Near-infrared Wavelength Region Research Articles

Spectral indices to assess the carotenoid/chlorophyll ratio from adaxial and abaxial leaf reflectance

ABSTRACTThe ratio between the carotenoid and chlorophyll concentrations can indicate the physiology and phenology of plants. Most of the vegetation indices related to the ratio between the carotenoid and chlorophyll contents only consider the reflectance from the adaxial leaf surface. In this study, it was found that the leaf reflectance from the abaxial surface is lower than that of the adaxial surface in the visible wavelength region. On the contrary, the reflectance is higher on the adaxial surface in the near-infrared wavelength region. The difference ratio index resulted in the best correlation with the carotenoid/chlorophyll ratio and was the most robust among all the spectral indices studied when the spectral information on the adaxial and abaxial surfaces was pooled. The result indicated that this index can accurately estimate the carotenoid/chlorophyll ratio because of the insensitivity to the differences between adaxial and abaxial leaf surfaces.

Broadband polarizing beam splitter based on two-layer metal grating with a high refractive index dielectric layer

A polarizing beam splitter (PBS) based on a two-layer metal grating operating in the near-infrared wavelength region is proposed. The PBS structure comprises a high refractive index dielectric layer and a subwavelength grating layer, which increases the transmittance and the extinction ratio of the grating. Using the rigorous coupled-wave analysis (RCWA) method, the parameters of the proposed polarizing beam splitter were simulated and optimized. The results show that transmission of more than 97% for the transverse-magnetic (TM) wave polarization and reflection of more than 98% for the transverse-electric (TE) wave polarization are achieved within the 1220–1690nm wavelength range. The corresponding maximum extinction ratios for the transmittance and reflectance are 33dB and 34dB, respectively. When compared with a single-layer PBS grating, the proposed two-layer structure shows greater design flexibility. The proposed PBS shows potential for application to devices such as routers and switches.

Near infrared light-controlled therapeutic molecules release of nanocarriers in cancer therapy

Spurred by the development in materials chemistry, stimuli-responsive nanocarriers that could show sharp responses to various environmental changes have found applications in many fields including controlled drug delivery in the past few years. Among all the available stimuli, light has recently attracted much attention owing to their non-invasiveness and the possibility of remote spatiotemporal control. A large amount of photoresponsive systems have been constructed to achieve on-demand drug, gene or other kinds of cytotoxic species release in responsive to illumination of a specific wavelength in near-infrared region (NIR), which shows better tissue penetration compared to visible or ultraviolet (UV) light with shorter wavelengths. Exploration of NIR light-responsive therapeutic cargoes delivery systems opens up a new and exciting possibility for applications in nanomedicine. In this review article, we mainly focus on the recent progress in nanocarriers with different kinds of strategies to achieve NIR light-based control over the delivery process, with special emphasis on their application in NIR photo-response controlled therapeutic cargoes release and subsequent therapy. The final section reviews current challenges in the use of NIR responsive nanomaterials and potential solutions.

Peptide Functionalized Gold Nanoparticles as a Stimuli Responsive Contrast Medium in Multiphoton Microscopy.

There is a need for biochemical contrast mediators with high signal-to-noise ratios enabling noninvasive biomedical sensing, for example, for neural sensing and protein-protein interactions, in addition to cancer diagnostics. The translational challenge is to develop a biocompatible approach ensuring high biochemical contrast while avoiding a raise of the background signal. We here present a concept where gold nanoparticles (AuNPs) can be utilized as a stimuli responsive contrast medium by chemically triggering their ability to exhibit multiphoton-induced luminescence (MIL) when performing multiphoton laser scanning microscopy (MPM). Proof-of-principle is demonstrated using peptide-functionalized AuNPs sensitive to zinc ions (Zn2+). Dispersed particles are invisible in the MPM until addition of millimolar concentrations of Zn2+ upon which MIL is enabled through particle aggregation caused by specific peptide interactions and folding. The process can be reversed by removal of the Zn2+ using a chelator, thereby resuspending the AuNPs. In addition, the concept was demonstrated by exposing the particles to matrix metalloproteinase-7 (MMP-7) causing peptide digestion resulting in AuNP aggregation, significantly elevating the MIL signal from the background. The approach is based on the principle that aggregation shifts the plasmon resonance, elevating the absorption cross section in the near-infrared wavelength region enabling onset of MIL. This Letter demonstrates how biochemical sensing can be obtained in far-field MPM and should be further exploited as a future tool for noninvasive optical biosensing.

Synthesis, Characterization and Optical Constants of Silicon Oxycarbide

High refractive index glasses are preferred in integrated photonics applications to realize higher integration scale of passive devices. With a refractive index that can be tuned between SiO 2 (1.45) and a-SiC (3.2), silicon oxycarbide SiOC offers this flexibility. In the present work, silicon oxycarbide thin films from 0.1 – 2.0 μm thickness are synthesized by reactive radio frequency magnetron sputtering a silicon carbide SiC target in a controlled argon and oxygen environment. The refractive index n and material extinction coefficient k of the silicon oxycarbide films are acquired with variable angle spectroscopic ellipsometry over the UV-Vis-NIR wavelength range. Keeping argon and oxygen gases in the constant ratio, the refractive index n is found in the range from 1.41 to 1.93 at 600 nm which is almost linearly dependent on RF power of sputtering. The material extinction coefficient k has been estimated to be less than 10 -4 for the deposited silicon oxycarbide films in the visible and near-infrared wavelength regions. Morphological and structural characterizations with SEM and XRD confirms the amorphous phase of the SiOC films.

Multiplexed fluorescence mediated tomography with temporal and spectral data

We recently developed an algorithm for multiplexed fluorescence tomographic imaging of at least four fluorophores concurrently in the red and near-infrared wavelength region by jointly using spectral and temporal data. We report the design of a fluorescence tomography instrument that acquires spectral and temporal data, and validate its use in tissue-mimicking phantoms with four embedded fluorescent targets with highly overlapped spectral signatures. Critically, this requires measurement or computation of extended fluorophore signature libraries, which capture the variability in the measured signal due to the unknown position of the targets in the media. We demonstrate that we can demix and tomographically image all four fluorophores with zero image cross-talk, and 1 mm or better spatial resolution.

Photoluminescence and Photoelectrochemical Properties of ZnTe-AgInTe2 Solid Solution Nanocrystals

Introduction Much attention has been paid to near-infrared light (NIR)-absorbing and -emitting semiconductor nanocrystals (NCs) due to their unique physicochemical properties, such as tunable energy structure depending on their size and multiple exciton generation. The most widely studied NIR responsive NCs are based on II-VI and IV-VI semiconductors such as CdTe, PbS, and PbSe. However, their high toxicity is an obstacle to practical application of these NCs, because of potential risks for the human health and the environment. Recently, increasing attention has been paid to I-III-VI2 semiconductor NCs such as CuInS2, AgInSe2, and AgInTe2 [1 -2 ] for the application to in vivo imaging or photoenergy conversion system, because they contain no highly toxic heavy metals and have intense photoluminescence (PL) and absorption in near-infrared region. Furthermore their absorption and emission wavelength can be varied by making solid solutions between I-III-VI2 and II-VI semiconductors. We have successfully prepared nanocrystals of ZnS-AgInS2 [2] and ZnSe-AgInSe2 [3] solid solutions and controlled the optical properties by changing their chemical composition. In this study, we report a solution phase synthesis of ZnTe-AgInTe2 solid solution ((AgIn)xZn2(1 - x)Te2, ZAITe) NCs having a tunable optical properties in near-infrared light wavelength region and their photoelectrochemical properties. Experimental ZAITe NCs were synthesized by a thermal reaction of corresponding metal acetates and a Te precursor in 1-dodecanethiol at 180°C for 180 min. Photoelectrochemical properties of ZAITe NCs were measured in an aqueous solution containing 0.2 mol dm-3 Eu(NO3)3as an electron scavenger. The Ag/AgCl electrode and Pt wire were used as reference and counter electrodes respectively. Results and discussions TEM observations revealed that rod-shaped NCs with width of ca. 4 nm and length of ca. 11 nm were formed regardless of chemical composition of particles, that is, the x value. Thus-obtained NCs exhibited broad peaks in their XRD patterns, each peak position being gradually shifted to higher diffraction angle from the corresponding peak of hexagonal AgInTe2 with a decrease in the x value. Figure 1 shows the absorption and PL spectra of ZAITe NCs. The absorption onset was blue-shifted from 1100 to 810 nm with a decrease in x from 1.0 to 0.25. These results indicated that the obtained NCs were composed of ZAITe solid solution, the composition of which could be controlled by varying the fraction of Zn precursor in preparation, and that their energy gap could be varied depending on their chemical composition. The NCs exhibited near-band-edge PL peak located near the corresponding absorption onset except for x = 0.25, the peak wavelength being blue-shifted with a decrease in x value. The main PL peak observed for NCs with x = 0.25 was largely red-shifted from their absorption onset, suggesting that electronic states in band gap, such as donor and acceptor sites or surface defect sites, were formed at the xvalue smaller than 0.5. Layer-by-layer deposition enabled the accumulation of ZAITe NCs on an ITO electrode. The thus-obtained particle films exhibited a photoresponse similar to p-type semiconductor electrode regardless of x value. Action spectra of the photocurrent were in good agreement with absorption spectra of ZAITe NCs immobilized. The potentials of the valence band and conduction band edges were successfully determined from the onset potentials of cathodic photocurrents and the energy gaps estimated from absorption spectra. ZAITe NCs had a tunable electronic energy structure depending on xvalue. These demonstrate the potential use of ZAITe NCs as photovoltaic materials in near-infrared region. Reference [1] M. Langevin et al., Nanoscale Res. Lett., 2015, 10, 255. [2] T. Kameyama, et al., Nanoscale, 2016, 8, 5435. [3] T. Torimoto, et al., J. Am. Chem. Soc., 2007, 129, 12388. [4] T. Kameyama, T. Torimoto, et al., J. Phys. Chem. C, 2015, 119, 24740. Figure 1

Free-standing gold elliptical nanoantenna with tunable wavelength in near-infrared region for enhanced Raman spectroscopy

The purpose of this work is to present a surface-enhanced Raman scattering (SERS) amplifying antenna for the possible usage in the near-infrared region. Instead of the visible-light range amplifying antenna such as a bowtie, the finite-difference time-domain (FDTD) simulation results indicate that elliptical antenna could provide large electromagnetic field enhancement at near-infrared wavelength by combining the free-standing enhancement property with large aspect ratios of the ellipse geometry. The simulation results consist with the enhancement factors characterized by SERS measurements at the excited wavelength of 785 nm for different aspect ratios and periodicities. In addition to the redshift of the resonance wavelength as the aspect ratio of ellipse increases, the free-standing structure modifies the resonance behavior and the dielectric environment of antenna by elevating the elliptical disk from the substrate. To interpret the simulation results, the analytical solution of resonance wavelength for ellipsoid dimmer is derived based on Lorentz–Mie theory, and comparisons are made between the analytical solution and simulation results. The quasi-static analytical solution provides a way to characterize the resonance behavior of two ellipsoid particles as a function of the gap distance, aspect ratio, and dielectric environment. The electrodynamic analysis for the periodic structure was performed in our FDTD simulations.

Narrow-band enhanced absorption of monolayer graphene at near-infrared (NIR) sandwiched by dual gratings

One possibility of enhancing light absorption in monolayer graphene at near-infrared (NIR) wavelength region with grating structures is proposed and investigated. It is demonstrated that it is possible to achieve near-perfect absorption when a single monolayer graphene is sandwiched between two gratings with optimized geometric parameters at normal incidence for transverse electric (TE) polarization. By means of the rigorous coupled-wave analysis (RCWA), the effects of technological tolerances on the optical response of the structure by varying geometric parameters and incident angle are studied. The proposed photonic structure could be efficiently exploited as a building block for innovative optical absorbers or photodetectors in combination with active materials.

Highly transparent conductive Ga doped ZnO films in the near-infrared wavelength range

Highly transparent Ga doped ZnO thin films were prepared on (0001) sapphire substrates by pulsed laser deposition. Hall-effect measurement reveals that electron concentration of the ZnO films can be controlled between 1018 and 1021 cm−3 by adjusting Ga contents in the targets. Optical measurements show the transmittance is above 60 % in the near-infrared wavelength region for all Ga doped ZnO films. Meanwhile, these films also have high crystal quality and smooth surface when the electron concentration up to 1021 cm−3, suggesting that the Ga doped ZnO is a promising material for using as transparent electrode for near infrared optoelectronic devices.

Size-Controlled Synthesis of Near-IR-Light-Emitting AgInTe2 Nanocrystals for Biological Imaging

Near-infrared (NIR)-light-emitting semiconductor nanocrystals (NCs) are regarded as promising biological markers for in vivo imaging due to their chemical stability and tunable emission properties depending on their size. To date, several high-quality NIR-emitting binary semiconductor NCs, such as CdTe, PbS and PbSe, have been developed, but they often contained highly toxic heavy metals such as Cd or Pb, limiting the range of their usage. Recently, we have successfully prepared highly luminescent and low toxic Ag-III-VI2-based multinary semiconductor NCs of ZnS-AgInS2 solid solution by using colloidal synthetic method, where these NCs have tunable photoluminescence (PL) (maximum quantum yield of 80 %) in visible light wavelength region.[1,2] Since an Ag-III-VI2 semiconductor of AgInTe2 was reported to have a bulk band gap of approximately 1.0 eV, size-controlled AgInTe2 NCs show promise as NIR-light-emitting markers. However, with the exception of the recent preparation of spherical, approximately 11-nm AgInTe2 NCs,[3] no attempts have been made to fabricate highly photoluminescent AgInTe2 NCs with sizes less than several tens of nanometers. Here, we report rod-shaped AgInTe2 NCs with controlled widths. The obtained NCs exhibit intense PL and the peak wavelength in the NIR region is tunable by changing the rod width. AgInTe2 NCs were synthesized by a thermal reaction of silver and indium acetates and trioctylphosphine telluride in 1-dodecanethiol at 180-300°C for 10 min under N2 atmosphere. Thus-obtained NCs were isolated by the addition of ethanol and then dissolved in octane to measure their optical properties. In XRD patterns, the NCs prepared at higher than 280°C exhibited three broad peaks corresponding to tetragonal AgInTe2. On the other hand, different diffraction patterns were observed for particles prepared at less than 250°C, which was not consistent with any patterns reported for AgInTe2 or other conceivable crystal phases such as AgIn8Te5, Ag2Te, and In2Te3. We simulated the diffraction patterns of hexagonal crystal structure for bulk AgInTe2 which was in good agreement with XRD pattern of NCs obtained at 180°C. To the best of our knowledge, this is the first report of the formation of hexagonal AgInTe2 including bulk materials. TEM observations revealed that rod-shaped NCs were formed regardless of reaction temperature. The average width of the NCs increased monotonically from 5.5 to 8.3 nm with increasing reaction temperature from 180°C to 300°C, accompanied by an increase in the average length from 11.4 to 13.5 nm. The solutions containing AgInTe2 NCs were deep-black in color due to strong light absorption in the visible and NIR wavelength regions. The NCs exhibited near-band-edge PL peak located near the corresponding absorption onset, and the peak wavelength was red-shifted with increasing reaction temperature as shown in Figure 1. The PL QY was enhanced with a decrease in the width of the rod-shaped AgInTe2 NCs, in which the maximum PL QY of 18% was obtained for the hexagonal phase AgInTe2 NCs prepared at 180°C. Although this value was approximately half of the PL QYs observed for conventional NIR-emissive semiconductor nanocrystals of PbS or PbSe, it was comparable to that of indocyanine green, which has practical uses as a dye for biological imaging. Hence, the relatively intense NIR emission of the AgInTe2 NCs demonstrates their potential use as an NIR marker for biological imaging. Reference [1] T. Torimoto, et al., J. Am. Chem. Soc., 2007, 129, 12388. [2] T. Kameyama, T. Torimoto, et al., J. Phys. Chem. C, 2015, 119, 24740. [3] M. Langevin et al., Nanoscale Res. Lett., 2015, 10, 255. Figure 1

Dispersion curve-based sensitivity engineering for enhanced surface plasmon resonance detection

Manipulation of dispersion curve for enhancing surface plasmon resonance (SPR) detection is proposed. Based on strong correlation between slope of dispersion curve and SPR angle shift, it is confirmed that dispersion curve characteristics can be employed as an analysis tool to evaluate SPR sensor performance and to predict anomalous plasmonic behaviors. Complicated resonance shift in SPR angle, especially in the presence of metallic nanograting, such as negative shift, can be controlled reliably by engineering the dispersion curve. As it has a dependence on geometrical parameters of metallic films and gratings, dispersion relation engineering is also useful in optimizing the sensor sensitivity. For a wavelength of λ=630nm, introduction of a gold nanograting shows a significant improvement in sensitivity by more than 5 times, compared to a traditional thin-film-based SPR structure. In addition, we find that use of a longer wavelength in near-infrared region can be advantageous for avoiding a negative SPR shift and obtaining a narrow and deep SPR curve. Our approach is expected to extend the applicability of dispersion-based sensitivity engineering technique to a variety of SPR platforms for highly enhanced SPR detection.

Performance characteristics of a passively locked cavity-enhanced absorption spectrometer with wideband-tunable multimode near-infrared light source

A trace material detection system was developed on the basis of cavity-enhanced absorption spectroscopy (CEAS) using a fiber-coupled passively locked external cavity diode laser (PLEC-DL) in the near-infrared (NIR) wavelength region. The oscillation range of an antireflection-coated diode laser (AR-DL) coupled into an external cavity could be simply selected with a narrowband bandpass filter (1 nm), resulting in a stable wavelength oscillation in the wideband tunability between 1640 and 1680 nm. The external cavity acts as a trace material sensor that exhibits excellent flexibility because it is free from the DL source and is carefully designed with mirrors having reflectivities of ca. 99.995 and 99.99%. Trace-level detection was successfully demonstrated with the developed sensor having a minimum detectable absorption coefficient of 2.4 × 10−8 cm−1, which corresponds to 0.15 ppm for CH4 concentration without interference from H2O absorption lines under atmospheric pressure.

Crystal phase-controlled synthesis of rod-shaped AgInTe2 nanocrystals for in vivo imaging in the near-infrared wavelength region.

Rod-shaped AgInTe2 nanocrystals (NCs) exhibiting intense near-band edge photoluminescence in the near-infrared (NIR) wavelength region, were successfully prepared by the thermal reaction of metal acetates and Te precursors in 1-dodecanethiol. Increasing the reaction temperature resulted in the formation of larger AgInTe2 NCs with crystal structures varying from hexagonal to tetragonal at reaction temperatures of 280 °C or higher. The energy gap was increased from 1.13 to 1.20 eV with a decrease in rod width from 8.3 to 5.6 nm, accompanied by a blue shift in the photoluminescence (PL) peak wavelength from 1097 to 1033 nm. The optimal PL quantum yield was approximately 18% for AgInTe2 NCs with rod widths of 5.6 nm. The applicability of AgInTe2 NCs as a NIR-emitting material for in vivo biological imaging was examined by injecting AgInTe2 NC-incorporated liposomes into the back of a C57BL/6 mouse, followed by in vivo photoluminescence imaging in the NIR region.

Machining on Rear Surface of a Silicon Substrate by an Infrared Femtosecond Laser via Non-linear Absorption Processes

Silicon (Si) is a semiconductor material widely used in modern technologies such as microelectronics, MEMS, and photonics. Si is an opaque material in visible to near-infrared wavelength region but it transmits any light longer than 1127nm, which corresponds to its band gap energy of 1.12eV. Therefore, Si can be considered as transparent material for radiations longer than 1127nm. Here we have proposed a new laser microprocessing method of Si, which increases the efficiency, accuracy and flexibility in machining. The thickness of the Si substrate used was 320μm and a femtosecond laser at 1552nm was focused by a 100x infrared objective lens on the rear surface of the substrate. However, only a shallow groove was formed: its depth was approximately 170nm or less. It is expected that when the laser is focused on the Si rear surface, where it is contacting with an etchant, wet etching will occur due to the temperature rise caused by the laser irradiation. Therefore, to increase the machining rate, we tried laser-assisted backside wet-etching using KOH solution as the etchant. The maximum groove depth was increased to more than 3μm. The effects of laser irradiation conditions on machined grooves were examined. The results achieved showed rather scattered values and indicated that the maximum groove depth was not always produced at high energy deposition conditions. One of the reasons might be the formation of hydrogen bubbles from the chemical reaction between Si and KOH, which block the contact of Si and KOH.

Nanoporous TiO2-Based Distributed Bragg Reflectors for Near-Infrared Wavelength Applications.

We reported the fabrication and characteristics of distributed Bragg reflectors (DBRs), made of titanium dioxide (TiO2) dense/nanoporous film stacks, operating in the near-infrared wavelength region of 0.8-1.1 μm. To form the nanoporous TiO2 films with a low refractive index (low-n), the oblique angle deposition (OAD) technique was employed at a high incident vapor flux angle of 80 degrees. For the fabricated DBRs consisting of TiO2 dense/nanoporous (high-n/low-n) thin films, the high reflectance band was gradually increased and the stop bandwidth was narrowed with increasing the number of DBR pairs. Particularly, the TiO2 DBR with only 6 pairs exhibited a normalized stop bandwidth (Δλ/λ(c)) of -11.6% at a center wavelength (λ(c)) of 0.96 μm as well as high reflectance values of > 95% over a wide mid-infrared wavelength region of 0.9-1.01 μm (i.e., Δλ = 0.111 μm). Furthermore, the reflectance characteristics were investigated at incident light angles of 20-70 degrees for different polarized lights. For theoretical optical analyses, the reflectance calculations were also performed by a rigorous coupled-wave analysis method, showing a similar tendency to the experimentally measured data.

Shoreline detection, in Tanjung Piai, Malaysia by improving the low brightness and contrast of SPOT-5 images using the NIR-HE method

ABSTRACTSatellite images taken in hazy conditions tend to have low brightness and contrast, and to address this problem, a simple and optimised method using near-infrared (NIR) histogram equalisation has been proposed, in order to improve the brightness and contrast of the SPOT-5 images taken by satellite. This helps to improve the detection of shoreline with a higher efficiency in edge detection, and produces results with a high success rate of more than 90%. In order to remove haze from SPOT-5 images, a false colour composite is used to prevent misclassified pixels of the shoreline, and ensure minimal error in image classification. The presence of an NIR channel is suitable for the detection of vegetation and waterbodies. The NIR channel is important for this study, in ensuring that contrast between vegetated areas and sea can be clarified, due to the high reflectance of vegetation leaves in the NIR wavelength region. This research used three areas of interest to show different results in shoreline detection. The results showed that the proposed method performed better than existing methods, when dealing with the low brightness or contrast ratio of SPOT-5 images.

Stable metallic 1T-WS2 ultrathin nanosheets as a promising agent for near-infrared photothermal ablation cancer therapy

In this study, we present the preparation of stable 1T-WS2 ultrathin nanosheets with NH4+ intercalation using a bottom-up hydrothermal method and the potential application of this material in light-induced photothermal cancer therapy. Our results revealed that nanosheets with a size of 150 nm were highly hydrophilic and exhibited strong light absorption and excellent photostability in the broad near-infrared wavelength region. The in vitro experimental results indicated good biocompatibility of the nanosheets. More notably, our in vivo antitumor experiments illustrated that light-induced photothermal ablation originating from irradiation of the 1T-WS2 nanosheets with an 808 nm laser could efficiently kill tumor cells; these effects were obtained not only at the cellular level but also in the living organs of mice. This result may lead to new applications of two-dimensional layered materials in novel photothermal therapies and other photothermal related fields.

Signal enhancement in multiphoton imaging by the use of coated glass substrates.

In nonlinear optical imaging of biological specimens, more than half of the generated luminescence signal is lost, when signal collection is performed in the epi-illuminated geometry. In this study, we enhanced the collected luminescence signal by the use of alternating multiply-coated layers of tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2) on standard microscope cover glasses that has high transmission in the near-infrared wavelength region and high reflection of the visible, luminescence signal. Our coating is biocompatible, allows visual examination of the specimens and optimize collection of the luminescence signal. We demonstrated this approach on a number of specimens including sulforhodamine solution, fluorescence microspheres, and labeled 3T3 cells. In all cases, the use of coated cover glass enhanced signal, optimally by a factor of about 2. Image analysis of labeled 3T3 cells also shows signal enhancement did not contribute to additional photobleaching. Our results show that properly designed coated cover glass can enhance detected signal in multiphoton microscopy and result in improved image quality.

Evaluation of light scattering and absorption properties of in vivo rat liver using a single-reflectance fiber probe during preischemia, ischemia-reperfusion, and postmortem.

Diffuse reflectance spectroscopy (DRS) has been extensively used for characterization of biological tissues as a noninvasive optical technique to evaluate the optical properties of tissue. We investigated a method for evaluating the reduced scattering coefficient μ(s)', the absorption coefficient μ(a), the tissue oxygen saturation StO₂, and the reduction of heme aa3 in cytochrome c oxidase CcO of in vivo liver tissue using a single-reflectance fiber probe with two source-collector geometries. We performed in vivo recordings of diffuse reflectance spectra for exposed rat liver during the ischemia-reperfusion induced by the hepatic portal (hepatic artery, portal vein, and bile duct) occlusion. The time courses of μ a at 500, 530, 570, and 584 nm indicated the hemodynamic change in liver tissue as well as StO₂. Significant increase in μ(a)(605)/μ(a)(620) during ischemia and after euthanasia induced by nitrogen breathing was observed, which indicates the reduction of heme aa3, representing a sign of mitochondrial energy failure. The time courses of μ(s)' at 500, 530, 570, and 584 nm were well correlated with those of μ(a), which also reflect the scattering by red blood cells. On the other hand, at 700 and 800 nm, a temporary increase in μ(s)' and an irreversible decrease in μ(s)' were observed during ischemia-reperfusion and after euthanasia induced by nitrogen breathing, respectively. The change in μ(s)' in the near-infrared wavelength region during ischemia is indicative of the morphological changes in the cellular and subcellular structures induced by the ischemia, whereas that after euthanasia implies the hepatocyte vacuolation. The results of the present study indicate the potential application of the current DRS system for evaluating the pathophysiological conditions of in vivo liver tissue.