells such as dendritic cells and the NIR-II mechanoluminescence of FURIN provides real-time optical feedback signals for immune activation. This work points to a FUS mediated, spatiotemporal selective immune activation strategy in vivo with the feedback control of luminescence signals via ultrasound responsive nanocomposite, which is of great significance in improving the efficacy and reducing the side effect of immune regulation for the development of potential immunotherapeutic methods in the future.

Near-Infrared-II Nanomaterials for Activatable Photodiagnosis and Phototherapy.

Near-Infrared-II (NIR-II) spans wavelengths between 1,000 to 1,700 nanometers, featuring deep tissue penetration and reduced tissue scattering and absorption characteristics, providing robust support for cancer treatment and tumor imaging research. This review explores the utilization of activatable NIR-II photodiagnosis and phototherapy based on tumor microenvironments (e. g., reactive oxygen species, pH, glutathione, hypoxia) and external stimulation (e. g., laser, ultrasound, photothermal) for precise tumor treatment and imaging. Special emphasis is placed on the advancements and advantages of activatable NIR-II nanomedicines in novel therapeutic modalities like photodynamic therapy, photothermal therapy, and photoacoustic imaging. This encompasses achieving deep tumor penetration, real-time monitoring of the treatment process, and obtaining high-resolution, high signal-to-noise ratio images even at low material concentrations. Lastly, from a clinical perspective, the challenges faced by activatable NIR-II phototherapy are discussed, alongside potential strategies to overcome these hurdles.

Novel Near-Infrared-II In Vivo Visualization Revealed Rapid Calcium Intestine Turnover in Daphnia magna with Delayed Impact by Cadmium and Acidification.

Calcium is a highly demanded metal, and its transport across the intestine of Daphnia magna remains a significant unresolved question. Due to technical constraints, the visualization of the kinetic process of Ca passage through D. magna has been challenging. Here, we developed the second near-infrared Ca sensor (NIR-II Ca) and conducted real-time in vivo imaging of Ca in daphnids with a high signal-to-noise ratio, deep tissue penetration, and minimal damage. Through the utilization of the NIR-II Ca sensor, we for the first time visualized and quantified the kinetic process of Ca passage in the intestine in real time. The results revealed that trophically available Ca passed through the intestines in 24 h, whereas waterborne Ca required only 35 min. This rapid "flushing through" mechanism established waterborne Ca as the primary source of Ca absorption. However, environmental stressors such as water acidification and cadmium significantly delayed the Ca passage and absorption. The development of NIR imaging and sensors allows for real-time dynamic visualization of contaminants/nutrients in organisms and holds great potential as a powerful tool for future studies into material kinetic processes in living animals.

In vivo fluorescence imaging of nanocarriers in near-infrared window II based on aggregation-caused quenching.

Accurate fluorescence imaging of nanocarriers in vivo remains a challenge owing to interference derived mainly from biological tissues and free probes. To address both issues, the current study explored fluorophores in the near-infrared (NIR)-II window with aggregation-caused quenching (ACQ) properties to improve imaging accuracy. Candidate fluorophores with NIR-II emission, ACQ984 (λem = 984 nm) and IR-1060 (λem = 1060 nm), from the aza-BODIPY and cyanine families, respectively, were compared with the commercial fluorophore ICG with NIR-II tail emission and the NIR-I fluorophore P2 from the aza-BODIPY family. ACQ984 demonstrates high water sensitivity with complete fluorescence quenching at a water fraction greater than 50%. Physically embedding the fluorophores illuminates various nanocarriers, while free fluorophores cause negligible interference owing to the ACQ effect. Imaging based on ACQ984 revealed fine structures in the vascular system at high resolution. Moreover, good in vivo and ex vivo correlations in the monitoring of blood nanocarriers can be established, enabling real-time noninvasive in situ investigation of blood pharmacokinetics and dynamic distribution in various tissues. IR-1060 also has a good ACQ effect, but the lack of sufficient photostability and steady post-labeling fluorescence undermines its potential for nanocarrier bioimaging. P2 has an excellent ACQ effect, but its NIR-I emission only provides nondiscriminative ambiguous images. The failure of the non-ACQ probe ICG to display the biodistribution details serves as counterevidence for the improved imaging accuracy by NIR-II ACQ probes. Taken together, it is concluded that fluorescence imaging of nanocarriers based on NIR-II ACQ probes enables accurate in vivo bioimaging and real-time in situ pharmacokinetic analysis.

In vivo NIR-II structured-illumination light-sheet microscopy.

Noninvasive optical imaging with deep tissue penetration depth and high spatiotemporal resolution is important to longitudinally studying the biology at the single-cell level in live mammals, but has been challenging due to light scattering. Here, we developed near-infrared II (NIR-II) (1,000 to 1,700 nm) structured-illumination light-sheet microscopy (NIR-II SIM) with ultralong excitation and emission wavelengths up to ∼1,540 and ∼1,700 nm, respectively, suppressing light scattering to afford large volumetric three-dimensional (3D) imaging of tissues with deep-axial penetration depths. Integrating structured illumination into NIR-II light-sheet microscopy further diminished background and improved spatial resolution by approximately twofold. In vivo oblique NIR-II SIM was performed noninvasively for 3D volumetric multiplexed molecular imaging of the CT26 tumor microenvironment in mice, longitudinally mapping out CD4, CD8, and OX40 at the single-cell level in response to immunotherapy by cytosine-phosphate-guanine (CpG), a Toll-like receptor 9 (TLR-9) agonist combined with OX40 antibody treatment. NIR-II SIM affords an additional tool for noninvasive volumetric molecular imaging of immune cells in live mammals.

Structurally Modulated Formation of Cyanine J-Aggregates with Sharp and Tunable Spectra for Multiplexed Optoacoustic and Fluorescence Bioimaging.

J-aggregation brings intriguing optical and electronic properties to molecular dyes and significantly expands their applicability across diverse domains, yet the challenge for rationally designing J-aggregating dyes persists. Herein, we developed a large number of J-aggregating dyes from scratch by progressively refining structure of a common heptamethine cyanine. J-aggregates with sharp spectral bands (full-width at half-maximum≤38 nm) are attained by introducing a branched structure featuring a benzyl and a trifluoroacetyl group at meso-position of dyes. Fine-tuning the benzyl group enables spectral regulation of J-aggregates. Analysis of single crystal data of nine dyes reveals a correlation between J-aggregation propensity and molecular arrangement within crystals. Some J-aggregates are successfully implemented in multiplexed optoacoustic and fluorescence imaging in animals. Notably, three-color multispectral optoacoustic tomography imaging with high spatiotemporal resolution is achieved, owing to the sharp and distinct absorption bands of the J-aggregates.

Spinel-Type Structured Phosphor Near-Infrared-II Emission: Intervalence Charge Transfer and Hetero-Valent Chromium Pairs.

Near-infrared (NIR) emitting phosphors draw much attention because they show great applicability and development prospects in many fields. Herein, a series of inverse spinel-type structured LiGa5O8 phosphors with a high concentration of Cr3+ activators is reported with a dual emission band covering NIR-I and II regions. Except for strong ionic exchange interactions such as Cr3+-Cr3+ and Cr3+ clusters, an intervalence charge transfer (IVCT) process between aggregated Cr ion pairs is proposed as the mechanism for the ~1210 nm NIR-II emission. Comprehensive structural and luminescence characterization points to IVCT between two Cr3+ being induced by structural distortion and further enhanced by irradiation. Construction of the configurational energy level diagram enabled elucidation of this transition within the IVCT process. Therefore, this work provides insight into the emission mechanism within the high Cr3+ concentration system, revealing a new design strategy for NIR-II emitting phosphors to promote its response.

NIR-II Perylene Monoimide-Based Photothermal Agent with Strengthened Donor-Acceptor Conjugation for Deep Orthotopic Glioblastoma Phototheranostics.

Extensive efforts have been devoted to the design of organic photothermal agents (PTAs) that absorb in the second near-infrared (NIR-II) bio-window, which can provide deeper tissue penetration that is significant for phototheranostics of lethal brain tumors. Herein, the first example of NIR-II-absorbing small organic molecule (N1) derived from perylene monoamide (PMI) and its bio-application after nano-encapsulation of N1 to function as a nano-agent for phototheranostics of deep orthotopic glioblastoma (GBM) is reported. By adopting a dual modification strategy of introducing a donor-acceptor unit and extending π-conjugation, the obtained N1 can absorb in 1000-1400 nm region and exhibit high photothermal conversation due to the apparent intramolecular charge transfer (ICT). A choline analogue, 2-methacryloyloxyethyl phosphorylcholine, capable of interacting specifically with receptors on the surface of the blood-brain barrier (BBB), is used to fabricate the amphiphilic copolymer for the nano-encapsulation of N1. The obtained nanoparticles demonstrate efficient BBB-crossing due to the receptor-mediated transcytosis as well as the small nanoparticle size of approximately 26 nm. The prepared nanoparticles exhibit excellent photoacoustic imaging and significant growth inhibition of deep orthotopic GBM. The current study demonstrates the enormous potential of PMI-based NIR-II PTAs and provides an efficient phototheranostic paradigm for deep orthotopic GBM.

Single Atom-Engineered NIR-II Gold Clusters with Ultrahigh Brightness and Stability for Acute Kidney Injury.

Near-infrared-II (NIR-II) imaging has shown great potential for monitoring the pathological progression and deep tissue imaging but is limited to present unmet NIR-II agent. Present fluorophores show a promising prospect for NIR-II imaging, but brightness and photostability are still highly challenging during real-time monitoring. In this work, atom-engineered NIR-II Au24 Cd1  clusters with ultrahigh brightness, stability, and photostability are developed via single atomic Cd doping. Single atom Cd substitutions contribute to Cd 4d state in HOMO and redistribution of energy level near the gap, exhibiting 56-fold fluorescence enhancement of Au24 Cd1  clusters. Meanwhile, single atomic Cd reinforces CdAu bond energy, formation energy, and stabilized cluster structure, leading to persistent stability for up to 1 month without decay, as well as excellent photostability of 1 h without photobleaching, much longer than clinically approved indocyanine green (<5 min). In vivo imaging shows gold clusters can monitor acute kidney injury (AKI) even after 72 h of injury, enabling evaluating progression at a very long window. Meanwhile, the bioactive gold clusters can alleviate AKI-induced oxidative stress damage and acute neuroinflammation. Single atom-engineered gold clusters exhibit molecular tracking and diagnostic prospect in kidney-related diseases.

Near-infrared II photobiomodulation augments nitric oxide bioavailability via phosphorylation of endothelial nitric oxide synthase.

There is solid evidence of the beneficial effect of photobiomodulation (PBM) with low-power near-infrared (NIR) light in the NIR-I window in increasing bioavailable nitric oxide (NO). However, it is not established whether this effect can be extended to NIR-II light, limiting broader applications of this therapeutic modality. Since we have demonstrated PBM with NIR laser in the NIR-II window, we determined the causal relationship between NIR-II irradiation and its specific biological effects on NO bioavailability. We analyzed the impact of NIR-II irradiation on NO release in cultured human endothelial cells using a NO-sensitive fluorescence probe and single-cell live imaging. Two distinct wavelengths of NIR-II laser (1064 and 1270 nm) and NIR-I (808 nm) at an irradiance of 10 mW/cm2 induced NO release from endothelial cells. These lasers also enhanced Akt phosphorylation at Ser 473, endothelial nitric oxide synthase (eNOS) phosphorylation at Ser 1177, and endothelial cell migration. Moreover, the NO release and phosphorylation of eNOS were abolished by inhibiting mitochondrial respiration, suggesting that Akt activation caused by NIR-II laser exposure involves mitochondrial retrograde signaling. Other inhibitors that inhibit known Akt activation pathways, including a specific inhibitor of PI3K, Src family PKC, did not affect this response. These two wavelengths of NIR-II laser induced no appreciable NO generation in cultured neuronal cells expressing neuronal NOS (nNOS). In short, NIR-II laser enhances bioavailable NO in endothelial cells. Since a hallmark of endothelial dysfunction is suppressed eNOS with concomitant NO deficiency, NIR-II laser technology could be broadly used to restore endothelial NO and treat or prevent cardiovascular diseases.

Dual near-infrared II laser modulates the cellular redox state of T cells and augments the efficacy of cancer immunotherapy.

Immunotherapy, including immune checkpoint inhibitors, has revolutionized cancer treatment, but only a minor fraction of patients shows durable responses. A new approach to overcome this limitation is yet to be identified. Recently, we have shown that photobiomodulation (PBM) with near-infrared (NIR) light in the NIR-II window reduces oxidative stress and supports the proliferation of CD8+ T cells, suggesting that PBM with NIR-II light could augment anti-cancer immunity. Here, we report a novel approach to support tumor-infiltrating CD8+ T cells upon PBM with NIR-II laser with high tissue penetration depth. Brief treatments of a murine model of breast cancer with dual 1064 and 1270 nm lasers reduced the expression of the programmed cell death protein 1 (PD-1) in CD8+ T cells in a syngeneic mouse model of breast cancer. The direct effect of the NIR-II laser treatment on T cells was confirmed by the enhanced tumor growth delay by the adoptive transfer of laser-treated CD8+ T cells ex vivo against a model tumor antigen. We further demonstrated that specific NIR-II laser parameters augmented the effect of the immune checkpoint inhibitor on tumor growth. PBM with NIR-II light augments the efficacy of cancer immunotherapy by supporting CD8+ T cells. Unlike the current immunotherapy with risks of undesirable drug-drug interactions and severe adverse events, the laser is safe and low-cost. It can be broadly combined with other therapy without modification to achieve clinical significance. In addition, our study established a path to develop a novel laser-based therapy to treat cancer effectively.

The pursuit of xanthenoid fluorophores with near-infrared-II emission for in vivo applications.

As fluorescence imaging in the second near-infrared window (NIR-II, 1000-1700 nm) has gained increasing attention, it is inevitable that NIR-II fluorophores, the cornerstone of NIR-II imaging, have come to the middle of the stage. NIR-II xanthenoid fluorophores with good stability, high brightness, and fluorescence adjustability are becoming popular. We here reviewed the recent progress of xanthenoid fluorophores with NIR-II emission for in vivo applications. Especially, we focus on the strategies used for longer wavelength and fluorescence regulation to construct OFF-ON or ratiometric NIR-II fluorescent probes.

Visualization of photothermal therapy by semiconducting polymer dots mediated photoacoustic detection in NIR II.

Visualization of photothermal therapy mediated by photothermal transduction agents (PTAs) is important to promote individual treatment of patients with low side effects. Photoacoustic detection has emerged as a promising noninvasive method for the visualization of PTAs distribution but still has limitations in temperature measurement, including poor measurement accuracy and low tissue penetration depth. In this study, we developed biocompatible semiconducting polymer dots (SPD) for in situ coupling of photothermal and photoacoustic detection in the near-infrared II window. SPD has dual photostability under pulsed laser and continuous-wave laser irradiation with a photothermal conversion efficiency of 42.77%. Meanwhile, a strong correlation between the photoacoustic signal and the actual temperature of SPD can be observed. The standard deviation of SPD-mediated photoacoustic thermometry can reach 0.13 °C when the penetration depth of gelatin phantom is 9.49 mm. Preliminary experimental results in vivo show that SPD-mediated photoacoustic signal has a high signal-to-noise ratio, as well as good performance in temperature response and tumor enrichment. Such a study not only offers a new nanomaterial for the visualization of photothermal therapy but will also promote the theranostic platform for clinical applications.

Organic Amine-Bridged Quasi-2D Perovskite/PbS Colloidal Quantum Dots Composites for High-Gain Near-Infrared Photodetectors.

Near-infrared (NIR) II detection at weak flux intensity is required in medical imaging and is especially urgent in light of the low quantum efficiency of NIR-II dyes. The low responsivity of traditional photodetectors in this region limits image quality. Here, we report a NIR-II photodetector with high gain based on perovskite coupled PbS colloidal quantum dots (CQDs). Tailoring the trap density of CQDs by designing surface ligands with dual functionality contributed to control over trap-induced charge-injection upon light illumination. As a result, a detector with high gain is realized, showing external quantum efficiency of 1260% at 1200 nm and achieving the lowest detectable light intensity, that is, as low as 0.67 pW cm-2 with a linear dynamic range of 200 dB. Devices maintain over 90% of responsivity after 150 days of storage. We acquired images of a butterfly wing, showing the skeleton texture with a maximum spatial resolution of 3.9 lp/mm.

Bispalladium(II) Complexes of di-p-Pyrirubyrin Derivatives as Promising Near-Infrared Photoacoustic Dyes.

The insertion of palladium(II) into di-p-pyrirubyrin results in mutually convertible bimetallic complexes. Post-synthetic functionalization of one of them yielded bispalladium(II) dioxo-di-p-pyrirubyrin and, after demetallation, dioxo-di-p-pyrirubyrin, introducing for the first time the α,ß'-pyridin-2-one unit into the macrocyclic frame. Bispalladium(II) di-p-pyrirubyrin 6, bispalladium(II) dioxo-di-p-pyrirubyrin 9, and dioxo-di-p-pyrirubyrin 10 absorb and emit light around 1000 nm and are characterized by high photostability. Thus, they are promising candidates for near-infrared photoacoustic dyes, ideally targeting (9) the wavelength of Yb-based fiber lasers. The incorporation of an α,ß'-pyridine moiety into expanded porphyrins opens a highly interesting area of research due to the attractive optical and coordination properties of the resulting molecules.

Gas-Mediated Tumor Energy Remodeling for Sensitizing Mild Photothermal Therapy.

The metabolic reprogramming of tumors requires high levels of adenosine triphosphate (ATP) to maintain therapeutic resistance, posing a major challenge for photothermal therapy (PTT). Although raising the temperature helps in tumor ablation, it frequently leads to severe side effects. Therefore, improving the therapeutic response and promoting healing are critical considerations in the development of PTT. Here, we proposed a gas-mediated energy remodeling strategy to improve mild PTT efficacy while minimizing side effects. In the proof-of-concept study, a Food and Drug Administration (FDA)-approved drug-based hydrogen sulfide (H2 S) donor was developed to provide a sustained supply of H2 S to tumor sites, serving as an adjuvant to PTT. This approach proved to be highly effective in disrupting the mitochondrial respiratory chain, inhibiting ATP generation, and reducing the overexpression of heat shock protein 90 (HSP90), which ultimately amplified the therapeutic outcome. With the ability to reverse tumor thermotolerance, this strategy delivered a greatly potent antitumor response, achieving complete tumor ablation in a single treatment while minimizing harm to healthy tissues. Thus, it holds great promise to be a universal solution for overcoming the limitations of PTT and may serve as a valuable paradigm for the future clinical translation of photothermal nanoagents.

"Dual-Key-and-Lock" NIR-II NSCyanines Enable High-Contrast Activatable Phototheranostics in Extrahepatic Diseases.

Conventional cyanine dyes with a symmetric structure are "always-on", which can easily accumulate in the liver and display high liver background fluorescence, inevitably interfering the accurate diagnosis and therapy in extrahepatic diseases. We herein report a platform of NIR-II non-symmetric cyanine (NSCyanine) dyes by harnessing a non-symmetric strategy, which are extremely sensitive to pH/viscosity and can be activated via a "dual-key-and-lock" strategy. These NSCyanine dyes with a low pKa (<4.0) only show weak fluorescence at lysosome pH (key1), however, the fluorescence can be completely switched on and significantly enhanced by intracellular viscosity (key2) in disease tissues, exhibiting high target-to-liver ratios up to 19.5/1. Notably, high-contrast phototheranostics in extrahepatic diseases are achieved, including intestinal metastasis-imaging, acute gastritis-imaging, bacteria infected wound healing, and tumor ablation via targeted combined photothermal therapy and chemotherapy.

Near-Infrared II Plasmonic Phototheranostics with Glutathione Depletion for Multimodal Imaging-Guided Hypoxia-Tolerant Chemodynamic-Photocatalytic-Photothermal Cancer Therapy Triggered by a Single Laser.

Tumor microenvironment (TME)-activatable phototheranostics is highly desirable in cancer management but still remains challenging for clinical applications owing to the lack of multifunctional theranostic agents and the limited tissue penetration depth. Reported here is an "all-in-one" phototheranostic platform based on near-infrared II (NIR-II) dual-plasmonic Au@Cu2-x Se core-shell nanocrystals (dpGCS NCs) for combined photoacoustic (PA)/photothermal (PT) imaging-guided chemodynamic therapy (CDT)/photocatalytic therapy (PCT)/photothermal therapy (PTT) all triggered by a single NIR-II laser. The dpGCS NCs feature excellent NIR-II plasmonic and PT properties, which guarantee their capabilities of NIR-II PA and PT imaging for real-time visual observation of tumor size and location during cancer treatment. Additionally, the TME-activated in situ •OH production via dpGCS NC-catalyzed Fenton-like reaction is further enhanced by the NIR-II irradiation, while photoexcited plasmonic hole-induced formation of extra •OH is also evidenced for PCT. Both in vitro and in vivo experiments confirm remarkable therapeutic efficacy of the present phototheranostic platform under NIR-II laser through the CDT/PCT/PTT trimodal combination therapy, achieving complete inhibition of tumor growth in tumor-bearing mice after administration of dpGCS NCs plus a single NIR-II laser irradiation. This work provides a distinctive paradigm for the development of NIR-II phototheranostic platforms for imaging-guided cancer therapy using a single laser.

Near-Infrared-II Quantum Dots for In Vivo Imaging and Cancer Therapy.

In vivo fluorescence imaging can perform real-time, noninvasive, and high spatiotemporal resolution imaging to accurately obtain the dynamic biological information in vivo, which plays significant roles in the early diagnosis and treatment of cancer. However, traditional in vivo fluorescence imaging usually operates in the visible and near-infrared (NIR)-I windows, which are severely interfered by the strong tissue absorption, tissue scattering, and autofluorescence. The emergence of NIR-II imaging at 1000-1700 nm significantly breaks through the imaging limitations in deep tissues, due to less tissue scattering and absorption. Benefiting from the outstanding optical properties of NIR-II quantum dots (QDs), such as high brightness and good photostability, in vivo fluorescence imaging exhibits excellent temporal-spatial resolution and large penetration depth, and QDs have become a kind of promising fluorescent biomarkers in the field of in vivo fluorescence imaging. Herein, the authors review NIR-II QDs from preparation to modification, and summarize recent applications of NIR-II QDs, including in vivo imaging and imaging-guided therapies. Finally, they discuss the special concerns when NIR-II QDs are shifted from in vivo imaging applications to further in-depth applications.