Small-Molecule Phototheranostic Agent with Extended π-Conjugation for Efficient NIR-II Photoacoustic-Imaging-Guided Photothermal Therapy.

Photoacoustic imaging (PAI) and photothermal therapy (PTT) conducted over the near-infrared-II (NIR-II) window offer the benefits of noninvasiveness and deep tissue penetration. This necessitates the development of highly effective therapeutic agents with NIR-II photoresponsivity. Currently, the predominant organic diagnostic agents used in NIR-II PAI-guided PTT are conjugated polymeric materials. However, they exhibit a low in vivo clearance rate and long-term biotoxicity, limiting their clinical translation. In this study, an organic small molecule (CY-1234) with NIR-II absorption and nanoencapsulation (CY-1234 nanoparticles (NPs)) for PAI-guided PTT is reported. Extended π-conjugation is achieved in the molecule by introducing donor-acceptor units at both ends of the molecule. Consequently, CY-1234 exhibits a maximum absorption peak at 1234 nm in tetrahydrofuran. Nanoaggregates of CY-1234 are synthesized via F-127 encapsulation. They exhibit an excellent photothermal conversion efficiency of 76.01% upon NIR-II light irradiation. After intravenous injection of CY-1234 NPs into tumor-bearing mice, strong PA signals and excellent tumor ablation are observed under 1064 nm laser irradiation. This preliminary study can pave the way for the development of small-molecule organic nanoformulations for future clinical applications.

Recent advances in near-infrared II imaging technology for biological detection.

Molecular imaging technology enables us to observe the physiological or pathological processes in living tissue at the molecular level to accurately diagnose diseases at an early stage. Optical imaging can be employed to achieve the dynamic monitoring of tissue and pathological processes and has promising applications in biomedicine. The traditional first near-infrared (NIR-I) window (NIR-I, range from 700 to 900 nm) imaging technique has been available for more than two decades and has been extensively utilized in clinical diagnosis, treatment and scientific research. Compared with NIR-I, the second NIR window optical imaging (NIR-II, range from 1000 to 1700 nm) technology has low autofluorescence, a high signal-to-noise ratio, a high tissue penetration depth and a large Stokes shift. Recently, this technology has attracted significant attention and has also become a heavily researched topic in biomedicine. In this study, the optical characteristics of different fluorescence nanoprobes and the latest reports regarding the application of NIR-II nanoprobes in different biological tissues will be described. Furthermore, the existing problems and future application perspectives of NIR-II optical imaging probes will also be discussed.

Applications of indocyanine green in brain tumor surgery: review of clinical evidence and emerging technologies.

Indocyanine green (ICG) is a water-soluble dye that was approved by the FDA for biomedical purposes in 1956. Initially used to measure cardiocirculatory and hepatic functions, ICG's fluorescent properties in the near-infrared (NIR) spectrum soon led to its application in ophthalmic angiography. In the early 2000s, ICG was formally introduced in neurosurgery as an angiographic tool. In 2016, the authors' group pioneered a novel technique with ICG named second-window ICG (SWIG), which involves infusion of a high dose of ICG (5.0 mg/kg) in patients 24 hours prior to surgery. To date, applications of SWIG have been reported in patients with high-grade gliomas, meningiomas, brain metastases, pituitary adenomas, craniopharyngiomas, chordomas, and pinealomas.The applications of ICG have clearly expanded rapidly across different specialties since its initial development. As an NIR fluorophore, ICG has advantages over other FDA-approved fluorophores, all of which are currently in the visible-light spectrum, because of NIR fluorescence's increased tissue penetration and decreased autofluorescence. Recently, interest in the latest applications of ICG in brain tumor surgery has grown beyond its role as an NIR fluorophore, extending into shortwave infrared imaging and integration into nanotechnology. This review aims to summarize reported clinical studies on ICG fluorescence-guided surgery of intracranial tumors, as well as to provide an overview of the literature on emerging technologies related to the utility of ICG in neuro-oncological surgeries, including the following aspects: 1) ICG fluorescence in the NIR-II window; 2) ICG for photoacoustic imaging; and 3) ICG nanoparticles for combined diagnostic imaging and therapy (theranostic) applications.

Miniature Hollow Gold Nanorods with Enhanced Effect for In Vivo Photoacoustic Imaging in the NIR-II Window.

The miniaturization of gold nanorods exhibits a bright prospect for intravital photoacoustic imaging (PAI) and the hollow structure possesses a better plasmonic property. Herein, miniature hollow gold nanorods (M-AuHNRs) (≈46 nm in length) possessing strong plasmonic absorbance in the second near-infrared (NIR-II) window (1000-1350 nm) are developed, which are considered as the most suitable range for the intravital PAI. The as-prepared M-AuHNRs exhibit 3.5 times stronger photoacoustic signal intensity than the large hollow Au nanorods (≈105 nm in length) at 0.2 optical density under 1064 nm laser irradiation. The in vivo biodistribution measurement shows that the accumulation in tumor of miniature nanorods is twofold as high as that of the large counterpart. After modifying with a tumor-targeting molecule and fluorochrome, in living tumor-bearing mice, the M-AuHNRs group gives a high fluorescence intensity in tumors, which is 3.6-fold that of the large ones with the same functionalization. Moreover, in the intravital PAI of living tumor-bearing mice, the M-AuHNRs generate longer-lasting and stronger photoacoustic signal than the large counterpart in the NIR-II window. Overall, this study presents the fabrication of M-AuHNRs as a promising contrast agent for intravital PAI.

Yolk-Shell Structured Au Nanostar@Metal-Organic Framework for Synergistic Chemo-photothermal Therapy in the Second Near-Infrared Window.

Light-sensitive yolk-shell nanoparticles (YSNs) as remote-controlled and stimuli-responsive theranostic platforms provide an attractive method for synergistic cancer therapy. Herein, a kind of novel stimuli-responsive multifunctional YSNs has been successfully constructed by integrating star-shaped gold (Au star) nanoparticles as the second near-infrared (NIR-II) photothermal yolks and biodegradable crystalline zeolitic imidazolate framework-8 (ZIF-8) as the shells. In this platform, a chemotherapeutic drug (doxorubicin hydrochloride, DOX) was encapsulated into the cavity, which can show the behavior of controlled release due to the degradation process of ZIF-8 in the mildly acidic tumor microenvironment. Upon the 1064 nm (NIR-II biowindow) laser irradiation, gold nanostar@ZIF-8 (Au@MOF) nanoparticles exhibited outstanding synergistic anticancer effect based on their photothermal and promoted cargo release properties. Moreover, the strong NIR region absorbance endows the Au@MOF of NIR thermal imaging and photoacoustic (PA) imaging properties. This work contributes to design a stimuli-responsive "all-in-one" nanocarrier that realizes bimodal imaging diagnosis and chemo-photothermal synergistic therapy.

Molecular imaging in the second near-infrared window.

In the past decade, noticeable progress has been achieved regarding fluorescence imaging in the second near-infrared (NIR-II) window. Fluorescence imaging in the NIR-II window demonstrates superiorities of deep tissue penetration and high spatial and temporal resolution, which are beneficial for profiling physiological processes. Meanwhile, molecular imaging has emerged as an efficient tool to decipher biological activities on the molecular and cellular level. Extending molecular imaging into the NIR-II window would enhance the imaging performance, providing more detailed and accurate information of the biological system. In this progress report, selected achievements made in NIR-II molecular imaging are summarized. The organization of this report is based on strategies underlying rational designs of NIR-II imaging probes and their applications in molecular imaging are highlighted. This progress report may provide guidance and reference for further development of functional NIR-II probes designed for high-performance molecular imaging.

Ultrasmall Pb:Ag2 S Quantum Dots with Uniform Particle Size and Bright Tunable Fluorescence in the NIR-II Window.

Ag2 S 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 Ag2 S crystal, which causes plenty of cation deficiency and crystal defects, may be responsible mainly for the low photoluminescence quantum yield (PLQY) of Ag2 S QDs. Herein, a cation-doping strategy is presented via introducing a certain dosage of transition metal Pb2+ ions into Ag2 S nanocrystals to mitigate this intrinsic shortcoming. The Pb-doped Ag2 S QDs (designated as Pb:Ag2 S 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:Ag2 S 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 Ag2 S QDs and modulation of their optical properties.

Cytometry in the Short-Wave Infrared.

Cytometry plays a crucial role in characterizing cell properties, but its restricted optical window (400-850 nm) limits the number of stained fluorophores that can be detected simultaneously and hampers the study and utilization of short-wave infrared (SWIR; 900-1700 nm) fluorophores in cells. Here we introduce two SWIR-based methods to address these limitations: SWIR flow cytometry and SWIR image cytometry. We develop a quantification protocol for deducing cellular fluorophore mass. Both systems achieve a limit of detection of ∼0.1 fg cell-1 within a 30 min experimental time frame, using individualized, high-purity (6,5) single-wall carbon nanotubes as a model fluorophore and macrophage-like RAW264.7 as a model cell line. This high-sensitivity feature reveals that low-dose (6,5) serves as an antioxidant, and cell morphology and oxidative stress dose-dependently correlate with (6,5) uptake. Our SWIR cytometry holds immediate applicability for existing SWIR fluorophores and offers a solution to the issue of spectral overlapping in conventional cytometry.

Conjugated Oligoelectrolytes for Long-Term Tumor Tracking with Incremental NIR-II Emission.

The design and synthesis of the near-infrared (NIR)-II emissive conjugated oligoelectrolyte COE-BBT are reported. COE-BBT has a solubility in aqueous media greater than 50 mg mL-1 , low toxicity, and a propensity to intercalate lipid bilayers, wherein it exhibits a higher emission quantum yield relative to aqueous media. Addition of COE-BBT to cells provides two emission channels, at ≈500 and ≈1020 nm, depending on the excitation wavelength, which facilitates in vitro confocal microscopy and in vivo animal imaging. The NIR-II emission of COE-BBT is used to track intracranial and subcutaneous tumor progression in mice. Of relevance is that the total NIR-II intensity increases over time. This phenomenon is attributed to a progressive attenuation of a COE-BBT self-quenching effect within the cells due to the expected dye dilution per cell as the tumor proliferates.

High Performance Gold Nanorods@DNA Self-Assembled Drug-Loading System for Cancer Thermo-Chemotherapy in the Second Near-Infrared Optical Window.

In terms of synergistic cancer therapy, biological nanomaterials with a second near-infrared (NIR-II) window response can greatly increase photothermal effects and photoacoustic imaging performance. Herein, we report a novel stimuli-responsive multifunctional drug-loading system which was constructed by integrating miniature gold nanorods (GNR) as the NIR-II photothermal nanorods and cyclic ternary aptamer (CTA) composition as a carrier for chemotherapy drugs. In this system, doxorubicin hydrochloride (DOX, a chemotherapy drug) binds to the G-C base pairs of the CTA, which exhibited a controlled release behavior based on the instability of G-C base pairs in the slightly acidic tumor microenvironment. Upon the 1064 nm (NIR-II biowindow) laser irradiation, the strong photothermal and promoted cargo release properties endow gold nanorods@CTA (GNR@CTA) nanoparticles displaying excellent synergistic anti-cancer effect. Moreover, the GNR@CTA of NIR also possesses thermal imaging and photoacoustic (PA) imaging properties due to the strong NIR region absorbance. This work enables to obtaining a stimuli-responsive "all-in-one" nanocarrier, which are promising candidate for bimodal imaging diagnosis and chemo-photothermal synergistic therapy.

Biodegradable Polymer with Effective Near-Infrared-II Absorption as a Photothermal Agent for Deep Tumor Therapy.

Photothermal therapy holds great promise for cancer treatment due to its effective tumor ablation and minimal invasiveness. Herein a new class of biodegradable photothermal agents with effective adsorption in both near-infrared-I (NIR-I) and NIR-II windows is reported for deep tumor therapy. As demonstrated in a deep-seated ovarian cancer model, photothermal therapy using 1064 nm irradiation effectively inhibits tumor progression and prolongs survival spans. This work provides a new design of photothermal agents toward a more effective therapy of tumors.

Second window ICG predicts postoperative MRI gadolinium enhancement in high grade gliomas and brain metastases.

A prospective trial evaluating the utility of second window indocyanine green (SWIG) in predicting postoperative MRI gadolinium enhancement was performed on high-grade gliomas (HGGs) and brain metastases. Compared to white light alone, SWIG demonstrated a higher sensitivity, negative predictive value, and accuracy in predicting residual neoplasm on MRI. The specificity of SWIG for predicting MRI enhancement was higher in HGGs than brain metastases. Clinically, near-infrared (NIR) imaging was better able to predict tumor recurrence than postoperative MRI. These results illustrate how SWIG is able to take advantage of gadolinium-like distribution properties to extravasate into the tumor microenvironment, enabling guidance in surgical resection. The video can be found here: https://stream.cadmore.media/r10.3171/2021.10.FOCVID21204.

Evaluation of the Targeting and Therapeutic Efficiency of Anti-EGFR Functionalised Nanoparticles in Head and Neck Cancer Cells for Use in NIR-II Optical Window.

Gold nanoparticles have been indicated for use in a diagnostic and/or therapeutic role in several cancer types. The use of gold nanorods (AuNRs) with a surface plasmon resonance (SPR) in the second near-infrared II (NIR-II) optical window promises deeper anatomical penetration through increased maximum permissible exposure and lower optical attenuation. In this study, the targeting and therapeutic efficiency of anti-epidermal growth factor receptor (EGFR)-antibody-functionalised AuNRs with an SPR at 1064 nm was evaluated in vitro. Four cell lines, KYSE-30, CAL-27, Hep-G2 and MCF-7, which either over- or under-expressed EGFR, were used once confirmed by flow cytometry and immunofluorescence. Optical microscopy demonstrated a significant difference (p < 0.0001) between targeted AuNRs (tAuNRs) and untargeted AuNRs (uAuNRs) in all four cancer cell lines. This study demonstrated that anti-EGFR functionalisation significantly increased the association of tAuNRs with each EGFR-positive cancer cell. Considering this, the MTT assay showed that photothermal therapy (PTT) significantly increased cancer cell death (>97%) in head and neck cancer cell line CAL-27 using tAuNRs but not uAuNRs, apoptosis being the major mechanism of cell death. This successful targeting and therapeutic outcome highlight the future use of tAuNRs for molecular photoacoustic imaging or tumour treatment through plasmonic photothermal therapy.

Activatable NIR-II Plasmonic Nanotheranostics for Efficient Photoacoustic Imaging and Photothermal Cancer Therapy.

Precise manipulation of optical properties through the structure-evolution of plasmonic nanoparticles is of great interest in biomedical fields including bioimaging and phototherapy. However, previous success has been limited to fixed assembled structures or visible-NIR-I absorption. Here, an activatable NIR-II plasmonic theranostics system based on silica-encapsulated self-assembled gold nanochains (AuNCs@SiO2 ) for accurate tumor diagnosis and effective treatment is reported. This transformable chain structure breaks through the traditional molecular imaging window, whose absorption can be redshifted from the visible to the NIR-II region owing to the fusion between adjacent gold nanoparticles in the restricted local space of AuNCs@SiO2 triggered by the high H2 O2 level in the tumor microenvironment (TME), leading to the generation of a new string-like structure with strong NIR-II absorption, which is further confirmed by finite-difference-time-domain (FDTD) simulation. With the TME-activated characteristics, AuNCs@SiO2 exhibits excellent properties for photoacoustic imaging and a high photothermal conversion efficiency of 82.2% at 1064 nm leading to severe cell death and remarkable tumor growth inhibition in vivo. These prominent intelligent TME-responsive features of AuNCs@SiO2 may open up a new avenue to explore optical regulated nano-platform for intelligent, accurate, and noninvasive theranostics in NIR-II window.

Considerations for NIR-I and short-wave infrared (SWIR) fluorescence imaging within a clinical operating room.

Short-wave infrared (SWIR/NIR-II) fluorescence imaging has received increased attention for use in fluorescence-guided surgery (FGS) due to the potential for higher resolution imaging of subsurface structures and reduced autofluorescence compared to conventional NIR-I imaging. As with any fluorescence imaging modality introduced in the operating room, an appropriate accounting of contaminating background signal from other light sources in the operating room is an important step. Herein, we report the background signals in the SWIR and NIR-I emitted from commonly-used equipment in the OR, such as ambient and operating lights, LCD screens and surgical guidance systems. These results can guide implementation of protocols to reduce background signal.

Polycation-Carbon Nanohybrids with Superior Rough Hollow Morphology for the NIR-II Responsive Multimodal Therapy.

Polymer-inorganic hybrid nanomaterials have attracted much attention for the multimodal cancer therapy, while it is still desirable to explore hybrids with superior morphologies for two or more therapeutic modalities. In this work, four types of carbon nanoparticles with distinct morphologies were prepared by an elaborate template-carbonization corrosion process and then functionalized with a similar amount of the superior polycationic gene vector, CD-PGEA [consisting of one ß-cyclodextrin core (CD) and two cationic ethanolamine-functionalized poly(glycidyl methacrylate) (PGEA) arms] to evaluate the morphology-influenced gene and photothermal (PT) therapy. Benefiting from the starting rough hollow nanosphere (RHNS) core, the resultant nanohybrids RHNS-PGEA exhibited the highest gene transfection (including luciferase, fluorescent protein plasmid, and antioncogene p53) and NIR PT conversion efficiency among the four types of nanohybrids. Moreover, the efficient PT effect endowed RHNS-PGEA with PA imaging enhancement and an effective imaging guide for the tumor therapy. In addition, anticancer drug 10-hydroxy camptothecin was successfully encapsulated in RHNS with polycation coating, which also displayed the second near-infrared (NIR-II)-responsive drug release. Taking advantages of the superior gene delivery/PT effect and NIR-II-enhanced drug delivery, RHNS-PGEA realized a remarkable therapeutic effect of trimodal gene/PT/chemotherapy of malignant breast cancer treatment in vitro and in vivo. The present work offers a promising approach for the rational design of polymer-inorganic nanohybrids with superior morphology for the multimodal cancer therapy.

Rational Design of Conjugated Small Molecules for Superior Photothermal Theranostics in the NIR-II Biowindow.

Extensive recent progress has been made on the design and applications of organic photothermal agents for biomedical applications because of their excellent biocompatibility comparing with inorganic materials. One major hurdle for the further development and applications of organic photothermal agents is the rarity of high-performance materials in the second near-infrared (NIR-II) window, which allows deep tissue penetration and causes minimized side effects. Up till now, there have been few reported NIR-II-active photothermal agents and their photothermal conversion efficiencies are relatively low. Herein, optical absorption of π-conjugated small molecules from the first NIR window to the NIR-II window is precisely regulated by molecular surgery of substituting an individual atom. With this technique, the first demonstration of a conjugated oligomer (IR-SS) with an absorption peak beyond 1000 nm is presented, and its nanoparticle achieves a record-high photothermal conversion efficiency of 77% under 1064 nm excitation. The nanoparticles show a good photoacoustic response, photothermal therapeutic efficacy, and biocompatibility in vitro and in vivo. This work develops a strategy to boost the light-harvesting efficiency in the NIR-II window for cancer theranostics, offering an important step forward in advancing the design and application of NIR-II photothermal agents.

Photothermal Nano-antibiotic for Effective Treatment of Multidrug-Resistant Bacterial Infection.

Bacteria's antibiotic resistance is one of the major challenges in the treatment of infectious diseases. With increasing difficulty in discovering antibiotics, there is an urgent need to develop antibiotic-free therapeutic strategies to address this grand challenge. In this report, we developed a polypyrrole (PPy)-based photothermal nano-antibiotic (PTNA) for effective treatment of multidrug-resistant (MDR) bacterial infection. PTNA was fabricated by polymerizing pyrrole onto an anionic vesicle to integrate the cationic and photothermal properties of PPy for combinatory killing against bacteria. PTNA exhibits a strong photothermal effect in the NIR-II (1064 nm) biowindow, thus it is feasible for in vivo therapy due to deeper tissue penetration. Our in vitro experiments revealed that PTNA can significantly inhibit the growth of MDR bacteria (Salmonella typhimurium), alleviate inflammatory response of infected cells, and prevent biofilm formation. More importantly, PTNA showed a significant therapeutic effect in an S. typhimurium-infected animal disease model of acute systemic infection by inhibiting bacterial growth, lowering inflammatory responses and pathological changes, and eventually improving the survival rate of mice. Finally, PTNA had safe profiles in vitro and in vivo with no visible toxicity detected. Therefore, we believe PTNA may serve as a promising antibiotic-free antimicrobial material for the effective treatment of MDR bacterial infection.

Multi-angle projection imaging of short-wave infrared (SWIR) fluorescence for small animal optical tomography.

Short-wave infrared imaging in tissue in the 1000-2000 nm range is characterized by reduced photon scatter and comparable or higher absorption compared to the NIR-I regime. These characteristics have implications for the performance of fluorescence molecular tomography (FMT) techniques, potentially improving the resolution of sub-surface structure, possibly at the expense of depth sensitivity. To examine these questions, we have developed a SWIR small animal fluorescence tomography system. This instrument acquires multi-angle SWIR projection images of a stationary platform through a rotating gantry technique. These images are then processed for tomographic reconstruction of the SWIR fluorescence activity. Herein, we describe the development of this system and show multi-angle images from a mouse carcass containing a SWIR-specific fluorophore inclusion.

W-doped TiO2 nanoparticles with strong absorption in the NIR-II window for photoacoustic/CT dual-modal imaging and synergistic thermoradiotherapy of tumors.

Multifunctional nanomaterials that have integrated diagnostic and therapeutic functions and low toxicity, and can enhance treatment efficacy through combination therapy have drawn tremendous amounts of attention. Herein, a newly developed multifunctional theranostic agent is reported, which is PEGylated W-doped TiO2 (WTO) nanoparticles (NPs) synthesized via a facile organic route, and the results demonstrated strong absorbance of these WTO NPs in the second near-infrared (NIR-II) window due to successful doping with W. These PEGylated WTO NPs can absorb both NIR-II laser and ionizing radiation, rendering them well suited for dual-modal computed tomography/NIR-II photoacoustic imaging and synergistic NIR-II photothermal/radiotherapy of tumors. In addition, the long-term in vivo studies indicated that these PEGylated WTO NPs had no obvious toxicity on mice in vivo, and they can be cleared after a 30-day period. In summary, this multifunctional theranostic agent can absorb both NIR-II laser and ionizing radiation with negligible toxicity and rapid clearance, therefore it has great promise for applications in imaging and therapeutics in biomedicine.