Raman Probe Research Articles

New perspective for probe development assessing salivary biomarkers in periodontal affected diabetic patients

The study was performed to have chairside identification of specific biomarkers for diagnosing periodontal disease in diabetic patients at a very early stage using spectroscopic probe design and parameters. Patients were divided into groups: Group (A) - healthy patients, Group (B) - patients with type 2 Diabetes Mellitus (DM) without chronic periodontitis, Group (C) - mild chronic periodontitis patients without type 2 DM, Group (D) - moderate chronic periodontitis patients without type 2 DM, Group (E) - mild chronic periodontitis patients with type 2 DM, and Group (F) - moderate chronic periodontitis patients with type 2 DM. Conceptual and practical design for achieving chairside Raman probe has specific tips and optics applied based on temperature of the mouth. Activation of Matrix metalloproteinase-8 (MMP-8) within salivary specimens were analysed. For molecular docking studies, binding pocket was selected with larger SiteScore. MMP-8 and C-terminal cross-linked telopeptide (CTX) of type I collagen levels in saliva were analysed using MMP-8 Immunoassay. Raman measurements were carried out of salivary specimens. Continuous variables were compared by one‑way analysis of variance. Rate of MMP-8/CTX release was significantly higher in diabetes chronic moderate periodontitis group (p < 0.05). Heat map colour scheme of green indicates increase while the yellow track lines indicate a decrease. Striking difference is seen in Amide regions amongst different groups with lowest intensities seen in diabetic chronic moderate groups and the highest amongst healthy patients (p < 0.05). Major peak at 1447 cm−1 differed in intensities between all groups. Chairside identification of specific biomarkers to diagnosing periodontal disease at a very early stage using spectroscopic probe design and parameters has shown potential.

A Highly Stable Two-Photon Ratiometric Fluorescence Probe for Real-Time Biosensing and Imaging of Nitric Oxide in Brain Tissues and Larval Zebrafish

A Highly Stable Two-Photon Ratiometric Fluorescence Probe for Real-Time Biosensing and Imaging of Nitric Oxide in Brain Tissues and Larval Zebrafish

Multi-functional plasmonic fabrics: A flexible SERS substrate and anti-counterfeiting security labels with tunable encoding information

Multi-functional plasmonic fabric comprised of silver nanoparticles (Ag NPs) and cotton gauze was fabricated through an in-situ growth method. Ag NPs with high density were immobilized on the surface of cotton fibers. The plasmonic cotton gauze exhibits excellent flexible features, temporal stability and SERS enhancement factors close to 105 × . The plasmonic cotton gauze was labelled with multiplexed Raman probes and used for anti-counterfeiting applications. The encoding information could be readily changed by adjusting the ratio between components in the mixture of Raman probe molecules. This novel strategy could create rich Raman information based on the combination of a few Raman probes, which significantly increases the security levels in anti-counterfeiting. The plasmonic cotton gauze was also employed as a flexible SERS substrate for sensing pesticide from irregular surfaces of orange by a simple swiping process.

Investigating microcrystalline cellulose crystallinity using Raman spectroscopy

Microcrystalline cellulose (MCC) is a semi-crystalline material with inherent variable crystallinity due to raw material source and variable manufacturing conditions. MCC crystallinity variability can result in downstream process variability. The aim of this study was to develop models to determine MCC crystallinity index (%CI) from Raman spectra of 30 commercial batches using Raman probes with spot sizes of 100 µm (MR probe) and 6 mm (PhAT probe). A principal component analysis model separated Raman spectra of the same samples captured using the different probes. The %CI was determined using a previously reported univariate model based on the ratio of the peaks at 380 and 1096 cm−1. The univariate model was adjusted for each probe. The %CI was also predicted from spectral data from each probe using partial least squares regression models (where Raman spectra and univariate %CI were the dependent and independent variables, respectively). Both models showed adequate predictive power. For these models a general reference amorphous spectrum was proposed for each instrument. The development of the PLS model substantially reduced the analysis time as it eliminates the need for spectral deconvolution. A web application containing all the models was developed.Graphic abstract

Transparent, Flexible Plasmonic Ag NP/PMMA Substrates Using Chemically Patterned Ferroelectric Crystals for Detecting Pesticides on Curved Surfaces.

Transparent and flexible surface-enhanced Raman scattering (SERS) substrates have attracted much interest for the detection of probe molecules on the curved surfaces of real samples, but a facile route to fabricate such substrates is still lacking. Herein, we present a rationally designed, high-performance flexible SERS substrate fabricated using a simple drop and peel-off technique for the ultrasensitive detection of pesticides. The proposed SERS substrate consists of a polymethyl methacrylate (PMMA) film anchored with plasmonic silver nanoparticles (Ag NPs), which are photoreduced using chemically patterned ferroelectric templates. The photoreduced Ag NPs extracted onto the PMMA film offer strong electromagnetic enhancement and produce intensive hotspots for the effective enhancement of the Raman signal. They provide superior SERS performance for the detection of parathion (PT) and fenitrothion (FNT) at trace-level concentrations of 10-9 M and 10-10 M with excellent enhancement factors in the order of 108 and 109, respectively. Moreover, the Ag NP/PMMA SERS substrate has good spot-to-spot uniformity and batch-to-batch reproducibility with the reservation of high detection sensitivity even after the mechanical deformation of bending and torsion up to 50 cycles. The multiplex detection ability is also investigated for the simultaneous detection of PT and FNT. To ensure the practical feasibility, the in-situ, real-time detection of PT and FNT on the curved surfaces of tomato and lemon using a fiber-coupled Raman probe is performed with limits of detection of 4.24 × 10-8 M and 2.74 × 10-9 M. The proposed Ag NP/PMMA flexible SERS substrate possesses unique features, such as easy fabrication through a simple, economical, rapid process, and facilitates straightforward implementation of in-situ SERS detection on curved fruit/vegetable surfaces.

Sub millimetre flexible fibre probe for background and fluorescence free Raman spectroscopy.

Using the shifted-excitation Raman difference spectroscopy technique and an optical fibre featuring a negative curvature excitation core and a coaxial ring of high numerical aperture collection cores, we have developed a portable, background and fluorescence free, endoscopic Raman probe. The probe consists of a single fibre with a diameter of less than 0.25 mm packaged in a sub-millimetre tubing, making it compatible with standard bronchoscopes. The Raman excitation light in the fibre is guided in air and therefore interacts little with silica, enabling an almost background free transmission of the excitation light. In addition, we used the shifted-excitation Raman difference spectroscopy technique and a tunable 785 nm laser to separate the fluorescence and the Raman spectrum from highly fluorescent samples, demonstrating the suitability of the probe for biomedical applications. Using this probe we also acquired fluorescence free human lung tissue data.

Fabrication and Application of SERS-Active Cellulose Fibers Regenerated from Waste Resource.

The flexible SERS substrate were prepared base on regenerated cellulose fibers, in which the Au nanoparticles were controllably assembled on fiber through electrostatic interaction. The cellulose fiber was regenerated from waste paper through the dry-jet wet spinning method, an eco-friendly and convenient approach by using ionic liquid. The Au NPs could be controllably distributed on the surface of fiber by adjusting the conditions during the process of assembling. Finite-difference time-domain theoretical simulations verified the intense local electromagnetic fields of plasmonic composites. The flexible SERS fibers show excellent SERS sensitivity and adsorption capability. A typical Raman probe molecule, 4-Mercaptobenzoicacid (4-MBA), was used to verify the SERS cellulose fibers, the sensitivity could achieve to 10−9 M. The flexible SERS fibers were successfully used for identifying dimetridazole (DMZ) from aqueous solution. Furthermore, the flexible SERS fibers were used for detecting DMZ from the surface of fish by simply swabbing process. It is clear that the fabricated plasmonic composite can be applied for the identifying toxins and chemicals.

Quantification of soluble solids and individual sugars in apples by Raman spectroscopy: A feasibility study

This study reports the feasibility of using Raman spectroscopy for quantification of soluble solids and individual sugars in apples. Six different commercial apple varieties were measured by Raman spectroscopy at three different steps: 1) Intact apples with skin, 2) apples without skin and 3) juices obtained from apples. Results indicated that it is possible to measure Raman signals to a depth of 8 mm into the apple with a wide area Raman probe. Multivariate calibration models were established to evaluate how well Raman spectra can be used to estimate the quality parameters SSC (%), total sugars, glucose, fructose and sucrose. Estimation accuracy for SSC was comparable with what is achievable with near-infrared spectroscopy: Root mean square error of cross-validation (RMSECV) = 0.66, 0.46 and 0.72 % and coefficients of determination (R2) = 0.70, 0.85 and 0.63 for intact apples, apples without skin and juices, respectively. Sucrose and glucose were well estimated with RMSECV of 2.8, 1.9, 2.1 mg/mL for glucose and 5.8, 3.9 and 3.7 mg/mL for sucrose, for the three sample cases, respectively. Coefficient of determination was higher than 0.82 for all models. Regression coefficients for all calibration models highlighted identifiable Raman bands that could be related to the target sugars.

Intraoperative imaging device for glioblastoma multiforme surgery: Review of Raman‐based intraoperative imaging and introduction of a novel handheld probe technology

AbstractGlioblastoma multiforme (GBM) is a malignant primary brain tumor with poor prognosis. Degree of resection contributes greatly to improved prognosis. Review of the literature for intraoperative hand‐held Raman probes technology to enhance maximal gross total resection was conducted. Additionally, we introduce study of Raman shift of graphene, as the biosensing interface with tumor, to enhance the current model of hand‐held probes. Retrospective analysis of the literature was conducted using pubMed database to delineate various intraoperative hand‐held probes with a particular focus on Raman spectroscopic (RS) technology in neuronal tissue. Summary of our group's recent publications in this area is included. Literature review demonstrates ability of Raman Spectroscopy (RS) to distinguish normal glial tissue from that of pathologic tissue (GBM) with great accuracy, sensitivity, and specificity. Furthermore, addition of nano sensors, such as gold particles, has proven successful in enhancing the detection of tumor and normal brain interface. Our work has previously demonstrated graphene as a feasible biosensor to be used in conjunction with RS in detecting GBM cells. Intra operative handheld Raman probes (RP) have advanced overtime as an additive tool to help surgeons clearly distinguish tumor and normal brain interface. Optimal biosensors can significantly enhance the detection of such margins, thereby, aiding in more precise gross total resection.

Skeletal Structure of the Chromophore of Photoactive Yellow Protein in the Excited State Investigated by Ultraviolet Femtosecond Stimulated Raman Spectroscopy.

We studied ultrafast structural dynamics of photoactive yellow protein (PYP) using ultraviolet femtosecond stimulated Raman spectroscopy. By employing the Raman pump and probe pulses in the ultraviolet region, resonantly enhanced, rich vibrational features of the excited-state chromophore were observed in the fingerprint region. In contrast to the marked spectral change reported for the excited-state chromophore in solution, in the protein, all of the observed Raman bands in the fingerprint region did not show any noticeable spectral shifts nor band shape changes during the excited-state lifetime of PYP. This indicates that the significant skeletal change does not occur on the chromophore in the excited state of PYP and that the trans conformation is retained in its lifetime. Based on the femtosecond Raman data of PYP obtained so far, we discuss a comprehensive picture of the excited-state structural dynamics of PYP.

Multiplexed live-cell profiling with Raman probes

Single-cell multiparameter measurement has been increasingly recognized as a key technology toward systematic understandings of complex molecular and cellular functions in biological systems. Despite extensive efforts in analytical techniques, it is still generally challenging for existing methods to decipher a large number of phenotypes in a single living cell. Herein we devise a multiplexed Raman probe panel with sharp and mutually resolvable Raman peaks to simultaneously quantify cell surface proteins, endocytosis activities, and metabolic dynamics of an individual live cell. When coupling it to whole-cell spontaneous Raman micro-spectroscopy, we demonstrate the utility of this technique in 14-plexed live-cell profiling and phenotyping under various drug perturbations. In particular, single-cell multiparameter measurement enables powerful clustering, correlation, and network analysis with biological insights. This profiling platform is compatible with live-cell cytometry, of low instrument complexity and capable of highly multiplexed measurement in a robust and straightforward manner, thereby contributing a valuable tool for both basic single-cell biology and translation applications such as high-content cell sorting and drug discovery.

Raman spectroscopy for real-time and in situ monitoring of mechanochemical milling reactions.

Solid-state milling has emerged as an alternative, sustainable approach for preparing virtually all classes of compounds and materials. In situ reaction monitoring is essential to understanding the kinetics and mechanisms of these reactions, but it has proved difficult to use standard analytical techniques to analyze the contents of the closed, rapidly moving reaction chamber (jar). Monitoring by Raman spectroscopy is an attractive choice, because it allows uninterrupted data collection from the outside of a translucent milling jar. It complements the already established in situ monitoring based on powder X-ray diffraction, which has limited accessibility to the wider research community, because it requires a synchrotron X-ray source. The Raman spectroscopy monitoring setup used in this protocol consists of an affordable, small portable spectrometer, a laser source and a Raman probe. Translucent reaction jars, most commonly made from a plastic material, enable interaction of the laser beam with the solid sample residing inside the closed reaction jar and collection of Raman-scattered photons while the ball mill is in operation. Acquired Raman spectra are analyzed using commercial or open-source software for data analysis (e.g., MATLAB, Octave, Python, R). Plotting the Raman spectra versus time enables qualitative analysis of reaction paths. This is demonstrated for an example reaction: the formation in the solid state of a cocrystal between nicotinamide and salicylic acid. A more rigorous data analysis can be achieved using multivariate analysis.

In Situ Growth Large Area Silver Nanostructure on Metal Phenolic Network Coated NAAO Film and Its SERS Sensing Application for Monofluoroacetic Acid.

Rapid screening monofluoroacetic acid (FAcOH) is responsible for preventing chemical poisoning and food safety events. Whereas surface enhanced Raman scattering (SERS) spectra is an effective tool for detecting forbidden chemicals, it is difficult to directly detect FAcOH due to its small Raman scattering cross section as well as weak adsorption on SERS substrates. In this work, the metal phenolic supramolecular networks (MPNs, i.e., the tannic acid and Fe3+ complex) were fabricated on the commercial nanoanodic aluminum oxide film (NAAO) for assisting in situ chemical deposition highly uniform Ag nanostructure over large areas (the NAAO@AgNS). The low cost and simple fabrication process made the NAAO@AgNS a single-use consumable. For FAcOH detection, a specific derivative reaction between FAcOH and thiosalicylic acid (TSA) was introduced. By taking TSA as the Raman probe, its SERS signal attenuated constantly with the increasing amount of FAcOH. For improving quantitative accuracy, thiocyanate (SCN-) was introduced on the NAAO@AgNS as an internal standard; thus, the characteristic peak intensity ratios associated with TSA and SCN- (I1035/I2125) were fitted to the concentration of FAcOH. It was demonstrated that the SERS assay achieved good sensitivity and selection toward FAcOH with the limit of quantitation (LOD) as low as 50 nmol L-1. The NAAO@AgNS featured with highly sensitive, uniform, and consistent SERS performances could easily extend to wide SERS applications.

Microplasma-Engineered Nanoassembly of Core-Shell Plasmonic Nanoparticles for Ultrasensitive Flexible Surface-Enhanced Raman Scattering Substrates

Surface enhance Raman scattering (SERS) is emerging as a powerful technology for the label-free detection of various biological and chemical species. One of the important but often overlooked considerations in the design of surface-enhanced Raman scattering (SERS) substrates for trace detection is the efficiency of sample collection. Conventional designs based on rigid substrates such as silicon, alumina, and glass resist conformal contact with the surface under investigation, making the sample collection inefficient.The aim of our work is to develop an effective paper-based test strip to achieve high SERS performance for biosensing. Here we present one-step green-fabrication of bimetallic nanoparticles Au/Ag (3D porous stricture) loaded on filter paper using microplasma system. This approach requires a minimal fabrication effort and cost, also contains nanoisland and nanogaps (<20nm) on paper substrate to generate a high density of hot spot(~2000/um2). The 3D biomimetric substrate shows a low detection limit for Rhodamine 6G, high averaged enhancement factor, excellent signal uniformity, good stability and suitability in biosensing. In addition, the novel substrate was applied in label-free folic acid, dopamine and other Raman probe detection with small amount and low concentration of analyte, and it exhibited effective SERS platform potential for bio-detection and bio-sensing. Figure 1

Switchable stimulated Raman scattering microscopy with photochromic vibrational probes

Photochromic probes with reversible fluorescence have revolutionized the fields of single molecule spectroscopy and super-resolution microscopy, but lack sufficient chemical specificity. In contrast, Raman probes with stimulated Raman scattering (SRS) microscopy provides superb chemical resolution for super-multiplexed imaging, but are relatively inert. Here we report vibrational photochromism by engineering alkyne tagged diarylethene to realize photo-switchable SRS imaging. The narrow Raman peak of the alkyne group shifts reversibly upon photoisomerization of the conjugated diarylethene when irradiated by ultraviolet (UV) or visible light, yielding “on” or “off” SRS images taken at the photoactive Raman frequency. We demonstrated photo-rewritable patterning and encryption on thin films, painting/erasing of cells with labelled alkyne-diarylethene, as well as pulse-chase experiments of mitochondria diffusion in living cells. The design principle provides potentials for super-resolution microscopy, optical memories and switches with vibrational specificity.

Study on SERS activity of Au-Ag bimetallic nanostructures synthesized using different reducing agents

Abstract The Au-Ag bimetallic nanostructures were synthesized independently using three different reducing agents [ascorbic acid (C6H8O6), sodium borohydride (NaBH4) and tri-sodium citrate dihydrate (C6H9Na3O9)] to understand their effect on the morphology of the nanostructures. The nanostructures obtained using the reducing agents mentioned in above order, were found in sprouted potato, cubical, and prolate spheroid (PS) shapes. All the synthesized nanostructures were characterized using energy-dispersive X-ray spectroscopy and extinction spectroscopy. The surface enhanced Raman scattering (SERS) activity of all these nanostructures was studied using Raman probe solutions with micro and nanomolar concentrations. Relatively, the PS shaped nanostructures were found to be more stable and better for SERS studies. Therefore, these nanostructures were further characterized by Transmission electron microscopy and X-ray photoelectron spectroscopy. The usefulness of PS shaped Au-Ag nanostructures was also demonstrated by recording the spectra of both methylene blue (MB) and 4-Aminothiophenol (4-ATP) solutions with femtomolar concentration. The experimental enhancement factor (EEF) was found to be around 1.1 × 1011 in case of MB solution with femtomolar concentration. The possible origin for the EEF is explained using quasi-static theory and Finite Element Method (FEM) based simulations.

Effective fabrication of porous Au-Ag alloy nanorods for in situ Raman monitoring catalytic oxidation and reduction reactions

Porous metal nanostructures exhibit excellent catalytic properties due to their high surface-to-volume ratios and abundant catalytic active sites. However, it is still challenging to control nanopores density and structural features in a facile route and the preparation of porous alloy nanorods for catalytic application has not been well explored. In this work, we demonstrate a synthetic strategy to fabricate highly porous Au–Ag alloy nanorods (P-AuAgNRs) by critically dealloying Ag atoms from homogeneous solid Au–Ag alloy nanorods (AuAgNRs). Combining the merits of the tunable plasmonic properties of noble metal nanorods, excellent stabilities of alloys, and superior catalytic activities of porous structures, we use the P-AuAgNRs as a Raman probe for the in situ monitoring of the catalytic oxidation of 3,3’,5,5’ tetramethylbenzidine (TMB) and reduction of 4-nitrothiophenol (4-NTP). We also compare their composition-dependent catalytic activities. The results show that P-AuAgNRs possess superior chemical stability and higher catalytic activity than those of core-shell structures due to synergistic structural and chemical mechanisms. This strategy provides a predictive design approach for the next-generation alloy catalysts with high-performance.

Azo-Enhanced Raman Scattering for Enhancing the Sensitivity and Tuning the Frequency of Molecular Vibrations.

Raman scattering provides stable narrow-banded signals that potentially allow for multicolor microscopic imaging. The major obstacle for the applications of Raman spectroscopy and microscopy is the small cross section of Raman scattering that results in low sensitivity. Here, we report a new concept of azo-enhanced Raman scattering (AERS) by designing the intrinsic molecular structures using resonance Raman and concomitant fluorescence quenching strategies. Based on the selection of vibrational modes and the enhancing unit of azobenzenes, we obtained a library of AERS molecules with specific Raman signals in the fingerprint and silent frequency regions. The spectral characterization and molecular simulation revealed that the azobenzene unit conjugated to the vibrational modes significantly enhanced Raman signals due to the mechanism of extending the conjugation system, coupling the electronic–vibrational transitions, and improving the symmetry of vibrational modes. The nonradiative decay of azobenzene from the excited state quenched the commitment fluorescence, thus providing a clean background for identifying Raman scattering. The most sensitive AERS molecules produced Raman signals of more than 4 orders of magnitude compared to 5-ethynyl-2′-deoxyuridine (EdU). In addition, a frequency tunability of 10 distinct Raman bands was achieved by selecting different types of vibrational modes. This methodology of AERS allows for designing small-molecule Raman probes to visualize various entities in complex systems by multicolor spontaneous Raman imaging. It will open new prospects to explore innovative applications of AERS in interdisciplinary research fields.

Real-Time Monitoring of Aqueous Organic Reduction Reactions Using Ex Situ Fiber Optic Raman Spectroscopy

Here, we demonstrate the use of Raman spectroscopy for real-time monitoring and analysis of the reduction of nitroarenes and ketones in an aqueous medium using an external fiber optic probe. In one case, the catalytic reduction of nitroarenes using hydrazine hydrate and a nickel boron composite catalyst was studied by monitoring the disappearance of the distinct nitro stretching frequency at 1350 cm–¹. Quantitative Raman spectroscopic techniques showed that the aqueous reduction reaction proceeds with pseudo-first-order kinetics. The biphasic reduction of cyclic ketones by aqueous dimethylamine borane (DMAB) was also examined. A nonpolar carbonyl compound and aqueous DMAB were mixed and an external Raman probe monitored the loss of the starting material via the carbonyl stretch at 1713 cm–¹ in the top organic phase. We also found that saturated aliphatic carbonyl compounds were reduced much faster than α,β-unsaturated and aromatic carbonyl compounds. Additionally, DMAB was found to be unreactive toward epoxides and esters, allowing for selective reduction of aliphatic ketones. Density functional theory analysis suggests that carbonyl reduction occurred through a dissociation mechanism followed by a concerted hydride transfer pathway.

Competitive immunosensor for sensitive and optical anti-interference detection of imidacloprid by surface-enhanced Raman scattering

The sensitive detection of pesticides in complex environment is important but still challenging in presence of organic-rich water sample and food matrix. Herein, we reported a nitrile-mediated SERS immunosensor for sensitive and optical anti-interference determination of imidacloprid. Raman tag contained CN bond could provide a sharp characteristic peak in the Raman-silent spectral window (1800 ~ 2800 cm−1), which could resist the optical noises from the fingerprint region (<1800 cm−1). Aucore-Agshell bimetallic nanocuboid (AuNR@Ag) connected with antigen and Raman tag was used as Raman probe, while Fe3O4 magnetic nanoparticle functionalized with anti-imidacloprid antibody was applied as signal enhancer. Owing to the specific recognition ability between antigen and antibody, the competitive system with imidacloprid was formed. Under the optimal condition, the linear relationship was developed in the range of 10–400 nM. Finally, the SERS immunosensor was successfully applied to determine imidacloprid in real samples with recoveries from 96.8% to 100.5%.