Detection of hepatocarcinoma in rats by integration of the fluorescence spectrum: Experimental model

The incorporation of spectroscopic techniques into diagnostic procedures may greatly improve the chances for precise diagnostics. One promising technique is fluorescence spectroscopy, which has recently been used to detect many different types of diseases. In this work, we use laser-induced tissue fluorescence to detect hepatocarcinoma in rats using excitation light at wavelengths of 443 and 532 nm. Hepatocarcinoma was induced chemically in Wistar rats. The collected fluorescence spectrum ranges from the excitation wavelength up to 850 nm. A mathematical procedure carried out on the spectrum determines a figure of merit value, which allows the detection of hepatocarcinoma. The figure of merit involves a procedure which evaluates the ratio between the backscattered excitation wavelength and the broad emission fluorescence band. We demonstrate that a normalization allowed by integration of the fluorescence spectra is a simple operation that may allow the detection of hepatocarcinoma.     

Enhancing molecular formation in a Rb-MOT

In this paper, we report observation of an enhancement of the ground state molecule Rb₂ formation in a Rb magneto-optical trap due to a photoassociation laser. Such an enhancement effect is due to flux enhancement of atomic pairs at short internuclear distances. Our experimental observations consist in the measurement of the molecular formation rate constant due to a probe laser as a function of the trap laser intensity. The results are compared with a simple semi-classical model, showing good agreement. We conclude that the production of cold Rb₂ may be enhanced using appropriate laser parameters; this may be useful for future experiments involving production and trapping of ultracold ground state molecules.     

Structural determination of 5'-OH alpha-ribofuranoside modified cobalamins via 13C and DEPT NMR

A protocol for the rapid NMR characterization of cobalamin (vitamin B(12)) analogues with 5'-hydroxy-alpha-ribofuranoside modification is reported. The structure of cyanocobalamin in DMSO-d(6) has been assigned using COSY, NOESY, HSQC, and HMBC NMR methods. The robust precision of (13)C NMR assignments in DMSO-d(6) allows for the rapid structural determination of 5'-hydroxy-alpha-ribofuranosyl cyanocobalamin derivatives with solely 1-D (13)C and DEPT NMR spectra and only 10 mg of derivatized cobalamin. Using this method, the (13)C NMR resonances of four cobalamin analogues were determined with the most significant variance of (13)C chemical shifts occurring in the alpha-ribofuranoside ring. In DMSO-d(6), cobalamin concentrations greater than 30 mM can be achieved for an improved signal-to-noise ratio.     

Alternative to the hyperfine-change-collision interpretation for the behavior of magneto-optical-trap losses at low light intensity

Usually, the large trap loss rates observed in MOTs at the low light intensity regime have been associated with hyperfine change collisions (HCC). We propose an alternative mechanism to explain the sudden raise up of trap loss rates at low intensity without relying on HCC. Using the Gallagher-Pritchard model [Phys. Rev. Lett. 63, 957 (1989)] together with an intensity dependent escape velocity, we were able to reproduce qualitatively well some existing experimental results, including recent observations by Nesnidal et al. [Phys. Rev. A 62, 030701(R) (2000)]. This result reopens the discussion in order to better understand the physical mechanisms and their actual contribution to the trap losses.     

Previous illumination of a water soluble chlorine photosensitizer increases its cytotoxicity

Photodithazine (PDZ) is an N-methyl-D-glucosamine derivative of chlorine e6 that is water soluble and has an intense absorption in the range of 650?C680 nm. PDZ photobleaching and photoproduct formation were induced by illumination with laser at two wavelengths: 514 nm (ion argon laser) as well as in 630 nm (dye laser). The time constants of PDZ photobleaching were: 18 min for 630 nm irradiation and 50 min for 514 nm irradiation, suggesting that degradation after irradiation with red light is faster than with green light. Photoproducts formation was evidenced by the appearance of a new absorption band at 668 nm with slight broaden of the Soret band, suggesting that there was no break of the macrocycle. The cytotoxicity of the photodegradated PDZ was investigated and showed to be lower in the dark and higher than non irradiated PDZ. These results may have important clinical implications for PDT such as the possibility to use the previously irradiated PDZ just before clinical application in order to get increased efficiency.     

Femtosecond laser ablation profile near an interface: Analysis based on the correlation with superficial properties of individual materials

Femtosecond laser ablation of materials is turning to be an important tool for micromachining as well as for selective removal of biological tissues. In a great number of applications, laser ablation has to process through interfaces separating media of different properties. The investigation of the ablation behavior within materials and passing through interfaces is the main aim of this study. Especially, the analysis of the discontinuity in the ablation profile close to interfaces between distinct materials can reveal some of the phenomena involved in the formation of an ablated microcavity geometry. We have used a method that correlates the ablation cross sectional area with the local laser intensity. The effective intensity ablation properties were obtained from surface ablation data of distinct materials. The application of this method allows the prediction of the occurrence of a size discontinuity in the ablation geometry at the interface of distinct media, a fact which becomes important when planning applications in different media.     

Thermal and structural properties of commercial dental resins light-cured with blue emitting diodes (LEDs)

We have investigated the thermal and structural properties of different commercial dental resins: Filtek^TM Z-350, Grandio^®, Tetric Ceram^®, and TPH Spectrum^®. The purpose of the present study was to evaluate quantitatively the photo-polymerization behavior and the effect of filler contents on the kinetic cures of the dental resins by using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FT-IR) techniques. We have successfully obtained the low and high glass transition T _g values of the dental composite resins from DSC curves. It was also observed a good agreement between the both T _g values, activation energies from thermal degradation, and the degree of conversion obtained for all samples. The results have shown that Tetric Ceram^® dental resin presented the higher T _g values, activation energy of 215 ± 6 KJ mol^?1, and the higher degree of conversion (63%) when compared to the other resins studied herein.     

Direct determination of total mercury in phosphate rock using alkaline fusion digestion

The aim of this work was to develop a new method to determine the mercury (Hg) concentrations in phosphate rock using a dedicated analytical instrument (the DMA80 Tricell by Milestone) that employs an integrated sequence of thermal decomposition followed by catalyst conversion, amalgamation and atomic absorption spectrophotometry. However, this instrument underestimates Hg concentrations when phosphorite and apatite rocks are investigated with a classic thermal decomposition treatment that complies with US EPA method 7473.     

Chemiluminescence as a PDT light source for microbial control

The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem? concentration varied from 0 to 75 μg/ml and the illumination time varied from 60 min to 240 min.The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at μW/cm2 level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources.