Excitation Wavelength Λex Research Articles

Cell‐Mediated Assembly of Phototherapeutics

AbstractLight‐activatable drugs offer the promise of controlled release with exquisite temporal and spatial resolution. However, light‐sensitive prodrugs are typically converted to their active forms using short‐wavelength irradiation, which displays poor tissue penetrance. We report herein erythrocyte‐mediated assembly of long‐wavelength‐sensitive phototherapeutics. The activating wavelength of the constructs is readily preassigned by using fluorophores with the desired excitation wavelength λex. Drug release from the erythrocyte carrier was confirmed by standard analytical tools and by the expected biological consequences of the liberated drugs in cell culture: methotrexate, binding to intracellular dihydrofolate reductase; colchicine, inhibition of microtubule polymerization; dexamethasone, induced nuclear migration of the glucocorticoid receptor.

DNA Damage Processing by Human 8-Oxoguanine-DNA Glycosylase Mutants with the Occluded Active Site

8-Oxoguanine-DNA glycosylase (OGG1) removes premutagenic lesion 8-oxoguanine (8-oxo-G) from DNA and then nicks the nascent abasic (apurinic/apyrimidinic) site by β-elimination. Although the structure of OGG1 bound to damaged DNA is known, the dynamic aspects of 8-oxo-G recognition are not well understood. To comprehend the mechanisms of substrate recognition and processing, we have constructed OGG1 mutants with the active site occluded by replacement of Cys-253, which forms a wall of the base-binding pocket, with bulky leucine or isoleucine. The conformational dynamics of OGG1 mutants were characterized by single-turnover kinetics and stopped-flow kinetics with fluorescent detection. Additionally, the conformational mobility of wild type and the mutant OGG1 substrate complex was assessed using molecular dynamics simulations. Although pocket occlusion distorted the active site and greatly decreased the catalytic activity of OGG1, it did not fully prevent processing of 8-oxo-G and apurinic/apyrimidinic sites. Both mutants were notably stimulated in the presence of free 8-bromoguanine, indicating that this base can bind to the distorted OGG1 and facilitate β-elimination. The results agree with the concept of enzyme plasticity, suggesting that the active site of OGG1 is flexible enough to compensate partially for distortions caused by mutation.

Mechanism of the subband excitation of photoluminescence from erbium ions in silicon under high-intensity optical pumping

The photoluminescence (PL) excitation spectra of erbium and band-to-band silicon in Si:Er/Si epitaxial structures under high-intensity pulsed optical excitation are studied. It is shown that the nonmonotonic dependence of the PL intensity on the excitation wavelength λex near the absorption edge of silicon is due to inhomogeneity in the optical excitation of the Si:Er active layer. The sharp rise in the erbium PL intensity in the spectral range λex = 980−1030 nm is due to an increase in the excited part of the Si:Er emitting layer on passing to subband light pumping (λex > 980 nm) with a low absorption coefficient in silicon because of the effective propagation of the excitation light in the bulk of the structures under study. It is shown that, under the subband optical pumping of Si:Er/Si structures, as also in the case of interband pumping, the exciton mechanism of erbium ion excitation is operative. Excitons are generated under the specified conditions as a result of a two-stage absorption process involving impurity states in the band gap of silicon.

Multispectral Endoscopic Imaging of Colorectal Dysplasia In Vivo

Light provides a broad range of colors in the visible and near-infrared (400–900 nm) spectrum that can be used to transmit information about molecular expression in normal and diseased tissues. The absorbance spectrum of hemoglobin, the primary chromophore in tissue, is shown in Fig. 1A. Genetic changes that occur in cancer transformation can be heterogeneous, and several signaling pathways may be activated concurrently.1 Moreover, molecular activity levels may vary between individual patients, at different time points, and within the tumor. Thus, a single genetic mutation is unlikely to characterize most disease processes over a general population. Unfortunately, most endoscopic imaging methods are sensitive to only one molecular parameter.2 Thus, a methodology that can image multiple molecular targets simultaneously is better suited to address the heterogeneity of cancer and achieve disease detection with high sensitivity and specificity desired for efficient surveillance. In addition, these multiplexed strategies can potentially visualize the interactions between signaling pathways and allow for better understanding of disease pathogenesis on a systems level. Figure 1 A) The visible and near-infrared spectrum of light provides a broad range of colors to generate molecular images from digestive tract mucosa that can be collected with a B) 1.6 mm diameter multispectral scanning fiber endoscope. C) Excitation is delivered ... Recently, significant progress has been made in advancing new methods of endoscopic imaging to target disease in the digestive tract, including the development of novel instruments and specific contrast agents.3 In this video journal, we aim to demonstrate the application of a novel, multispectral endoscope that uses a scanning fiber to image multiple targets at the same time. Fluorescence imaging can be achieved with high target-to-background ratios, and allow us to see the different target expression patterns in an Apc-mutation dependent mouse model of spontaneous colorectal adenomas using multiple peptides as targeting ligands.4

Chemical Trapping of the Dynamic MutS-MutL Complex Formed in DNA Mismatch Repair in Escherichia coli

The ternary complex comprising MutS, MutL, and DNA is a key intermediate in DNA mismatch repair. We used chemical cross-linking and fluorescence resonance energy transfer (FRET) to study the interaction between MutS and MutL and to shed light onto the structure of this complex. Via chemical cross-linking, we could stabilize this dynamic complex and identify the structural features of key events in DNA mismatch repair. We could show that in the complex between MutS and MutL the mismatch-binding and connector domains of MutS are in proximity to the N-terminal ATPase domain of MutL. The DNA- and nucleotide-dependent complex formation could be monitored by FRET using single cysteine variants labeled in the connector domain of MutS and the transducer domain of MutL, respectively. In addition, we could trap MutS after an ATP-induced conformational change by an intramolecular cross-link between Cys-93 of the mismatch-binding domain and Cys-239 of the connector domain.

A Note on Determining the Extent of the Water Raman Peak in Fluorescence Spectroscopy

A method is proposed for automatically determining the upper and lower boundaries of the Raman scatter peak in fluorescence spectroscopy from empirical data. Accurate peak boundaries are needed to calculate accurate Raman peak areas, used for normalizing fluorescence signals to produce data in units that are comparable between instruments. Comparisons of Raman peak boundaries across nine individual instruments (FluoroMax 3 (FM3) fluorometers from HORIBA Jobin Yvon and Cary Eclipse (CE) fluorometers from Varian Inc.) at the excitation wavelength λex = 350 nm reveal consistent results. At 350 nm excitation, the Raman peak was confined by the emission wavelengths of 382–418 nm, with boundaries determined for the FM3 fluorometers deviating by no more than 0.5 nm and 1.5 nm with respect to the start and end of the peak, and CE fluorometers deviating by up to 1.5 nm and 2 nm, respectively. Peak width was a function of fluorometer type and excitation wavelength. For the FM3 instruments, widths increased from approximately 30 nm at λex = 300 nm to 40 nm at λex = 380 nm, while for the CE instruments, peaks were approximately 5–8 nm narrower. Code for implementing the procedure in MATLAB, which allows for the adjustment of input parameters to compensate for noisy data, is provided in the Supplemental Material (available online).

Characterization of Vegetable Oils by Fluorescence Spectroscopy

Results presented in this paper show the ability to analyze vegetable oils with very cheap and easy method based on fluorescence spectroscopy. We have recorded, with a very simple experimental set up, fluorescence spectra for several vegetable oils at excitation wavelength λex = 370 nm. After deconvolution, using a Lorentzian profile, and identification of the stripes forming the spectra, a normalization of the intensities was made with respect to the vitamin E band with λ= 525 nm taken as reference. A statistical method based on Principal Component Analysis (PCA) is used to emphasize differences between refined and unrefined oils. We also noticed a significant difference between fluorescence of the argan cosmetic oil and edible argan oil due to the heating of the second one during its preparation. Stability to thermal oxidation of high oleic sunflower oil compared to the extra virgin olive, argan cosmetic and refined corn oils is also shown.

Characterizing lamina propria of human gastric mucosa by multiphoton microscopy

Lamina propria (LP) of gastric mucosa plays an important role in progression of gastric cancer because of the site at where inflammatory reactions occur. Multiphoton imaging has been recently employed for microscopic examination of intact tissue. In this paper, using multiphoton microscopy (MPM) based on two-photon excited fluorescence (TPEF) and second harmonic generation (SHG), high resolution multiphoton microscopic images of lamina propria (LP) are obtained in normal human gastric mucosa at excitation wavelength λex = 800 nm. The main source of tissue TPEF originated from the cells of gastric glands, and loose connective tissue, collagen, produced SHG signals. Our results demonstrated that MPM can be effective for characterizing the microstructure of LP in human gastric mucosa. The findings will be helpful for diagnosing and staging early gastric cancer in the clinics.

Studies on the growth of pure double-walled carbon nanotube and its phonon spectra

Double-walled carbon nanotubes (DWCNTs) with a purity higher than 99% were synthesized by chemical vapor deposition, and their Raman spectra were observed at different excitation wavelengths λex. The spectra had a unique feature compared with single-walled carbon nanotubes (SWCNTs): the G-band shape was distinctly different from that of SWCNTs and showed a clear λex dependence. The pure DWCNT samples showed complex radial breathing modes (RBM) spectra. The mode peaks were unambiguously classified into those for the inner and outer tubes by applying a simple analytic model considering the interwall interaction. After isolation treatment of the pure bundled samples, we observed RBM signals of DWCNTs having an identical inner tube with different outer tubes. The peculiar behavior of the G-band shape was interpreted by resonance enhancement of the outer tube.

The Influence of Processing Parameters on Photoluminescent Properties of Ba2ZnS3:Mn Phosphors by Double-Crucible Method

AbstractRed light emitting of Mn2+doped Ba2ZnS3phosphor powders have been synthesized by double-crucible method at different thermal treatments. XRD results indicate that the raw materials are completely sulfurized above 950°C, and the Ba2ZnS3: Mn2+powders don't change its orthorhombic crystal structure with increasing doping concentration from 0 to 0.8 mol%. The photoluminescence of Ba2ZnS3: Mn2+powders fulfilled the most efficient emission at the excitation wavelength λex=358 nm and showed the red emission light with peak wavelength λem=627nm at the doping concentration of Mn2+ion between 0.2 and 0.8 mol%. The high-luminance red emission results from the4T1(4G)—6A1(6S) transition in the Mn2+ion. Ba2ZnS3: Mn2+phosphors synthesized by double-crucible method have broad emission spectra (550nm∼750nm) with FWHM (full width at half maximum broadband) about 66nm. In our research, the Ba2ZnS3doped with 0.4 mol% Mn2+has the highest luminescent intensity as thermal treatment at 950°C for 16 hours and the CIE coordinate is x=0.66, y=0.33.

On the syntheses and photochemical properties of heterocyclic ketones as photosensitizers

The syntheses, and the electrochemical and photochemical properties of the fluorenone analogues 9H-pyrrolo[1,2-a]indole-9-one (1), and 9H-pyrido[3,4,b] pyrrolizin-9-one (2), which absorb in the visible region (ε400nm = 4711 mol−1 cm−1 for 1 and ε400nm = 872 1 mol cm−1 for 2), are described. 9-Fluorenone as well as compounds 1 and 2 were able to reduce methyl viologen in the presence of 2-propanol under irradiation with UV light (λ⪢ 280 nm). Compounds 1 and 2 showed an interesting absorption and fluorescence behavior depending on concentration, solvent and pH value. Aqueous solutions of compound 1 gave two fluorescence maxima at 395 and 478 nm, when excited by λEX = 302 and 368 nm, respectively. In contrast, aqueous solutions of compound 2 showed only one emission maximum at 417 nm (excited by λEX = 296 or 378 nm). Fluorescence quantum yields (solvent: propanol, excitation wavelength λEx = 436 nm) for compounds 1 and 2 were 0.2%. Compounds 1 and 2 showed irreversible reduction potentials at −850 and −560 mV (vs NHE), respectively. The results were compared with benzophenone and 9-fluorenone.