Raman Scattering Research Articles

A simple, rapid, and low-cost approach for colloidal nanoparticle-based surface enhanced Raman Scattering detection of endosulfan pesticide at trace levels

Abstract Surface Enhanced Raman Spectroscopy (SERS) is a highly specific, sensitive, and portable technique with great potential for on-site pesticide detection and monitoring. Endosulfan, an organochlorine pesticide known for its high toxicity, slow degradation, and bioaccumulation, has poor affinity for metallic SERS substrates. This study presents a label-free SERS detection method for endosulfan, using aggregating agents like potassium chloride (KCl), potassium hydroxide (KOH), potassium bromide (KBr), and sodium hydroxide (NaOH) to modify the behavior of Ag colloidal nanoparticles (NPs) and enhance the SERS signal of endosulfan molecules trapped within formed hot-spots. We analyzed the UV–Vis spectra, the hydrodynamic diameter, and zeta-potential of Ag NPs with the addition of these agents and endosulfan. Successful detection of both α- and ß- endosulfan isomers at μM concentrations in both ethanol and methanol was achieved with KOH-treated Ag NPs. The method was also applied to detect endosulfan in real water samples, along with simultaneous detection of λ-cyhalothrin, showcasing its capability to identify multiple analytes. The selectivity and specificity were confirmed using a mixture of endosulfan and thiabendazole, highlighting the crucial role of selecting the appropriate aggregating agent for each analyte. Overall, the findings emphasize the potential of aggregating agents to mediate the SERS enhancement of endosulfan, facilitating simple and rapid protocols for environmental pollutant detection, while shedding light on the intricate interplay between NP behavior, surface chemistry, and analyte interaction.

Digital-twin-based active input refinement for insertion loss estimation and QoT optimization in C and C + L networks

Quality of transmission (QoT) prediction is a fundamental function in optical networks. It is typically embedded within a digital twin and used for operational tasks, including service establishment, service rerouting, and (per-channel or per-amplifier) power management to optimize the working point of services and hence to maximize their capacity. Inaccuracy in QoT prediction results in additional, unwanted design margins. A key contributor to QoT inaccuracy is the uncertain knowledge of fiber insertion loss, e.g., the attenuation due to connector losses at the beginning or at the end of each fiber span, as such loss cannot be directly monitored. Indeed, insertion losses drive the choice of the launch power in fiber spans, which in turn drive key physical effects, including the Kerr and stimulated Raman scattering (SRS) effects, which affect services’ QoT. It is thus important to estimate (and detect possibly anomalous) fiber insertion losses at each span. We thereby propose a novel active input refinement (AIR) technique using active probing to estimate insertion losses in C and C + L systems. Here, active probing consists of adjusting amplifier gains span by span to slightly alter SRS. The amount of adjustment must be sufficient to be measurable (such that insertion losses can be inferred from the measures) but small enough to have a negligible impact on running services in a live network. The method is validated by simulations on a European network with 30 optical multiplex sections (OMSs) in C and C + L configurations and by lab experiments on a C-band network, demonstrating that AIR significantly improves insertion loss estimation, network QoT optimization, and QoT prediction compared with other state-of-the-art monitoring techniques. This work underscores the critical role of accurate estimation of QoT inputs in enhancing optical network performance.

Development of an Enhanced Surface-Enhanced Raman Scattering (SERS) Plasmonic Sensor for the Detection of Klebsiella Pneumoniae Bacteria

Development of an Enhanced Surface-Enhanced Raman Scattering (SERS) Plasmonic Sensor for the Detection of Klebsiella Pneumoniae Bacteria

Efficient generation of multi-order Raman radiation in aqueous solutions derived from -CH2 and -NH2 vibrations via cascaded four-wave mixing and Stokes processes.

Multiple coherent radiations are achieved in a water-3-aminopropanol (3AP) mixed solution through cascaded four-wave mixing (C-FWM) and cascaded Stokes (C-Stokes) processes, both driven by stimulated Raman scattering (SRS) in this work. The O-H vibration peak from water is replaced by the emergence of the -NH2 symmetric stretching Raman peaks from 3AP, with intensity approaching that of the -CH2 symmetric stretching peak. The dual-wavelength SRS signals for the -NH2 and -CH2 stretching vibrations have a relatively small frequency interval of about 400 cm-1 (16 nm). By varying the 3AP concentration and pump energy, these two peaks from 3AP act as new pump sources, enabling the successful generation of up to 16th-order Stokes and 5th-order anti-Stokes radiation through C-FWM and C-Stokes processes. The resulting spectrum spans a broad wavenumber range from -3318 to 6629 cm-1 (452 to 822 nm), offering a new approach for broadband coherent light sources and multi-order Raman spectra in liquid media.

Correction to “Customization of Nanogap Arrays Using Stereolithography and Nanoskiving for Surface-Enhanced Raman Scattering”

Correction to “Customization of Nanogap Arrays Using Stereolithography and Nanoskiving for Surface-Enhanced Raman Scattering”

An Activity-Based Sensing Approach to Multiplex Mapping of Labile Copper Pools by Stimulated Raman Scattering.

Molecular imaging with analyte-responsive probes offers a powerful chemical approach to studying biological processes. Many reagents for bioimaging employ a fluorescence readout, but the relatively broad emission bands of this modality and the need to alter the chemical structure of the fluorophore for different signal colors can potentially limit multiplex imaging. Here, we report a generalizable approach to multiplex analyte imaging by leveraging the comparably narrow spectral signatures of stimulated Raman scattering (SRS) in activity-based sensing (ABS) mode. We illustrate this concept with two copper Raman probes (CRPs), CRP2181 and CRP2153.2, that react selectively with loosely bound Cu(I/II) and Cu(II) ions, respectively, termed the labile copper pool, through copper-directed acyl imidazole (CDAI) chemistry. These reagents label proximal proteins in a copper-dependent manner using a dye scaffold bearing a 13C≡N or 13C≡15N isotopic SRS tag with nearly identical physiochemical properties in terms of shape and size. SRS imaging with the CRP reagents enables duplex monitoring of changes in intracellular labile Cu(I) and Cu(II) pools upon exogenous copper supplementation or copper depletion or genetic perturbations to copper transport proteins. Moreover, CRP imaging reveals reciprocal increases in labile Cu(II) pools upon decreases in activity of the antioxidant response nuclear factor-erythroid 2-related factor 2 (NRF2) in cellular models of lung adenocarcinoma. By showcasing the use of narrow-bandwidth ABS probes for multiplex imaging of copper pools in different oxidation states and identifying alterations in labile metal nutrient pools in cancer, this work establishes a foundation for broader SRS applications in analyte-responsive imaging in biological systems.

Detection of brain metastases from blood using Brain nanoMET sensor: Extracellular vesicles as a dynamic marker for metastatic brain tumors

Brain metastases account for a significant number of cancer-related deaths with poor prognosis and limited treatment options. Current diagnostic methods have limitations in resolution, sensitivity, inability to differentiate between primary and metastatic brain tumors, and invasiveness. Liquid biopsy is a promising non-invasive alternative; however, current approaches have shown limited efficacy for diagnosing brain metastases due to biomarker instability and low levels of detectable tumor-specific biomarkers. This study introduces an innovative liquid biopsy technique using extracellular vesicles (EVs) as a biomarker for brain metastases, employing the Brain nanoMET sensor. The sensor was fabricated through an ultrashort femtosecond laser ablation process and provides excellent surface-enhanced Raman Scattering functionality. We developed an in vitro model of metastatic tumors to understand the tumor microenvironment and secretomes influencing brain metastases from breast and lung cancers. Molecular profiling of EVs derived from brain-seeking metastatic tumors revealed unique, brain-specific signatures, which were also validated in the peripheral circulation of brain metastasis patients. Compared to primary brain tumor EVs, we also observed an upregulation of PD-L1 marker in the metastatic EVs. A machine learning model trained on these EV molecular profiles achieved 97% sensitivity in differentiating metastatic brain cancer from primary brain cancer, with 94% accuracy in predicting the primary tissue of origin for breast metastasis and 100% accuracy for lung metastasis. The results from this pilot validation suggest that this technique holds significant potential for improving metastasis diagnosis and targeted treatment strategies for brain metastases, addressing a critical unmet need in neuro-oncology.

Distinctive Electrochemical Surface-Enhanced Raman Spectroscopy and Its Application for DNA-Sensor

Raman scattering is used in basic research on the physical chemistry of molecules and practical analysis applications for molecular detection. To obtain sufficient intensity of Raman scattering, Surface-enhanced Raman Scattering (SERS) is adopted, in which signals are amplified by the localized surface plasmons of metallic nanomaterials. Electrochemical surface-enhanced Raman spectroscopy (EC-SERS) is employed to further enhance SERS signals. Conventional EC-SERS further enhances signals by simply biasing the SERS substrate and forming a resonance condition in which a charge transfer between the SERS substrate and Raman-active molecules can occur.We amplified Raman signals using an electrochemical reaction in a different way from conventional EC-SERS. We provided a potential to the SERS substrate in the presence of a plasmonic precursor to generate secondary plasmonic layer and to induce additional chemical enhancement, resulting in the significant amplification of SERS signal. To deepen our understanding of the phenomena occurring in the EC-SERS process, we fabricated a nanoporous Au substrate and systematically varied its characteristics (e.g., pore size, thickness of a porous layer) and observed the dynamic response of the EC-SERS signal. The condition of the SERS substrate that maximizes the EC-SERS signal was explored.An application experiment was conducted to detect DNA with high sensitivity under these experimental conditions. DNA capture was achieved via a sandwich hybridization procedure: capture DNA was immobilized onto the SERS substrate and bound to a portion of the target DNA, while probe DNA with a tethered Raman-active probe bound to the remaining portion. Raman-active probes were positioned near SERS substrate only in the presence of target DNA. EC-SERS signals were measured by inducing a secondary plasmonic surface through an electrochemical reaction. We confirmed that these EC-SERS could serve as effective DNA-sensor, providing higher detection sensitivity than SERS.

Artificial Intelligence-Assisted Stimulated Raman Histology: New Frontiers in Vibrational Tissue Imaging.

Frozen section biopsy, introduced in the early 1900s, still remains the gold standard methodology for rapid histologic evaluations. Although a valuable tool, it is labor-, time-, and cost-intensive. Other challenges include visual and diagnostic variability, which may complicate interpretation and potentially compromise the quality of clinical decisions. Raman spectroscopy, with its high specificity and non-invasive nature, can be an effective tool for dependable and quick histopathology. The most promising modality in this context is stimulated Raman histology (SRH), a label-free, non-linear optical process which generates conventional H&E-like images in short time frames. SRH overcomes limitations of conventional Raman scattering by leveraging the qualities of stimulated Raman scattering (SRS), wherein the energy gets transferred from a high-power pump beam to a probe beam, resulting in high-energy, high-intensity scattering. SRH's high resolution and non-requirement of preprocessing steps make it particularly suitable when it comes to intrasurgical histology. Combining SRH with artificial intelligence (AI) can lead to greater precision and less reliance on manual interpretation, potentially easing the burden of the overburdened global histopathology workforce. We review the recent applications and advances in SRH and how it is tapping into AI to evolve as a revolutionary tool for rapid histologic analysis.

Electrochemical and in Situ Raman Spectroscopic Characterization of Ni Surface Using Inorganic Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

・Introduction Anion exchange membrane water electrolyzer (AEMWE) is expected to reduce the production cost by using base metals for the electrocatalysts and to have high electrolytic efficiency due to its membrane electrode assembly (MEA) structure. The improvement of electrochemical activity and durability of the catalysts remains one of the essential issues for practical application. At present, Ni based oxide is one of the essentially candidate catalysts for both the anode and cathode of AEMWE.Ni is easily oxidized and formed the oxygen-containing adsorbates. The formation of Ni surface oxides depends strongly on the synthesis condition, dopant elements, and the applied potentials. Their peak assignment in the potential-dependent spectra are only possible with well-controlled surfaces. Therefore, an accurate understanding of the surface states and the catalytic reaction process on Ni oxide surface requires the Ni catalyst with well-controlled surface and a highly sensitive analytic technique. Herein, we introduced the inorganic shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to confirm the surface states and surface reaction precisely.The SHINERS is the advanced mode of the surface-enhanced Raman Scattering (SERS) and can detect the Raman signals enhanced by the local electromagnetic field generated on the surface of the nano-amplifier by an applied laser. The SERS has some priorities to detect the signals non-destructively at in situ/operando conditions from extremely small amount of samples at the molecular level, such as self-assembled monolayers and partial surface adsorbates. Introduction of the inorganic shell on the surface of nano-amplifier prevents direct contact and interaction between the sample and the nano-amplifier, selectively detecting intrinsic surface information of samples. In this experiment, the SHINERS technique can provide spectral features of the thin layers of the Ni oxide with high sensitivity and surface selectivity to detect the surface adsorbates in detail.・Experiment In situ SHINERS measurements were performed in 0.1 mol L-1 KOH aqueous electrolyte (Ar-saturated) at room temperature, using a homemade in situ Raman cell equipped with a Ag/AgCl reference electrode and a Pt counter electrode, while all potentials were quoted vs. the reversible hydrogen electrode (RHE). In the Raman measurements, Au nanoparticles coated with an alkaline-resistant zirconia shell were introduced as an optical nano-amplifier at the surface coverage of ca. 20%. Raman spectra were acquired using the Confocal Microscope Laser Raman Spectrometer (Horiba Jobin Yvon LabRAM HR Evolution). The excitation laser source was 632.8 nm He-Ne laser with the typical power of max. 0.1 mW on the surface. The spectrometer was equipped with an 800 mm focal length monochrometer with a long working distance objective lens (50× magnification, OLYMPUS).・Results and discussion Electrochemical measurements and in situ SHINERS have captured a detail surface features at different potential range, including the redox profile between metallic Ni and α-Ni(OH)2, the phase transition from α-Ni(OH)2 to β-Ni(OH)2, as well as the oxidation process from β-Ni(OH)2 to β-Ni(O)OH on a flat Ni electrode in alkaline condition, together with the formation of the γ-Ni(O)OH and the precursor species of the oxygen evolution reaction (OER) on the Ni electrode. Weak bands of each oxygen-containing adsorbate in the few layers of surface oxide film were assigned in the function of applied potential, revealing difference with those in literatures observed on the thick layers of Ni oxides. In situ SHINERS studies, incorporated with the electrochemical studies, on a flat Ni electrode allow us to propose a general scheme presenting relationships between the metallic Ni and various oxygen-containing adsorbates formed during the potential scan in the range between hydrogen and oxygen evolution reaction. In addition, the potential-dependent catalytic activity of Ni surface and nano-catalysts with be discussed at the conference. Figure 1

Detangling Ion Transport and Lithium Dendritic Growth Using Stimulated Raman Scattering Microscopy

Ion transport is one of the fundamental processes in batteries, directly impacting energy density, power density, and cycling lifetime. However, ion concentration in electrolyte is usually low (0.01 M to 1 M), while ion diffusion coefficient is extremely high (10^-6 cm^2/s), making characterization of this process extremely difficult. Conventional characterization techniques such as transmission electron microscopy, nuclear magnetic resonance, and synchrotron radiation have encountered significant challenges on this topic, leaving ion transport process inside working batteries largely unknown.Stimulated Raman Scattering microscopy (SRS) is a recently emerging imaging technique, offering a speed approximately 10^8 times faster than conventional Raman spectrometers. It provides extremely high concentration, time, and spatial resolution, along with high selectivity and non-invasiveness. In our study, SRS was employed for the first time to dynamically image ion depletion within batteries and the growth of lithium dendrites in situ, providing visualization and quantitative analysis of ion distribution in liquid electrolytes. A three-stage lithium deposition process is uncovered, corresponding to no depletion, partial depletion, and full depletion of lithium ions. Further analysis reveals a feedback mechanism between the lithium dendrite growth and heterogeneity of local ionic concentration on lithium metal electrode, which can be effectively suppressed by artificial solid electrolyte interphase.We further explored lithium dendrite growth in PEO solid polymer electrolyte, but found unexpected opposite behaviors in solid polymer electrolytes: concentration polarization can induce phase transformation in a PEO electrolyte, forming a new PEO-rich but salt-/plasticizer-poor phase at the lithium/electrolyte interface, as unveiled by SRS. The new phase has a significantly higher Young’s modulus (1–3 GPa) than a bulk polymer electrolyte (<1 MPa). We hereby propose a design rule for PEO electrolytes: their compositions should be near the boundary between single-phase and two-phase regions in the phase diagram so that the applied current can induce the formation of a mechanically rigid PEO-rich phase to suppress lithium whiskers.This study revealed the growth mechanism of lithium dendrites and proposed solutions to suppress metallic lithium dendrites. SRS offers unprecedented ability over conventional characterization tools in studying reaction mechanisms, and is going to play a crucial role in research fields such as batteries, supercapacitors, and catalysis in the future.

(Invited) Porous Silicon Nanowires for SERS Platforms and Thermo-Electrical Materials

Since the discovery of Metal Assisted Chemical Etching (MACE) 1, the direct dependence of the resulting silicon nanostructures as extruded by the metal mask has led to several applications on large area, like photovoltaics2, Surface Enhanced Raman Scattering platforms 3, energy harvesting and thermo-electrics4. Coupling MACE with nanosphere lithography5 allowed the fabrication of silicon nanowire arrays with desired dimensions and functionalities over a large area.In this communication, an overview of some applications of porous silicon nanowires will be given with particular attention to the realization of porous nanowires, losing structural stiffness and gaining high flexibility, used for the development of gold-coated active substrates for surface-enhanced Raman spectroscopy (SERS) and for the development of thermoelectric devices where the thermal transport properties of single nanowires are of interest.Surface-enhanced Raman spectroscopy, discovered in 19746, is a promising analytical tool for detecting chemical and biological species at single molecule levels in liquid and gas phases. Its specificity and sensitivity have led to applications in electrochemistry, environmental analysis, and bio-sensing. Thanks to the development of electromagnetic and chemical theories to explain SERS, it is now widely accepted that the phenomenon is primarily attributed to electromagnetic field enhancement. The light enhancement is achieved through the excitation of localized surface plasmon resonances (LSPRs) in gaps, crevices, or sharp features of plasmonic materials, typically noble and coinage metals with nanoscale features. This process generates Raman hot spots due to the proximity of metal nanostructures separated by a few nanometers. In our work, we optimized the fabrication of gold-coated flexible porous silicon nanowires understanding the formation of the hot spots at the tip-to-tip sites of nanowires bundles7 and controlling the patterning over large area obtained by nanospheres self-assembly to correlate the nanospheres distribution in a monolayer to the final SERS substrates enhancement performances and homogeneity8. Moreover, we integrated the SERS measurements with the absolute quantification of the number of active molecules contributing to the SERS signal by means of reference-free synchrotron-based X-ray fluorescence measurements9. The progress in this work on SERS will be discussed.Furthermore, in the field of thermoelectric materials and devices, an accurate evaluation of the thermal and electrical conductivity of single nanowires is mandatory, so our efforts are addressed to the production and the advanced characterization of single porous silicon nanowires. MACE represents the most suitable method to produce long nanowires with desired diameter and aspect ratio (> 1:200) for single-wire electrical and thermal characterization10. Porous silicon nanowires of 100 nm of diameter obtained by MACE from highly doped substrates have been nanomanipulated, bonded and measured on a custom-designed MEMS platform 18, and the thermal conductivity resulted being of 0.8 W/MK, lower than thermal silicon dioxide values and almost two orders of magnitude less than crystalline bulk silicon. The thermal and electrical conductivity of the silicon nanowires can be modified by conformally coating the nanostructures with ALD-based deposition of ZnO. The STEM characterization of the structural properties of the coated single nanowires is discussed together with the thermal and electrical conductivity. Acknowledgements Part of this work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101007417, having benefited from the access provided by CEA LETI in Grenoble within the framework of the NFFA-Europe Pilot Transnational Access Activity, proposal [ID310]. Part of this work has been carried out at Nanofacility Piemonte, a laboratory supported by the ‘‘Compagnia di San Paolo’’ Foundation, and at QR Lab - Micro & Nanolaboratories, INRiM. References Li, X. & Bohn, P. W. Appl. Phys. Lett. 77, 2572–2574 (2000). Peng, K. Q. & Lee, S. T. Advanced Materials vol. 23 (2011). Qiu, T., Wu, X. L., Shen, J. C., Ha, P. C. T. & Chu, P. K. Nanotechnology 17, (2006). Dávila, D. et al. J. Micromechanics Microengineering 21, 104007 (2011). Huang, Z., Geyer, N., Werner, P., De Boor, J. & Gösele, U. Advanced Materials vol. 23 285–308 (2011). McQuillan, A. J. Notes Rec. R. Soc. Lond. 63, 105–109 (2009). Kara, S. A. et al. RSC Adv. 6, 93649–93659 (2016). Cara, E., Mandrile, L., Ferrarese Lupi, F., Giovannozzi, A.M., Dialameh, M., Portesi, C., Sparnacci, K., De Leo, N., Rossi, A.M. and Boarino, L., Sci. Rep, 8(1), 11305 (2018). Cara, E., Mandrile, L., Sacco, A., Giovannozzi, A.M., Rossi, A.M., Celegato, F., De Leo, N., Hönicke, P., Kayser, Y., Beckhoff, B. and Marchi, D., Journal of Materials Chemistry C, 8(46), 16513-16519 (2020).Ferrando-Villalba, P. et al. Sci. Rep. 8, (2018). Figure 1

Neuromorphic Computing Based on Few-Molecule Vibration Dynamics Achieved By Surface-Enhanced Raman Scattering and Ion-Gating Stimulation

1. ObjectiveArtificial intelligence (AI), which has achieved high-level capabilities in cognition, learning, and inference through technological innovations such as deep learning, has greatly benefited human society, however, problems such as high energy consumption and increased communication traffic have also emerged. As a solution to these problems, physical reservoir computing (PRC), a kind of neuromorphic computing that uses the nonlinear behavior of physical systems to efficiently process information, has been attracting attention.[1-5] Although various methods of PRC have been reported (e.g., memristors, electrochemical cells, optical circuits, soft bodies, and spintronics devices), the molecular computing approach is promising to realize the ultimate compact and integrated PRC. However, the number of molecules in a conventional molecular reservoir system is huge, and the information processing capability of a single molecule to several molecules has not been elucidated.[2,3] In this study, we developed a few-molecule reservoir computing (FM-RC) that utilizes the molecular vibration dynamics of single to few molecules of para-mercaptobenzoic acid (pMBA). The information processing capability of few molecules was evaluated by performing information processing tasks such as blood glucose level prediction on FM-RC. [4]2. ExperimentsFigure 1a shows a schematic diagram of the measurement system of FM-RC. In order to accurately track the nonlinear dynamics of a few molecules, surface-enhanced Raman scattering (SERS) measurements using WOx nanorods/silver nanoparticles (WOx@Ag-NPs) were performed, and molecular vibration reflecting the structural change of pMBA based on the local proton adsorption change due to ion-gating stimulation was observed in the molecular dynamics (Fig. 1b) reflecting the conformational changes of pMBA based on the local proton adsorption changes induced by ion-gating stimuli. The obtained SERS spectra were regarded as independent artificial neurons (nodes) at specific sampling wavenumbers, and these node states were used to perform various information processing tasks (Fig. 1c).3. Results and DiscussionAlthough FM-RC consists of only a few molecules, it achieved a high accuracy of 95.1% to 97.7% in the nonlinear waveform transformation task and 94.3% in the analysis task of second-order nonlinear equations, and achieved the highest computational performance among physical reservoirs in the task of predicting blood glucose levels for type I pediatric diabetes patients (Fig. 1d).[4-6] These high computational performances are attributed to the independent nonlinearity of the nodes distributed in the wavenumber direction, i.e., the high dimensionality achieved by the complex and diverse response characteristics of each vibrational mode to the proton adsorption amount. In this presentation, the origin of the high computational performance of FM-RC will be discussed in terms of nonlinearity and high dimensionality, which are the main properties that determine the performance of PRCs.

Simple Preparation of Au Nanoparticles by Arc Plasma Deposition (APD) and Its Application for SERS Sensing

Nanoparticles express many beneficial properties. For examples, large specific surface area and high catalytic activity. These properties are used in fuel cell catalysis and other applications such as biosensing since porous nanoparticles have a high adsorption area for substances. Nanoparticles for biosensing technology are used to not only bind with biomolecules but also observe the behavior of the biomolecules, such as cells. In this study, we focused on Au nanoparticles with plasmon resonance, i.e., one of the optical properties. When metal nanoparticles, such as Au or Ag, are irradiated with light, free electrons of metal nanoparticles are affected by the electric field of the light and cause plasmon resonance, which produces a unique optical phenomenon. On the plasmon resonance, the light with a specific wavelength is strongly absorbed and scattered, resulting in vivid colors in the near-infrared range. This phenomenon is called Localized Surface Plasmon Resonance (LSPR). This phenomenon is used in sensors (to detect changes in refractive index and use as markers) as well as Surface-Enhanced Raman Scattering (SERS), which is used to evaluate material identification. In this study, we focused on SERS sensing. SERS is powerful tool to identify and quantify the materials since Raman spectrum reflect chemical bonds of substances and concentration. Because Raman spectrometers can non-destructively measure substances through glass, bags, or opaque containers, they are used to investigate explosives, toxic chemicals, and other counter-terrorism measures. Therefore, a SERS sensor with a simple fabrication process is required.There are two methods for producing the nanoparticles: a physical method (pulverization method), and a chemical method (agglomeration method). Physical methods create nanoparticles by crushing powder, but it is difficult to control the particle size. By contrast, chemical methods can be mainly classified into wet methods and dry methods. The wet method is reducing ions in liquid therefore it requires waste liquid treatment, which places a burden on the environment. Therefore, we focused on Arc Plasma Deposition (APD), which is one of dry methods and a low environmental impact. APD allows nanoparticles to be easily produced in one step. Nanoparticles were fabricated using APD and applied to SERS sensor. APD can control the deposition molecules by digital, meaning the number of pulses. The parameters of APD are capacitance of trigger capacitor, applied voltage, the number of pulses, and substrate temperature. At first, we investigated its vapor deposition characteristics when the substrate temperature is kept at room temperature.The amount of deposited molecules is proportional to the square of the discharge voltage (V), directly proportional to the capacitance (C), and dependent on the number of pulses (n) :(E=1/2×nCV2). Applied volage was ragged from 70 to 100 V, a capacitance was set as 2200 μF, and the number of pulses were from 5 to 80 times. The pressure during vapor deposition was 1.3×10-3 Pa. The average particle diameter and coverage ratio were calculated by observing the prepared sample via a Scanning Transmission Electron Microscope (STEM). It was clear that particle diameter and coverage ratio increased with the applied voltage and the number of pulses. We evaluated the fabricated sensor exhibited SERS activity using rhodamine 6G (R6G), a fluorescent substance. In this study, we evaluated analytical enhancement factor (AEF) to quantify our SERS The experimental results show that theAEF was determined as 2.13×10³. We also created a calibration curve for R6G ranging from 10-7 to 10-4 M. As the results, R6G-derived peaks were not identified at 10⁻⁷ M, but we identified them from 10-6 to 10-4 M (Fig. 1) and were able to create the linear calibration curve. Figure 1

Multi-pass Cavity-Enhanced Raman Spectroscopy of Complex Natural Gas Components

BackgroundThe concentration of natural gas components significantly impacts the transportation, storage, and utilization of natural gas. Consequently, implementing online monitoring and leak detection systems is vital to guarantee the efficient use of natural gas and to uphold its safe and stable operation. Raman spectroscopy offers distinctive benefits, including high selectivity, superior precision, and the capability to detect multiple gas components simultaneously using a single-wavelength laser. Nevertheless, the inherent weakness of the Raman effect in gases results in limited detection sensitivity for Raman spectroscopy, which may not suffice for specific practical applications. ResultsThis paper presents a study investigating the detection of natural gas's complex components using a high-sensitivity multi-cavity enhanced Raman spectroscopy technique. An enhanced folded Z-shaped multi-pass cavity has been constructed to amplify the interaction length between the laser and the gas, thereby significantly boosting the Raman signal intensity by 1000 times. The detection limits for CH4, C2H6, C3H8, n-C4H10, i-C4H10, n-C5H12, i-C5H12, and n-C6H14 gases reached 0.12, 0.53, 0.55, 0.67, 0.28, 0.46, 0.34, and 0.71 ppm, respectively. The least squares method was utilized to establish quantitative relationships between the characteristic peak heights and the concentrations of gases, encompassing both single-component and mixed multi-component systems. Additionally, the natural gas samples were configured and subsequently detected and analyzed. SignificanceAs proposed in this paper, the results indicate that the MPC-CERS system boasts several advantages, including a low detection limit, high quantitative accuracy, excellent detection repeatability, and robust system stability. Furthermore, its capability for real-time monitoring is well-suited to meet the gas detection requirements in practical applications. Consequently, the research presented in this paper offers innovative insights for the online tracking and leak detection of distributed energy natural gas systems.

One‐Pot Polyol Syntheses of Ag Right Bipyramids and Nanocubes, and their Surface‐Enhanced Raman Scattering Properties

One‐Pot Polyol Syntheses of Ag Right Bipyramids and Nanocubes, and their Surface‐Enhanced Raman Scattering Properties

Spaced Hybrid TiO2/Au Nanotube Arrays with Tailored Optical Properties for Surface-Enhanced Raman Scattering.

Controlling the overall geometry of plasmonic materials allows for tailoring their optical response and the effects that can be exploited to enhance the performance of a wide range of devices. This study demonstrates a simple method to control the size and distribution of gold (Au) nanoparticles grown on the surface of spaced titanium dioxide (TiO2) nanotubes by varying the deposition time of magnetron sputtering. While shorter depositions led to small and well-separated Au nanoparticles, longer depositions promoted the formation of quasi-continuous layers with small interparticle gaps. The optical spectra of Au/TiO2 nanotubes showed a region of strong absorption (200-550 nm) for all samples and a region of decreasing absorption with an increase of effective Au thickness (550-1100 nm). This behavior led to distinct trends in the Raman signal enhancement of the underlying TiO2 nanotubes depending on the excitation laser wavelength. Furthermore, the quasi-continuous layers formed at higher effective Au thicknesses promoted an amplification of the signal and an improvement in the detection limit of target molecules in surface-enhanced Raman scattering (SERS) experiments. These findings suggest a simple method for designing efficient devices with tailored light absorption and potential applications in detectors and other optical devices.

Dynamic Phase Behavior of Amorphous Solid Dispersions Revealed with In Situ Stimulated Raman Scattering Microscopy.

This study reports the application of in situ stimulated Raman scattering (SRS) microscopy for real-time chemically specific imaging of dynamic phase phenomena in amorphous solid dispersions (ASDs). Using binary ritonavir and poly(vinylpyrrolidone-vinyl acetate) films with different drug loadings (0-100% w/w) as model systems, we employed SRS microscopy with fast spectral focusing to analyze ASD behavior upon contact with a dissolution medium. Multivariate unmixing of the SRS spectra allowed changes in the distributions of the drug, polymer, and water to be (semi)quantitatively imaged in real time, both in the film and the adjacent dissolution medium. The SRS analyses were further augmented with complementary correlative sum frequency generation and confocal reflection for additional crystallinity and phase sensitivity. In the ASDs with drug loadings of 20, 40, and 60% w/w, the water penetration front within the film, followed by both surface-directed and bulk phase separation in the film, was apparent but differed quantitatively. Additionally, drug-loading and phase-dependent polymer and drug release behavior was imaged, and liquid-liquid phase separation was observed for the 20% drug loading ASD. Overall, SRS microscopy with fast spectral focusing provides quantitative insights into water-induced ASD phase phenomena, with chemical, solid-state, temporal, and spatial resolution. These insights are important for optimal ASD formulation development.

Strategic modal management for enhanced stimulated Raman scattering in optical fibers

Raman fiber lasers have attracted significant attention for their unique ability to generate high-power output at specific wavelengths. Theoretically, the quantum loss associated with the nonlinear Stokes frequency shift in Raman scattering is lower than that from energy level transitions in conventional ytterbium-doped lasers, suggesting that Raman lasers should achieve higher conversion efficiencies. However, in practice, the efficiency of high-power Raman lasers often fails to reach these theoretical limits, with power scaling being impeded by 2 nd order Raman effects. In this article, we delve into the dynamics of stimulated Raman scattering within few-mode fibers, offering an in-depth analysis of the underlying physical mechanisms from multiple perspectives. Our research combines theoretical analysis with experimental research, covering the frequency domain, spatial domain, and nonlinear behavior. The experimental findings indicate that strategically increasing the proportion of higher-order modes in the injected light can enhance the conversion efficiency of the Raman process and effectively suppress higher-order Raman and four-wave mixing nonlinear processes. This study provides profound theoretical insights and practical guidance, contributing significantly to the ongoing development and optimization of Raman laser technology.

Multimodal Imaging Unveils the Impact of Nanotopography on Cellular Metabolic Activities.

Nanoscale surface topography is an effective approach in modulating cell-material interactions, significantly impacting cellular and nuclear morphologies, as well as their functionality. However, the adaptive changes in cellular metabolism induced by the mechanical and geometrical microenvironment of the nanotopography remain poorly understood. In this study, we investigated the metabolic activities in cells cultured on engineered nanopillar substrates by using a label-free multimodal optical imaging platform. This multimodal imaging platform, integrating two photon fluorescence (TPF) and stimulated Raman scattering (SRS) microscopy, allowed us to directly visualize and quantify metabolic activities of cells in 3D at the subcellular scale. We discovered that the nanopillar structure significantly reduced the cell spreading area and circularity compared to flat surfaces. Nanopillar-induced mechanical cues significantly modulate cellular metabolic activities with variations in nanopillar geometry further influencing these metabolic processes. Cells cultured on nanopillars exhibited reduced oxidative stress, decreased protein and lipid synthesis, and lower lipid unsaturation in comparison to those on flat substrates. Hierarchical clustering also revealed that pitch differences in the nanopillar had a more significant impact on cell metabolic activity than diameter variations. These insights improve our understanding of how engineered nanotopographies can be used to control cellular metabolism, offering possibilities for designing advanced cell culture platforms which can modulate cell behaviors and mimic natural cellular environment and optimize cell-based applications. By leveraging the unique metabolic effects of nanopillar arrays, one can develop more effective strategies for directing the fate of cells, enhancing the performance of cell-based therapies, and creating regenerative medicine applications.