Dr. Sushant Sahu Profile

Dr. Sushant Sahu

at Louisiana State Univ

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Publications (2)

Proceedings Article | 4 March 2019 Presentation + Paper

Dark-field hyperspectral imaging of single plasmonic gold nanorods and their scattering characteristics in complex biological environments

Nishir Mehta, Sushant Sahu, Shahensha Shaik, Syed Hasan, Ram Devireddy, Manas Ranjan Gartia

Proceedings Volume 10881, 1088119 (2019) https://doi.org/10.1117/12.2510836

KEYWORDS: Nanorods, Gold, Stem cells, Plasmonics, Transmission electron microscopy, Scattering, Nanostructures, Particles, Hyperspectral imaging

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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.

Proceedings Article | 4 March 2019 Presentation + Paper

Non-invasive spectral analysis of osteogenic and adipogenic differentiation in adipose derived stem cells using dark-field hyperspectral imaging technique

Nishir Mehta, Shahensha Shaik, Sushant Sahu, Ram Devireddy, Manas Ranjan Gartia

Proceedings Volume 10890, 108901B (2019) https://doi.org/10.1117/12.2508731

KEYWORDS: Hyperspectral imaging, Stem cells, Tissues, Glasses, Microscopy, Associative arrays, Microscopes, Detection and tracking algorithms, Analytical research, Surgery

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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.

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