Near-infrared Optical Properties Research Articles

Networks of gold nanoparticles and bacteriophage as biological sensors and cell-targeting agents.

Biological molecular assemblies are excellent models for the development of nanoengineered systems with desirable biomedical properties. Here we report an approach for fabrication of spontaneous, biologically active molecular networks consisting of bacteriophage (phage) directly assembled with gold (Au) nanoparticles (termed Au-phage). We show that when the phage are engineered so that each phage particle displays a peptide, such networks preserve the cell surface receptor binding and internalization attributes of the displayed peptide. The spontaneous organization of these targeted networks can be manipulated further by incorporation of imidazole (Au-phage-imid), which induces changes in fractal structure and near-infrared optical properties. The networks can be used as labels for enhanced fluorescence and dark-field microscopy, surface-enhanced Raman scattering detection, and near-infrared photon-to-heat conversion. Together, the physical and biological features within these targeted networks offer convenient multifunctional integration within a single entity with potential for nanotechnology-based biomedical applications.

Magnetic field effects on near-infrared optical properties of cytochrome oxidase

This paper reports the possible effects of intense magnetic fields on the near-infrared optical properties of cytochrome oxidase. Optical measurements performed on both cytochrome aa3 suspension and in vivo showed changes in optical absorbance at 690–830 nm under magnetic field exposure. Magnetic fields of up to 14 T generated by a superconducting current were able to change the oxidation of the oxidized cytochrome aa3 periodically depending on the density of the magnetic flux. Measurements with a cooled CCD system revealed that the absorbance at 830 nm was slightly increased by a magnetic field of 8 T. We performed an animal experiment on the head of a living rabbit, and obtained results showing the enhancement of cytochrome aa3 oxidation in the mitochondria of cells under the magnetic fields. The effects of magnetic fields on the paramagnetic behavior of oxygen, electron transfer in cytochromes, and cell membrane conformation in mitochondria may playa role in increasing the sensitivity to NIR light for detecting cyto-ox oxidation, which is one of the primary indicators of cellular activity.

Tunable near‐infrared optical properties based on poly(methyl methacrylate)–oxide waveguide materials

AbstractIn this study, two classes of low‐loss optical planar waveguides were prepared from trialkoxysilane‐capped poly(methyl methacrylate) (PMMA)–silica and PMMA–titania hybrid materials, respectively. The prepared hybrid films had very uniform structure and surface planarity. The incorporation of the silica or titania segments into the acrylic polymer matrix reduced the intermolecular interaction and thus induced an increase in anharmonicity of the C‐H bond in the acrylic segment. Therefore, the third harmonic stretching vibration absorption of the C‐H bond was red‐shifted and resulted in a tuning of near‐infrared (NIR) optical absorption. The optical loss of the studied waveguides was reduced from 0.65 dB/cm of the PMMA waveguide to 0.26 and 0.28 dB/cm with increasing the silica and titania content in the hybrid materials, respectively. The reduction of the C‐H number density and shifting of the NIR absorption spectra accounted for the relationship between the optical loss and the inorganic oxide content. The increased anharmonicity through the incorporation of the inorganic moiety in the hybrid materials provides another approach for tuning the NIR optical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1224–1228, 2005

Erbia-modified electrospun titania nanofibres for selective infrared emitters

Tetraisopropyl titanate (TPT) was mixed with a solution of polyvinylpyrrolidone(PVP) and the solution electrospun into nanofibres. Thermal annealing at900 °C was used to pyrolyse the PVP, leaving nanofibres of rutile-phase titania. Erbium (III) oxideparticles were also added into the solution before electrospinning, and selectively modifiedthe near-infrared optical properties of the titania nanofibres as verified by both absorptionand emission spectra. We thereby demonstrate the production of high-temperatureoptically functionalized nanostructures that can be used in a thermophotovoltaic energyconversion system.

Near-infrared nonlinear optical properties of single-wall carbon nanotubes embedded in polymer film

A free-standing film made of a single-wall carbon nanotube (SWCNT)–polyvinylalchol (PVA) composite material was fabricated by pretreatment of SWCNTs with ultrasonication in water with the aid of a surfactant that promotes unbundling of aggregated SWNCTs. Characterizations using optical absorption spectroscopy, optical microscopy, and micro-Raman spectroscopy revealed that the film has an optical absorption at approximately 1.5 μm, suitable for the occurrence of saturable absorption (a promising nonlinear optical effect) in optical telecommunication wavelengths, and that SWCNTs in the film are dispersed uniformly with a low scattering loss. The saturable absorption properties of the film at 1.56 μm measured using the Z-scan method was basically similar to those of the SWCNTs deposited on quartz glass, indicating that the free-standing SWCNT–PVA film is as promising as the SWCNT film deposited directly on a substrate.

Tuning Near-Infrared Optical Properties of Aromatic Model Compounds by Substituents

In this study, the effects of substituents on the near-infrared (NIR) absorption spectra of model compounds were examined theoretically and experimentally, including benzene (B), fluorobenzene (FB), 1,4-difluorobenzene (DFB), and 1,4-bis(trifluoromethyl) benzene (6FB). It was found that a stronger electron-withdrawing substituent resulted in a smaller C–H bond length and thus a blue-shifted overtone position. Thus, the order of B > FB > DFB > 6FB was found for the positions of C–H fundamentals and overtones. The variations of optical windows were primarily influenced by the C–H molar density as well as by the shifting of the absorption band by the substituent. A pseudo compound (PC) with the same C–H number density as the 6FB but with the same band position as B was used to address the effect of a polarized substituent on the optical window. It was found that 6FB could have the optical window at the lower wavelength regions of the S-band (1480–1530 nm) and C-band (1530–1570 nm) but that of the PC at the higher wavelength regions of the C-band and L-band (1570–1610 nm). The present study provides another approach for designing new organic polymers for optical waveguides besides the current approach of reducing the C–H number density.

Effects of Molecular Structures on the Near-Infrared Optical Properties of Polyimide Derivatives and Their Corresponding Optical Waveguides

Polyimides have been demonstrated to be a potential candidate as optical waveguide materials. Previous studies were focusing on the reducing the optical loss by decreasing the C−H bonding density of the molecular structure. The tuning of the near-infrared (NIR) overtone absorption position from the polarizability of the bridge group in polyimides is rarely studied. In this study, a series of polyimides prepared from pyromellitic dianhydride (PMDA) and diamines with various bridge groups were used to investigate the structure−NIR optical property relationships. The bridge groups include −SO2−, −S−, −O−, and −CH2−. Both the experimental and ab initio calculation on the model compounds and polyimide derivatives revealed that the stronger the electron-withdrawing ability of the neighboring bridge group, the shorter the aromatic C−H bond length. This results in the shifting of the overtone frequencies of the C−H bond to higher frequencies. Such bridge effects played an important role in the optical loss of the corresponding polyimide waveguides. It was found that the optical loss was resulted from both the C−H bonding density and the shifting of the overtone absorption by the bridge group. It indicates that tuning of NIR optical loss from the molecular structures of polyimides could be achieved.

Effects of the Menstrual Cycle on the Red and Near-infrared Optical Properties of the Human Breast ¶

Time-resolved reflectance and transmittance spectroscopy was applied to measure in vivo the absorption and transport scattering spectra of the female breast from 610 to 1010 nm. Three measurement configurations were used to probe different breast regions, and data were collected two or three times in each of the five phases of the menstrual cycle. The absorption spectra were best-fitted with a linear combination of the spectra of the main tissue constituents (water, lipids, oxy- and deoxyhemoglobin). This allowed us to evaluate percentage contents of water and lipids, total hemoglobin content and hemoglobin oxygen saturation. The scattering spectra were interpreted with a function derived from Mie theory, providing information on the density and average size of the tissue scatterers. Significant changes in the estimated variables were observed with measurement geometry, reflecting the heterogeneous nature of the breast, and with time, in agreement with expected physiological changes over the menstrual cycle.

Broad bandwidth frequency domain instrument for quantitative tissue optical spectroscopy

Near-infrared (NIR) optical properties of turbid media, e.g., tissue, can be accurately quantified noninvasively using methods based on diffuse reflectance or transmittance, such as frequency domain photon migration (FDPM). Factors which govern the accuracy and sensitivity of FDPM-measured optical properties include instrument performance, the light propagation model, and fitting algorithms used to calculate optical properties from measured data. In this article, we characterize instrument, model, and fitting uncertaintics of an FDPM system designed for clinical use and investigate how each of these factors affects the quantification of NIR absorption (μa) and reduced scattering (μs′) parameters in tissue phantoms. The instrument is based on a 500 MHz, multiwavelength platform that sweeps through 201 discrete frequencies in as little as 675 ms. Phase and amplitude of intensity modulated light launched into tissue, i.e., diffuse photon density waves (PDW), are measured with an accuracy of ±0.30° and ±3.5%, while phase and amplitude precision are ±0.025° and ±0.20%, respectively. At this level of instrument uncertainty, simultaneous fitting of frequency-dependent phase and amplitude nonlinear model functions derived from a photon diffusion approximation provides an accurate and robust strategy for determining optical properties from FDPM data, especially for media with high absorption. In an optical property range that is characteristic of most human tissues in the NIR (5×10−3<μa<5×10−2 mm−1, 0.5<μs′<2 mm−1), we theoretically and experimentally demonstrate that the multifrequency, simultaneous-fit approach allows μa and μs′ to be quantified with an accuracy of ±5% and ±3%, respectively. Although exceptionally high levels of precision can be obtained using this approach (<1% of the estimated absorption and scattering values), we show that the absolute accuracy of optical property measurements is highly dependent on specific factors associated with instrument performance, model function relevance, and details of the fitting strategy used to calculate μa and μs′.

Interaction of acetylene on Si(111): Growth and luminescence study of Si1−xCx thin layers

Abstract The different carbonization processes of a Si(111) 7 × 7 reconstructed surface exposed to acetylene (C2H2) were studied by ultrahigh-vacuum electronic and luminescence techniques. We found that the molecule breaks at about 450°C and for temperature up to 600°C a Si1−xCx alloy is fonned in the near-surface region of the sample. For higher temperatures, up to 850°C, crystalline SiC crystallite precipitation epitaxially grown on the Si surface is observed. The luminescence spectra obtained at each stage of carbonization revealed the formation of well defined Si1−xCx phases (with x equal to a few per cent) and it clearly demonstrates that the exposure to C2H2 is highly efficient procedure to change in a continuous way the near-infrared optical properties of Si surfaces in the spectral range from 0.9 to 1.1 eV. The observation at 650°C exposure of an intense and broadened photoluminescence emission in the range 1.2–1.6eV is particularly interesting. This indicates the possibility that in the near-surface region a local concentration of the first-nearest-neighbour Si–C bond of between 15–20% is present, indicating the formation of a high C-rich layer.

Effects of the Menstrual Cycle on the Red and Near-infrared Optical Properties of the Human Breast¶

Time-resolved reflectance and transmittance spectroscopy was applied to measure in vivo the absorption and transport scattering spectra of the female breast from 610 to 1010 nm. Three measurement configurations were used to probe different breast regions, and data were collected two or three times in each of the five phases of the menstrual cycle. The absorption spectra were best-fitted with a linear combination of the spectra of the main tissue constituents (water, lipids, oxy- and deoxyhemoglobin). This allowed us to evaluate percentage contents of water and lipids, total hemoglobin content and hemoglobin oxygen saturation. The scattering spectra were interpreted with a function derived from Mie theory, providing information on the density and average size of the tissue scatterers. Significant changes in the estimated variables were observed with measurement geometry, reflecting the heterogeneous nature of the breast, and with time, in agreement with expected physiological changes over the menstrual cycle.

Quantitative near-infrared spectroscopy of cervical dysplasia in vivo.

The aims of this study were: (i) to quantify near-infrared optical properties of normal cervical tissues and high-grade squamous intra-epithelial lesions (H-SIL); (ii) to assess the feasibility of differentiating normal cervical tissues from H-SIL on the basis of these properties; and (iii) to determine how cervical tissue optical properties change following photodynamic therapy (PDT) of H-SIL in vivo. Using the frequency domain photon migration technique, non-invasive measurements of normal and dysplastic ecto-cervical tissue optical properties, i.e. absorption (mu(a)) and effective scattering coefficients, and physiological parameters, i.e. tissue water and haemoglobin concentration, percentage oxygen saturation (%SO(2)), were performed on 10 patients scheduled for PDT of histologically-proven H-SIL. Cervix absorption and effective scattering parameters were up to 15% lower in H-SIL sites compared with normal cervical tissue for all wavelengths studied (674, 811, 849, 956 nm). Following PDT, all mu(a) values increased significantly, due to elevated tissue blood and water content associated with PDT-induced hyperaemia and oedema. Tissue total haemoglobin concentration ([TotHb]) and arterio-venous oxygen saturation measured in H-SIL sites were lower than normal sites ([TotHb]: 88.6 +/- 35.8 micromol/l versus 124.7 +/- 22.6 micromol/l; %SO(2): 76.5 +/- 14.7% versus 84.9 +/- 3.4%).

Near-infrared optical properties of ex vivo human uterus determined by the Monte Carlo inversion technique

The optical properties, absorption (µa) and reduced scattering coefficient (µs´), of ex vivo human myometrium and leiomyoma (fibroid) have been determined by the Monte Carlo inversion technique over the wavelength range 600 - 1000 nm. This region is currently of interest for new, minimal-access, surgical laser procedures such as photodynamic therapy (PDT) for abnormalities of the uterus, and interstitial laser photocoagulation (ILP) for the thermal ablation of fibroids. In the region 630 - 675 nm (corresponding to PDT), the optical coefficients of myometrium are µa = 0.041±0.012 mm-1 and µs´ = 1.37±0.19 mm-1. For the wavelength range 800-1000 nm (associated with infrared lasers for ILP), the optical coefficients of fibroid were found to be µa = 0.020±0.003 mm-1 and µs´ = 0.56±0.03 mm-1. Overall, the optical properties of fibroid were found to be lower than myometrium, and this was attributed to the differences in both anatomy and vascularity. The results show that PDT for ablation of the uterine endometrium is most unlikely to affect any tissues beyond the myometrium, and that the region around 800 nm is the most effective for ablation of fibroids using ILP as the penetration depth of light is greatest at this wavelength.

Si 1− xC x formation by reaction of Si(111) with acetylene: growth mode, electronic structure and luminescence investigation

The carbonization process of a Si(111) 7×7 reconstructed surface exposed to acetylene (C 2H 2) has been investigated by combining several structural, electronic, and luminescence techniques. The aim was to give a comprehensive scenario of the different carbonaceous phases formed on the clean silicon surface starting from the C 2H 2 molecule chemisorbed at room temperature up to the formation of a crystalline c-SiC compound. We found that the molecule breaks at about 450°C and for temperatures up to 600°C a Si 1− x C x alloy is formed inside the sample. For higher temperatures, up to 850°C, c-SiC crystallite precipitation epitaxially grown on the Si surface is observed. The near-edge-energy loss spectra at the carbon K edge ensures that for C 2H 2 deposition temperatures higher than 600°C the carbon bonds are sp 3-like, thus demonstrating the absence of non-substitutional carbon concentration. The luminescence spectra performed at each stage of carbonization revealed the formation of well-defined Si 1− x C x phases (with x of a few percent) and clearly demonstrate that the exposure to C 2H 2 is a highly efficient method to change in a continuous way the near-infrared optical properties of silicon surfaces in the spectral range from 0.9 to 1.1 eV.

Near-infrared optical properties of ex vivo human skin and subcutaneous tissues measured using the Monte Carlo inversion technique

The absorption and transport scattering coefficients of caucasian and negroid dermis, subdermal fat and muscle have been measured for all wavelengths between 620 and 1000 nm. Samples of tissue 2 mm thick were measured ex vivo to determine their reflectance and transmittance. A Monte Carlo model of the measurement system and light transport in tissue was then used to recover the optical coefficients. The sample reflectance and transmittance were measured using a single integrating sphere `comparison' method. This has the advantage over conventional double-sphere techniques in that no corrections are required for sphere properties, and so measurements sufficiently accurate to recover the absorption coefficient reliably could be made. The optical properties of caucasian dermis were found to be approximately twice those of the underlying fat layer. At 633 nm, the mean optical properties over 12 samples were and for absorption coefficient and and for transport scattering coefficient for caucasian dermis and the underlying fat layer respectively. The transport scattering coefficient for all biological samples showed a monotonic decrease with increasing wavelength. The method was calibrated using solid tissue phantoms and by comparison with a temporally resolved technique.

Nondestructive Detection of Section Drying, an Internal Disorder in Tangerine

Near infrared (NIR) absorption spectrometry and X-ray computed tomography (CT) were used to nondestructively determine the presence of section drying, an internal disorder in tangerines (Citrus reticulata Blanco, cv. Dancy). X-ray CT scan images clearly differentiated areas with section drying from healthy sections of the fruit. Delineation was due to differences in X-ray absorption resulting from lower tissue density and water content in vesicles having the disorder. Second derivative NIR optical density values at 768 and 960 nm correlated strongly with the presence or absence of section drying, indicating that NIR optical properties of vesicles with section drying differed from those without the disorder. These results suggest that, compared with X-ray—based techniques, NIR absorption spectroscopy could be a less expensive, safe, and rapid method for the nondestructive sensing of section drying in citrus fruit.

Temperature dependence of the infrared optical properties of YBa2Cu3O7: A plasmon damping model

The temperature dependence observed in the mid- and near-infrared optical properties of YBa2Cu3O7 is explained in terms of the Drude model for free charge carriers. In the Drude model, the linear temperature dependence of the dc resistivity arises from the free charge carriers having a temperature-dependent mean free path. This temperature dependence results in the plasmon contribution to the dielectric constant having a damping coefficient which also varies linearly with temperature. We find that the temperature dependence which is observed in the absorption and reflection spectra of YBa2Cu3O7 is consistent with this simple model.

Transport and near-infrared optical properties of ErSi2 thin films

We present the study of the resistivity and Hall coefficient of ErSi2 thin films epitaxially grown on a Si substrate as a function of temperature and film thickness. Then, we report the first study of the complex index at energies below the silicon band gap (0.5–1 eV). From these data we calculate the absorption length in ErSi2, which is a critical parameter for the design of an efficient silicide silicon photodetector.

Comparison between infrared Martian disk spectra and optical properties of terrestrial analogs

Medium spectral resolution (20 kaysers) infrared measurements of the Martian disk made between 2900 and 5600 kaysers from the NASA Lear Airborne Observatory have been successfully compared with predictions derived from a model of the Martian soil and atmosphere. Modeling of the Martian atmosphere permitted the extraction of Martian soil reflectance in the CO2 bands centered at 3657 kaysers. Three Martian soil analogs previously considered acceptable - limonite, montmorillonite, and basalt - were analyzed to determine the optical complex indices of refraction in the same range as the airborne observations, for mathematical modeling. A characteristic surface particle size approximately 1 to 3 microns diameter is indicated. It is concluded that the Martian soil surface near-infrared optical properties are consistent with a soil composition similar to montmorillonite or limonite, mixed with a basalt.