Abstract:An original scheme for sensitive absorption measurements, particularly well-suited for low analyte concentrations, is presented. The technique is based on multiscattering-enhanced absorption spectroscopy (MEAS) and benefits from the advantages of conventional absorption spectroscopy: simplicity, rapidity, and low costs. The technique relies on extending the optical path through the sensing volume by suspending dielectric beads in the solution containing the analytes of interest, resulting in multiple scatterin… Show more
“…Using this approach, sensitivity and LOD of commercially available bioassays can be improved. This has been shown for OxiSelect, an assay for H 2 O 2 detection [75]. Fig.…”
“…A simple and versatile technique, was presented by Koman et al [75]. In order to extend the OPL and, thus, the sensitivity, advantages were taken from disordered media where the OPL is increased via multiple scattering since spatial variations of the refractive index prevent the light to follow the shortest trajectory.…”
“…In a configuration containing suspended polystyrene (PS) beads, as schematically shown in Fig. 4, the limit of detection (LOD) was improved substantially [75]. Fig.…”
“…The absorbance A of standard and multiscattering experiments are displayed in Fig. 5 [75]. Using this approach, sensitivity and LOD of commercially available bioassays can be improved.…”
“…The simulations showed excellent agreement with experimental results and allow prediction of OPLs for different concentrations, refractive indexes and sizes of the scatterers. Due to bead–bead interactions the proposed numerical approach is not accurate for high filling factors F [79] nevertheless, for F < 10% good numerical/experimental agreements were found [75]. Fig.…”
Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs raise concerns about their safety for the environment and humans. There is growing evidence showing that if engineered nanomaterials are released into the environment, there is a possibility that they could cause harm to aquatic microorganisms. Among the divers effects triggering their toxicity the ability of ENMs to generate reactive oxygen species (ROS) capable of oxidizing biomolecules is currently considered a central mechanism of toxicity. Therefore, development of sensitive tools for quantification of the ROS generation and oxidative stress are highly sought. After briefly introducing ENMs-induced ROS generation and oxidative stress in the aquatic microorganisms (AMOs), this overview paper focuses on a new optical biosensor allowing sensitive and dynamic measurements of H2O2 in real-time using multiscattering enhanced absorption spectroscopy. Its principle is based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous FeII and ferric FeIII. For biological applications cytochrome c was embedded in porous random media resulting in an extended optical path length through multiple scattering of light, which lowers the limit of detection to a few nM of H2O2. The sensor was also integrated in a microfluidic system containing micro-valves and sieves enabling more complex experimental conditions. To demonstrate its performance, abiotic absorption measurements of low concentrations of dye molecules and 10 nm gold particles were carried out achieving limits of detection in the low nM range. Other biologically relevant reactive oxygen species can be measured at sub-μM concentrations, which was shown for glucose and lactate through enzymatic reactions producing H2O2. In ecotoxicological investigations H2O2 excreted by aquatic microorganisms exposed to various stressors were measured. Pro-oxidant effects of nano-TiO2 and nano-CuO towards green alga Chlamydomonas reinhardtii were explored in various exposure media and under different light illuminations. Dynamics of Cd2+ induced effects on photosynthetic activity, sensitisation and recovery of cells of C. reinhardtii was also studied.
“…Using this approach, sensitivity and LOD of commercially available bioassays can be improved. This has been shown for OxiSelect, an assay for H 2 O 2 detection [75]. Fig.…”
“…A simple and versatile technique, was presented by Koman et al [75]. In order to extend the OPL and, thus, the sensitivity, advantages were taken from disordered media where the OPL is increased via multiple scattering since spatial variations of the refractive index prevent the light to follow the shortest trajectory.…”
“…In a configuration containing suspended polystyrene (PS) beads, as schematically shown in Fig. 4, the limit of detection (LOD) was improved substantially [75]. Fig.…”
“…The absorbance A of standard and multiscattering experiments are displayed in Fig. 5 [75]. Using this approach, sensitivity and LOD of commercially available bioassays can be improved.…”
“…The simulations showed excellent agreement with experimental results and allow prediction of OPLs for different concentrations, refractive indexes and sizes of the scatterers. Due to bead–bead interactions the proposed numerical approach is not accurate for high filling factors F [79] nevertheless, for F < 10% good numerical/experimental agreements were found [75]. Fig.…”
Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs raise concerns about their safety for the environment and humans. There is growing evidence showing that if engineered nanomaterials are released into the environment, there is a possibility that they could cause harm to aquatic microorganisms. Among the divers effects triggering their toxicity the ability of ENMs to generate reactive oxygen species (ROS) capable of oxidizing biomolecules is currently considered a central mechanism of toxicity. Therefore, development of sensitive tools for quantification of the ROS generation and oxidative stress are highly sought. After briefly introducing ENMs-induced ROS generation and oxidative stress in the aquatic microorganisms (AMOs), this overview paper focuses on a new optical biosensor allowing sensitive and dynamic measurements of H2O2 in real-time using multiscattering enhanced absorption spectroscopy. Its principle is based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous FeII and ferric FeIII. For biological applications cytochrome c was embedded in porous random media resulting in an extended optical path length through multiple scattering of light, which lowers the limit of detection to a few nM of H2O2. The sensor was also integrated in a microfluidic system containing micro-valves and sieves enabling more complex experimental conditions. To demonstrate its performance, abiotic absorption measurements of low concentrations of dye molecules and 10 nm gold particles were carried out achieving limits of detection in the low nM range. Other biologically relevant reactive oxygen species can be measured at sub-μM concentrations, which was shown for glucose and lactate through enzymatic reactions producing H2O2. In ecotoxicological investigations H2O2 excreted by aquatic microorganisms exposed to various stressors were measured. Pro-oxidant effects of nano-TiO2 and nano-CuO towards green alga Chlamydomonas reinhardtii were explored in various exposure media and under different light illuminations. Dynamics of Cd2+ induced effects on photosynthetic activity, sensitisation and recovery of cells of C. reinhardtii was also studied.
Producing colors with colorless metals such as silver or aluminum is a fascinating application of plasmonic systems. [1][2][3][4][5][6] Such systems can be as simple as a single metal particle, where material, size, shape, and refractive index of the surrounding medium determine the color impression of the particle. [7][8][9][10][11] Indeed, all these parameters influence the absorption amplitude and the wavelength of the localized plasmon resonance within the particle. [12,13] On the other hand, one can also use a system supporting propagating surface plasmon-polaritons or in short surface plasmons. [14][15][16] These systems are often periodic at a length scale below the wavelength of visible light and have been optimized for color generation in transmission [17][18][19] as well as reflection, [20,21] where recently polarization-tunable colors were demonstrated. [22,23] In that case of periodic systems, the color is mainly determined by the material, periodicity, shape, and the refractive index of the surrounding medium. [24] The color generation of plasmonic systems is based on absorption due to the excitation of surface plasmons and not on an interference-based effect, where the periodicity determines the wavelengths which can excite surface plasmons. [14] In this article, we generate vivid colors by strongly enhanced absorption of dye lacquers applied conformally on square crossed metallic grating surfaces with identical periodicity in both dimensions. [25] Unlike previously published works, we focus here not only on the generation of color by the grating itself, [20,21] but explore its possible interactions with a dye lacquer to strongly enhance the dye absorption. Instead of the conventional approach that consists in embedding a plasmonic system in a nonabsorbing dielectric medium, [1,20] we apply a partially absorbing dye lacquer conformally and in direct contact to the grating surface.This idea is inspired by works of others, who measured a significant fluorescence emission enhancement for molecules placed at well-defined distances atop a metallic grating. [26,27] This concept was also used for light extraction to improve the efficiency of a light-emitting diode. [28] Instead of fluorescence emission, we focus here on the enhanced absorption of submicrometer thick (semi-) transparent dye lacquers applied conformally to metallic crossed gratings. Rather than varying the distance of the absorbing material to the metal surface, we vary the thickness and extinction coefficient κ of these lacquers. This detailed study reveals the mechanisms of enhancing absorption within the dye lacquer. The findings are not limited to color generation and may find applications in other fields, such as solar cell absorption improvement, [29] Raman spectroscopy, [30] or highly sensitive sensing applications. [31] 2. Results and Discussion 2.1. Measurement and Simulation of Gratings Self-Color
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