This study aims to develop a comprehensive analytical and numerical framework for monitoring and quantifying carbon dioxide (CO2) concentration using a multimode fiber-optic probe coated with a nanoporous structure. We have characterized the proposed sensor by investigating various performance parameters, such as sensitivity, Full-Width Half Maxima (FWHM) and Figure of Merit (FOM). Theoretical analysis of the probe showed a CO2 gas sensitivity seven times higher than that for Hydrogen and about three times higher than Nitrogen. The model analyzes transmission spectra based on the refractive index and thickness of a multilayer structure, with transfer matrices elucidating the interaction of light with each layer. The effective refractive index of the porous structure was calculated using effective medium theories. The use of this theoretical modeling approach before experimentation and field implementation can enable the selection of optimal fiber and coating materials, including their dimensions, customized to the target operational conditions. It also enables the comparison of theoretical predictions with experimental and field observations, which is essential for accurate quantification of CO2 leaks and emissions.
The progression of obesity can be influenced by lipid metabolism and alterations in fatty acid levels. This study utilized Raman techniques to analyze the impact of High-Fat Diet (HFD) consumption on White Adipose Tissue (WAT) in an animal model (mice). Our results from statistical examination of Raman spectra indicated a substantial increase in unsaturated lipid levels in Visceral WAT (VWAT) fat pads when exposed to a high-fat die. The VWAT tissues were analyzed and mapped using a targeted Raman image analysis method employing Direct Classical Least Squares (DCLS) approaches to characterize lipid species such as ω-3 and ω-6 fatty acids. The analysis showed higher concentrations of ω3, ω6, cholesterol, and triglycerides in adipose tissues from the high-fat diet group compared to the Low-Fat Diet (LFD) group. The study demonstrated that Raman spectroscopy and microscopy, as a reliable and non-invasive technique, offered important understanding at the molecular level into the process of lipid species remodeling and the spatial distribution of adipose tissues during a high-fat diet.
Resonant propagation of light is important for building novel light source and chip-scale optical interconnects. Here, we introduced an optoplasmonic amplifier which is operating in the visible range and generating Raman signal internally with injection seeding. We introduced the microspheres as a chain with different arrangements such as – single sphere; two spheres with equal and unequal sizes; three spheres with equal sizes and multi spheres with different sizes. We analyzed the effect of excitation and polarization with respect to different spheres and position of excitation. We noticed a shift of mode position with respect to different sizes of microspheres. We also had different kind of underlying substrates such as silicon nanopillar, polymer nanopillar, pyramid polymer and nanohole polymer and investigate the effect of these substrates on various chains of microspheres.
We numerically design and experimentally test a SERS-active substrate for enhancing the SERS signal of a monolayer of graphene in water. The monolayer is placed on top of an array of silver-covered nanoholes in a polymer and is covered with water. Here we report a large enhancement of up to 200000 in the SERS signal of the graphene monolayer on the patterned plasmonic nanostructure for a 532 nm excitation laser wavelength. Our numerical calculations of both the excitation field and the emission rate enhancements support the experimental results. We also propose a highly compact structure for near total light absorption in a monolayer of graphene in the visible. The structure consists of a grating slab covered with the graphene monolayer. The grating slab is separated from a metallic back reflector by a dielectric spacer. The proposed structure could find applications in the design of efficient nanoscale visible-light photodetectors and modulators.
Adipose tissue derived stem cells (ASCs) has applications in soft tissue replacement-based tissue engineering. ASCs can potentially reduce many of the disadvantages of autologous fat transplantation such as donor-site morbidity and immune system rejection. Although, ASCs hold clinical relevance as a potential cell therapy candidate, widespread use of them is hampered due to inadequate data on the fate of stem cells after transplant. Hence a method to facilitate long term tracking of the cells will enable better understanding of stem cell fate in stem cell-based therapeutics. Here, we employ biocompatible surface functionalized nanorods for tracking the adipogenesis and osteogenesis differentiation of ASCs. Anisotropic plasmonic nanostructures based on silver (Ag) and gold (Au) have received much attention owing to their tunable size and shape dependent localized surface plasmon resonance (LSPR) with multiple applications such as biological contrast agents, photothermal conversion, plasmon-enhanced spectroscopies, optical sensors and in catalysis. Hyperspectral microscopy combining both nanoscale imaging and spectral characteristics from plasmonic nanostructures provides a powerful tool for their identification and quantitative spectral analysis of plasmonic nanostructures with unprecedented level of details. Here, we present the analysis of single particle spectroscopy of gold nanorods and their orientation dependent scattering properties using hyperspectral microscopy and validated with correlated high-resolution electron microscopy. Fairly monodisperse gold nanorods with bright longitudinal SPR centered at about 663 nm were synthesized using bromide-free surfactant mixture consisting of cetyltrimethylammonium chloride and sodium oleate. The nanorods were successfully characterized by UV-Visible spectroscopy, DLS, XPS, and TEM results. Dark-field hyperspectral and second harmonic generation (SHG) microscopy were performed on individual gold nanorods and their optical scattering spectra were analyzed for imaging orientation of single nanorods. The initial results revealed scattering spectra from individual gold nanorods displayed measurable spectral-shifts from their collective LSPR spectrum from bulk measurements performed using UV-Visible spectroscopy. The analysis and utility of gold nanorods for labeling stem cells and the orientation dependent spectral features of nanorods inside the cells will be characterized and discussed in detail. The cell viability, differentiation capacity, gene expression, potential cytotoxicity due to nanorods such as inflammatory molecule and reactive oxygen species production, adipogenic and osteogenic potential will be evaluated using histochemical staining and quantitative polymerase chain reaction (qPCR). The study has implications towards tracking individual nanorods in complex biological systems and beyond.
Mesenchymal stem cells derived from adult adipose tissue possess the ability to differentiate into adipocytes, osteocytes, and chondrocytes which in turn can be developed into adipose tissues, cartilages, and bones. This regenerative characteristics has fueled the need to define improved stem-cell analysis protocol for enabling investigation of the differentiation process efficiently, economically, and non-invasively by start-of-the art imaging modalities. Here, we have demonstrated hyperspectral microscopy-based label-free imaging approach to study ASCs at a single-cell level. ASCs has been stimulated to become osteocytes using the growth media containing β –glycerophosphate, L-ascorbic acid 2-phosphate sesquimagnesium salt hydrate, and dexamethasone. Further, ASCs were stimulated to form adipocytes using the growth media containing biotin, pantothenate, bovine insulin, IBMX, penicillin, rosiglitazone, and dexamethasone.
In the present study, dark-field based hyperspectral Imaging (HSI) technique has been utilized to image single as well as multiple osteoblasts and adipocytes in salt media grown on the glass substrate. The spectral response of the cells at each pixel of the images were recorded in the visible-NIR range (400-900 nm). Response is stored in the three dimensional data-cube formed with two spatial dimensions and one spectral dimension. No special tagging or staining of the ASCs and derived osteoblasts, adipocytes has been done, as more likely required in traditional microscopy techniques. Incident light is diffracted at multiple angles and hence scattering response received after transmission is different even within the single cell due to sub-cellular heterogeneities present in the control and differentiating ASCs.
Based on dark-field images of control and differentiated sample, we found significant structural and spectral distinctiveness at day 14 onwards for differentiated osteoblasts and at day 6 onwards for adipocytes. Fourier filtering of images provides good visual inspection of structural modifications. Spectral data from the cellular surface and intracellular markers, and secreted molecules is stored to build the spectral libraries. Matrix-assisted laser deposition/ionization (MALDI) spectrometry technique is performed on control and differentiated cells to obtain insight of sub-cellular single molecules, mineral deposits, fats, proteins, and other biological mono-constituents. In the hyperspectral images, the entire spectrum is stored within each pixel as a vector where the number of spectral bands (wavelength range) equals vector dimension and the corresponding intensity signifies the component of the individual vector. Spectral signatures from the identified lipids are then matched to the in vitro stem-cells via spectral angle mapping (SAM) algorithms. By computing angle between two pixels, remarkable spectral similarity and dissimilarity are identified between control and differentiated stem cells. Pseudo-colored differentiating maps are produced by calibrating ‘match’ threshold. Secondary validation to the HSI is provided by evaluating optical images with template-match and edge-detection algorithms as well as second-harmonic generation microscopy to investigate osteoblasts.
Establishing this label-free protocol with minimum specimen preparation enables promising outcomes to overcome phototoxicity effect of traditional microscopy such as fluorescence/staining bleaching errors. The study would lead to high-throughput identification of patient specific derived cells for clinical use preventing mass rejection, and advance our understanding of the behavior of stem cellular clusters undergoing adipogenic and osteogenic differentiation.
Orientation of plasmonic nanostructures is an important feature in many nanoscale applications such as catalyst, biosensors DNA interactions, protein detections, hotspot of surface enhanced Raman spectroscopy (SERS), and fluorescence resonant energy transfer (FRET) experiments. However, due to diffraction limit, it is challenging to obtain the exact orientation of the nanostructure using standard optical microscope. Hyperspectral Imaging Microscopy is a state-of-the-art visualization technology that combines modern optics with hyperspectral imaging and computer system to provide the identification and quantitative spectral analysis of nano- and microscale structures. In this work, initially we use transmitted dark field imaging technique to locate single nanoparticle on a glass substrate. Then we employ hyperspectral imaging technique at the same spot to investigate orientation of single nanoparticle. No special tagging or staining of nanoparticle has been done, as more likely required in traditional microscopy techniques. Different orientations have been identified by carefully understanding and calibrating shift in spectral response from each different orientations of similar sized nanoparticles. Wavelengths recorded are between 300 nm to 900 nm. The orientations measured by hyperspectral microscopy was validated using finite difference time domain (FDTD) electrodynamics calculations and scanning electron microscopy (SEM) analysis. The combination of high resolution nanometer-scale imaging techniques and the modern numerical modeling capacities thus enables a meaningful advance in our knowledge of manipulating and fabricating shaped nanostructures. This work will advance our understanding of the behavior of small nanoparticle clusters useful for sensing, nanomedicine, and surface sciences.
Second-harmonic generation (SHG) microscopy is a label-free imaging technique to study collagenous materials in extracellular matrix environment with high resolution and contrast. However, like many other microscopy techniques, the actual spatial resolution achievable by SHG microscopy is reduced by out-of-focus blur and optical aberrations that degrade particularly the amplitude of the detectable higher spatial frequencies. Being a two-photon scattering process, it is challenging to define a point spread function (PSF) for the SHG imaging modality. As a result, in comparison with other two-photon imaging systems like two-photon fluorescence, it is difficult to apply any PSF-engineering techniques to enhance the experimental spatial resolution closer to the diffraction limit. Here, we present a method to improve the spatial resolution in SHG microscopy using an advanced maximum likelihood estimation (AdvMLE) algorithm to recover the otherwise degraded higher spatial frequencies in an SHG image. Through adaptation and iteration, the AdvMLE algorithm calculates an improved PSF for an SHG image and enhances the spatial resolution by decreasing the full-width-at-halfmaximum (FWHM) by ~20%. Similar results are consistently observed for biological tissues with varying SHG sources, such as gold nanoparticles and collagen in porcine feet tendons. By obtaining an experimental transverse spatial resolution of ~400 nm, we show that the AdvMLE algorithm brings the practical spatial resolution closer to the theoretical diffraction limit. Our approach is suitable for adaptation in micro-nano CT and MRI imaging, which has the potential to impact diagnosis and treatment of human diseases.
It has been shown that surface enhanced Raman spectroscopy (SERS) has many promising applications in ultrasensitive detection of Raman signal of substances. However, optimizing the enhancement in SERS signal for different applications typically requires several levels of fabrication of active plasmonic SERS substrates. In this paper, we report the enhancement of SERS signal of a single layer of graphene located on a plasmonic nano-Lycurgus cup array after placing water droplets on it. The experimental data shows that addition of water droplets can enhance the SERS signal of the single layer of graphene about 10 times without requiring any modifications to the nano-Lycurgus cup array. Using fullwave electromagnetic simulations, we show that addition of water droplets enhances the local electric field at the graphene layer, resulting in stronger light-graphene interaction at the excitation pump laser wavelength. We also show that the addition of water droplets on the graphene layer enables us to modify the band diagram of the structure, in order to enhance the local density of optical states at the Raman emission wavelengths of the graphene layer. Numerical calculations of both the excitation field enhancement at the location of the graphene layer, and the emission enhancement due to enhanced local density of optical states, support the experimental results. Our results demonstrate an approach to boost the SERS signal of a target material by controlling the band diagram of the active nanostructured SERS substrate through the use of fluidic dielectrics. These results could find potential applications in biomedical and environmental technologies.
With the goal of improving photo-absorption of photovoltaic device and for plasmonic application we have fabricated
nanopillar black silicon devices through etching-passivation technique which does not require any photomask and whole
wafer scale uniformity is achieved at room temperature in a short time. We have carried out thorough optical
characterization for nanopillar black silicon devices to be used for solar cell and plasmonic applications.
Cathodoluminescence (CL), current dependent CL spectroscopy, photoluminescence (at room temperature and 77 K),
Raman spectroscopy, reflectance and absorption measurement have been performed on the device. A thin layer of Ag is
deposited to render with plasmonic property and the plasmonic effect is probed using surface plasmon enhanced
fluorescence, angle dependent reflectance measurements, high resolution cathodoluminescence (CL), surface enhanced
Raman spectroscopy (SERS) measurement and Fluorescence Lifetime Imaging Microscopy (FLIM) experiment. We
obtained reduction in optical reflection of ~ 12 times on b-Si substrate from UV to NIR range, the nanostructured
fluorescence enhancement of ~40 times and the Raman scattering enhancement factor of 6.4×107.
KEYWORDS: Luminescence, Nanoplasmonics, Silver, Confocal microscopy, Metals, Resonance enhancement, 3D image processing, Near field optics, 3D image enhancement, Surface plasmons
We have created an enhanced cell-imaging platform for 3D confocal fluorescence cell imaging where fluorescence
sensitivity is amplified for more than 100 folds especially for cell membrane and cytoplasm. The observed
unprecedented three-dimensional fluorescence intensity enhancement on the entire cell microstructure including cell
membrane 10 μm above the substrate surface is attributed to a novel far field enhancement mechanism, nanoplasmon
coupled optical resonance excitation (CORE) mechanism which permits enhanced surface plasmon on the substrate
being evanescently coupled to Whispering Gallery mode optical resonance inside the spheroidal cell membrane
microcavity. Theoretical model of the hypothesis is explained using coupled mode theory. In addition, preliminary result
has been provided for the observation of early stage of transfection in a cancer cell.
We demonstrate surface plasmon-induced enhancements in optical imaging and spectroscopy on silver coated silicon
nanocones which we call black silver substrate. The black silver substrate with dense and homogeneous nanocone forest
structure is fabricated on wafer level with a mass producible nanomanufacturing method. The black silver substrate is
able to efficiently trap and convert incident photons into localized plasmons in a broad wavelength range, which permits
the enhancement in optical absorption from UV to NIR range by 12 times, the visible fluorescence enhancement of ~30
times and the NIR Raman scattering enhancement factor up to ~108. We show a considerable potential of the black silver
substrate in high sensitivity and broadband optical sensing and imaging of chemical and biological molecules.one)
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