Optical properties and antimicrobial effects of silver nanoparticles synthesized by femtosecond laser photoreduction

Silver nanoparticles exhibit a powerful antimicrobial action showing a pronounced potential to be widely used against drug resistance bacteria. The present work describes the optical properties and antimicrobial effect of silver nanoparticles produced by femtosecond laser photoreduction of AgNO3 in the presence of tryptophan water solution. The advantages of this method are the absence of hazardous chemical reducing agents in the solution, and the versatile dimensional control achieved. The synthesized silver nanoparticles were characterized by absorption and fluorescence spectroscopy and their antibacterial activity were determined by monitoring the cell viability of Escherichia coli. The effects of the silver nanoparticles concentration and laser parameters (exposure time and pulse energy), on the formation of the nanoparticles, and its influence on the bacteria growth inhibition were studied. The prepared silver nanoparticles exhibited suitable antimicrobial properties. The results demonstrated that the nanoparticles concentration plays an important role in their bactericidal efficacy. The increase in the laser energy caused an increase in E. coli growth inhibition. Irradiations with energies around 300?µJ for 60?min presented high antimicrobial activity due to the presence of kynurenine, sub product of tryptophan photolysis. The first-time formation mechanism of tryptophan silver nanoparticles in high optical intensities was also discussed.

Optical properties and antimicrobial effects of silver nanoparticles synthesized by femtosecond laser photoreduction

Silver nanoparticles exhibit a powerful antimicrobial action showing a pronounced potential to be widely used against drug resistance bacteria. The present work describes the optical properties and antimicrobial effect of silver nanoparticles produced by femtosecond laser photoreduction of AgNO3 in the presence of tryptophan water solution. The advantages of this method are the absence of hazardous chemical reducing agents in the solution, and the versatile dimensional control achieved. The synthesized silver nanoparticles were characterized by absorption and fluorescence spectroscopy and their antibacterial activity were determined by monitoring the cell viability of Escherichia coli. The effects of the silver nanoparticles concentration and laser parameters (exposure time and pulse energy), on the formation of the nanoparticles, and its influence on the bacteria growth inhibition were studied. The prepared silver nanoparticles exhibited suitable antimicrobial properties. The results demonstrated that the nanoparticles concentration plays an important role in their bactericidal efficacy. The increase in the laser energy caused an increase in E. coli growth inhibition. Irradiations with energies around 300?µJ for 60?min presented high antimicrobial activity due to the presence of kynurenine, sub product of tryptophan photolysis. The first-time formation mechanism of tryptophan silver nanoparticles in high optical intensities was also discussed.

Microtensile bond strength to Er: YAG laser pretreated dentin / Avaliação da adesão em dentina irradiada pelo laser de Er: YAG

Objective: Although the effects of Er:YAG (erbium:yttrium aluminium garnet) laser on cavity preparation as well as on dentin bonding to composite have been described in the literature, the longevity of this bond is still unknown. So, this study evaluated the short-term microtensile bond strength to dentin samples after different protocols of surface treatment. Materials and Methods: 60 bovine incisors were cleaned, worn to expose a dentin area and subdivided into groups according to treatment conditions: surface treatment (no irradiation – control group; dentin irradiation with Er:YAG laser 250 mJ/4 Hz; 160 mJ/10 Hz), adhesive system (Clearfil SE Bond - Kuraray; Adper Single Bond 2 - 3M/ESPE), and storage time (24 h; 90 days). After adhesive procedures, a block of Z250 composite resin (3M/ESPE) was built-up on each tooth. The teeth were sectioned to obtain samples for the microtensile bond strength test. Half of the samples were tested 24 h after cutting, and the other half were stored in distilled water for 90 days before testing. Intergroup analysis was also performed considering the same variables using ANOVA for multiple comparisons with Tukey test with a significance level of 5%. Data showed weaker bond strength for groups previously treated with laser (p < 0.05) compared with control groups, and these were not influenced by adhesive system used, nor by storage period. Stereoscopic microscope observations showed that fractures occurred predominantly at the adhesive interface in the groups irradiated with the Er:YAG laser. Conclusion: Within the parameters and variables used in this study, the Er:YAG laser could not provide an additional improvement in dentin-resin bond strength, irrespective of the type of adhesive system used or the storage period evaluated.

Objetivo: Ainda que a ação do laser de Er:YAG no condicionamento e preparo do substrato dentinário, bem como na resistência de união à resina composta já tenha sido descrita na literatura, a longevidade da adesão decorrente deste processo ainda não está bem estabelecida. Material e Métodos: Neste estudo, ensaios de microtração foram realizados em palitos obtidos de 60 incisivos bovinos, subdivididos em 12 grupos constituídos pela combinação das variáveis: tratamento dentinário prévio com o laser de Er:YAG (250 mJ/ 4 Hz; 160 mJ / 10 Hz) e sem irradiação (grupo controle), sistema adesivo (Clearfil SE Bond /Kuraray; Adper Single Bond / 3M ESPE) e período de armazenagem (24 h; 90 dias). Os resultados mostraram menor resistência à microtração (com diferença estatisticamente significante p = 0,05) em relação aos grupos não tratados com o laser, não importando o sistema adesivo empregado, nem o período de armazenagem. A observação ao microscópio estereoscópico mostrou que as fraturas ocorreram predominantemente na interface adesiva para os grupos submetidos ao laser de Er:YAG. Conclusão: Portanto, a irradiação com o laser, nos parâmetros e variáveis utilizados e em comparação com os grupos controle, afetou negativamente a adesão à dentina, não havendo alteração relevante na longevidade da adesão para os períodos de armazenagem avaliados.

D-Scan measurement of ablation threshold incubation effects for ultrashort laser pulses.

We report the validation of the Diagonal Scan (D-Scan) technique to determine the incubation parameter for ultrashort laser pulses ablation. A theory to calculate the laser pulses superposition and a procedure for quantifying incubation effects are described, and the results obtained for BK7 samples in the 100 fs regime are compared to the ones given by the traditional method, showing a good agreement.

Morphological assessment of dentine and cementum following apicectomy with Zekrya burs and Er:YAG laser associated with direct and indirect Nd:YAG laser irradiation.

OBJECTIVES: This study aimed to assess the apical surface morphology of maxillary central incisors resected 3.0 mm from the tooth apex using Zekrya burs or Er:YAG laser, with or without subsequent direct Nd:YAG laser irradiation (apical and buccal surfaces) and indirect irradiation (palatal surface). STUDY DESIGN: Forty maxillary central incisors were instrumented and obturated. The roots were divided into 4 groups according to the root resection method (Zekrya bur or Er:YAG laser - 1.8 W, 450 mJ, 4 Hz, 113 J/cm(2)) and further surface treatment (none or Nd:YAG laser - 2.0 W, 100 mJ, 20 Hz, 124 J/cm(2)). The teeth were prepared for SEM analysis. Scores ranging from 1 to 4 were attributed to cut quality and morphological changes. The data were analyzed by the Kruskal-Wallis test and by Dunn's test. RESULTS: SEM images showed irregular surfaces on the apical portions resected with Zekrya burs, with smear layer and grooves in the resected dentine and slight gutta-percha displacement and plasticization. On the other hand, apicectomies carried out with Er:YAG laser showed morphological changes compatible with ablated dentine, with rough surfaces and craters. In spite of the presence of plasticized gutta-percha, with the presence of bubbles, an irregular adaptation of the filling material to the root walls was also observed. Direct Nd:YAG laser irradiation of the apical and buccal surfaces of the resected roots resulted in areas of resolidification and fusion in the dentine and cementum, with a vitrified aspect; indirect Nd:YAG laser irradiation of the palatal surfaces yielded a lower number of changes in the cementum, with irregular resolidification areas. CONCLUSIONS: There were no differences in terms of cut quality between the use of burs and Er:YAG laser or between the 2 surfaces (apical and buccal) treated with Nd:YAG laser with direct irradiation. However, morphological changes were significantly less frequent on surfaces submitted to indirect irradiation (palatal) when compared with those directly irradiated.

Prospective ultramorphological characterization of human hair by optical coherence tomography.

BACKGROUND/PURPOSE: The continuous advancement in cosmetic science has led to an increasing demand for the development of non-invasive, reliable scientific techniques directed toward claim substantiation, which is of utmost relevance, to obtain data regarding the efficacy and safety of cosmetic products. METHODS: In this work, we used the optical coherence tomography (OCT) technique to produce in vitro transversal section-images of human hair. We also compared the OCT signal before and after chemical treatment with an 18% w/w ammonium thioglycolate solution. RESULTS: The mean diameter of the medulla was 29+/-7 microm and the hair diameter was 122+/-16 microm in our samples of standard Afro-ethnic hair. A three-dimensional (3D) image was constructed starting from 601 cross-sectional images (slices). Each slice was taken in steps of 6.0 microm at eight frames per second, and the entire 3D image was constructed in 60 s. CONCLUSION: It was possible to identify, using the A-scan protocol, the principal structures: the cuticle, cortex and medulla. After chemical treatment, it was not possible to identify the main structures of hair fiber due to index matching promoted by deleterious action of the chemical agent.

Correlation between autofluorescence intensity and tumor area in mice bearing renal cell carcinoma.

Protoporphyrin IX (PpIX) is a porphyrin derivative that is accumulated in cancerous tissue in consequence of the tumor-specific metabolic alterations. The aim of this study was to evaluate the accumulation of PpIX in mice bearing renal cell carcinoma by spectroscopy analysis. A total of 24 male Balb/c mice, 6 weeks old, were divided into six groups: Normal (without inoculation of tumor cells) and 4, 8, 13, 16, and 20 days after inoculation of tumor cells. The orthotopic tumor model of renal cancer was used. Murine renal cell carcinoma (Renca cells) were inoculated into the subcapsular space of the kidney. Normal and tumor-bearing kidneys in different progression stages were removed and analyzed by ex-vivo spectroscopy and by microscopy, for tumor histometric analysis. Emission spectra were obtained by exciting the samples at 405 nm. Significant differences between normal and tumor-bearing kidneys in autofluorescence shape occurred in the 600-700 nm spectral region. A good correlation was found between emission band intensity at 635 nm and the tumor area.

Study of blood porphyrin spectral profile for diagnosis of tumor progression.

Renal cell carcinoma (RCC) accounts for approximately 3% of new cancer incidence and mortality in the United States. Unfortunately many RCC masses remain asymptomatic and nonpalpable until they are advanced. Diagnosis and localization of early carcinoma play an important role in the prevention and curative treatment of RCC. The autofluorescence of blood porphyrin of healthy and tumor induced in male SCID mice was analyzed using fluorescence and excitation spectroscopy. A significant contrast between normal and tumor blood could be established. Blood porphyrin fluorophore showed enhanced fluorescence band (around 630 nm) in function of the tumor growth. This indicates that either the autofluorescence intensity of the blood fluorescence may provide a good parameter for the "first approximation" characterization of the tumor stage.