Near-infrared Optical Window Research Articles

Molecular Fluorescence and Photoacoustic Imaging in the Second Near-Infrared Optical Window Using Organic Contrast Agents.

Noninvasive near-infrared (NIR) light ranging from 650 to 1000 nm (NIR-I) is widely employed in fundamental research and clinical applications; however, a recently discovered second NIR (NIR-II) window from 1000 to 1700 nm exhibits even better deep-tissue imaging capability due to reduced photon scattering, minimized tissue autofluorescence, and increased applicable power at longer wavelengths. This review focuses on recent advances of organic contrast agents developed for in vivo fluorescence and photoacoustic imaging in the NIR-II optical window. The superiority of the NIR-II over the NIR-I window for molecular imaging is first discussed in detail, followed by discussion of fluorescence and photoacoustic imaging of cancer, vasculature, and the brain using organic contrast agents in the NIR-II window. At last, challenges and perspectives of organic contrast agents for NIR-II in vivo imaging are suggested.

Laser Pulse Duration Optimization for Photothermal Therapy with Gold Nanostars

Photothermal therapy (PTT), which utilizes light radiation to create localized heating effect in the targeted areas, is a promising solution for highly specific yet minimally invasive cancer therapy. PTT uses photothermal agents, which are usually nanoparticles that absorb strongly in the near-infrared optical window where minimal tissue absorption occurs. Photothermal agents are also highly functionalized to target at specific tumor sites. Gold nanostar is an ideal candidate for photothermal agents, because it not only has a Surface Plasmon Resonance in the near-infrared, but also can be easily produced and purified, and is extremely versatile in the drug delivery process. In order to achieve maximum amount of localized heating, pulse lasers are usually used in laser ablation processes like photothermal therapy. However, intensive laser radiation can cause damage to regular tissues as well the nanostructures themselves. Therefore, identifying the optimal pulse duration to effectively generate localized heating in the tumorous tissues while keeping the normal tissues and the nanostructures intact is important to achieving optimal photo-therapeutic results. This manuscript provides a numerical calculation method with Comsol Multiphysics to optimize the pulse condition of the gold nanostars under photothermal therapy settings. Based on results, gold nanostar displays significant temperature heterogeneity under femtosecond and picosecond laser radiation, while nanosecond laser only induces rather uniform heating effects across the entire gold nanostar particle. This finding indicates that femtosecond laser, which is the most common type of laser used for ablation, is likely to melt the tip of the gold nanostar before the nanostar body reaches a reasonably high temperature. Picosecond and nanosecond lasers are much less likely to induce such dramatic morphology change. This study offers important insight into finding the optimal condition for photothermal therapy with maximal efficacy and minimal damage.

Next-generation in vivo fluorescence imaging for deep tissue in the second near-infrared optical window

Next-generation <i>in vivo</i> fluorescence imaging for deep tissue in the second near-infrared optical window

Mesoporous Carbon Nanospheres as a Multifunctional Carrier for Cancer Theranostics.

Optical nanomaterials with intense absorption in near-infrared (NIR) region hold great promise for biomedical applications such as photothermal therapy (PTT) and photoacoustic imaging (PAI). In this work, we report mesoporous carbon nanospheres (Meso-CNs) with broadband and intense absorption in the UV-Vis-NIR region (300-1400 nm) and explore their potential as a multifunctional platform for photoacoustic imaging and chemo-photothermal therapy.Methods: Meso-CNs were prepared by a “silica-assisted” synthesis strategy and characterized by transmission electron microscope and optical spectroscopy. We investigated the photothermal conversion and photoacoustic imaging of Meso-CNs in comparison with single-walled carbon nanotubes (SWCNTs), graphene and gold nanorods (GNRs). In vitro cellular assays and in vivo chemo-photothermal combination therapy were performed.Results: The absorption coefficients of Meso-CNs are 1.5-2 times higher than those of SWCNTs and graphene and are comparable to those of GNRs in both the first and the second near-infrared optical windows (NIR-I and NIR-II) of tissues. When exposed to an NIR laser, the photothermal and photoacoustic signal generation of Meso-CNs are also stronger than those of SWCNTs, graphene, and GNRs. DOX was loaded into Meso-CNs with a high efficiency (35 wt%) owing to the unique mesoporous structure. Particularly, the drug release from Meso-CNs is sensitive to both pH and NIR light stimulation. In vivo chemo-photothermal combination therapy demonstrates a remarkable inhibition effect on tumor growth under NIR laser treatment.Conclusions: We have developed Meso-CNs for photothermal conversion and photoacoustic imaging. The porous structure also serves as a drug carrier and the drug release can be controlled by pH and external light. The high drug loading capacity, superior photothermal and photoacoustic generation, together with the apparent chemo-photothermal therapeutic effect, make Meso-CNs a promising platform for cancer theranostics.

Fiber chirped pulse amplification of a short wavelength mode-locked thulium-doped fiber laser

Exploiting the promising third near-infrared optical window (1600–1870 nm) for deep bioimaging is largely underdeveloped, mostly because of the lack of stable femtosecond laser sources in leveraging the less scattering loss and locally reduced water absorption. In this letter, we demonstrate the fiber chirped pulse amplification of a short wavelength mode-locked thulium-doped fiber laser (TDFL) at 1785 nm. The mode-locked TDFL (via nonlinear polarization rotation) operates stably at the soliton pulsing regime with a fundamental repetition rate of 46.375 MHz. Utilizing a two-stage fiber amplifier incorporated along the pulse chirping fiber, the power of the laser pulse is boosted up to 690 mW. After dechirping with a diffraction grating pair, laser pulse with a duration of 445 fs, pulse energy of 5.7 nJ, and peak power of 12 kW is achieved. Higher power can be achieved by exploiting low-loss high power fiber components at this special wavelength range.

Photostable Ratiometric Pdot Probe for in Vitro and in Vivo Imaging of Hypochlorous Acid.

Developing probes for the detection of reactive oxygen species (ROS), a hallmark of many pathophysiological process, is imperative to both understanding the precise roles of ROS in many life-threatening diseases and optimizing therapeutic interventions. We herein report an all-in-one fluorescent semiconducting polymer based far-red to near-infrared (NIR) Pdot nanoprobe for the ratiometric detection of hypochlorous acid (HOCl). The fabrication takes the advantage of flexible polymer design by incorporating target-sensitive and target-inert fluorophores into a single conjugated polymer to avoid leakage or differential photobleaching problems existed in other nanoprobes. The obtained nanoprobe has improved performance in HOCl sensing, such as high brightness, ideal far-red to NIR optical window, excellent photostability, self-referenced ratiometric response, fast response, and high selectivity. The dual-emission property allows the sensitive imaging of HOCl fluctuations produced in living macrophage cells and peritonitis of living mice with high contrast. This study not only provides a powerful and promising nanoprobe to be potentially used in the investigations of in situ HOCl status of diseases in living systems but also puts forward the design strategy of a new category of ratiometric fluorescent probes facilitating precise and reliable measurement in biological systems.

Intraparticle Energy Level Alignment of Semiconducting Polymer Nanoparticles to Amplify Chemiluminescence for Ultrasensitive In Vivo Imaging of Reactive Oxygen Species.

Detection of reactive oxygen species (ROS), a hallmark of many pathological processes, is imperative to understanding, detection and treatment of many life-threatening diseases. However, methods capable of real-time in situ imaging of ROS in living animals are still very limited. We herein report the development and optimization of chemiluminescent semiconducting polymer nanoparticles (SPNs) for ultrasensitive in vivo imaging of hydrogen peroxide (H2O2). The chemiluminescence is amplified by adjusting the energy levels between the luminescence reporter and the chemiluminescence substrate to facilitate intermolecular electron transfer in the process of H2O2-activated luminescence. The optimized SPN can emit chemiluminescence with the quantum yield up to 2.30 × 10(-2) einsteins/mol and detect H2O2 down to 5 nM, which substantially outperforms the previous probes. Further doping of this SPN with a naphthalocyanine dye creates intraparticle chemiluminescence resonance energy transfer (CRET), leading to the near-infrared (NIR) luminescence responding to H2O2. By virtue of high brightness and ideal NIR optical window, SPN-NIR permits ultrasensitive imaging of H2O2 in the mouse models of peritonitis and neuroinflammation with the minute administration quantity. Thus, this study not only provides a category of optical probes that eliminates the need of external light excitation for imaging of H2O2, but also reveals the underlying principle to enhance the brightness of chemiluminescence systems.

Chlorosome-Inspired Synthesis of Templated Metallochlorin-Lipid Nanoassemblies for Biomedical Applications.

Chlorosomes are vesicular light-harvesting organelles found in photosynthetic green sulfur bacteria. These organisms thrive in low photon flux environments due to the most efficient light-to-chemical energy conversion, promoted by a protein-less assembly of chlorin pigments. These assemblies possess collective absorption properties and can be adapted for contrast-enhanced bioimaging applications, where maximized light absorption in the near-infrared optical window is desired. Here, we report a strategy for tuning light absorption toward the near-infrared region by engineering a chlorosome-inspired assembly of synthetic metallochlorins in a biocompatible lipid scaffold. In a series of synthesized chlorin analogues, we discovered that lipid conjugation, central coordination of a zinc metal into the chlorin ring, and a 3(1)-methoxy substitution were critical for the formation of dye assemblies in lipid nanovesicles. The substitutions result in a specific optical shift, characterized by a bathochromically shifted (72 nm) Qy absorption band, along with an increase in absorbance and circular dichroism as the ratio of dye-conjugated lipid was increased. These alterations in optical spectra are indicative of the formation of delocalized excitons states across each molecular assembly. This strategy of tuning absorption by mimicking the structures found in photosynthetic organisms may spur new opportunities in the development of biophotonic contrast agents for medical applications.

Transmission in near-infrared optical windows for deep brain imaging.

Near-infrared (NIR) radiation has been employed using one- and two-photon excitation of fluorescence imaging at wavelengths 650-950nm (optical window I) for deep brain imaging; however, longer wavelengths in NIR have been overlooked due to a lack of suitable NIR-low band gap semiconductor imaging detectors and/or femtosecond laser sources. This research introduces three new optical windows in NIR and demonstrates their potential for deep brain tissue imaging. The transmittances are measured in rat brain tissue in the second (II, 1,100-1,350nm), third (III, 1,600-1,870nm), and fourth (IV, centered at 2,200nm) NIR optical tissue windows. The relationship between transmission and tissue thickness is measured and compared with the theory. Due to a reduction in scattering and minimal absorption, window III is shown to be the best for deep brain imaging, and windows II and IV show similar but better potential for deep imaging than window I.

Cell perforation mediated by plasmonic bubbles generated by a single near infrared femtosecond laser pulse.

We report on transient membrane perforation of living cancer cells using plasmonic gold nanoparticles (AuNPs) enhanced single near infrared (NIR) femtosecond (fs) laser pulse. Under optimized laser energy fluence, single pulse treatment (τ = 45 fs, λ = 800 nm) resulted in 77% cell perforation efficiency and 90% cell viability. Using dark field and ultrafast imaging, we demonstrated that the generation of submicron bubbles around the AuNPs is the necessary condition for the cell membrane perforation. AuNP clustering increased drastically the bubble generation efficiency, thus enabling an effective laser treatment using low energy dose in the NIR optical therapeutical window.

Quantum dot imaging in the second near-infrared optical window: studies on reflectance fluorescence imaging depths by effective fluence rate and multiple image acquisition.

Quantum dot (QD) imaging capability was investigated by the imaging depth at a near-infrared second optical window (SOW; 1000 to 1400 nm) using time-modulated pulsed laser excitations to control the effective fluence rate. Various media, such as liquid phantoms, tissues, and in vivo small animals, were used and the imaging depths were compared with our predicted values. The QD imaging depth under excitation of continuous 20 mW/cm(2) laser was determined to be 10.3 mm for 2 wt%hemoglobin phantom medium and 5.85 mm for 1 wt% intralipid phantom, which were extended by more than two times on increasing the effective fluence rate to 2000 mW/cm(2). Bovine liver and porcine skin tissues also showed similar enhancement in the contrast-to-noise ratio (CNR) values. A QD sample was inserted into the abdomen of a mouse.With a higher effective fluence rate, the CNR increased more than twofold and the QD sample became clearly visualized, which was completely undetectable under continuous excitation.Multiple acquisitions of QD images and averaging process pixel by pixel were performed to overcome the thermal noise issue of the detector in SOW, which yielded significant enhancement in the imaging capability, showing up to a 1.5 times increase in the CNR.

Aggregation-induced near-infrared absorption of squaraine dye in an albumin nanocomplex for photoacoustic tomography in vivo.

Photoacoustic tomography (PAT) is a newly emerging noninvasive imaging modality that could be further enhanced using near-infrared (NIR)-absorbing materials as contrast agents. To date, the most extensively studied photoacoustic imaging agents are inorganic nanomaterials because organic materials with NIR-absorption capabilities are limited. In this study, a NIR-absorbing nanocomplex composed of a squaraine dye (SQ) and albumin was prepared based on the aggregation-induced NIR absorption of SQ. Through aggregation, the absorption spectrum of SQ was widened from the visible-light region to the NIR region, which facilitated photoacoustic signal generation in the tissue-transparent NIR optical window (700-900 nm). Blood analysis and histology measurements revealed that the nanocomplex can be used for PAT applications in vivo without obvious toxicity to living mice.

Deep optical imaging of tissue using the second and third near-infrared spectral windows.

Light at wavelengths in the near-infrared (NIR) region allows for deep penetration and minimal absorption through high scattering tissue media. NIR light has been conventionally used through the first NIR optical tissue window with wavelengths from 650 to 950 nm. Longer NIR wavelengths had been overlooked due to major water absorption peaks and a lack of NIR-CCD detectors. The second NIR spectral window from 1100 to 1350 nm and a new spectral window from 1600 to 1870 nm, known as the third NIR optical window, were investigated. Optical attenuation measurements from thin tissue slices of normal and malignant breast and prostate tissues, pig brain, and chicken tissue were obtained in the spectral range from 400 to 2500 nm. Optical images of chicken tissue overlying three black wires were also obtained using the second and third spectral windows. Due to a reduction in scattering and minimal absorption, longer attenuation lengths and clearer optical images could be seen in the second and third NIR optical windows compared to the conventional first NIR optical window. A possible fourth optical window centered at 2200 nm was noted.

In vivo image analysis using iRFP transgenic mice.

Fluorescent proteins with light wavelengths within the optical window are one of the improvements in in vivo imaging techniques. Near-infrared (NIR) fluorescent protein (iRFP) is a stable, nontoxic protein that emits fluorescence within the NIR optical window without the addition of exogenous substrate. However, studies utilizing an in vivo iRFP model have not yet been published. Here, we report the generation of transgenic iRFP mice with ubiquitous NIR fluorescence expression. iRFP expression was observed in approximately 50% of the offspring from a matings between iRFP transgenic and WT mice. The serum and blood cell indices and body weights of iRFP mice were similar to those of WT mice. Red fluorescence with an excitation wavelength of 690 nm and an emission wavelength of 713 nm was detected in both newborn and adult iRFP mice. We also detected fluorescence emission in whole organs of the iRFP mice, including the brain, heart, liver, kidney, spleen, lung, pancreas, bone, testis, thymus, and adipose tissue. Therefore, iRFP transgenic mice may therefore be a useful tool for various types of in vivo imaging.

Near‐Infrared SERS Nanoprobes with Plasmonic Au/Ag Hollow‐Shell Assemblies for In Vivo Multiplex Detection

AbstractFor the effective application of surface‐enhanced Raman scattering (SERS) nanoprobes for in vivo targeting, the tissue transparency of the probe signals should be as high as it can be in order to increase detection sensitivity and signal reproducibility. Here, near‐infrared (NIR)‐sensitive SERS nanoprobes (NIR SERS dots) are demonstrated for in vivo multiplex detection. The NIR SERS dots consist of plasmonic Au/Ag hollow‐shell (HS) assemblies on the surface of silica nanospheres and simple aromatic Raman labels. The diameter of the HS interior is adjusted from 3 to 11 nm by varying the amount of Au3+ added, which results in a red‐shift of the plasmonic extinction of the Au/Ag nanoparticles toward the NIR (700–900 nm). The red‐shifted plasmonic extinction of NIR SERS dots causes enhanced SERS signals in the NIR optical window where endogenous tissue absorption coefficients are more than two orders of magnitude lower than those for ultraviolet and visible light. The signals from NIR SERS dots are detectable from 8‐mm deep in animal tissues. Three kinds of NIR SERS dots, which are injected into live animal tissues, produce strong SERS signals from deep tissues without spectral overlap, demonstrating their potential for in vivo multiplex detection of specific target molecules.

Bright and stable near-infrared fluorescent protein for in vivo imaging

The ability of non-invasive monitoring of deep-tissue developmental, metabolic, and pathogenic processes will advance modern biotechnology. Imaging of live mammals using fluorescent probes is more feasible within a “near-infrared optical window” (NIRW)1. Here we report a phytochrome-based near infra-red fluorescent protein (iRFP) with the excitation/emission maxima at 690/713 nm. Bright fluorescence in a living mouse proved iRFP to be a superior probe for non-invasive imaging of internal mammalian tissues. Its high intracellular stability, low cytotoxicity, and lack of the requirement to add external biliverdin-chromophore makes iRFP as easy to use as conventional GFP-like proteins. Compared to earlier phytochrome-derived fluorescent probes, the iRFP protein has better in vitro characteristics and performs well in cells and in vivo, having greater effective brightness and photostability. Compared to the far-red GFP-like proteins, iRFP has substantially higher signal to background ratio in a mouse model owing to its infra-red shifted spectra.