Raman Probe Research Articles

Robotic Raman Spectroscopy for Rapid Fatty Acid Measurement in Salmon Fillets

In this work, we present a robotic solution to measure the content of omega-3 fatty acids in salmon fillets using Raman spectroscopy. Fatty acid composition is a significant quality parameter for the salmon farming industry as a high content contributes to consumer health, a redder fillet, and fewer unwanted dark spots, leading to a higher fillet price. The current methodology for evaluating omega-3 fatty acids in salmon fillets is conducted manually using a Raman probe, which is tiresome, error-prone, time-consuming, and demands labor. To overcome these drawbacks, we propose a semi-autonomous robotic scanning platform composed of a visual servoing system and a motion planning algorithm. We then develop a proof-of-concept demonstration using commercial Raman technology, a 6-DoF robot arm, an RGB camera, and a linear conveyor module, emulating an industrial environment on a laboratory scale. The proposed robot and sensor integration methodology effectively performs real-time measurement of fatty acid content in salmon fillets moving on a conveyor belt at low and high speeds, preventing human-prone errors and increasing operating efficiency.

High wavenumber Raman spectroscopy for intraoperative assessment of breast tumour margins.

Optimal oncological results and patient outcomes are achieved in surgery for early breast cancer with breast conserving surgery (BCS) where this is appropriate. A limitation of BCS occurs when cancer is present at, or close, to the resection margin - termed a 'positive' margin - and re-excision is recommended to reduce recurrence rate. This is occurs in 17% of BCS in the UK and there is therefore a critical need for a way to assess margin status intraoperatively to ensure complete excision with adequate margins at the first operation. This study presents the potential of high wavenumber (HWN) Raman spectroscopy to address this. Freshly excised specimens from thirty patients undergoing surgery for breast cancer were measured using a surface Raman probe, and a multivariate classification model to predict normal versus tumour was developed from the data. This model achieved 77.1% sensitivity and 90.8% specificity following leave one patient out cross validation, with the defining features being differences in water content and lipid versus protein content. This demonstrates the feasibility of HWN Raman spectroscopy to facilitate future intraoperative margin assessment at specific locations. Clinical utility of the approach will require further research.

Emergence of Raman Spectroscopy as a Probing Tool for Theranostics.

Although medical advances have increased our grasp of the amazing morphological, genetic, and phenotypic diversity of diseases, there are still significant technological barriers to understanding their complex and dynamic character. Specifically, the complexities of the biological systems throw a diverse set of challenges in developing efficient theranostic tools and methodologies that can probe and treat pathologies. Among several emerging theranostic techniques such as photodynamic therapy, photothermal therapy, magnetic resonance imaging, and computed tomography, Raman spectroscopy (RS) is emerging as a promising tool that is a label-free, cost-effective, and non-destructive technique. It can also provide real-time diagnostic information and can employ multimodal probes for detection and therapy. These attributes make it a perfect candidate for the analytical counterpart of the existing theranostic probes. The use of biocompatible nanomaterials for the fabrication of Raman probes provides rich structural information about the biological molecules, cells, and tissues and highly sensitive information down to single-molecule levels when integrated with advanced RS tools. This review discusses the fundamentals of Raman spectroscopic tools such as surface-enhanced Raman spectroscopy and Resonance Raman spectroscopy, their variants, and the associated theranostic applications. Besides the advantages, the current limitations, and future challenges of using RS in disease diagnosis and therapy have also been discussed.

Hydrophobic interaction enables rapid enrichment of volatile metabolites on Au/TiO2 based SERS substrates for ultrasensitive bacteria detection.

Bacterial contamination in diets is a major threat to human health and a global health problem. The development of sensitive methods for rapid discrimination of benign and pathogenic bacteria is essential. Herein, using self-standing Au/TiO2 nanotubes as a surface-enhanced Raman spectroscopy (SERS) substrate, rapid and sensitive bacteria discrimination is achieved via the hydrophobic interaction between the volatile metabolites released from pathogenic bacteria and the SERS substrate. With the modification of hydrocarbon moieties, the SERS substrate demonstrates improved binding ability and rapid enrichment performance towards volatile metabolites through the hydrophobic interaction. The metabolites enriched on the hytocarbon moieties then drive the replacements of Raman probes from the SERS substrate, as demonstrated by the remarkably decreased Raman signals in the silent region (1800-2800 cm-1). Using Escherichia coli (E. coli) as the model pathogenic bacteria, the SERS platform exhibits good discrimination ability between benign and pathogenic bacteria within 4 min and allows detection of E. coli at a level of as few as 3 × 100 cells per mL. Considering that volatile metabolites are associated with the activity of bacteria, this technique can be further applied as a guide for antibiotic treatment, demonstrating reliable and rapid guidance for interrelated bacteria therapy.

Surface-enhanced Raman scattering of a gold core-silver shell-sponge substrate for detection of thiram and diquat.

Aiming at the difficulty of traditional pesticide sampling, a low-cost and convenient flexible surface enhanced Raman scattering (SERS) gold core-silver shell-sponge (Au-Ag-sponge) substrate was synthesized by chemical reduction. The SERS substrate consisted of Au-AgNPs and a melamine sponge. The sponge had a rich open pore structure, which could well "capture" Au-AgNPs, generating a large number of "hot spots". The SERS enhancement activity of the flexible substrate was characterized with rhodamine 6G (R6G) Raman probe molecules. The substrate showed good activity to 10-12 M rhodamine 6G with an enhancement factor (EF) of 7.72 × 106. Applying this substrate to the qualitative and quantitative detection of pesticide residues, the results showed that the Raman intensity was well related to the concentration of pesticide solution with the range of 0.1-10 mg L-1 of thiram and 1-10 mg L-1 of diquat. Furthermore, the substrate was analyzed by finite difference time domain (FDTD) simulation and the results were in good agreement with the experimental results. The reason for the difference in Raman signals of pesticide molecules on the same substrate was the different binding modes of Au-AgNPs on the sponge. Finally, we pointed out the advantages of flexible substrates in the field of pesticide residues, as well as future opportunities and challenges.

In Situ High-Temperature Raman Spectroscopy via a Remote Fiber-Optic Raman Probe

This study demonstrated for the first time an in situ high-temperature fiber-optic Raman probe to study the structure of glass and slag samples at temperatures up to 1400 °C. A customized external telescope was integrated into a portable fiber-optic Raman probe to extend the optical working distance to allow the probe to work in a high-temperature environment. Three samples were evaluated to demonstrate the functionality of the high-temperature fiber-optic Raman probe. Room temperature and high-temperature Raman spectra were successfully collected and analyzed. In addition, a deconvolution algorithm was used to identify peaks in the spectrum that could then be related to the molecular structure of components in each sample. This flexible and reliable high-temperature Raman measurement method has great potential for various applications, such as materials development, composition, and structure monitoring during high-temperature processing, chemical identification, and process monitoring in industrial production.

Quantitative fat analysis of milk using a line-illumination spatially offset Raman probe through carton packaging.

Milk is a popular dairy product that provides various nutrients, but consuming too much saturated fat from milk can increase the risk of diseases and obesity. Adulterated milk containing toxic substances can be harmful to human health, and toxic substances can enter the milk at any stage of production. Thus, analytical technologies for detecting various nutrients and harmful substances inside the package are a key requisite for the assessment of dairy products on the market. In this study, we developed a Raman spectroscopic method as a quantitative tool for assessing the milk fat composition and detecting toxic chemicals in packaged milk. Using a line-illumination deep Raman system based on both conventional optics and novel optical fibers, we could quantitatively discriminate the Raman signals of milk fat from those of the packaging materials. Finally, the present system allowed the detection of melamine in adulterated milk (employed as a toxicity model) using a multiple-depth fiber probe.

An all metasurface-based fiber needle probe for Raman spectroscopy

Optical fiber-based spectroscopy sensors are widely used for industrial and biomedical applications. They normally consist of at least one excitation fiber and one collection fiber. However, the excitation and collection fibers are placed side by side, so the focal spots do not coincide. In addition, Raman probes whose excitation and emission span a wide wavelength range are limited by wavelength-dependent focal length variation, low sensitivity, and bulky size impeding their clinical adoption. To overcome the challenges, we propose an all metasurface integrated fiber solution. The metasurface technology is well suited for this application because it relies on specially designed nanostructures to manipulate light properties in an ultrathin footprint. Here we used our earlier demonstrated dual-wavelength excitation Raman probe as an example. The two excitation fibers at 671 nm and 785 nm feature a hybrid metasurface lens (metalens) including a narrow band pass filter and an off-axis focusing metalens. The collection fiber at 810—910 nm features an achromatic broadband on-axis focusing metalens. Simulation results show that by integrating the metalenses, the focal spots of the excitation beams and the collection beam coincide with a beam size of 4.6 µm, 4.6 µm, and 11.3 µm in the x-, y-, and z-axis, respectively. Moreover, the probe size shrinks by 100 times and becomes a needle probe. The needle probe will enable new applications such as small animal in vivo experiments, medical endoscopy experiments, and neonatal skin analysis for hard-to-reach areas. Furthermore, the proposed solution can be applied to work with any optical fiber-based spectroscopy sensors because the designs can be readily fabricated and put into practical use.

Frequency Changes in Terminal Alkynes Provide Strong, Sensitive, and Solvatochromic Raman Probes of Biochemical Environments.

The C≡C stretching frequencies of terminal alkynes appear in the "clear" window of vibrational spectra, so they are attractive and increasingly popular as site-specific probes in complicated biological systems like proteins, cells, and tissues. In this work, we collected infrared (IR) absorption and Raman scattering spectra of model compounds, artificial amino acids, and model proteins that contain terminal alkyne groups, and we used our results to draw conclusions about the signal strength and sensitivity to the local environment of both aliphatic and aromatic terminal alkyne C≡C stretching bands. While the IR bands of alkynyl model compounds displayed surprisingly broad solvatochromism, their absorptions were weak enough that alkynes can be ruled out as effective IR probes. The same solvatochromism was observed in model compounds' Raman spectra, and comparisons to published empirical solvent scales (including a linear regression against four meta-aggregated solvent parameters) suggested that the alkyne C≡C stretching frequency mainly reports on local electronic interactions (i.e., short-range electron donor-acceptor interactions) with solvent molecules and neighboring functional groups. The strong solvatochromism observed here for alkyne stretching bands introduces an important consideration for Raman imaging studies based on these signals. Raman signals for alkynes (especially those that are π-conjugated) can be exceptionally strong and should permit alkynyl Raman signals to function as probes at very low concentrations, as compared to other widely used vibrational probe groups like azides and nitriles. We incorporated homopropargyl glycine into a transmembrane helical peptide via peptide synthesis, and we installed p-ethynylphenylalanine into the interior of the Escherichia coli fatty acid acyl carrier protein using a genetic code expansion technique. The Raman spectra from each of these test systems indicate that alkynyl C≡C bands can act as effective and unique probes of their local biomolecular environments. We provide guidance for the best possible future uses of alkynes as solvatochromic Raman probes, and while empirical explanations of the alkyne solvatochromism are offered, open questions about its physical basis are enunciated.

Self-Referenced Synthetic Urinary Biomarker for Quantitative Monitoring of Cancer Development.

Urinary monitoring of diseases has gained considerable attention due to its simple and non-invasive sampling. However, urinalysis remains limited by the dearth of reliable urinary biomarkers and the intrinsically enormous heterogeneity of urine samples. Herein, we report, to our knowledge, the first renal-clearable Raman probe encoded by an internal standard (IS)-conjugated reporter that acts as a quantifiable urinary biomarker for reliable monitoring of cancer development, simultaneously eliminating the impact of sample heterogeneity. Upon delivery of the probes into tumor microenvironments, the endogenously overexpressed β-glucuronidase (GUSB) can cleave the target-responsive residues of the probes to produce IS-retained gold nanoclusters, which were excreted into host urine and analyzed by Au growth-based surface-enhanced Raman spectroscopy. As a result, the in vivo GUSB activity was transformed into in vitro quantitative urinary signals. Based on this IS-encoded synthetic biomarker, both the cancer progression and therapy efficacy were quantitatively monitored, potentiating clinical implications.

9-Cyano-10-telluriumpyronin Derivatives as Red-light-activatable Raman Probes.

Photoactivatable fluorescence probes can track the dynamics of specific cells or biomolecules with high spatiotemporal resolution, but their broad absorption and emission peaks limit the number of wavelength windows that can be employed simultaneously. In contrast, the narrower peak width of Raman signals offers more scope for simultaneous discrimination of multiple targets, and therefore a palette of photoactivatable Raman probes would enable more comprehensive investigation of biological phenomena. Herein we report 9-cyano-10-telluriumpyronin (9CN-TeP) derivatives as photoactivatable Raman probes whose stimulated Raman scattering (SRS) intensity is enhanced by photooxidation of the tellurium atom. Modification to increase the stability of the oxidation product led to a julolidine-like derivative, 9CN-diMeJTeP, which is photo-oxidized at the tellurium atom by red light irradiation to afford a sufficiently stable oxidation product with strong electronic pre-resonance, resulting in a bathochromic shift of the absorption spectrum and increased SRS intensity.

Structural and functional imaging of brains.

Analyzing the complex structures and functions of brain is the key issue to understanding the physiological and pathological processes. Although neuronal morphology and local distribution of neurons/blood vessels in the brain have been known, the subcellular structures of cells remain challenging, especially in the live brain. In addition, the complicated brain functions involve numerous functional molecules, but the concentrations, distributions and interactions of these molecules in the brain are still poorly understood. In this review, frontier techniques available for multiscale structure imaging from organelles to the whole brain are first overviewed, including magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), serial-section electron microscopy (ssEM), light microscopy (LM) and synchrotron-based X-ray microscopy (XRM). Specially, XRM for three-dimensional (3D) imaging of large-scale brain tissue with high resolution and fast imaging speed is highlighted. Additionally, the development of elegant methods for acquisition of brain functions from electrical/chemical signals in the brain is outlined. In particular, the new electrophysiology technologies for neural recordings at the single-neuron level and in the brain are also summarized. We also focus on the construction of electrochemical probes based on dual-recognition strategy and surface/interface chemistry for determination of chemical species in the brain with high selectivity and long-term stability, as well as electrochemophysiological microarray for simultaneously recording of electrochemical and electrophysiological signals in the brain. Moreover, the recent development of brain MRI probes with high contrast-to-noise ratio (CNR) and sensitivity based on hyperpolarized techniques and multi-nuclear chemistry is introduced. Furthermore, multiple optical probes and instruments, especially the optophysiological Raman probes and fiber Raman photometry, for imaging and biosensing in live brain are emphasized. Finally, a brief perspective on existing challenges and further research development is provided.

OGC P28 Raman Needle Probe Lymph Node Assessment for Oesophageal Cancer: The DOLOMITE Study

Abstract Background Oesophageal cancer (OC) accounts for 3% of all new cancer diagnosis in the UK. Presentation is often late, reflected in a poor 5-year survival rate of 12%. The importance of identifying lymph node (LN) metastases has been demonstrated as the single biggest prognostic factor. The current ‘gold standard’ diagnosis of LN metastases is from histopathological assessment of the tissue after surgical resection of the primary tumour and surrounding tissue. The use of imaging techniques to try and gain this information preoperatively is standard practice but far from perfect. Raman spectroscopy (RS) has been investigated as a diagnostic tool to detect cancer and pre-cancerous change in the oesophagus, and preliminary work demonstrating the application of vibrational spectroscopy (Raman and FTIR) to LN analysis has been undertaken. The development of Raman needle probes (RNP) with potential for use in-vivo furthers the clinical impact. The DOLOMITE study started recruitment in the summer of 2022 to investigate the ability of RNP to identify the presence of malignant deposits in resected lymph nodes. Methods Patients identified by the clinical team as needing oesophagectomy to treat their OC were invited to participate in the study. After the specimen has been resected, prior to formalin fixation, three lymph nodes are dissected representing gastric, para-oesophageal and sub-carinal nodes. These are bisected longitudinally with half remaining with the specimen. The half for research is snap frozen in liquid nitrogen until needed for analysis. Adjacent sections are cut from the nodes to create slides for Raman mapping and conventional H&E staining. The bulk node left is used for Raman probe analysis. Spectral data is then analysed using MATlab. Results At this early stage, our initial measurements have provided information used for calibration in advance of completing recruitment. The Raman mapping has been assessed for correlation with the pathology identified in the H&E slides taken from the lymph node block. This data in turn has provided the background for developing interpretation of the Raman probe data, with further samples we will use this to create a classification model. Conclusions With ongoing recruitment the study will be able to fully report by September 2023.

Raman Signal Enhancement by DABCYL-Substitution on DNA Aptamer for Identification of Cellular ATP.

Raman probes have attracted widespread attention for the visualization and identification of biomolecules, because they can be applied to identify detailed chemical structures, detect multiple molecules simultaneously, and visualize cellular functional molecules. However, the biological application of Raman probes is still limited because of their weak signal intensity. Herein, we present a molecular system that shows an enhanced Raman signal using a nonfluorescent dye. We introduced a DABCYL molecule bearing an acetylene unit into thymidine at the 5-position. The resulting modified nucleobase, dDAU, showed a robust signal around 2200 cm-1, which was attributed to the acetylene unit, due to resonance Raman induced by the DABCYL group. We further prepared a DNA aptamer modified with dDAU, and characterized the change of the Raman spectra. Combination with gold nanoparticles, which enhanced the Raman signal by surface-enhanced Raman scattering (SERS), allowed sensitive detection of cellular adenosine derivatives including ATP. Thus, the present system is a promising tool for the detection of biological materials by Raman spectroscopy.

Facile fabrication of field deployable surface enhanced Raman scattering smart sand from sea sand

This paper proposed a simple strategy for the preparation of field deployable SERS sensor, namely the SERS smart sand (SERS3), by modifying sea sand with Ag NPs. The as prepared SERS3 sensor could be easily spread onto the surface of interest for sensing, and was able to detect ppb level of Raman probe with low magnification lens. The feasibility for in situ detection of KNO3 in soil was also demonstrated.

Arduino-based wireless spectrometer: a practical application

We provide a technical report on designing an Arduino-based wireless spectrometer using an old spectrometer. The designed spectrometer is environmentally friendly and cost-effective and can be used in physical and analytical laboratories. The Arduino-based wireless spectrometer enables students to understand the fundamental theory of spectroscopy and wireless communication among instruments. The rotating motions of the mirror and grating turret inside the spectrometer are controlled by a pre-written source code based on the Arduino program. This procedure can give an insight into spectroscopic analysis and telecommunication skills using computer-based software. Using our customized spectrometer, we measure Raman spectra from a silicon wafer, 4-nitrobenzenethiol, and rhodamine 6G, which serve as representative Raman probe molecules. From our results, we conclude that our approach provides intuitions for wide applications of Arduino-based chemical instruments.Graphical

Contactless and robust dielectric microspheres-assisted surface-enhanced Raman scattering sensitivity improvement for anthrax biomarker detection.

This report presents a contactless and robust dielectric microspheres (DMs)-assisted surface enhanced Raman scattering (SERS) enhancement method to improve SERS detection sensitivity detection sensitivity. DMs that could focus and collect light were embedded within the polydimethylsiloxane (PDMS) film to avoid direct contact with the analytical solution and improve detection reliability. The as prepared DMs embedded PDMS DMs PD MS film was integrated with a microfluidic technique to enhance the SERS signal of a liquid substrate. Detection in microfluidic systems can reduce reagent consumption, shorten assay time, and avoid evaporation of the colloid substrate solution. The robustness and potential influencing factors of DMs PDMS film assisted SERS enhancement (DERS) were evaluated using 4-aminothiophenol (4-ATP) as the Raman probe. The sensing performance of the proposed method toward dipicolinic acid (DPA) was evaluated, and an evident signal intensification was obtained. Remarkably, the DMs PDMS film can also be implemented on solid substrates. A proof-of-concept experiment was performed by covering the DMs PDMS film directly over an AgNPs@Si solid substrate wherein a 5.7-fold sensitivity improvement was achieved.

Photonic Technology for In Vivo Monitoring of Hypoxia-Ischemia.

Surveillance of physiological parameters of newborns during delivery triggers medical decision-making, can rescue life and health, and helps avoid unnecessary cesareans. Here, the development of a photonic technology for monitoring perinatal asphyxia is presented and validated in vivo in a preclinical stage. Contrary to state of the art, the technology provides continuous data in real-time in a non-invasive manner. Moreover, the technology does not rely on a single parameter as pH or lactate, instead monitors changes of the entirety of physiological parameters accessible by Raman spectroscopy. By a fiber-coupled Raman probe that is in controlled contact with the skin of the subject, near-infrared Raman spectra are measured and analyzed by machine learning algorithms to develop classification models. As a performance benchmarking, various hybrid and non-hybrid classifiers are tested. In an asphyxia model in newborn pigs, more than 1000 Raman spectra are acquired at three different clinical phases-basal condition, hypoxia-ischemia, and post-hypoxia-ischemia stage. In this preclinical proof-of-concept study, figuresof merit reach 90% levels for classifying the clinical phases and demonstrate the power of the technology as an innovative medical tool for diagnosing a perinatal adverseoutcome.

Molecular Planarization of Raman Probes to Avoid Background Interference for High-Precision Intraoperative Imaging of Tumor Micrometastases and Lymph Nodes.

The intraoperative imaging applications of a large number of Raman probes are hampered by the overlap of their signals with the background Raman signals generated by biological tissues. Here, we describe a molecular planarization strategy for adjusting the Raman shift of these Raman probes to avoid interference. Using this strategy, we modify the backbone of thiophene polymer-poly(3-hexylthiophene) (P3HT), and obtain the adjacent thiophene units planarized polycyclopenta[2,1-b;3,4-b']dithiophene (PCPDT). Compared with P3HT whose signal is disturbed by the Raman signal of lipids in tissues, PCPDT exhibits a 60 cm-1 blueshift in its characteristic signal. Therefore, the PCPDT probe successfully avoids the signal of lipids, and achieves intraoperative imaging of lymph nodes and tumor micrometastasis as small as 0.30 × 0.36 mm. In summary, our study presents a concise molecular planarization strategy for regulating the signal shift of Raman probes, and brings a tunable thiophene polymer probe for high-precision intraoperative Raman imaging.

Development of a coaxial DCF-GRIN fiberoptic Raman probe for enhancing in vivo epithelial tissue Raman measurements.

We report on the development of a novel, to the best of our knowledge, coaxial double-clad-fiber (DCF) and graded-index (GRIN) fiberoptic Raman probe for enhancing epithelial tissue Raman measurements in vivo. The ultra-thin (140 µm outer diameter) DCF-GRIN fiberoptic Raman probe is designed and fabricated with an efficient coaxial optical configuration, whereby a GRIN fiber is spliced onto the DCF to enhance both the excitation/collection efficiency and depth-resolved selectivity. We demonstrate that the DCF-GRIN Raman probe can be used to acquire high-quality in vivo Raman spectra from various oral tissues (e.g., buccal mucosa, labial mucosa, gingiva, mouth floor, palate, and tongue) covering both the fingerprint (800-1800 cm-1) and high-wavenumber (2800-3600 cm-1) regions within sub-seconds. The subtle biochemical differences between different epithelial tissues in the oral cavity can also be detected with high sensitivity, suggesting the potential of the DCF-GRIN fiberoptic Raman probe for in vivo diagnosis and characterization in epithelial tissue.