Large Near-infrared Research Articles

Coumarins to Cyanines: Synthesis of Hemicyanines.

Near-infrared (NIR) emitting fluorophores are powerful tools for optical imaging. However, there are only a handful of broadly employed NIR-emitting scaffolds, and the synthetic methods to prepare these molecules are often problematic. Here, we describe a novel, three-step synthesis of chromene-containing hemicyanine probes exhibiting large Stokes shifts and NIR emissions. We develop a pH-activatable probe for visualizing lysosomal trafficking of mAb conjugates. These studies provide a concise approach to hemicyanines with promising properties.

Tunable Three-Dimensional Plasmonic Arrays for Large Near-Infrared Fluorescence Enhancement.

Metal-enhanced fluorescence (MEF), resulting from the near-field interaction of fluorophores with metallic nanostructures, has emerged as a powerful tool for dramatically improving the performance of fluorescence-based biomedical applications. Allowing for lower autofluorescence and minimal photoinduced damage, the development of multifunctional and multiplexed MEF platforms in the near-infrared (NIR) windows is particularly desirable. Here, a low-cost fabrication method based on nanosphere lithography is applied to produce tunable three-dimensional (3D) gold (Au) nanohole-disc arrays (Au-NHDAs). The arrays consist of nanoscale glass pillars atop nanoholes in a Au thin film: the top surfaces of the pillars are Au-covered (effectively nanodiscs), and small Au nanoparticles (nanodots) are located on the sidewalls of the pillars. This 3D hole-disc (and possibly nanodot) construct is critical to the properties of the device. The versatility of our approach is illustrated through the production of uniform and highly reproducible Au-NHDAs with controlled structural properties and tunable optical features in the NIR windows. Au-NHDAs allow for a very large NIR fluorescence enhancement (more than 400 times), which is attributed to the 3D plasmonic structure of the arrays that allows strong surface plasmon polariton and localized surface plasmon resonance coupling through glass nanogaps. By considering arrays with the same resonance peak and the same nanodisc separation distance, we show that the enhancement factor varies with nanodisc diameter. Using computational electromagnetic modeling, the electric field enhancement at 790 nm was calculated to provide insights into excitation enhancement, which occurs due to an increase in the intensity of the electric field. Fluorescence lifetime measurements indicate that the total fluorescence enhancement may depend on controlling excitation enhancement and therefore the array morphology. Our findings provide important insights into the mechanism of MEF from 3D plasmonic arrays and establish a low-cost versatile approach that could pave the way for novel NIR-MEF bioapplications.

A near-infrared ratiometric/turn-on fluorescent probe for in vivo imaging of hydrogen peroxide in a murine model of acute inflammation

Much attention has been paid to develop optical probes for noninvasive, quantitative, in vivo monitoring of hydrogen peroxide (H2O2) due to its important roles in the initiation and development of numerous diseases. Motivated to meet this need, we herein report the synthesis of a near-infrared (NIR) fluorescent probe (AB1) for H2O2 by modulating intramolecular charge transfer (ICT) process of the dye 9H-1,3-Dichloro-7-hydroxy-9,9-dimethylacridine-2-one (DDAO). The probe AB1 exhibits both a large NIR fluorescence turn-on and a ratiometric response to H2O2 with high sensitivity and specificity. The fluorescence response of AB1 has a good linear relationship with H2O2 over a wide concentration range from 1 μM to 100 μM, thus affording a detection limit of 0.42 μM. Confocal microscopic experiments demonstrated that AB1 could ratiometrically detect exogenous and endogenous H2O2 in living cells. Moreover, owing to the NIR emission of DDAO, the probe was also utilized to image endogenous H2O2 from the peritoneal cavity in a mouse model of lipopolysaccharide-induced acute inflammation, based on the fluorescence turn-on mode. This new probe shows great potential as a reliable chemical tool to study the development and progression of H2O2-associated diseases in living animals.

Highly sensitive near infrared organic phototransistors based on conjugated polymer nanowire networks

Highly sensitive near-infrared (NIR) organic phototransistors (OPTs) were fabricated using nanowire network based on a narrow bandgap donor-acceptor (D-A) polymer as the photoactive channel. The D-A polymer nanowire network-based NIR-OPTs exhibit high responsivity of ∼246 A/W under an NIR illumination source (850 nm) with a light intensity of ∼0.1 mW/cm2. This value is over one order of magnitude higher than that of the structurally identical planar D-A polymer thin film OPTs. The high performance of the nanowire network-based phototransistors is attributed to the excellent hole transport ability, reduced density of the structural defects in the polymer nanowires, and improved contact at the channel layer/electrode interfaces. The high sensitivity and low cost solution-fabrication process render this OPT technology appealing and practically viable for application in large area NIR sensors.

Microcrystalline Silicon Photodiode For Large Area NIR Light Detection Applications

This letter reports on microcrystalline silicon near infrared (NIR) photodiode detector. The fabricated device shows dynamic ratio of 200 at 850 nm wavelength per 0.2 mW/cm 2 of incident power density at reverse bias voltage of -1 V with response time of 400 μs. The dynamic ratio achieved here is 15 times higher than the state of art large area inorganic a-SiGe:H phototransistor and twice the one for state of art organic cyanine based NIR detector. The speed of this device is 40 times faster than the a-SiGe:H detector. The overall advantage of high dynamic ratio and fast response alongside with compatibility with standard a-Si:H thin film transistor industry makes this device suitable for large area NIR detection applications.

Keto-benzo[h]-Coumarin-Based Near-Infrared Dyes with Large Stokes Shifts for Bioimaging Applications.

Fluorescence imaging is a promising tool for the visualization of biomolecules in living systems and there is great demand for new fluorescent dyes that absorb and emit in the near-infrared (NIR) region. Herein, we constructed three new fluorescent dyes (NBC dyes) based on keto-benzo[h]coumarin (k-BC) and benzopyrilium salts. These dyes showed large Stokes shifts (>100 nm) and NIR emission (>800 nm). The relationship between the structures and optical properties of these dyes was further investigated by using density functional theory calculations at the B3LYP/6-3G level of theory. Fluorescence images indicated that the fabricated dyes exhibited good photostability and low cytotoxicity and, thus, have potential applications as imaging agents in living cells and animals.

Biocompatible conjugated polymer nanoparticles for efficient photothermal tumor therapy.

Conjugated polymers (CPs) with strong near-infrared (NIR) absorption and high heat conversion efficiency have emerged as a new generation of photothermal therapy (PTT) agents for cancer therapy. An efficient strategy to design NIR absorbing CPs with good water dispersibility is essential to achieve excellent therapeutic effect. In this work, poly[9,9-bis(4-(2-ethylhexyl)phenyl)fluorene-alt-co-6,7-bis(4-(hexyloxy)phenyl)-4,9-di(thiophen-2-yl)-thiadiazoloquinoxaline] (PFTTQ) is synthesized through the combination of donor-acceptor moieties by Suzuki polymerization. PFTTQ nanoparticles (NPs) are fabricated through a precipitation approach using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG2000 ) as the encapsulation matrix. Due to the large NIR absorption coefficient (3.6 L g(-1) cm(-1) ), the temperature of PFTTQ NP suspension (0.5 mg/mL) could be rapidly increased to more than 50 °C upon continuous 808 nm laser irradiation (0.75 W/cm(2) ) for 5 min. The PFTTQ NPs show good biocompatibility to both MDA-MB-231 cells and Hela cells at 400 μg/mL of NPs, while upon laser irradiation, effective cancer cell killing is observed at a NP concentration of 50 μg/mL. Moreover, PFTTQ NPs could efficiently ablate tumor in in vivo study using a Hela tumor mouse model. Considering the large amount of NIR absorbing CPs available, the general encapsulation strategy will enable the development of more efficient PTT agents for cancer or tumor therapy.

TRIGGERED STAR FORMATION IN A BRIGHT-RIMMED CLOUD (BRC 5) OF IC 1805

We report recent optical, near-infrared (NIR), and millimeter observations which have revealed some new features of the bright-rimmed cloud BRC 5 associated with W4. With slitless spectroscopy, we detected 17 Hα emission stars around the cloud; 4 are near the surface of the cloud, and 1 is toward IRAS 02252+6120. NIR photometry shows that the central Hα emission star, together with one bright infrared source, has large NIR excesses and Class I spectral energy distributions. These two Class I objects are associated with the 2.9 mm continuum peaks and with a bipolar outflow, and are in between two separate, elongated C18O(J = 1-0) cores. The C18O cores and the two Class I sources are aligned along a line at position angle ~240°, somewhat less than perpendicular to the direction of UV radiation from the OB stars. Most of the detected Hα emission stars, all T Tauri candidates, are located within ~3' of the cloud on the exciting star side. An estimate of the age of the stars based on a color-magnitude diagram suggests that these T Tauri candidates have ages of ~1 Myr or less, but are more evolved objects than the central young stellar objects. This age sequence suggests sequential star formation within the BRC 5 cloud. The 13CO(J = 1-0) emission shows three elongated structures, which indicates the asymmetric structure toward the UV incident axis. We present our exploratory simulation results by using a smoothed particle hydrodynamic code that suggests that the asymmetrical BRC 5 structure could possibly result from the evolution of a preexisting prolate molecular cloud subject to radiation-driven implosion (RDI). Our best-fit prolate cloud has an initial mass of ~400 M ☉, an axial ratio of ~1.7, and a semi-major axis of ~1.6 pc, pointing away from the ionization flux by an angle of 15°. The simulated cloud structure not only closely matches the observed asymmetric morphological structure of BRC 5, but also reveals the possibility of the development of two major cores at the head of BRC 5. For the first time, the possibility of forming two stars by an RDI mechanism in a BRC is investigated.

A Unique Approach to Development of Near-Infrared Fluorescent Sensors for in Vivo Imaging

Near-infrared (NIR) fluorescent sensors have emerged as promising molecular tools for imaging biomolecules in living systems. However, NIR fluorescent sensors are very challenging to be developed. Herein, we describe the discovery of a new class of NIR fluorescent dyes represented by 1a/1c/1e, which are superior to the traditional 7-hydroxycoumarin and fluorescein with both absorption and emission in the NIR region while retaining an optically tunable hydroxyl group. Quantum chemical calculations with the B3LYP exchange functional employing 6-31G(d) basis sets provide insights into the optical property distinctions between 1a/1c/1e and their alkoxy derivatives. The unique optical properties of the new type of fluorescent dyes can be exploited as a useful strategy for development of NIR fluorescent sensors. Employing this strategy, two different types of NIR fluorescent sensors, NIR-H(2)O(2) and NIR-thiol, for H(2)O(2) and thiols, respectively, were constructed. These novel sensors respond to H(2)O(2) or thiols with a large turn-on NIR fluorescence signal upon excitation in the NIR region. Furthermore, NIR-H(2)O(2) and NIR-thiol are capable of imaging endogenously produced H(2)O(2) and thiols, respectively, not only in living cells but also in living mice, demonstrating the value of the new NIR fluorescent sensor design strategy. The new type of NIR dyes presented herein may open up new opportunities for the development of NIR fluorescent sensors based on the hydroxyl functionalized reactive sites for biological imaging applications in living animals.

An improved boosting partial least squares method for near-infrared spectroscopic quantitative analysis

Boosting partial least squares (PLS) has been used for regression to improve the predictive accuracy of PLS models, however, there are still problems when the outliers exist in the calibration dataset. To make the method robust and enhance its prediction ability, an improved boosting PLS is proposed and applied in quantitative analysis of near-infrared (NIR) spectral datasets. In the method, a robust step is added to weaken the effect of the outliers on the model. On the other hand, the loss function defined with relative errors is suggested for updating the sampling weight during the boosting procedure. In addition, the ensemble prediction by the weighted mean of the models in the boosting series is found to be more effective than the commonly used weighted median. The performance of the improved method is tested with two large NIR datasets of industrial production. The method was found to have a marked superiority in robustness and prediction ability, particularly when outliers exist.

Near infrared flares of Sagittarius A*

We report on the results of new simulations of near-infrared (NIR) observations of the Sagittarius A* (Sgr A*) counterpart associated with the super-massive black hole at the Galactic Center. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope and CIAO NIR camera on the Subaru telescope (13 June 2004, 30 July 2005, 1 June 2006, 15 May 2007, 17 May 2007 and 28 May 2008). We used a model of synchrotron emission from relativistic electrons in the inner parts of an accretion disk. The relativistic simulations have been carried out using the Karas-Yaqoob (KY) ray-tracing code. We probe the existence of a correlation between the modulations of the observed flux density light curves and changes in polarimetric data. Furthermore, we confirm that the same correlation is also predicted by the hot spot model. Correlations between intensity and polarimetric parameters of the observed light curves as well as a comparison of predicted and observed light curve features through a pattern recognition algorithm result in the detection of a signature of orbiting matter under the influence of strong gravity. This pattern is detected statistically significant against randomly polarized red noise. Expected results from future observations of VLT interferometry like GRAVITY experiment are also discussed.

A Multi-Site, Multi-Species near Infrared Calibration for the Prediction of Cellulose Content in Eucalypt Woodmeal

Calibrations between spectra derived from near infrared (NIR) spectroscopy and chemical analyses can be used to predict cellulose content in samples of ground eucalypt woodmeal. Past calibrations have used small sample sets (<100 samples) often representing a single stand or region and only one species, making their application to wider populations of samples problematic. A robust, nondestructive prediction capability for eucalypt wood cellulose that works across stands, regions and species would find many applications in tree breeding and resource assessment. Here, we describe the development and test the performance of a large (> 1000 samples) multi-site and species NIR calibration for predicting cellulose content of eucalypt woodmeal obtained from increment cores, wood chips and stem cross-sections. Most of the samples came from Eucalyptus globulus and E. nitens. The calibration was tested against four independent sample sets and explained between 65% and 84% of the variance in each set. A higher proportion of variance was explained in those sample sets that had a wider range of cellulose content. Standard errors of prediction were between 0.5% and 1.5% cellulose for the four independent sample sets. The test samples were added to the large calibration and a new calibration with 1260 samples was constructed. Principal components analysis suggests additional wood samples with more diverse chemistries are required to enable the calibration to capture more fully the chemical variation present in the genus.

Wavelength band optimization in spectral near-infrared optical tomography improves accuracy while reducing data acquisition and computational burden

Multispectral near-infrared (NIR) tomographic imaging has the potential to provide information about molecules absorbing light in tissue, as well as subcellular structures scattering light, based on transmission measurements. However, the choice of possible wavelengths used is crucial for the accurate separation of these parameters, as well as for diminishing crosstalk between the contributing chromophores. While multispectral systems are often restricted by the wavelengths of laser diodes available, continuous-wave broadband systems exist that have the advantage of providing broadband NIR spectroscopy data, albeit without the benefit of the temporal data. In this work, the use of large spectral NIR datasets is analyzed, and an objective function to find optimal spectral ranges (windows) is examined. The optimally identified wavelength bands derived from this method are tested using both simulations and experimental data. It is found that the proposed method achieves images as qualitatively accurate as using the full spectrum, but improves crosstalk between parameters. Additionally, the judicious use of these spectral windows reduces the amount of data needed for full spectral tomographic imaging by 50%, therefore increasing computation time dramatically.