Raman Fingerprint Research Articles

Cellular imaging by targeted assembly of hot-spot SERS and photoacoustic nanoprobes using split-fluorescent protein scaffolds

The in cellulo assembly of plasmonic nanomaterials into photo-responsive probes is of great interest for many bioimaging and nanophotonic applications but remains challenging with traditional nucleic acid scaffolds-based bottom-up methods. Here, we address this quandary using split-fluorescent protein (FP) fragments as molecular glue and switchable Raman reporters to assemble gold or silver plasmonic nanoparticles (NPs) into photonic clusters directly in live cells. When targeted to diffusing surface biomarkers in cancer cells, the NPs self-assemble into surface-enhanced Raman-scattering (SERS) nanoclusters having hot spots homogenously seeded by the reconstruction of full-length FPs. Within plasmonic hot spots, autocatalytic activation of the FP chromophore and near-field amplification of its Raman fingerprints enable selective and sensitive SERS imaging of targeted cells. This FP-driven assembly of metal colloids also yields enhanced photoacoustic signals, allowing the hybrid FP/NP nanoclusters to serve as contrast agents for multimodal SERS and photoacoustic microscopy with single-cell sensitivity.

Raman fingerprints of amyloid structures.

Structural differences in pathological and functional amyloid fibrils have been investigated by Raman microspectroscopy. Second-derivative analyses of amide-I and amide-III bands distinguish parallel in-register β-sheets from a β-solenoid. Further, spatially resolved Raman spectra reveal molecular heterogeneity in amyloid structures.

Advances in surface-enhanced Raman spectroscopy (SERS) substrates for lipid and protein characterization: sensing and beyond.

Surface-enhanced Raman spectroscopy (SERS) has become an essential ultrasensitive analytical tool for biomolecular analysis of small molecules, macromolecular proteins, and even cells. SERS enables label-free, direct detection of molecules through their intrinsic Raman fingerprint. In particular, protein and lipid bilayers are dynamic three-dimensional structures that necessitate label-free methods of characterization. Beyond direct detection and quantitation, the structural information contained in SERS spectra also enables deeper biophysical characterization of biomolecules near metallic surfaces. Therefore, SERS offers enormous potential for such systems, although making measurements in a nonperturbative manner that captures the full range of interactions and activity remains a challenge. Many of these challenges have been overcome through advances in SERS substrate development, which have expanded the applications and targets of SERS for direct biomolecular quantitation and biophysical characterization. In this review, we will first discuss different categories of SERS substrates including solution-phase, solid-supported, tip-enhanced Raman spectroscopy (TERS), and single-molecule substrates for biomolecular analysis. We then discuss detection of protein and biological lipid membranes. Lastly, biophysical insights into proteins, lipids and live cells gained through SERS measurements of these systems are reviewed.

The Raman fingerprint of plutonium dioxide: Some example applications for the detection of PuO2 in host matrices

Some example applications are presented, in which the peculiar Raman fingerprint of PuO2 can be used for the detection of crystalline Pu4+ with cubic symmetry in an oxide environment in various host materials, like mixed oxide fuels, inert matrices and corium sub-systems. The PuO2 Raman fingerprint was previously observed to consist of one main T2g vibrational mode at 478 cm−1 and two crystal electric field transition lines at 2130 cm−1 and 2610 cm−1. This particular use of Raman spectroscopy is promising for applications in nuclear waste management, safety and safeguard.

Raman spectroscopy for accurately characterizing biomolecular changes in androgen-independent prostate cancer cells.

Metastatic prostate cancer resistant to hormonal manipulation is considered the advanced stage of the disease and leads to most cancer‐related mortality. With new research focusing on modulating cancer growth, it is essential to understand the biochemical changes in cells that can then be exploited for drug discovery and for improving responsiveness to treatment. Raman spectroscopy has a high chemical specificity and can be used to detect and quantify molecular changes at the cellular level. Collection of large data sets generated from biological samples can be employed to form discriminatory algorithms for detection of subtle and early changes in cancer cells. The present study describes Raman finger printing of normal and metastatic hormone‐resistant prostate cancer cells including analyses with principal component analysis and linear discrimination. Amino acid‐specific signals were identified, especially loss of arginine band. Androgen‐resistant prostate cancer cells presented a higher content of phenylalanine, tyrosine, DNA and Amide III in comparison to PNT2 cells, which possessed greater amounts of L‐arginine and had a B conformation of DNA. The analysis utilized in this study could reliably differentiate the 2 cell lines (sensitivity 95%; specificity 88%).

Isolation and Characterization of Few-Layer Manganese Thiophosphite.

This work reports an experimental study on an antiferromagnetic honeycomb lattice of MnPS3 that couples the valley degree of freedom to a macroscopic antiferromagnetic order. The crystal structure of MnPS3 is identified by high-resolution scanning transmission electron microscopy. Layer-dependent angle-resolved polarized Raman fingerprints of the MnPS3 crystal are obtained, and the Raman peak at 383 cm-1 exhibits 100% polarity. Temperature dependences of anisotropic magnetic susceptibility of the MnPS3 crystal are measured in a superconducting quantum interference device. Anisotropic behaviors of the magnetic moment are explored on the basis of the mean field approximation model. Ambipolar electronic conducting channels in MnPS3 are realized by the liquid gating technique. The conducting channel of MnPS3 offers a platform for exploring the spin/valleytronics and magnetic orders in 2D limitation.

First-principles determination of the Raman fingerprint of rhombohedral graphite

Multi-layer graphene with rhombohedral stacking is a promising carbon phase possibly displaying correlated states like magnetism or superconductivity due to the occurrence of a flat surface band at the Fermi level. Recently, flakes of thickness up to 17 layers were tentatively attributed ABC sequences although the Raman fingerprint of rhombohedral multilayer graphene is currently unknown and the 2D resonant Raman spectrum of Bernal graphite not understood. We provide a first principles description of the 2D Raman peak in three and four layers graphene (all stackings) as well as in Bernal, rhombohedral and an alternation of Bernal and rhombohedral graphite. We give practical prescriptions to identify long range sequences of ABC multi-layer graphene. Our work is a prerequisite to experimental non-destructive identification and synthesis of rhombohedral graphite.

Characterization and Discrimination of Gram-Positive Bacteria Using Raman Spectroscopy with the Aid of Principal Component Analysis.

Raman scattering and its particular effect, surface-enhanced Raman scattering (SERS), are whole-organism fingerprinting spectroscopic techniques that gain more and more popularity in bacterial detection. In this work, two relevant Gram-positive bacteria species, Lactobacillus casei (L. casei) and Listeria monocytogenes (L. monocytogenes) were characterized based on their Raman and SERS spectral fingerprints. The SERS spectra were used to identify the biochemical structures of the bacterial cell wall. Two synthesis methods of the SERS-active nanomaterials were used and the recorded spectra were analyzed. L. casei and L. monocytogenes were successfully discriminated by applying Principal Component Analysis (PCA) to their specific spectral data.

Raman spectroscopy uncovers biochemical tissue-related features of extracellular vesicles from mesenchymal stromal cells

Extracellular vesicles (EVs) from mesenchymal stromal cells (MSC) are emerging as valuable therapeutic agents for tissue regeneration and immunomodulation, but their clinical applications have so far been limited by the technical restraints of current isolation and characterisation procedures. This study shows for the first time the successful application of Raman spectroscopy as label-free, sensitive and reproducible means of carrying out the routine bulk characterisation of MSC-derived vesicles before their use in vitro or in vivo, thus promoting the translation of EV research to clinical practice. The Raman spectra of the EVs of bone marrow and adipose tissue-derived MSCs were compared with human dermal fibroblast EVs in order to demonstrate the ability of the method to distinguish the vesicles of the three cytotypes automatically with an accuracy of 93.7%. Our data attribute a Raman fingerprint to EVs from undifferentiated and differentiated cells of diverse tissue origin, and provide insights into the biochemical characteristics of EVs from different sources and into the differential contribution of sphingomyelin, gangliosides and phosphatidilcholine to the Raman spectra themselves.

Chemometric classification and quantification of olive oil in blends with any edible vegetable oils using FTIR-ATR and Raman spectroscopy

Samples of olive oils (n = 67) from different qualities and samples of other vegetable edible oils (including soybean, sunflower, rapeseed, corn oil etc; n = 79) were used in this study as pure oils. Previous to spectroscopy analysis, a transesterification step was applied to the pure vegetable oil samples and all the different oil blends were then prepared to create in-house blended samples. Spectral acquisition was performed with typical parameters to collect the FTIR and Raman fingerprints. For the olive/non-olive classification model, three classification strategies have been applied: (i) one input-class (1iC) classification; (ii) two input-class (2iC) classification; and (iii) one input-class plus one 'dummy' class classification (or pseudo two input-class (p2iC) classification). The multivariate classification methods used were k-nearest neighbours (kNN), partial least squared-discriminant analysis (PLS-DA), one-class partial least squares (OCPLS), support vector machine classification (SVM-C), and soft independent modelling of class analogies (SIMCA). The multivariate quantification method used was partial least square-regression (PLS-R). FTIR fingerprints showed excellent classification ability to distinguish pure olive from non-olive oil. When PLS-DA or SVM-C techniques are applied, 100% of olive oil samples and 92% of other vegetable edible oils are correctly classified. In general FTIR fingerprints were more discriminative than Raman's in both classification and regression scenarios.

DFT-Assisted Polymorph Identification from Lattice Raman Fingerprinting.

A combined experimental and theoretical approach, consisting of lattice phonon Raman spectroscopy and density functional theory (DFT) calculations, is proposed as a tool for lattice dynamics characterization and polymorph phase identification. To illustrate the reliability of the method, the lattice phonon Raman spectra of two polymorphs of the molecule 2,7-dioctyloxy[1]benzothieno[3,2-b]benzothiophene are investigated. We show that DFT calculations of the lattice vibrations based on the known crystal structures, including many-body dispersion van der Waals (MBD-vdW) corrections, predict experimental data within an accuracy of ≪5 cm–1 (≪0.6 meV). Due to the high accuracy of the simulations, they can be used to unambiguously identify different polymorphs and to characterize the nature of the lattice vibrations and their relationship to the structural properties. More generally, this work implies that DFT-MBD-vdW is a promising method to describe also other physical properties that depend on lattice dynamics like charge transport.

Label-free SERS analysis of proteins and exosomes with large-scale substrates from recordable compact disks

A central aspect to fully reach the biosensing scope of plasmonics beyond the research environment is its implementation in inexpensive and homogeneous functional nanostructured materials that can be manufactured in a large-scale fashion. Herein, we study the capabilities of consumer-grade compact disk technology for label-free SERS analysis of complex biological targets. Substrates from regular recordable disks (CD-R and DVD-R) coated with silver exhibit significant Raman enhancement. The magnitude of this enhancement depends on the nanostructure on the polycarbonate substrate, the silver thickness, and the excitation wavelength. The Raman fingerprint of hemoglobin and exosome samples were experimentally obtained in label-free conditions, which demonstrates the biosensing potential of this approach and suggests prospective developments towards fully exploiting the bioanalytical capabilities of SERS in point-of-care settings.

Exploration of Biogenic Nano-chemobiotics Fabricated by Silver Nanoparticle and Galactoxyloglucan with an Efficient Biodistribution in Solid Tumor Investigated by SERS Fingerprinting.

An incredible exploration ensued of a dual modality nanocomposite wherein chemotherapy in fusion with antibacterial efficacy is obtained in a biogenic fabrication, which transformed as a novel nano-chemobiotics (NCB) prevailing fundamental molecular level investigation by surface-enhanced Raman scattering (SERS) platform. The nanocomposite is a facile, robust, and ecofriendly constitution between silver nanoparticles (SNPs) and a naturally occurring galactoxyloglucan (PST001) denoted as SNP@PST, which displayed biocompatibility with an upgraded selective cytotoxicity toward cancer cells. The relatively nontoxic nature of the SNP@PST on normal cells and red blood cells was further proved by detailed toxicological profiling on BALB/c mice. As a unique outcome, we observed excellent antibacterial activity, which is complementary to the greater cytotoxicity by the NCB. In diagnostic aspect, SNP@PST was revealed to be a superior SERS substrate with multiscale Raman signal enhancement contributed by homogeneous hot-spot distribution. Finally, the inherent SERS feature enabled us to investigate the biodistribution of the NCB in tumor-challenged mice using Raman fingerprinting and mapping analysis. Hence, the unrevealed SNP@PST orchestrated with the surfactant-free green method resembled a potential theransonstic NCB construct with synergistic anticancer and antibacterial potential in a single platform.

Steps toward Maturation of Embryonic Stem Cell-Derived Cardiomyocytes by Defined Physical Signals.

SummaryCardiovascular disease remains a leading cause of mortality and morbidity worldwide. Embryonic stem cell-derived cardiomyocytes (ESC-CMs) may offer significant advances in creating in vitro cardiac tissues for disease modeling, drug testing, and elucidating developmental processes; however, the induction of ESCs to a more adult-like CM phenotype remains challenging. In this study, we developed a bioreactor system to employ pulsatile flow (1.48 mL/min), cyclic strain (5%), and extended culture time to improve the maturation of murine and human ESC-CMs. Dynamically-cultured ESC-CMs showed an increased expression of cardiac-associated proteins and genes, cardiac ion channel genes, as well as increased SERCA activity and a Raman fingerprint with the presence of maturation-associated peaks similar to primary CMs. We present a bioreactor platform that can serve as a foundation for the development of human-based cardiac in vitro models to verify drug candidates, and facilitates the study of cardiovascular development and disease.

Graphene Catalytic Growth on Copper for Glucose Sensing Applications

Recently, carbon nanomaterials have become a hot topic within the field of materials science because they have the potential to provide solutions to technological and environmental challenges in various areas. Among these materials, graphene is rapidly emerging as one of the most exciting materials for electro catalysts in electrochemical applications such as super-capacitors, Li-ion batteries, solar cells, and biosensors, due to its unique structure and electronic properties. Applications of graphene in biology are very appealing due to the possibility to have a conductive substrate prone to be modified to strictly interact with specific molecules if properly functionalized [1].Although a basic energy source for humans, dysfunctions in the metabolism of glucose are becoming more and more common. These metabolic diseases are called diabetes. At the beginning of the new millennium, 172 million people were affected by diabetes and, according to estimation, that number would have risen to 366 million in 2030 [2]. However, this latter number has already been reached and new estimation for 2035 foresee 595 million cases [3], with diabetes becoming the 7th cause of death [4]. In this work, deposition of graphene on thin and flexible electroplated copper surface by chemicalvapor deposition (CVD) has been researched for bottom-up glucose sensor building. Copper samples covered with graphene have then been used as electrodesin glucose sensors and their performances have been compared with that of bare copper.CVD is one of the most promising fabrication methods of graphene; this method is probably the best candidate to be used in the electronic industry, due to the high-quality and low defects layers it can yield. Electrodeposited copper substrates have been used as catalysts for the atmospheric pressure CVD process. These substrates have been used as deposited, or further processed to tailor their surface properties: for example, the effect of annealing in a reducing atmosphere and electropolishing have been researched. Graphene/FLG surface was then decorated with gold nanoparticles via immersion plating, to enhance sensor sensitivity. Finally, inkjet printing of copper oxide nanoparticles was implemented to test the properties of the so obtained nanohybrid. To assess the quality of grown graphene layers, Raman spectroscopy was employed, due to well-known graphene/FLG Raman fingerprints. Further characterization with a scanning electron microscope (SEM) and with X-ray photoemission spectroscopy (XPS) and UV photoemission spectroscopy (UPS) has been performed. [1] Sharma, N., Ojha, H., Bharadwaj, A., Pathak, D.P., Sharma, R.K., 2015. RSC Adv. 5 (66), 53381–53403. [2] Wild, S., Roglic, G., Green, A., Sicree, R. & King, H. 2004, "Global Prevalence of Diabetes: Estimates for the year 2000 and projections for 2030 ", Diabetes care, vol.27, no. 5, pp. 1047-1053. [3] http://www.expo2015.orgmagazineitlifestylediabete–tutti-i-numeri-in-italia-e-nelmondo.html [4] Tian, K., Prestgard, M. & Tiwari, A. 2014, "A review of recent advances in non-enzymatic systems", vol. 41, pp. 100-118.

Distinguishing Individual DNA Bases in a Network by Non-Resonant Tip-Enhanced Raman Scattering.

The importance of identifying DNA bases at the single-molecule level is well recognized for many biological applications. Although such identification can be achieved by electrical measurements using special setups, it is still not possible to identify single bases in real space by optical means owing to the diffraction limit. Herein, we demonstrate the outstanding ability of scanning tunneling microscope (STM)-controlled non-resonant tip-enhanced Raman scattering (TERS) to unambiguously distinguish two individual complementary DNA bases (adenine and thymine) with a spatial resolution down to 0.9 nm. The distinct Raman fingerprints identified for the two molecules allow to differentiate in real space individual DNA bases in coupled base pairs. The demonstrated ability of non-resonant Raman scattering with super-high spatial resolution will significantly extend the applicability of TERS, opening up new routes for single-molecule DNA sequencing.

Distinguishing Individual DNA Bases in a Network by Non‐Resonant Tip‐Enhanced Raman Scattering

AbstractThe importance of identifying DNA bases at the single‐molecule level is well recognized for many biological applications. Although such identification can be achieved by electrical measurements using special setups, it is still not possible to identify single bases in real space by optical means owing to the diffraction limit. Herein, we demonstrate the outstanding ability of scanning tunneling microscope (STM)‐controlled non‐resonant tip‐enhanced Raman scattering (TERS) to unambiguously distinguish two individual complementary DNA bases (adenine and thymine) with a spatial resolution down to 0.9 nm. The distinct Raman fingerprints identified for the two molecules allow to differentiate in real space individual DNA bases in coupled base pairs. The demonstrated ability of non‐resonant Raman scattering with super‐high spatial resolution will significantly extend the applicability of TERS, opening up new routes for single‐molecule DNA sequencing.

Raman spectrum of plutonium dioxide: Vibrational and crystal field modes

The Raman spectrum of plutonium dioxide is studied both experimentally and theoretically. Particular attention has been devoted to the identification of high-energy modes at $2120$ cm$^{-1}$ and $2625$ cm$^{-1}$, the attribution of which has so far been controversial. The temperature dependence of both modes suggests an electronic origin. Crystal Field (CF) calculations reported in this work shows that these two modes can be respectively assigned to the ${\Gamma}_{1}$ $\rightarrow$ ${\Gamma}_{5}$ and ${\Gamma}_{1}$ $\rightarrow $ ${\Gamma}_{3}$ CF transitions within the $^{5}I_{4}$ manifold. These two modes, together with the only vibrational line foreseen by the group theory for the Fm${-3}$m PuO$_{2}$ symmetry the T$_{2g}$ PuO stretching mode observed at $478$ cm$^{-1}$ can thus be used as Raman fingerprint of fcc plutonium dioxide.

Tuneable surface enhanced Raman spectroscopy hyphenated to chemically derivatized thin-layer chromatography plates for screening histamine in fish.

Reliable screening of histamine in fish was of urgent importance for food safety. This work presented a highly selective surface enhanced Raman spectroscopy (SERS) method mediated by thin-layer chromatography (TLC), which was tailored for identification and quantitation of histamine. Following separation and derivatization with fluram, plates were assayed with SERS, jointly using silver nanoparticle and NaCl. The latter dramatically suppressed the masking effect caused by excessive fluram throughout the plate, thus offering clear baseline and intensive Raman fingerprints specific to the analyte. Under optimized conditions, the usability of this method was validated by identifying the structural fingerprints of both targeted and unknown compounds in fish samples. Meanwhile, the quantitative results of this method agreed with those by an HPLC method officially suggested by EU for histamine determination. Showing remarkable cost-efficiency and user-friendliness, this facile TLC-SERS method was indeed screening-oriented and may be more attractive to controlling laboratories of limited resource.

Standoff spatial heterodyne Raman spectrometer for mineralogical analysis

Raman spectroscopy is ideally suited for planetary exploration because of its ability to unambiguously identify minerals, organic compounds, and biomarkers. Traditionally, Raman spectra were acquired with grating‐based dispersive spectrometers that require tens of micrometer‐sized entrance slits and thus limited light throughput. Recently, we have evaluated a new type of Fourier transform Raman spectrometer, the spatial heterodyne Raman spectrometer that provides high spectral resolution in a compact system without limiting light throughput. In this work, we present time‐resolved Raman spectra of carbonate, sulfate, and silicate minerals, including low Raman scattering efficiency olivine and feldspar minerals, in the 100–1260 cm−1 Raman fingerprint region with spatial heterodyne Raman spectrometer using 1.5‐cm‐diameter pulsed 532.078‐nm Nd:YAG laser beam. Copyright © 2017 John Wiley & Sons, Ltd.