Yashashwa Pandey


Last Name

Pandey

First Name

Yashashwa

ORCID

0000-0001-8377-3209

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2019 - 201912020 - 20236
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Publications1 - 7 of 7
  • Two-dimensional Polymers in Microscopy and Spatially Resolved Vibrational Analysis – A Review
    Item type: Review Article
    Niepel, Timo S.G.; Pandey, Yashashwa; Zenobi, Renato (2019)
    Chimia
  • Probing coke formation during the methanol-to-hydrocarbon reaction on zeolite ZSM-5 catalyst at the nanoscale using tip-enhanced fluorescence microscopy
    Item type: Journal Article
    Bienz, Siiri; van Vreeswijk, Sophie H.; Pandey, Yashashwa; et al. (2022)
    Catalysis Science & Technology
    The deactivation mechanism of the widely used zeolite ZSM-5 catalysts remains unclear to date due to the lack of analytical techniques with sufficient sensitivity and/or spatial resolution. Herein, a combination of hyperspectral confocal fluorescence microscopy (CFM) and tip-enhanced fluorescence (TEFL) microscopy is used to study the formation of different coke (precursor) species involved in the deactivation of zeolite ZSM-5 during the methanol-to-hydrocarbon (MTH) reaction. CFM submicron-scale imaging shows a preferential formation of graphite-like coke species at the edges of zeolite ZSM-5 crystals within 10 min of the MTH reaction (i.e., working catalyst), whilst the amount of graphite-like coke species uniformly increased over the entire zeolite ZSM-5 surface after 90 min (i.e., deactivated catalyst). Furthermore, TEFL nanoscale imaging with ∼35 nm spatial resolution revealed that formation of coke species on the zeolite ZSM-5 surface is non-uniform and a relatively larger amount of coke is formed at the crystal steps, indicating a higher initial catalytic activity.
  • Nanoscale Chemical Imaging of Supported Lipid Monolayers using Tip‐Enhanced Raman Spectroscopy
    Item type: Journal Article
    Pandey, Yashashwa; Kumar, Naresh; Goubert, Guillaume; et al. (2021)
    Angewandte Chemie. International Edition
    Visualizing the molecular organization of lipid membranes is essential to comprehend their biological functions. However, current analytical techniques fail to provide a non-destructive and label-free characterization of lipid films under ambient conditions at nanometer length scales. In this work, we demonstrate the capability of tip-enhanced Raman spectroscopy (TERS) to probe the molecular organization of supported DPPC monolayers on Au (111), prepared using the Langmuir–Blodgett (LB) technique. High-quality TERS spectra were obtained, that permitted a direct correlation of the topography of the lipid monolayer with its TERS image for the first time. Furthermore, hyperspectral TERS imaging revealed the presence of nanometer-sized holes within a continuous DPPC monolayer structure. This shows that a homogeneously transferred LB monolayer is heterogeneous at the nanoscale. Finally, the high sensitivity and spatial resolution down to 20 nm of TERS imaging enabled reproducible, hyperspectral visualization of molecular disorder in the DPPC monolayers, demonstrating that TERS is a promising nanoanalytical tool to investigate the molecular organization of lipid membranes.
  • Nanoscale chemical analysis of 2D molecular materials using tip-enhanced Raman spectroscopy
    Item type: Review Article
    Mrdenovic, Dusan; Cai, Zhenfeng; Pandey, Yashashwa; et al. (2023)
    Nanoscale
    Two-dimensional (2D) molecular materials have attracted immense attention due to their unique properties, promising a wide range of exciting applications. To understand the structure-property relationship of these low-dimensional materials, sensitive analytical tools capable of providing structural and chemical characterisation at the nanoscale are required. However, most conventional analytical techniques fail to meet this challenge, especially in a label-free and non-destructive manner under ambient conditions. In the last two decades, tip-enhanced Raman spectroscopy (TERS) has emerged as a powerful analytical technique for nanoscale chemical characterisation by combining the high spatial resolution of scanning probe microscopy and the chemical sensitivity and specificity of surface-enhanced Raman spectroscopy. In this review article, we provide an overview of the application of TERS for nanoscale chemical analysis of 2D molecular materials, including 2D polymers, biomimetic lipid membranes, biological cell membranes, and 2D reactive systems. The progress in the structural and chemical characterisation of these 2D materials is demonstrated with key examples from our as well as other laboratories. We highlight the unique information that TERS can provide as well as point out the common pitfalls in experimental work and data interpretation and the possible ways of averting them.
  • Regioselective Tip-Enhanced Raman Spectroscopy of Lipid Membranes with Sub-Nanometer Axial Resolution
    Item type: Journal Article
    Mrdenovic, Dusan; Tang, Zi-Xi; Pandey, Yashashwa; et al. (2023)
    Nano Letters
    Noninvasive and label-free analysis of cell membranes at the nanoscale is essential to comprehend vital cellular processes. However, conventional analytical tools generally fail to meet this challenge due to the lack of required sensitivity and/or spatial resolution. Herein, we demonstrate that tip-enhanced Raman spectroscopy (TERS) is a powerful nanoanalytical tool to analyze dipalmitoylphosphatidylcholine (DPPC) bilayers and human cell membranes with submolecular resolution in the vertical direction. Unlike the far-field Raman measurements, TERS spectra of the DPPC bilayers reproducibly exhibited a uniquely shaped C-H band. These unique spectral features were also reproducibly observed in the TERS spectrum of human pancreatic cancer cells. Spectral deconvolution and DFT simulations confirmed that the TERS signal primarily originated from vibrations of the CH3 groups in the choline headgroup of the lipids. The reproducible TERS results obtained in this study unequivocally demonstrate the ultrahigh sensitivity of TERS for nanoanalysis of lipid membranes under ambient conditions.
  • Probing the Role of Environmental and Sample Characteristics in Gap Mode Tip-Enhanced Raman Spectroscopy
    Item type: Journal Article
    Pandey, Yashashwa; Abbott, Daniel Francis; Mougel, Victor; et al. (2023)
    Analytical Chemistry
    Tip-enhanced Raman spectroscopy (TERS) has emerged asa powerfulanalytical tool for nondestructive and label-free molecular characterizationat the nanoscale. However, the influence of environmental factorsand sample characteristics on the occurrence of spurious signals,enhancement of TERS signals, and longevity of TERS probes is not wellunderstood yet. Herein, we present a detailed investigation of theinfluence of oxygen, humidity, and atmospheric carbon contaminantson scanning tunneling microscopy-TERS (STM-TERS) measurements of self-assembledmonolayer systems in ambient and inert environments. Our results reveala consistent increase of TERS signals, significant reduction of spurioussignals, and drastically improved longevity of TERS probes in theinert environment. Additionally, sample characteristics such as molecularpacking, chemisorption behavior, and hydrophilicity are found to havea direct impact on signal enhancement in the TERS measurements ofmolecular self-assembled monolayers (SAMs). The novel insights gainedin this study are expected to pave the way for a more robust dataanalysis and improved experimental design in the future gap mode STM-and atomic force microscopy-TERS (AFM-TERS) studies.
Publications1 - 7 of 7