Features and advantages of flexible silicon nanowires for SERS applications.

The paper reports on the features and advantages of horizontally oriented flexible silicon nanowires (SiNWs) substrates for surface-enhanced Raman spectroscopy (SERS) applications. The novel SERS substrates are described in detail considering three main aspects. First, the key synthesis parameters for the flexible nanostructure SERS substrates were optimized. It is shown that fabrication temperature and metal-plating duration significantly influence the flexibility of the SiNWs and, consequently, determine the SERS enhancement. Second, it is demonstrated how the immersion in a liquid followed by drying results in the formation of SiNWs bundles influencing the surface morphology. The morphology changes were described by fractal dimension and lacunar analyses and correlated with the duration of Ag plating and SERS measurements. SERS examination showed the optimal intensity values for SiNWs thickness values of 60-100 nm. That is, when the flexibility of the self-assembly SiNWs allowed hot spots occurrence. Finally, the test with 4-mercaptophenylboronic acid showed excellent SERS performance of the flexible, horizontally oriented SiNWs in comparison with several other commercially available substrates.

Different Protocols of Photobiomodulation Therapy of Hyposalivation.

OBJECTIVE: Photobiomodulation (PBM) therapy has proved to be effective for a wide range of oral pathologies including oral dryness, but the literature still lacks reports of clinical trials and protocols. The purpose of our study was to evaluate the effects of different wavelengths of PBM on salivation in patients suffering from hyposalivation aiming at determination of optimal treatment protocol. MATERIALS AND METHODS: This study included 30 patients whose major salivary glands were treated with low-intensity diode laser BTL2000 (Medical Technologies, s.r.o., Czech Republic) during 10 consecutive days. Patients were randomly assigned into two groups, each of 15 patients, and treated with PBM of 830 nm and PBM of 685 nm, respectively. The whole unstimulated and stimulated saliva quantities were measured each day during 10 days, before and after laser treatment, and at 10th day after treatment was ended. RESULTS: Results have shown that the laser treatment significantly improves salivation (p < 0.0001) in both groups after 10 days treatment. The salivation also remains improved 10 days after the end of treatment. The patients treated with PBM of 830 nm have had continuously higher values of quantity of saliva. CONCLUSIONS: Our results have shown that both laser wavelengths were effective in increasing salivary flow rate, and the improvement in salivation was statistically significant. The effect of treatment could be observed 10 days after the completion of treatment, thus providing evidence not only of stimulative effect but also indicating regenerative potential of PBM therapy.

Quantitative investigation of efficiency of ultraviolet and visible light in eradication of Candida albicans in vitro.

OBJECTIVE: The aim of this study was to quantitatively investigate the efficiency of the ultraviolet (UV) and visible light in eradication of Candida albicans in vitro; in particular, to determine, for selected wavelengths, the specific eradication coefficients and thresholds in terms of energy density levels required to effect 3.0log10 and 4.0log10 reduction. BACKGROUND DATA: Oral candidosis is the most common infection of the oral cavity and is caused by Candida species. The widespread use of topical and systemic antifungal agents as conventional treatment for oral candidosis has resulted in the development of resistance in C. albicans. Therefore, it has become necessary to develop alternative therapies for the treatment of oral candidosis. METHODS: C. albicans ATCC(®) 90028(™) was irradiated with 254 nm, 365 nm, 406 nm, 420 nm, and broadband Xe spectrum. For each wavelength, a fit of experimental data (survival fraction vs. applied energy density) with an exponential decay function enabled estimation of the specific eradication coefficients and thresholds. RESULTS: Based on estimated specific efficiencies (Δ) and eradication thresholds (ET) of the investigated wavelengths, the ranking in eradication efficiency of C. albicans (most to least effective) is: 254 nm (Δ=6.1 mJ/cm(-2), ET99.99=56 mJ/cm(-2)), broadband Xe spectrum (Δ=27.7 mJ/cm(-2), ET99.99=255 mJ/cm(-2)), 365 nm (Δ=4.3 J/cm(-2), ET99.99=39 J/cm(-2)), 420 nm (Δ=0.65 J/cm(-2), ET99.99=6 J/cm(-2)), and 406 nm (Δ=11.4 J/cm(-2), ET99.99=104 J/cm(-2)). CONCLUSIONS: The results provide insight into the wavelength-dependent dynamics of eradication of C. albicans. For each investigated wavelength, the eradication coefficient and corresponding eradication threshold were estimated. The observed different eradication efficiencies are consequence of different spectrally dependent inactivation mechanisms. The established methodology enables unambiguous quantitative comparison of eradication efficiencies of optical radiation and selection of most effective wavelengths for clinical and therapeutic use.

Performance assessment of methods for estimation of fractal dimension from scanning electron microscope images.

Processing of gray scale images in order to determine the corresponding fractal dimension is very important due to widespread use of imaging technologies and application of fractal analysis in many areas of science, technology, and medicine. To this end, many methods for estimation of fractal dimension from gray scale images have been developed and routinely used. Unfortunately different methods (dimension estimators) often yield significantly different results in a manner that makes interpretation difficult. Here, we report results of comparative assessment of performance of several most frequently used algorithms/methods for estimation of fractal dimension. To that purpose, we have used scanning electron microscope images of aluminum oxide surfaces with different fractal dimensions. The performance of algorithms/methods was evaluated using the statistical Z-score approach. The differences between performances of six various methods are discussed and further compared with results obtained by electrochemical impedance spectroscopy on the same samples. The analysis of results shows that the performance of investigated algorithms varies considerably and that systematically erroneous fractal dimensions could be estimated using certain methods. The differential cube counting, triangulation, and box counting algorithms showed satisfactory performance in the whole investigated range of fractal dimensions. Difference statistic is proved to be less reliable generating 4% of unsatisfactory results. The performances of the Power spectrum, Partitioning and EIS were unsatisfactory in 29%, 38%, and 75% of estimations, respectively. The results of this study should be useful and provide guidelines to researchers using/attempting fractal analysis of images obtained by scanning microscopy or atomic force microscopy.

Application of Brewster angle microscopy and fractal analysis in investigations of compressibility of Langmuir monolayers.

The aim of this study was to investigate the connection between the lipid/amphiphile monolayer structure at the interface and its macroscopic/rheological properties, in particular, to establish the link between the fractality of the monolayer structure and its compressibility modulus. To that purpose we have used fractal analysis of images obtained by Brewster angle microscopy to infer the fractal dimension of the monolayer structure and relate its change to the corresponding changes in compressibility derived from a simultaneously measured π-A isotherm. The results of the study confirmed the starting assumption based on theoretical considerations that the fractal dimension of an amphiphilic monolayer and its compressibility should be correlated. We have shown that there exists a strong correlation between the fractal dimension and the corresponding compressibility modulus of different amphiphilic materials. Thus, confirming the link between the short ordered structure on the molecular level and the macroscopic property-compressibility of the monolayer. The established correlation between the fractal dynamics and compressibility modulus of the monolayer enabled identification of onset of percolation-a second-order phase transition that is otherwise not easy and unambiguously detectable. We have found that the signature of percolation in a monolayer, regardless of its composition, is the occurrence of a sharp increase (a jump) of compressibility modulus (at macroscopic level) at the characteristic value of the corresponding fractal dimension D = 1.89. This is the result of the abrupt establishment of a connected structure on the molecular level, consequently involving a change in the elastic properties of the monolayer on a macroscopic scale. The results of this investigation provide means for unambiguous identification of the onset of percolation in the Langmuir layer and should facilitate a more efficient application of the percolation theory in further study of processes and structures at the interface during the monolayer compression.

The effect of low-level laser therapy on salivary glands in patients with xerostomia.

OBJECTIVE: The aim of this study was to investigate the effect of low-level laser irradiation on the secretory function of salivary glands in 34 patients with xerostomia (dry mouth). BACKGROUND DATA: Xerostomia, a common complaint of oral dryness within the elderly population, is caused by a reduction in normal salivary secretion due to different causes. Treatment is aimed at increasing salivary flow, although in most cases it remains palliative. MATERIALS AND METHODS: In this study, laser light from a pulsed Ga-As laser operating at 904 nm was applied bilaterally on each salivary gland area: extraorally on the parotid and submandibular gland areas and intraorally on the sublingual gland area. The operational probe distance from the irradiated area was 0.5 cm resulting in an irradiance of 246 mW/cm(2). The exposure time was 120 sec per daily treatment during 10 consecutive days. The average energy density per exposure was 29.5 J/cm(2). The control group consisted of 16 patients who were treated with 15 mL of a 2% citric acid solution applied as a mouth rinse for 30 sec. RESULTS: The average difference in the amount of salivation (dQ-sal, mL/min) before and after laser therapy increased linearly from dQ-sal = 0.05 mL/min on the first day, up to dQ-sal = 0.13 mL/min on the last (10th) day of therapy. In the control group, the average dQ-sal initially demonstrated a gradual increase, with a reversal of the trend toward the end of the therapy period and eventually yielding no correlation between the duration of therapy and dQ-sal. CONCLUSION: The results of our study indicate that the effects of low-level laser therapy on salivary glands are not only stimulating, but also regenerative to a degree since the glandular response to the same amount of applied laser energy increased linearly over time.

Effect of suspended particulate-size distribution on the backscattering ratio in the remote sensing of seawater.

Mie theory is used to study the influence of the particle-size distribution (PSD) on the backscattering ratio for case 1 and 2 waters. Several in situ measured PSDs from coastal water and the open ocean, representing typical case 2 and 1 waters, were used in this investigation. Calculation of the backscattering ratio requires integration of the PSD over a much broader size range than is usually measured. Consequently extrapolation from fitted data is necessary. To that purpose the measured data are fitted with hyperbolic (Junge) and the two-component model of the PSD. It is shown that the result of extrapolation, hence the backscattering ratio, critically depends on the chosen PSD model. For a particular PSD model the role of submicrometer particles and the applied integration limits on the backscattering ratio is discussed. The use of the hyperbolic PSD model largely overestimates the number of small (submicrometer) particles that significantly contribute to backscattering and consequently leads to an erroneously high backscattering ratio. The two-component model proves to be an adequate PSD model for use in backscattering/scattering calculations providing satisfactory results complying with experimental data. The results are relevant for the inversion of remotely sensed data and the prediction of optical properties and the concentration of phytoplankton pigments, suspended sediment, and yellow substance.