Photosynthesis on the Ultrafast Time Scale within the Confinements of Quantum Nanostructured Photosystems.

Fundamental information on the behavior of excited chlorophyll molecules packed within the confinements of nanosized photosystems I and II, following absorption of light, is presented. Using a 100 femtosecond laser with nanojoule (nJ) pulse energy and a one picosecond streak camera, we observed the light emitted from the nanostructured photosystems without oscillations or hops. The fluorescent exponential decay profiles and high efficiency within the nanostructure suggest that light coherently drains out as a unit. This implies that "quantumness" is linked to quantum confinement on the nano scale.

Enhanced stimulated raman scattering of solvent due to anharmonic energy transfer from resonance raman solute molecules.

A new nonlinear optical process, named enhanced stimulated Raman scattering (ESRS), is reported for the first time from resonance Raman in ß-carotene-methanol solution. It is well known that absorption decreases the efficiency of the nonlinear optical and laser processes; however, we observed enhanced stimulated Raman peaks at the first and second Stokes from methanol solvent at 2834 cm-1 with the addition of ß-carotene solutes. This enhanced SRS effect in methanol is attributed to the resonance Raman (RR) process in ß-carotene, which creates a significant number of vibrations from RR and the excess vibrations are transferred to methanol from anharmonic vibrational interactions between the ß-carotene solutes and the methanol solvent, and consequently leads to the increased Raman gain.

Comparison of continuous wave versus picosecond SRS and the resonance SRS effect.

Stimulated Raman scattering (SRS) is a powerful optical technique for probing the vibrational states of molecules in biological tissues and provides greater signal intensities than when using spontaneous Raman scattering. In this study, we examined the use of continuous wave (cw) and picosecond (ps) laser excitations to generate SRS signals in pure methanol, a carotene-methanol solution, acetone, and brain tissue samples. The cw-SRS system, which utilized two cw lasers, produced better signal-to-noise (S/N) than the conventional ps-SRS system, suggesting that the cw-SRS system is an efficient and cost-effective approach for studying SRS in complex systems like the brain. The cw-SRS approach will reduce the size of the SRS system, allowing for stimulated Raman gain/loss microscopy. In addition, we showed that there exists a resonance SRS (RSRS) effect from the carotene-methanol solution and brain tissue samples using cw laser excitations. The RSRS effect will further improve the signal-to-noise and may be utilized as an enhanced, label-free SRS microscopic tool for the study of biological tissues.

Alzheimer mouse brain tissue measured by time resolved fluorescence spectroscopy using single- and multi-photon excitation of label free native molecules.

Time resolved spectroscopic measurements with single-photon and multi-photon excitation of native molecules were performed ex vivo on brain tissues from an Alzheimer's disease (AD) and a wild type (WT) mouse model using a streak camera. The fluorescence decay times of native NADH and FAD show a longer relaxation time in AD than in WT tissue, suggesting less non-radiative processes in AD. The longer emission time of AD may be attributed to the coupling of the key native building block molecules to the amyloid-tau and/or to the caging of the native fluorophores by the deposition of amyloid-beta or tau plaques and neurofibrillary tangles that affect the local non-radiative interactions.

Near-infrared supercontinuum laser beam source in the second and third near-infrared optical windows used to image more deeply through thick tissue as compared with images from a lamp source.

With the use of longer near-infrared (NIR) wavelengths, image quality can be increased due to less scattering (described by the inverse wavelength power dependence 1/λ(n) where n ≥ 1 ) and minimal absorption from water molecules. Longer NIR windows, known as the second (1100 nm to 1350 nm) and third (1600 to 1870 nm) NIR windows are utilized to penetrate more deeply into tissue media and produce high-quality images. An NIR supercontinuum (SC) laser light source, with wavelengths in the second and third NIR optical windows to image tissue provides ballistic imaging of tissue. The SC ballistic beam can penetrate depths of up to 10 mm through tissue.

Differences in fluorescence profiles from breast cancer tissues due to changes in relative tryptophan content via energy transfer: tryptophan content correlates with histologic grade and tumor size but not with lymph node metastases.

The correlation between histologic grade, an increasingly important measure of prognosis for patients with breast cancer, and tryptophan levels from tissues of 15 breast carcinoma patients was investigated. Changes in the relative content of key native organic biomolecule tryptophan were seen from the fluorescence spectra of cancerous and paired normal tissues with excitation wavelengths of 280 and 300 nm. Due to a large spectral overlap and matching excitation­emission spectra, fluorescence resonance energy transfer from tryptophan-donor to reduced nicotinamide adenine dinucleotides-acceptor was noted. We used the ratios of fluorescence intensities at their spectral emission peaks, or spectral fingerprint peaks, at 340, 440, and 460 nm. Higher ratios correlated strongly with high histologic grade, while lower-grade tumors had low ratios. Large tumor size also correlated with high ratios, while the number of lymph node metastases, a major factor in staging, was not correlated with tryptophan levels. High histologic grade correlates strongly with increased content of tryptophan in breast cancer tissues and suggests that measurement of tryptophan content may be useful as a part of the evaluation of these patients.

Deep two-photon microscopic imaging through brain tissue using the second singlet state from fluorescent agent chlorophyll α in spinach leaf.

Two-photon (2P) excitation of the second singlet (S2) state was studied to achieve deep optical microscopic imaging in brain tissue when both the excitation (800 nm) and emission (685 nm) wavelengths lie in the "tissue optical window" (650 to 950 nm). S2 state technique was used to investigate chlorophyll α (Chl α) fluorescence inside a spinach leaf under a thick layer of freshly sliced rat brain tissue in combination with 2P microscopic imaging. Strong emission at the peak wavelength of 685 nm under the 2P S2 state of Chl α enabled the imaging depth up to 450 µm through rat brain tissue.

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.

Optical spectral fingerprints of tissues from patients with different breast cancer histologies using a novel fluorescence spectroscopic device.

The fluorescence of paired human breast malignant and normal tissue samples was investigated using a novel fluorescence spectroscopic (S3-LED) ratiometer unit with no moving parts. This device can measure the emission spectra of key native organic biomolecules such as tryptophan, tyrosine, collagen and elastin within tissues by using LED (light emitting diode) excitation sources coupled to an optical fiber. With this device, the spectral profiles of 11 paired breast cancerous and normal samples from 11 patients with breast carcinoma were obtained. In each of the 11 cases, marked increases in the tryptophan levels were found in the breast carcinoma samples when compared to the normal breast tissues. In the breast cancer samples, there were also consistently higher ratios of the 340 to 440 nm and the 340 to 460 nm intensity peaks after 280 nm excitation, likely representing an increased tryptophan to NADH ratio in the breast cancer samples. This difference was seen in the spectral profiles of the breast cancer patients regardless of whether they were HER2 positive or negative or hormone receptor positive or negative, and was found regardless of menopausal status, histology, stage, or tumor grade.

Aorta and skin tissues welded by near-infrared Cr4+:YAG laser.

OBJECTIVE: The aim of our study was to explore the wavelength dependence of welding efficacy. Ex vivo samples of human and porcine aorta and skin tissues were investigated using a tunable Cr(4+):yttrium aluminum garnet (YAG) laser. BACKGROUND DATA: Tissue welding is possible using laser light in the NIR spectral range. Collagen bonding in the tissue induced by thermal, photothermal, and photochemical reactions-or a combination of all of these-is thought to be responsible for tissue welding. Laser tissue welding (LTW) has gained success in the laboratory using animal models. Transition from laboratory to clinical application requires the optimization of welding parameters. MATERIALS AND METHODS: A near-infrared (NIR) Cr(4+):YAG laser was used to weld ex vivo samples of human and porcine aorta and skin at wavelengths from 1430 to 1470 nm. Welding efficacy was monitored by measuring the tensile strength of the welded tissue and the extent of collateral tissue damage. Tensile strengths were measured using a digital force gauge. Changes in tissue morphology were evaluated using optical and scanning electron microscope (SEM). Fluorescence imaging of the welded areas was also used to evaluate molecular changes following tissue welding. RESULTS: Full-thickness tissue bonding was observed with porcine aorta samples. No collateral damage of the aorta samples was observed. Tissue denaturation was observed with human aorta, human skin, and porcine skin samples. The optimum tensile strength for porcine and human aorta was 1.33 +/- 0.15 and 1.13 +/- 0.27 kg/cm2, respectively, at 1460 nm, while that for porcine and human skin was 0.94 +/- 0.15 and 1.05 +/- 0.19 kg/cm2, respectively, achieved at 1455 nm. The weld strength as a function of wavelength demonstrated a correlation with the absorption spectrum of water. Fluorescence imaging of welded aorta and skin demonstrated no significant changes in collagen and elastin emission at the weld site. CONCLUSION: The observation that welding strength as a function of wavelength follows the absorption bands of water suggests that absorption of light by water plays a significant role in laser tissue welding.