We developed a novel dopamine sensing and measurement technique based on aggregation of gold nanoparticles in random lasers. Dopamine combined with copper ions triggers the aggregation of gold nanoparticles and thus affects the performance of random lasers. Dopamine sensing can be achieved using four parameters which are sensitive to the presence of dopamine, that is emission peak shift, emission linewidth, signal-to-noise ratio (peak emission intensity / noise) and random lasing threshold. The dopamine is most sensitively detected by a change in the emission linewidth with a limit of detection of 1 × 10(-7) M, as well as by an increase in the lasing threshold. The dopamine concentration from 1 × 10(-7) M to 1 × 10(-2) M can be determined by calibrating with the laser threshold.
We investigated the spectral and coherence signatures of threshold in random lasers with incoherent feedback consisting of alumina colloidal nanoparticles suspended in rhodamine 6G methanol solution under nanosecond-pulsewidth pumping, based on measurement of temporal and spatial coherence properties and comparison with emission spectra. Feedback in this random laser was provided by multiple scattering from the alumina particles, and the effects of particle concentration and scattering length were studied for the weakly scattering and diffusive scattering regimes. At threshold, in each regime, the visibility of the interference fringes jumped abruptly, coinciding with a substantial increase in peak emission intensity and decrease in the linewidth of a single dominant emission peak.
Image processing requires an excellent image contrastenhancement technique to extract useful information invisible to the human or machine vision. Because of the histogram flattening, the widely used conventional histogram equalization image-enhancing technique suffers from severe brightness changes, rendering it undesirable. Hence, we introduce a contrast-enhancement dynamic histogram-equalization algorithm method that generates better output image by preserving the input mean brightness without introducing the unfavorable side effects of checkerboard effect, artefacts, and washed-out appearance. The first procedure of this technique is; normalizing input histogram and followed by smoothing process. Then, the break point detection process is done to divide the histogram into subhistograms before we can remap the gray level allocation. Lastly, the transformation function of each subhistogram is constructed independently. V
The main idea of this paper is to solve the coverage problem in Wireless Sensor Network (WSN) by increasing sensor nodes coverage percentages. Due to that, effect of number of sensor nodes, size of region of interest (ROI) and Particle Swarm Optimization (PSO) algorithm are studied. PSO is an optimization method that can be deployed to achieve higher coverage percentage.
We demonstrate improved characteristics in Rhodamine dye random lasers with the addition of gold nanoparticles. As a result of the strong plasmonic enhancement induced by gold nanoparticles, Rhodamine 640/gold random lasers have less than half the lasing threshold compared with Rhodamine 640/alumina random lasers in the weakly scattering regime for 10 −3 M dye concentration. The optimum concentration of gold nanoparticles occurs at ~8 × 10 10 cm −3 , close to the transition between the weakly scattering and diffusive regimes. Rhodamine 640 has a better performance compared with Rhodamine 6G which is attributed to the greater spectral overlap of the Rhodamine 6G fluorescence spectrum with the plasmon resonance of gold, leading to an increased energy transfer and fluorescence quenching for Rhodamine 6G by gold. We also observe the contrasting trends of lasing threshold between random dye lasers incorporating dielectric and metal nanoparticles in the diffusive scattering regime. The effects of gold nanoparticles in random dye lasers are discussed in the context of the tradeoff between local field enhancement and fluorescence quenching.
In this review, the concept of open
cavity lasing for ultrasensitive
sensing is explored, specifically in driving important innovations
as laser-based biosensorsa field mostly dominated by fluorescence-based
sensing. Laser-based sensing exhibits higher signal amplification
and lower signal-to-noise ratio due to narrow emission lines as well
as high sensitivity due to nonlinear components. The versatility of
open cavity random lasers for probing analytes directly which is ultrasensitive
to small changes in chemical composition and temperature fluctuations
paves the path of utilizing narrow emission lines for advanced sensing.
The concept of random lasing is first explained followed by a comparison
of the different lasing threshold that has been reported. This is
followed by a survey of reports on laser-based sensing and more specifically
as biosensors. Finally, a perspective on the way forward for open
cavity laser-based sensing is put forth.
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