Naresh Kumar

Last Name

Kumar

First Name

Naresh

ORCID

0000-0001-8953-5420

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03430 - Zenobi, Renato / Zenobi, Renato

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Publications1 - 10 of 40

Probing Chemical Complexity of Amyloid Plaques in Alzheimer’s Disease Mice using Hyperspectral Raman Imaging
Mrđenović, Dušan; Combes, Benjamin F.; Ni, Ruiqing; et al. (2024)
ACS Chemical Neuroscience
One of the distinctive pathological features of Alzheimer’s disease (AD) is the deposition of amyloid plaques within the brain of affected individuals. These plaques have traditionally been investigated using labeling techniques such as immunohistochemical imaging. However, the use of labeling can disrupt the structural integrity of the molecules being analyzed. Hence, it is imperative to employ label-free imaging methods for noninvasive examination of amyloid deposits in their native form, thereby providing more relevant information pertaining to AD. This study presents compelling evidence that label-free and nondestructive confocal Raman imaging is a highly effective approach for the identification and chemical characterization of amyloid plaques within cortical regions of an arcAβ mouse model of AD. Furthermore, this investigation elucidates how the spatial correlation of Raman signals can be exploited to identify robust Raman marker bands and discern proteins and lipids from amyloid plaques. Finally, this study uncovers the existence of distinct types of amyloid plaques in the arcAβ mouse brain, exhibiting significant disparities in terms of not only shape and size but also molecular composition.
Engineered Strain in 2D Materials by Direct Growth on Deterministically Patterned Grayscale Topographies
Erbas, Berke; Bala, Arindam; Furci, Hernan; et al. (2026)
Advanced Science
Strain is a proven technique for modifying the bandgap and enhancing carrier mobility in 2D materials. Most current strain engineering techniques rely on the post-growth transfer of these atomically thin materials from growth substrates to target surfaces, limiting their integration into nanoelectronics. Here, we present a new approach where strain in 2D materials is already introduced directly during their growth on grayscale-patterned topographies instead of flat surfaces. Both strain levels and orientations are deterministically engineered by controlling grayscale surface contour lengths through thermal expansion mismatches in nanostructured stacks, where the conformally grown and firmly attached 2D material is forced to match the underlying morphology change during cooling. With this method, we experimentally demonstrate precise control of localized tensile strain from 0 to 0.5% in grown MoS₂ monolayer along both uni- and multiaxial directions, while higher strain levels are shown to be theoretically possible. This strain-engineered growth of 2D material films directly on the target substrates is a generic and adaptable approach to various combinations of grayscale-thin-film/substrates and eliminates all the transfer-related limitations of previous approaches, thus paving the way for integrating strained 2D materials into next-generation nanoelectronics.
Genetic Impacts on the Structure and Mechanics of Cellulose Made by Bacteria
Laurent, Julie M.; Steinacher, Mathias; Kan, Anton; et al. (2025)
Advanced Science
The synthesis of cellulose pellicles by bacteria offers an enticing strategy for the biofabrication of sustainable materials and biomedical devices. To leverage this potential, bacterial strains that overproduce cellulose are identified through directed evolution technology. While cellulose overproduction is linked with a specific genetic mutation, the effect of such mutation on the intracellular protein landscape and on the structure and mechanical properties of the cellulose pellicles is not yet understood. Here, the proteome of bacteria evolved to overproduce cellulose is studied and its effect on the structure and mechanics of the resulting cellulose pellicles is investigated. Proteomic analysis reveals that the protein landscape of the evolved bacteria shows pronounced differences from that of native microorganisms. Thanks to concerted changes in the proteome, the evolved bacteria can generate cellulose pellicles with exquisite structure and improved mechanical properties for applications in textiles, packaging, and medical implants.
Near-Field Nanospectroscopy and Tip- Enhanced Raman Spectroscopy (TERS)
Krayev, Andrey; Schultz, Jeremy F.; Jiang, Nan; et al. (2023)
Nanoscopy and Nanospectroscopy
This chapter covers state-of-the-art development and results in tip-enhanced Raman spectroscopy (TERS) as a significant configuration of near-field nanospectroscopy. The chapter develops by drawing attention to the importance of TERS with a background motivation of the specific research area. Subsequently, the development of TERS instrumentation is discussed in detail, stretching its limit in terms of spatial resolution using atomic force microscopy (AFM) and scanning tunneling microscopy (STM) to circumvent the diffraction limit. To understand various chemical processes precisely, TERS studies in high- and ultrahigh-vacuum (UHV) for AFM- and STM-assisted measurements are elaborated with up-to-date information, including the study of a single molecule. Finally, low-temperature UHV-STM is described for molecular as well as submolecular level measurements using TERS. In describing various applications of TERS, the chapter elaborates on studies of inorganic materials of strategic importance, e.g., strained Si and quantum dots, along with other layered MXenes and Van der Waal bonded materials. An important area of molecular switching is also reported for the chemical identification at the nanoscale using TERS. The study of biomolecules is the most challenging yet most fascinating application of TERS, which is used for both DNA and RNA sequencing, including the study of bacteria and viruses. TERS being chemically sensitive, is also used for the understanding catalytic properties of plasmonic, bimetallic, and organometallic phthalocyanine materials. Tip-enhanced fluorescence microscopy is specifically reported for studying fluid cracking catalysts. The nano-spectroscopic study is further extended to imaging 2D transition metal dichalcogenide stacking as near-field second-harmonic generation efficiency is greatly enhanced by excitons. Finally, the chapter concludes with its important application of tip-enhanced photoluminescence measurements for understanding excitonic properties of semiconductors as luminescence characteristics are essentially confined to a few nm or sub-nm region owing to compositional variation, presence of defects or impurities, and strain.
Visualizing Nanoscale Valley Polarization in Transition Metal Dichalcogenides Using Tip-Enhanced Circularly Polarized Photoluminescence Imaging
Cheng, Yanlin; Wu, Hongxiu; Su, Weitao; et al. (2025)
Nano Letters
Mapping the spatial distribution of valley polarization at the nanoscale is essential for understanding the influence of local inhomogeneities to the performance of transition metal dichalcogenide (TMD) valleytronic devices but remains challenging due to the spatial resolution limits of conventional optical techniques. Herein, we introduce tip-enhanced circularly polarized photoluminescence (TECPPL) imaging, enabling the simultaneous mapping of exciton emission intensity and valley polarization. We investigate a monolayer (1L) MoS₂/WS₂heterojunction (HJ) and observe pronounced near-field (NF) photoluminescence (PL) enhancement under both σ⁺σ⁺and σ⁺σ^–polarization configurations. A NF circular polarization degree (P_c) of 0.67 is achieved, representing a 4-fold increase over the far-field (FF) measurement. The high local signal enhancement enables direct visualization of spatial variations in both the PL intensity and P_cwith a spatial resolution of ∼20 nm. Our results establish TECPPL as a powerful nanospectroscopic tool and offer new insights into the spatially resolved valleytronic behavior of TMD heterostructures.
Nanoscale chemical imaging of human cell membrane using Tip-enhanced Raman spectroscopy
Mrdenovic, Dusan; Ge, Wenjie; Kumar, Naresh; et al. (2022)
Angewandte Chemie. International Edition
Lack of appropriate tools for visualizing cell membrane molecules at the nanoscale in a non-invasive and label-free fashion limits our understanding of many vital cellular processes. Here, we use tip-enhanced Raman spectroscopy (TERS) to visualize the molecular distribution in pancreatic cancer cell (BxPC-3) membranes in ambient conditions without labelling, with a spatial resolution down to ca. 2.5 nm. TERS imaging reveals segregation of phenylalanine-, histidine-, phosphatidylcholine-, protein-, and cholesterol-rich BxPC-3 cell membrane domains at the nm length-scale. TERS imaging also showed a cell membrane region where cholesterol is mixed with protein. Interestingly, the higher resolution TERS imaging revealed that the molecular domains observed on the BxPC-3 cell membrane are not chemically “pure” but also contain other biomolecules. These results demonstrate the potential of TERS for non-destructive and label-free imaging of cell membranes with nanoscale resolution.
Mechanistic Insights into Nitroarene Hydrogenation Dynamics on Pt(111) via In Situ Tip-Enhanced Raman Spectroscopy
Cai , Zhen-Feng; Manae, Meghna A.; Tang , Zi-Xi; et al. (2025)
Journal of the American Chemical Society
Mechanistic insights into the molecular-level dynamics of nitroarene hydrogenation on Pt remain limited, largely because most prior studies rely on ex situ, ensemble-averaged measurements, or simulations considered in isolation. Here, we address this gap and demonstrate a novel methodology combining in situ tip-enhanced Raman spectroscopy (TERS) with density functional theory (DFT) modeling to track, at a well-defined single plasmonic junction, the hydrogenation of chloronitrothiophenol (CNTP) on atomically flat Pt(111). In situ TERS captures the dynamic transformation of CNTP → chloroaminothiophenol (CATP) under ambient H2exposure with a characteristic time scale of ∼6 s. Complementary DFT modeling maps the reaction energetics, revealing novel mechanistic insights: CNTP desorption is rapid initially (barrier 0.61 eV) but slows down once the Pt(111) surface is at about half-coverage; molecular bending on the half-covered Pt(111) surface is barrierless and exergonic; the first hydrogen addition to CNTP is facile (barrier 0.26 eV), while the second hydrogen addition is kinetically most demanding (barrier 0.83 eV), yielding a time scale of seconds that matches experimental results and identifies the rate-determining step. These findings advance molecular-level understanding of nitroarene hydrogenation on Pt(111) and demonstrate in situ TERS integrated with first-principles DFT modeling as a powerful platform for operando mechanistic studies of heterogeneous catalytic processes at the nanoscale.
Visualizing Surface Phase Separation in PS-PMMA Polymer Blends at the Nanoscale
Mrdenovic, Dusan; Abbott, Daniel Francis; Mougel, Victor; et al. (2022)
ACS Applied Materials & Interfaces
Phase-separated polymer blend films are an important class of functional materials with numerous technological applications in solar cells, catalysis, and biotechnology. These technologies are underpinned by the precise control of phase separation at the nanometer length-scales, which is highly challenging to visualize using conventional analytical tools. Herein, we introduce tip-enhanced Raman spectroscopy (TERS), in combination with atomic force microscopy (AFM), confocal Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), as a sensitive nanoanalytical method to determine lateral and vertical phase-separation in polystyrene (PS)-poly(methyl methacrylate) (PMMA) polymer blend films. Correlative topographical, molecular, and elemental information reveals a vertical phase separation of the polymers within the top ca. 20 nm of the blend surface in addition to the lateral phase separation in the bulk. Furthermore, complementary TERS and XPS measurements reveal the presence of PMMA within 9.2 nm of the surface and PS at the subsurface of the polymer blend. This fundamental work establishes TERS as a powerful analytical tool for surface characterization of this important class of polymers at nanometer length scales.
Monitoring the On-Surface Boronic Acid Condensation Process at the Nanoscale Using Tip-Enhanced Raman Spectroscopy
Xia, Yuanzhi; Greis, Kim; Xu, Chengcheng; et al. (2025)
ACS Nano
The on-surface condensation of boronic acids is a key step in fabricating functional interfaces with tailored properties; yet, a clear understanding of the molecular structural transformations involved remains a significant challenge. Here, we directly monitor the condensation reaction in a self-assembled monolayer of 4-mercaptophenylboronic acid (MPBA) on Au(111) using tip-enhanced Raman spectroscopy (TERS). The structural evolution in the MPBA adlayer is tracked via the emergence of new peaks, blue shifts, and intensity changes in characteristic Raman bands. Hyperspectral TERS imaging provides comprehensive insight into molecular transformations, including B-O-B bond formation, increased molecular constraints, and an evolution in molecular orientation. Furthermore, density functional theory simulations confirm that the boroxine trimer is the primary product of the on-surface condensation reaction. This study provides significant insights into on-surface boronic acid condensation chemistry for the rational design of functionalized surfaces with targeted chemical properties.
Hyperspectral TERS Imaging Reveals Strain Heterogeneity in Individual Nanoplastic Particles
Dutta, Anushree; Bienz, Siiri; Kumar, Naresh; et al. (2025)
Nano Letters
Nanoplastics pose growing environmental and health risks, yet their label-free, nondestructive detection and characterization, especially at the single-particle level, remain challenging. Here, we deploy AFM-based tip-enhanced Raman spectroscopy (AFM-TERS) to chemically characterize individual polystyrene (PS) nanoplastic particles via hyperspectral imaging under ambient conditions. TERS spectra from nanoparticles as small as 32 nm establish reliable single-particle sensitivity beyond the optical diffraction limit. Furthermore, hyperspectral TERS maps reveal pronounced intraparticle heterogeneity, reflected spatially as varying red-/blue-shifts of PS marker bands with broad frequency distributions, without any systematic dependence on particle size. Correlative AFM phase imaging exposes nanoscale variations in local stiffness indicating strain heterogeneity as the origin of the spectral shifts. These results demonstrate that AFM-TERS enables single-particle mapping of intraparticle heterogeneity in nanoplastics. This offers new possibilities to identify nanoplastics with molecular specificity and monitor chemical transformations at the single-particle level within complex biological and environmental matrices.

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Naresh Kumar

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