Near-infrared Biological Window Research Articles

Amphiprotism-Coupled Near-Infrared Emission in Extended Pyrazinacenes Containing Seven Linearly Fused Pyrazine Units.

Peripherally substituted tetradecaazaheptacene (N14Hp) compounds, exhibiting amphiprotism-coupled emission, have been synthesized. X-ray crystallography reveals a planar acene-like chromophore, and electronic absorption and emission occur in the near-infrared biological transparency window (650-900 nm). The compounds exhibit long-wavelength emission with photoluminescence quantum yields ΦPL up to ∼0.61 at 686 nm, with the monodeprotonated state ΦPL ≈ 0.58 at 712 nm. This unprecedented highly nitrogenous chromophore illustrates the stability and utility of the pyrazinacenes for different applications based on their photophysical properties and chemical structures.

Mo2 C-Derived Polyoxometalate for NIR-II Photoacoustic Imaging-Guided Chemodynamic/Photothermal Synergistic Therapy.

To overcome the current limitations of chemodynamic therapy (CDT), a Mo2 C-derived polyoxometalate (POM) is readily synthesized as a new CDT agent. It permits synergistic chemodynamic and photothermal therapy operating in the second near-infrared (NIR-II) biological transparent window for deep tissue penetration. POM aggregated in an acidic tumor micro-environment (TME) whereby enables specific tumor targeting. In addition to the strong ability to produce singlet oxygen (1 O2 ) presumably via Russell mechanism, its excellent photothermal conversion enhances the CDT effect, offers additional tumor ablation modality, and permits NIR-II photoacoustic imaging. Benefitting from the reversible redox property of molybdenum, the theranostics based on POM can escape from the antioxidant defense system. Moreover, combining the specific responsiveness to TME and localized laser irradiation, side-effects shall be largely avoided.

Efficient colloidal quantum dot light-emitting diodes operating in the second near-infrared biological window

Semiconductor colloidal quantum dots (CQDs) offer size- and composition-tunable luminescence of high colour purity. Importantly, their emission can be tuned deep into the second biological near-infrared (NIR-II) window (1,000–1,700 nm). However, applications are hindered by the low efficiencies achieved to date. Here, we report NIR-II CQD light-emitting diodes with an external quantum efficiency of 16.98% and a power conversion efficiency of 11.28% at wavelength 1,397 nm. This performance arises from device engineering that delivers a high photoluminescence quantum yield and charge balance close to unity. More specifically, we employed a binary emissive layer consisting of silica-encapsulated silver sulfide (Ag2S@SiO2) CQDs dispersed in a caesium-containing triple cation perovskite matrix that serves as an additional passivation medium and a carrier supplier to the emitting CQDs. The hole-injection contact also features a thin porphyrin interlayer to balance the device current and enhance carrier radiative recombination. Semiconductor nanocrystals with efficient tunable emission in the 1,000–1,700 nm window could prove useful for applications in deep biological imaging and sensing.

Hyperthermia and Controllable Free Radical Coenhanced Synergistic Therapy in Hypoxia Enabled by Near-Infrared-II Light Irradiation.

Tumor cell metabolism and tumor blood vessel proliferation are distinct from normal cells. The resulting tumor microenvironment presents a characteristic of hypoxia, which greatly limits the generation of oxygen free radicals and affects the therapeutic effect of photodynamic therapy. Here, we developed an oxygen-independent free radical generated nanosystem (CuFeSe2-AIPH@BSA) with dual-peak absorption in both near-infrared (NIR) regions and utilized it for imaging-guided synergistic treatment. The special absorption provides the nanosystem with high photothermal conversion efficiency and favorably matched photoactivity in both I and II NIR biological windows. Upon NIR light irradiation, the generated heat could prompt AIPH release and decompose to produce oxygen-independent free radicals for killing cancer cells effectively. The contrastive research results show that the enhanced therapeutic efficacy of NIR-II over NIR-I is principally due to its deeper tissue penetration and higher maximum permission exposure that benefits from a longer wavelength. Hyperthermia effect and the production of toxic free radicals upon NIR-II laser illumination are extremely effective in triggering apoptosis and death of cancer cells in the tumor hypoxia microenvironment. The high biocompatibility and excellent anticancer efficiency of CuFeSe2-AIPH@BSA allow it to be an ideal oxygen-independent nanosystem for imaging-guided and NIR-II-mediated synergistic therapy via systemic administration.

Biological Deep Temperature Imaging with Fluorescence Lifetime of Rare-Earth-Doped Ceramics Particles in the Second NIR Biological Window

Contactless thermal imaging generally relies on mid-infrared cameras and fluorescence imaging with temperature-sensitive phosphors. Fluorescent thermometry in the near-infrared (NIR) region is an emerging technique for analysing deep biological tissues but still requires observation depth calibration. We present an NIR fluorescence time-gated imaging (TGI) thermometry technology based on fluorescence lifetime, an intrinsic fluorophore time constant unrelated to observation depth. Fluorophore used is NaYF4 co-doped with Nd3+ and Yb3+ that emits fluorescence at 1000 nm. An agarose gel-based phantom with the fluorophore embedded at a 5-mm depth was covered by sheets of meat to vary the observation depth. The temperature was determined independently from depth by sequences of NIR fluorescence decay images, and the rate of change in the fluorescence lifetime per temperature was almost constant (−0.0092 ~ −0.010 °C−1) at depths ranging from 0 to 1.4 mm of meat, providing non-contact and absolute measurements of temperature in deep biological tissues.

Paper-Based Lateral Flow Immunoassay for Detection of Biomarkers in Human Fluids

Traumatic brain injuries (TBI) patients suffer from neurological deficits and increased risk of neurological disease, so there is a need for accurate, high throughput, and rapid diagnosis. Currently, TBI severity is detected and assessed using neurological examination and CT imaging, which require expensive hospital and doctors office visits. Protein biomarkers have emerged as an objective means to diagnose TBI; however, proteins are typically detected using time consuming and expensive methods such as ELISA and Western blot. In this work, a paper-based lateral flow assay (PLFA) has been developed for a rapid, low-cost means for detecting TBI biomarkers in blood plasma. PLFAs have received increasing attention due to their low cost and ease-of-use. However, these devices suffer from poor sensitivity and interference from the blood plasma matrix. In this study, surface-enhanced Raman scattering (SERS) was applied into a PLFA as the signal transducer to improve sensitivity and overcome biological interference. These advantages are attributed to the optical excitation in the near-infrared biological transparency window and SERS nanostructure design. The PLFA is designed using a plasmonic nanoarray chip and a blood plasma separation unit for highly sensitive TBI biomarker detection.

3D sub-diffraction imaging in a conventional confocal configuration by exploiting super-linear emitters

Sub-diffraction microscopy enables bio-imaging with unprecedented clarity. However, most super-resolution methods require complex, costly purpose-built systems, involve image post-processing and struggle with sub-diffraction imaging in 3D. Here, we realize a conceptually different super-resolution approach which circumvents these limitations and enables 3D sub-diffraction imaging on conventional confocal microscopes. We refer to it as super-linear excitation-emission (SEE) microscopy, as it relies on markers with super-linear dependence of the emission on the excitation power. Super-linear markers proposed here are upconversion nanoparticles of NaYF4, doped with 20% Yb and unconventionally high 8% Tm, which are conveniently excited in the near-infrared biological window. We develop a computational framework calculating the 3D resolution for any viable scanning beam shape and excitation-emission probe profile. Imaging of colominic acid-coated upconversion nanoparticles endocytosed by neuronal cells, at resolutions twice better than the diffraction limit both in lateral and axial directions, illustrates the applicability of SEE microscopy for sub-cellular biology.

A New Class of Blue-LED-Excitable NIR-II Luminescent Nanoprobes Based on Lanthanide-Doped CaS Nanoparticles.

Lanthanide (Ln3+ )-doped luminescent nanoparticles (NPs) with emission in the second near-infrared (NIR-II) biological window have shown great promise but their applications are currently limited by the low absorption efficiency of Ln3+ owing to the parity-forbidden 4f→4f electronic transition. Herein, we developed a strategy for the controlled synthesis of a new class of NIR-II luminescent nanoprobes based on Ce3+ /Er3+ and Ce3+ /Nd3+ co-doped CaS NPs, which can be effectively excited by using a low-cost blue light-emitting diode chip. Through sensitization by the allowed 4f→5d transition of Ce3+ , intense NIR-II luminescence from Er3+ and Nd3+ with quantum yields of 9.3 % and 7.7 % was achieved, respectively. By coating them with a layer of amphiphilic phospholipids, these NPs exhibit excellent stability in water and can be exploited as sensitive NIR-II luminescent nanoprobes for the accurate detection of an important disease biomarker, xanthine, with a detection limit of 32.0 nm.

Enhanced radiosensitization of ternary Cu3BiSe3 nanoparticles by photo-induced hyperthermia in the second near-infrared biological window.

The development of a new multifunctional nanomedicine capable of enhancing radiosensitization by photo-induced hyperthermia for the inhibition of cancer growth and metastasis is highly required for efficient treatment of cancer cells. Compared to the first near-infrared (NIR) window, the second NIR window light could provide a maximum penetration depth as well as minimizing autofluorescence due to its low scattering and energy absorption. Here, we report a new versatile theranostic agent based on ternary Cu3BiSe3 nanoparticles (NPs) modified by poly(vinylpyrollidone) (PVP-Cu3BiSe3). Benefiting from their preferable X-ray attenuation ability and strong NIR absorbance in the second NIR biological window, PVP-Cu3BiSe3 NPs can not only deposit more radiation doses to destroy the cancer cells, but also conduct the optical energy into hyperthermia for thermal eradication of tumor tissues and the improvement of the tumor oxygenation to overcome the hypoxia-associated radio-resistance of tumors. According to both in vitro and in vivo results, exposure to an X-ray plus 1064 nm laser completely kills cancer cells and even inhibits tumor metastasis, displaying no warning signs of a relapse. On the other hand, PVP-Cu3BiSe3 NPs can be used as a multi-model imaging agent for X-ray computer tomography (CT) and photoacoustic tomography (PAT) imaging. These demonstrate the potential of PVP-Cu3BiSe3 NPs in multimodal imaging-guided synergetic radiophotothermal therapy of deep-seated tumors and effective inhibition of their metastasis.

Towards multiplexed near-infrared cellular imaging using gold nanostar arrays with tunable fluorescence enhancement.

Sensitive detection of disease biomarkers expressed by human cells is critical to the development of novel diagnostic and therapeutic methods. Here we report that plasmonic arrays based on gold nanostar (AuNS) monolayers enable up to 19-fold fluorescence enhancement for cellular imaging in the near-infrared (NIR) biological window, allowing the application of low quantum yield fluorophores for sensitive cellular imaging. The high fluorescence enhancement together with low autofluorescence interference in this wavelength range enable higher signal-to-noise ratio compared to other diagnostic modalities. Using AuNSs of different geometries and therefore controllable electric field enhancement, cellular imaging with tunable enhancement factors is achieved, which may be useful for the development of multicolour and multiplexed platforms for a panel of biomarkers, allowing to distinguish different subcell populations at the single cell level. Finally, the uptake of AuNSs within HeLa cells and their high biocompatibility, pave the way for novel high-performance in vitro and in vivo diagnostic platforms.

Influence of sonication conditions and wrapping type on yield and fluorescent quality of noncovalently functionalized single-walled carbon nanotubes

As nanomaterials have become more accessible, nanoscale biosensor research has expanded to many useful applications. One such nanomaterial is the single-walled carbon nanotube (SWCNT), which fluoresces in the near-infrared biological window, making it ideal for in vivo applications. SWCNT can be suspended in water when non-covalently functionalized with an amphiphilic polymer or surfactant (e.g. ‘wrapped’); the suspended SWCNT can act as a simple optical probe or as a sensor by engineering the wrapping to have selective domains. The process of suspending nanotubes is typically achieved by sonication. While much application-focused research has been performed on SWCNT sensors and probes, little has been done to understand factors affecting SWCNT fluorescent quality after suspension. We explored effects of sonication power and duration on an array of nine potential wrappings including proteins, DNA, oligosaccharides, polysaccharides, synthetic polymers, and surfactant solutions. Optimal sonication conditions were found to vary on an individual wrapping basis. These trends may be used to predict optimal processing conditions to suspend SWCNT with maximal start fluorescence for various wrappings, improving dynamic range and sensitivity. These results also point to the need for control of sonication conditions in large scale synthesis to ensure tighter batch-to-batch reproducibility of nanotube sensors.

Detection of Intracellular Gold Nanoparticles: An Overview.

Photothermal therapy (PTT) takes advantage of unique properties of gold nanoparticles (AuNPs) (nanospheres, nanoshells (AuNSs), nanorods (AuNRs)) to destroy cancer cells or tumor tissues. This is made possible thanks principally to both to the so-called near-infrared biological transparency window, characterized by wavelengths falling in the range 700–1100 nm, where light has its maximum depth of penetration in tissue, and to the efficiency of cellular uptake mechanisms of AuNPs. Consequently, the possible identification of intracellular AuNPs plays a key role for estimating the effectiveness of PTT treatments. Here, we review the recognized detection techniques of such intracellular probes with a special emphasis to the exploitation of near-infrared biological transparency window.

(Invited) Luminescent Rare Earth Doped Nanoparticles

In recent years, rare earth doped nanoparticles have been proposed for a number of exciting applications in a wide-range of fields including nanomedicine, nanoelectronics, biosensing, bioimaging, photovoltaics, photocatalysis, etc. This is due, primarily, to their interesting and versatile optical properties including their inherent ability to convert low-energy near-infrared (NIR) light to higher energies spanning the UV, visible, and NIR regions of the spectrum via a process known as upconversion. Upconversion, inherent to the rare earths, results from the multitude of 4f electronic energy states, many of which are spaced equally and long-lived, that facilitate the absorption of multiple low energy photons to populate the higher energy emitting states. Thus, upconversion is a multiphoton process, but unlike other two-photon excited materials, the need for expensive ultrafast lasers is eliminated since the simultaneous absorption of multiple photons is not required; due to the long lifetimes of the rare earth ion excited states, sequential absorption occurs efficiently. Moreover, following NIR excitation, these nanoparticles can also undergo conventional luminescence and emit in the three NIR biological windows where tissues are optically transparent. Here, we will discuss the luminescence properties of rare earth doped nanoparticles and present a perspective on both their applicability as well as drawbacks for use in various applications. Finally, we will demonstrate that the intelligent combination of diverse materials, with different properties, will allow for the engineering of novel multifunctional nanostructures, which can usher in a new era for rare earth doped nanoparticles.

Real-Time and High-Resolution Bioimaging with Bright Aggregation-Induced Emission Dots in Short-Wave Infrared Region.

Fluorescence imaging in the spectral region beyond the conventional near-infrared biological window (700-900 nm) can theoretically afford high resolution and deep tissue penetration. Although some efforts have been devoted to developing a short-wave infrared (SWIR; 900-1700 nm) imaging modality in the past decade, long-wavelength biomedical imaging is still suboptimal owing to the unsatisfactory materials properties of SWIR fluorophores. Taking advantage of organic dots based on an aggregation-induced emission luminogen (AIEgen), herein microscopic vasculature imaging of brain and tumor is reported in living mice in the SWIR spectral region. The long-wavelength emission of AIE dots with certain brightness facilitates resolving brain capillaries with high spatial resolution (≈3 µm) and deep penetration (800 µm). Owning to the deep penetration depth and real-time imaging capability, in vivo SWIR microscopic angiography exhibits superior resolution in monitoring blood-brain barrier damage in mouse brain, and visualizing enhanced permeability and retention effect in tumor sites. Furthermore, the AIE dots show good biocompatibility, and no noticeable abnormalities, inflammations or lesions are observed in the main organs of the mice. This work will inspire new insights on development of advanced SWIR techniques for biomedical imaging.

Tuning the Distance of Rattle-Shaped IONP@Shell-in-Shell Nanoparticles for Magnetically-Targeted Photothermal Therapy in the Second Near-Infrared Window.

Construction of multifunctional nanoparticles (NPs) with near-infrared (NIR) plasmonic responses is considered a versatile and multifaceted platform for several biomedical applications. Herein, a double layer of Au/Ag alloy on the surface of truncated octahedral iron oxide NPs (IONPs) was prepared and the distance between the layers was controlled to exhibit broad and strong NIR absorption. The rattle-shaped IONP@shell-in-shell nanostructure showed light-response to the NIR biological window from 650 to 1300 nm for photothermal therapy (PTT) and magnetic guidance for hyperthermia and magnetic resonance imaging (MRI) diagnosis. Exposing the aqueous solution of IONP@shell-in-shell to a 1064 nm diode laser, its heat conversion efficiency was ∼28.3%. The in vitro cell viability at a gold concentration of 100 ppm was ∼85%, and decreased to ∼16% when the cells were treated with the NIR irradiation and magnetic attraction. T2-weighted MRI images showed a clear accumulation of IONP@shell-in-shell at the tumor site with magnetic attraction. In vivo luminescence tumor images explained that the IONP@shell-in-shell could reduce the U87MG-luc2 cancer cell proliferation in mice with the NIR irradiation and magnetic attraction. These results indicate the IONP@shell-in-shell as a promising nanomedicine for PTT, magnetic targeting, and magnetic resonance imaging (MRI).

Crucial breakthrough of second near-infrared biological window fluorophores: design and synthesis toward multimodal imaging and theranostics.

The development of fluorophores and molecular probes for the second near-infrared biological window (NIR-II, 1000-1700 nm) represents an important, newly emerging and dynamic field in molecular imaging, chemical biology and materials chemistry. Because of reduced scattering, minimal absorption and negligible autofluorescence, NIR-II imaging provides high resolution, a high signal-to-noise ratio, and deep tissue penetration capability. Among various state-of-the-art bioimaging modalities, one of the greatest challenges in developing novel probes is to achieve both high resolution and sensitivity. The chemical design and synthesis of NIR-II fluorophores suitable for multimodal imaging is thus emerging as a new and powerful strategy for obtaining high-definition images. NIR-II fluorophores may convert NIR-II photons into heat for photothermal therapy and be excited by NIR-II light to produce singlet oxygen for photodynamic therapy. The presence of simultaneous diagnostic and therapeutic capabilities in a single probe can be used for precise treatment. In this review, we have focused on recent advances in the chemical design and synthesis of NIR-II fluorophores from small organic molecules to organic and inorganic nanoparticles, and we have further discussed recent advances and key operational differences in reported NIR-II imaging systems and biomedical applications based on NIR-II imaging, such as multimodal imaging, photothermal and photodynamic therapy, guidance for intraoperative surgery, and drug delivery.

Fluorescence enhancement from single gold nanostars: towards ultra-bright emission in the first and second near-infrared biological windows.

Gold nanostars (AuNSs) are promising agents for the development of high-performance diagnostic devices, by enabling metal enhanced fluorescence (MEF) in the physiological near-infrared (NIR) and second near-infrared (NIR-II) windows. The local electric field near their sharp tips and between their branches can be enhanced by several orders of magnitude, holding great promise for large fluorescence enhancements from single AuNS particles, rather than relying on interparticle coupling in nanoparticle substrates. Here, guided by electric field simulations, two different types of AuNSs with controlled morphologies and plasmonic responses in the NIR and NIR-II regions are used to investigate the mechanism of MEF from colloidal AuNSs. Fluorophore conjugation to AuNSs allows significant fluorescence enhancement of up to 30 times in the NIR window, and up to 4-fold enhancement in the NIR-II region. Together with other inherent advantages of AuNSs, including their multispike morphology offering easy access to cell membranes and their large surface area providing flexible multifunctionality, AuNS are promising for the development of in vivo imaging applications. Using time-resolved fluorescence measurements to deconvolute semi-quantitatively excitation enhancement from emission enhancement, we show that a combination of enhanced excitation and an increased radiative decay rate, both contribute to the observed large enhancement. In accordance to our electric field modelling, however, excitation enhancement is the component that varies most with particle morphology. These findings provide important insights into the mechanism of MEF from AuNSs, and can be used to further guide particle design for high contrast enhancement, enabling the development of MEF biodetection technologies.

A Paper-Based Surface-Enhanced Raman Scattering Test Strip for Protein Biomarker Detection

Paper-based lateral flow strips (PLFS) have received increasing attention as point-of-care (POC) tools due to their low cost and simplicity to use. However, PLFS usually suffer from poor sensitivity and serious interference from their sample matrix when they are used with blood plasma containing samples. In our current study, surface-enhanced Raman scattering (SERS) was integrated as the signal transducer into PLFS for protein biomarker detection in blood plasma. Compared with the traditional colorimetric PLFS, the SERS PLFS exhibits advantages in terms of sensitivity and limit of detection (LOD) in a blood plasma sample matrix. These advantages are attributed to the wavelengths of both the excitation light and the Raman scattering signals being able to be tuned into the near-infrared biological window. Herein, our developed SERS PLFS has been successfully demonstrated for detection of neuron-specific enolase (NSE) in diluted blood plasma samples with a LOD of 1 ng/ml. Moreover, these SERS based test strips are in expensive, fast (30 min) and simple to be operated, holding a great potential in assisting screening of traumatic brain injury (TBI) patients in a point-of-care setting.

Rational Design of Ultrabright SERS Probes with Embedded Reporters for Bioimaging and Photothermal Therapy.

Plasmonic nanoparticles can be utilized as surface-enhanced Raman scattering (SERS) probes for bioimaging and as photothermal (PT) agents for cancer therapy. Typically, their SERS and PT efficiencies reach maximal values under the on-resonant condition, when the excitation wavelength overlaps the localized surface plasmon resonance (LSPR) wavelength preferably in the near-infrared (NIR) biological window. However, the photogenerated heat may inevitably disturb or even destroy biological samples during the imaging process. Herein, we develop ultrabright SERS probes composed of metallic Au@Ag core-shell rodlike nanomatryoshkas (RNMs) with embedded Raman reporters. By rationally controlling the Ag shell thickness, the LSPR of RNMs can be tuned from UV to NIR range, resulting in highly tunable SERS and PT properties. As bright NIR SERS imaging nanoprobes, RNMs with a thick Ag shell are designed for minimal PT damage to the biological targets under the off-resonance condition, as illustrated through monitoring the changes in mitochondrial membrane potential of cancer cells during SERS imaging procedure. By contrast, RNMs with a thin Ag shell are designed as multifunctional NIR theranostic probes that combine enhanced photothermal therapy capability, as exemplified by efficient PT killing of cancer cells, with reduced yet still efficient imaging properties at the on-resonance excitation.

Near-infrared emission and optical temperature sensing performance of Nd3+:SrF2 crystal powder prepared by combustion synthesis

Nd3+:SrF2 crystal powder prepared by combustion synthesis technique was analyzed for potential use in thermal sensing of biological systems. Near-infrared emission was observed under CW laser excitation at 532 nm. The near-infrared fluorescence spectrum consisting of two emission bands, corresponding to the 4F5/2 →4I9/2 and 4F3/2 →4I9/2 transitions, was recorded over a temperature range of 298–573 K. A noticeable change on the relative intensities of those transitions with temperature was observed as a consequence of the thermal coupling induced by the small energy bandgap between the electronic states 4F5/2 and 4F3/2. Using the fluorescence intensity ratio approach, we obtained the relative sensitivity of ∼1.7% K−1 at 300 K, which is among the highest values reported for this class of optical thermometer. We also performed the experiment using pulsed (5 ns) near-infrared excitation (750 nm) in a solution containing the Nd3+:SrF2 powder dispersed in water aiming to use this system for temperature sensing in the first near-infrared biological transparency window. The same sensor sensitivity, within experimental error, was obtained for different excitation wavelengths (532 and 750 nm) and surrounding media (air and water).