Portable Raman Spectrometer Research Articles

Fast and on-site detection of fenthion in rice using core-shell Au@Ag nanoparticles and a portable Raman spectrometer

The residue of pesticide fenthion is a common issue in food safety, and how to conveniently detect it is a challenge in the food industry. Therefore, combined with a portable Raman spectrometer, a surface enhanced Raman spectroscopy (SERS) method based on a high-performance substrate Au@AgNPs had been designed for the rapid and sensitive detection of fenthion. Au@AgNPs can be induced to generate more hot spots to improve SERS signals because of their core-shell structure. The quantitative detection of fenthion was achieved under the optimal conditions: pH 7.0, 10−3 M CaCl2, 70 % Au@AgNPs concentration, and 4 min of incubation time. The results showed that the method had a wider detection range of 0.1–100 mg/L, a low detection limit (LOD) of 0.036 mg/L, excellent anti-interference ability, and reproducibility. In addition, the method was successfully validated with the actual sample rice. Therefore, the method had the advantages of being fast, on-site, and easy to use, which is useful for promoting its application.

Inkjet Printing Patterned Plasmonic SERS Platform with Surface-Optimized Paper for Label-Free Detection of Illegal Drugs in Urine.

Rapid quantitative testing of illegal drugs is urgently needed for precisely cracking down on drug crimes. Herein, an optimized paper-based surface-enhanced Raman spectroscopy (SERS) platform with patterned printing of plasmonic nanoparticles was constructed for the on-site quick testing of illegal drugs in urine. The filter paper was first coated with a layer of positive-charged chitosan, so as to reduce its roughness by filling the holes of the cellulose matrix and enhance the adhesion of negative-charged silver ink. Subsequently, hydrophobic modification was performed based on the binary silylation reaction, which could obviously improve the sensitivity of the paper-based SERS substrate by concentrating the amount of analyte. Meanwhile, SERS-active silver ink was fabricated and further printed on the surface of the above modified paper with custom-designed pattern (3 × 6). The performance of this SERS platform was assessed by using crystal violet (CV) as a model tag, and the obtained results proved it possesses excellent sensitivity and reproducibility, in which the relative standard deviation (RSD) dropped remarkably. More importantly, as a proof of concept, rapid detection of standard methylamphetamine (MAMP), one of the most widely abused drugs, was achieved with a limit of detection (LOD) of 1.43 ppb using a portable Raman spectrometer. And it also had a good capability in human urine sample detection, with a correlation index (R2) up to 0.9927. This optimized paper-based SERS platform was easily manufactured, cheap, and portable, providing a new strategy for the on-site detection of illicit drugs.

Rapid identification of milk powder adulteration based on surface-enhanced Raman spectroscopy

In recent years, milk powder adulteration has emerged as a matter of great concern. In this study, a rapid, accurate, and efficient detection method based on surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA) was established to detect milk powder adulteration. The “coffee ring” effect-based gold nanoparticles (Au NPs) as the SERS-enhancing substrate were coupled with a portable Raman spectrometer, which enabled the differentiation of various brands of milk powder and the detection of melamine in milk powder. The substrate exhibited good SERS enhancement ability with an enhancement factor of 104. Furthermore, a strong linear correlation with a correlation coefficient (R2) of 0.9903 was observed between the melamine Raman intensity and concentration from 0.5 to 5.0 mg/kg. The calculated limit of detection of melamine (LOD) was 0.15 mg/kg, while the limit of quantitation (LOQ) was 0.5 mg/kg. In addition, when the method was applied to the detection of melamine in milk powder samples, this method achieved the recovery rates of melamine in milk powder samples ranged from 92.83% to 98.86% with relative standard deviations between 0.84% and 1.14%. In summary, the established method offers the advantages of cost-effectiveness, less sample requirement, and shorter detection time, meeting the needs for milk powder classification and rapid melamine detection.

Noninvasive Raman spectroscopy for the detection of rice bacterial leaf blight and bacterial leaf streak

Plant diseases pose significant threats to agricultural yields and are responsible for nearly 20 % of losses in total food production. Therefore, the rapid detection of plant pathogens is critically important for preventing the rapid development of plant diseases and minimizing crop damage. Raman spectroscopy (RS) has been shown to be effective for detecting living biological samples. Compared with traditional detection methods, RS is fast, sensitive, and non-destructive; it also does not require sample labeling. In this study, we used Laser tweezers Raman spectroscopy combined with convolutional neural networks to detect two closely related strains of bacteria, Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), exuded from bacteria-infected rice leaves. The accuracy of this technique was 97.5 %. For the application of RS in the field, we used the portable Raman spectrometer to detect mock-inoculated as well as Xoo- and Xoc-infected rice leaves at different disease courses. The identification accuracy via this technique was 87.02 % in the early stage, in which no obvious symptoms were apparent. This method also revealed spectral differences in rice leaves caused by the two bacteria, which could be leveraged for subsequent analysis of the molecular mechanism of infection. Our results indicate that RS is a promising approach for the early detection of bacterial diseases in rice in the field, as well as for in-depth single-cell analysis in laboratory settings.

Feasibility study on non-destructive detection of microplastic content in flour based on portable Raman spectroscopy system combined with mixed variable selection method

Microplastics, as emerging environmental pollutants, have garnered considerable attention due to their contamination of both the environment and food. Microplastics can infiltrate the human food chain through multiple pathways, potentially posing health risks to humans. Currently, non-destructive testing of microplastics in food is considered challenging. This study aims to investigate the feasibility of employing a portable Raman spectroscopy system for non-destructive detection of microplastic content (polystyrene, PS; polyethylene, PE) in flour. In this study, a portable spectrometer was used to collect flour spectra of different abundances of microplastics. To enhance the predictive performance of the partial least squares (PLS) model, a mixed variable selection strategy that combined the wavelength interval selection method (Synergy interval partial least squares, siPLS) and the wavelength point selection method (Least absolute shrinkage and selection operator, LASSO; Multiple feature-spaces ensemble by least absolute shrinkage and selection operator, MFE-LASSO) was proposed. Four regression models (PLS, siPLS, siPLS-LASSO, siPLS-MFE-LASSO) were developed and compared for detecting PS and PE content in flour. The siPLS-MFE-LASSO model exhibited the best generalization performance in the prediction set, and was considered to have the best generalization performance (PS: RP2 = 0.9889, RMSEP=0.0344 %; PE: RP2 = 0.9878, RMSEP=0.0361 %). In conclusion, this study has demonstrated the potential of using a portable Raman spectrometer in conjunction with a mixed variable selection algorithm for non-destructive detection of PS and PE content in flour, providing more possibilities for non-destructive detection of microplastic content in food.

Assembly and characterization of an optical fiber probe for use in a portable Raman spectrometer

This study describes the assembly and testing of an optical fiber Raman probe for use in a portable spectrometer using a 785 nm laser. The Raman probe was tested on edible vegetable oils (extra virgin olive, canola, sunflower, corn, and soybean), with the distal end of the probe immersed in each sample. The spectra of a dipyrone tablet and a mothball were also obtained. The silica peaks were subtracted by taking a spectrum with the probe tip immersed in water. The spectra of the samples exhibited characteristic peaks from vibrations of unsaturated fatty acids between 900 and 1800 cm−1, as well as characteristic peaks of silica from 600 to 1200 cm−1. The spectra of the samples after subtraction of the silica spectrum (probe in water) showed characteristic peaks without alterations in position or relative intensities compared without the probe. Exploratory analysis by principal component analysis was able to identify peaks of the constituent fatty acids in the oils and associate them with the oil type. A classification model based on partial least squares regression allowed for the classification of oil spectra with an accuracy of 77%. This study demonstrated the feasibility of coupling a probe to a portable Raman spectrometer with the goal of monitoring and controlling industrial processes.

A combinatorial approach to validate the surface plasmon resonance (SPR) biosensor response

Abstract One of the fundamental challenges of working with surface plasmon resonance (SPR) biosensors is their inherent lack of specificity. Being very sensitive to minute refractive index (RI) changes in their surrounding medium, SPR biosensors are highly susceptible to variations in pH, temperature, and buffer composition. Therefore, it is often necessary to include an additional validation step downstream to SPR biosensing, particularly for clinical analysis. In this proof-of-study work, we have tried to evaluate the utility of surface-enhanced Raman scattering (SERS) tags as secondary labels for validating SPR biosensor response. Accordingly, a Fibre-optic SPR (FO-SPR) biosensor set-up was fabricated by immobilizing anti-BSA antibodies on the sensor platform for capturing and sensing biotinylated-BSA as a model analyte. Subsequently, the bound analyte and the concomitant shift in SPR response were validated by employing streptavidin-functionalized SERS tags. Intriguingly, apart from validation of the SPR response, the SERS tags also significantly improved the sensitivity of the SPR response and provided semi-quantitative information on the bound analyte. Although utilizing SERS tags undermines the label-free tag of SPR biosensors, the huge improvement in sensitivity and specificity of the sensor makes it suitable for clinical analysis. Furthermore, SERS measurements with a portable Raman spectrometer utilized in this study further highlight the potential of this approach for achieving point-of-care (POC) sensing.

Application of Gap Mode Ultrasensitive P-GERTs in SERS-Based Rapid Detection

In surface-enhanced Raman scattering (SERS) detection research, the shape, structure, surface modification, and material selection of nanoparticles can significantly impact the SERS intensity. Petal-like gap-enhanced Raman tags (P-GERTs) possess numerous sharp tips and edges, which generate localized electric field enhancements, further amplifying the electric field enhancement effect on neighboring molecules and enhancing the SERS signal. Additionally, the surface of P-GERTs can be modified with functional molecules, enabling their application in the detection of disease biomarkers. Using COVID-19 as an example, the performance of P-GERTs in disease biomarker detection was validated, demonstrating that the signal intensity of this probe can reach 55 times that of regular gold nanoparticles and 36.7 times that of smooth shell gap-enhanced Raman tags (S-GERTs). Furthermore, in combination with magnetically retrievable magnetic bead substrates, the N-protein antigen was specifically detected in a one-step process. N-protein was detected within 15 min using a portable Raman spectrometer. The limit of detection (LOD) for the standard sample was 4.28 pg/mL, and the LOD for the actual throat swab sample system was 25.4 pg/mL. This workflow can be extended to the detection of other biomarkers, making it widely applicable.

Three-dimensional nanoporous gold/gold nanoparticles substrate for surface-enhanced Raman scattering detection of illegal additives in food

Owing to their nanoscale size and porous structure, both colloidal gold nanoparticles (AuNPs) and nanoporous gold (NPG) have demonstrated good and stable surface-enhanced Raman scattering (SERS) activity, and are therefore widely used as SERS substrates for the rapid detection of various components in food, environmental, biological, and other samples. In this study, we fabricated a novel, sensitive, and reproducible composite three-dimensional (3D) substrate for rapid SERS-based detection of illegal additives in food products. AuNPs and NPGs were prepared by chemical reduction and chemical dealloying methods, with the particle size of AuNPs about 60 nm and the pore size of NPG in the range of 5–36 nm. The AuNPs were then assembled on the surface of NPG to form the composite substrate 3D-NPG/AuNPs, which was characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and other methods. Finally, the new SERS substrate combined with a portable Raman spectrometer was used to detect the illegal food additives 6-benzylaminopurine and melamine, with detection limits of 1 × 10−9 M and 5 × 10−7 M respectively. We further analyzed the relationship between the dealloying time-controlled morphology and the SERS properties of NPG, demonstrating that 3D-NPG/AuNPs as a novel SERS substrate have strong practical application potential in the rapid detection of food additives and other substances.

Portable Hadamard-Transform Raman Spectrometer: A Powerful Analytical Tool for Point-of-Care Testing.

A portable Hadamard-transform Raman spectrometer with excellent performance was fabricated consisting of a 785 nm laser, an optical filter, an optical system, a control system, and a signal processing system. As the core of the spectrometer, the optical system was composed of a slit, collimator, optical grating, reflector, digital micromirror devices (DMD), lens system, and InGaAs photodetector. Compared with a conventional dispersive Raman spectrometer, the proposed Raman spectrometer adopted the DMD and corresponding controlling device (DLPC350 control chip) to collect the Raman spectrum. Thus, in our design, the gratings are fixed, while the full Raman spectrum was collected by the deflection of the micromirror. This design can greatly improve the vibration resistance ability of the spectrometer since the gratings are not rotating during the spectrum collecting. More importantly, Hadamard-transform was used as signal processing technology, which has the ability of faster calculation, the merits of high energy input, single detector multichannel simultaneous detection (imaging) ability, and high signal-to-noise ratio (SNR). Hence, the Hadamard-transform portable Raman spectrometer has the potential to be applied in the field of point-of-care testing (POCT).

Portable Copper-Based Electrochemical SERS Sensor for Point-of-Care Testing of Paraquat and Diquat by On-Site Electrostatic Preconcentration.

With the advent of portable Raman spectrometers, the deployment of surface-enhanced Raman spectroscopy (SERS) in point-of-care testing (POCT) has been initiated. Within any analytical framework employing SERS, the acuity and selectivity inherent to the SERS substrate are of paramount importance. In this article, we utilize in situ electrochemical passivation technology to fabricate CuI passivation film, which serves as a flexible copper-based SERS substrate. Furthermore, portable electrochemical SERS (EC-SERS) sensors were prepared by combining this with laser direct writing technology. The detection signal was amplified using electrostatic preconcentration technology, showcasing impressive sensitivity, selectivity, and stability in pesticide detection. The detected concentrations of paraquat and diquat in tea reached as low as 3.36 and 2.43 μg/kg, respectively. Furthermore, the application of electrostatic preconcentration facilitated selective target molecule aggregation on the SERS sensor, markedly increasing Raman signal strength and enabling single-molecule detection. This research introduces an innovative POCT method for pesticides, promising to advance environmental monitoring's analytical capabilities.

Assessment of marine and urban-industrial environmental impact on stone acting as the base of a quaternary bronze sculpture

This work investigates the influence of a marine and urban-industrial environment on the deterioration of a funerary memorial in Getxo (Basque Country, Spain). The sculpture and artificial stone materials as well as their degradation products were characterised via a multi-analytical approach. An in situ characterisation of the bronze statue and its artificial limestone base was carried out with portable Energy Dispersive X-Ray Fluorescence (ED-XRF) and Raman spectrometers. In addition, several samples of white crusts as well as metal runoff crusts and biological patina were collected and some of them were prepared as cross-sections. High Resolution Micro-X-ray fluorescence and micro-Raman spectroscopy were used as non-destructive methods to detect original and degradation compounds. The test of soluble salts was also carried out on the samples and ion chromatography was employed in the laboratory. Exclusively calcite salt-efflorescences were found at the monument side with ED-XRF and Raman spectroscopy. While their morphology was compact at unsheltered sites, they showed a lamellar structure at sheltered locations, whose increased volume strongly influences the destruction of the memorial. The spectroscopic characterization of metal runoff showed that its excessive occurrence on the memorial surface was due to the dissolution of the copper-alloy caused by chemical reactivity with the surrounding acidic atmosphere. The formation of brochantite Cu4(SO4)(OH)6, posnjakite Cu4(SO4)(OH)6·(H2O), langite Cu4(SO4)(OH)6·2(H2O), or malachite Cu2(CO3)(OH)2 was favored exclusively in metal runoff crusts at unsheltered locations. However, much thinner crusts collected at sheltered sites showed a different composition, with copper species such as moolooite (Cu(C2O4)·nH2O) and atacamite Cu2Cl(OH)3. The soluble salt extraction showed a variable concentration of soluble ions depending on the area where the samples come from. The sample from north west sheltered location showed the highest content of sulfate, nitrate and chloride compounds. In addition, the concentration of fluoride and nitrate reflects the impact of contamination of surrounding industries.

Identification of iron gall inks, logwood inks, and their mixtures using Raman spectroscopy, supplemented by reflection and transmission infrared spectroscopy

Raman spectral references for various formulations of iron gall inks, logwood inks and mixtures of both types were acquired during this study. The samples, either liquid or dry inks and applied on paper, were analysed using a portable Raman spectrometer, both with 852 and 785 nm excitation lines, and a confocal dispersive Raman microscope with two different excitations, namely 785 and 532 nm. It was found that longer wavelengths are more suitable for the analysis of iron gall inks and that the spectral response of logwood inks is relatively more dependent on the excitation line. For the mixtures, it is suggested analyses be performed with both longer and shorter wavelengths, since with a 785 nm line mainly the characteristic features of the metal-polyphenol complex in iron gall inks are detected, while the spectra collected with a 532 nm excitation contain information on the presence of logwood inks. The study was complemented by non-invasive reflectance infrared spectroscopy, which enabled the detection of tannic acid in iron gall inks and in the mixtures, and by micro-Fourier transform infrared (FTIR) spectroscopy to complement the reference set. The study aims to contribute to the development of non-invasive protocols for identification of inks in historic and artistic works on paper, such as manuscripts and drawings.Graphical

Simultaneous detection of two pesticide residues in tobacco leaves using SiO2@Ag-SERS substrate and portable Raman spectrometer

Surface-enhanced Raman spectroscopy (SERS) has great potential for rapid detection of trace levels of pesticides in food. Scientists have much interested in this analytical technique due to its sensitivity, rapid detection, simplicity, and low cost. However, most of researchers are only focusing on the detection of a single pesticide residue. In this paper, we firstly report the simultaneous detection of two pesticide residues in tobacco leaves by using composite SERS substrate of SiO2@Ag nanoparticles. The entire analysis time is less than 10 min. The detection results show satisfactory linearity in the range of 0.1–25 mg/kg and 1–25 mg/kg with the limit of detection of 0.1 mg/kg and 1 mg/kg for carbendazim and flumetralin in tobacco samples, respectively. The recovery rates of carbendazim and flumetralin in the tobacco leaves are 85.2 ∼ 112.12 % and 90.38 ∼ 113.42 %, respectively. The detection results also show good uniformity and reproducibility, with a relative standard deviation(RSD) value of 4.4 % between substrates. Our reported substrate combined with portable Raman spectrometer provides a powerful tool for simultaneous detection of multiple pesticide residues for food safety.

Rapid identification and quantitative analysis of malachite green in fish via SERS and 1D convolutional neural network

Rapid and quantitative detection of malachite green (MG) in aquaculture products is very important for safety assurance in food supply. Here, we develop a point-of-care testing (POCT) platform that combines a flexible and transparent surface-enhanced Raman scattering (SERS) substrate with deep learning network for achieving rapid and quantitative detection of MG in fish. The flexible and transparent SERS substrate was prepared by depositing silver (Ag) film on the polydimethylsiloxane (PDMS) film using laser molecular beam epitaxy (LMBE) technique. The wrinkled Ag NPs@PDMS film exhibits high SERS activity, excellent reproducibility and good mechanical stability. Additionally, the fast in situ detection of MG residues onfishscales was achieved by using the wrinkled Ag NPs/PDMS film and a portable Raman spectrometer, with a minimum detectable concentration of 10-6 M. Subsequently, a one-dimensional convolutional neural network (1D CNN) model was constructed for rapid quantification of MG concentration. The results demonstrated that the 1D CNN quantitative analysis model possessed superior predictive performance, with a coefficient of determination (R2) of 0.9947 and a mean squared error (MSE) of 0.0104. The proposed POCT platform, integrating a transparent flexible SERS substrate, a portable Raman spectrometer and a 1D CNN model, provides an efficient strategy for rapid identification and quantitative analysis of MG in fish.

Vibrational study of mycophenolic acid and its quantification with electrochemically assisted surface-enhanced Raman spectroscopy

Mycophenolic acid (MPA) is an immunosuppressant widely used in transplantations, for which therapeutic drug monitoring (TDM) has proven beneficial. There is furthermore a need to develop affordable, rapid, and benchtop analytical methods to perform TDM of MPA in a point-of-need setting. In this paper, we report for the first time the Raman fingerprint region and surface-enhanced Raman spectroscopy (SERS) vibrations of MPA through density functional theory calculations. The output of these simulations was compared with experimental data from electrochemically assisted SERS, i.e. application of a well-defined potential or sequence of potentials in SERS assays. The systematic electrochemically assisted SERS experimental study was carried out to understand the adsorption behaviour of MPA on gold nanopillars (AuNPs) when different potentials were applied. We found that MPA interacts with the AuNPs through its benzofuran heterocycle and carboxylic acid group. Applying different potentials on the SERS substrate resulted in band shifts, which we hypothesise to originate from molecular reorientation on the metal surface. Moreover, an electrochemically assisted SERS assay was developed and carried out on a portable Raman spectrometer. We show that MPA detection can be performed in less than 5 min in a clinically relevant concentration range (1 – 50 µM), with improved repeatability compared to a SERS assay without any applied potential (overall RSD decrease from 34.6 % to 18.5 %).

Falsified and problematic methandienone products available online: active pharmaceutical ingredient identification by portable Raman spectrometers and quantification by ultra-high-performance liquid chromatography–Fourier transform mass spectrometry

This study aimed on the one hand to clarify the quality, authenticity, safety, and other issues related to products of the anabolic-androgenic steroid methandienone advertised on the Internet and personally imported to Japan and on the other hand to evaluate the use of two portable Raman spectrometers in identifying the active pharmaceutical ingredient (API). The study found that all n = 15 samples purchased from 14 websites were problematic regarding their package, labeling, and/or content. Specifically, one sample (6.7%) was confirmed falsified, twelve samples (80%) were found either to be falsified or unlicensed as pharmaceutical product, and two samples (13.3%) were received without information on the manufacturers’ physical address or country of origin, with one sample (6.7%) having no labeling or other accompanying information at all. Both Raman spectrometers were able to identify the API in all samples as confirmed and quantified by ultra-high-performance liquid chromatography–Fourier transform mass spectrometry. Twelve samples contained on average less than 90% of the declared API content. By contacting national regulatory authorities in 44 countries, methandienone products were found to be approved in 1 country and not approved in 21 countries. To prevent health hazards and abuse, measures against the acquisition of anabolic-androgenic steroids from unknown sources are required. Portable Raman spectrometers may be suitable for the non-destructive and quick identification of methandienone in tablets.Graphical

In-situ detection of Pb2+ based on the ternary dihydrogen phosphate complex by surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) is a convenient and fast technique to detect toxic heavy metals such as lead ions (Pb2+). In this study, a silver nanoparticle-decorated hydrogel substrate by a one-pot method is prepared, addressing the instability of traditional sol substrates and the non-tunability of localized surface plasmon resonance (LSPR) of solid substrates, which can achieve in-situ detection of Pb2+ in real systems using a portable Raman spectrometer. Meanwhile, the characteristic SERS peaks attributed to the ternary complex of 4-MBA/H2PO4-/Pb2+ formed by the dihydrogen phosphate, 4-mercaptobenzoic acid, and Pb2+ are used firstly for Pb2+ detection to our knowledge, decreasing the cost of the classical strategy. The method is highly anti-interference, simple, and cost-effective, which exhibits a good linear correlation (y= 21.6x + 2711, R2=0.993) in the range of 3–500 μg/L with a detection limit of 1.6 μg/L that is one order of magnitude lower than that of the EPA regulations. This method is expected to realize the rapid and accurate on-site SERS detection of Pb2+ by the new strategy.

Quantitative analysis of four PAHs in oily sludge by surface-enhanced Raman spectroscopy (SERS) combined with partial least squares regression (PLS) based on a novel nano-silver-silicon coupling substrate

Polycyclic aromatic hydrocarbons (PAHs) present in oily sludge generated by the petroleum and petrochemical industries have emerged as a prominent concern within the realm of environmental conservation. The precise determination of PAHs holds immense significance in both petroleum geochemistry and environmental protection. In this study, a combination of surface-enhanced Raman spectroscopy (SERS) and solid–liquid extraction was employed for the screening of PAHs in oily sludge. Methanol was utilized as the extraction solvent for PAHs, while nanosilver-silicon coupling substrates were employed for their detection. The SERS spectrum was acquired using a portable Raman spectrometer. The nano silver-silicon coupling substrate exhibits excellent uniformity, with relative standard deviations (RSDs) of Phenanthrene, Fluoranthrene, Fluorene and Naphthalene (Phe, Flt, Flu and Nap) being 2.8%, 1.08%, 1.41%, and 5.44% respectively. Moreover, the limits of detection (LODs) achieved remarkable values of 0.542 μg/g, 0.342 μg/g, 0.541 μg/g, and 5.132 μg/g. The quantitative analysis of PAHs in oily sludge was investigated using SERS technology combined with partial least squares (PLS). The optimal PLS calibration model was optimized by combining spectral preprocessing methods and using the SiPLS (Synergy interval partial least squares)-VIP (Variable Importance in Projection) hybrid variable selection strategy. The prediction performance of the D1st (First derivative)-WT (Wavelet transform)-SiPLS-VIP-PLS model was deemed satisfactory, as evidenced by high R2P values of 0.9851, 0.9917, and 0.9925 for Phe, Flt, and Flu respectively; additionally, the corresponding MREP values were found to be 0.0580, 0.0668, and 0.0669 respectively. However, for Nap analysis, the D1st-WT-PLS model proved to be a better calibration model with an R2P value of 0.9864 and an MREP (Mean relative error of prediction) value of 0.0713. In summary, SERS technology combined with PLS based on different spectral pretreatment methods and mixed variable selection strategies is a promising method for quantitative analysis of PAHs in oily sludge, which will provide new ideas and methods for the quantitative analysis of PAHs in oily sludge.

Raman spectroscopy for esophageal tumor diagnosis and delineation using machine learning and the portable Raman spectrometer

Esophageal cancer is one of the leading causes of cancer-related deaths worldwide. The identification of residual tumor tissues in the surgical margin of esophageal cancer is essential for the treatment and prognosis of cancer patients. But the current diagnostic methods, either pathological frozen section or paraffin section examination, are laborious, time-consuming, and inconvenient. Raman spectroscopy is a label-free and non-invasive analytical technique that provides molecular information with high specificity. Here, we report the use of a portable Raman system and machine learning algorithms to achieve accurate diagnosis of esophageal tumor tissue in surgically resected specimens. We tested five machine learning-based classification methods, including k-Nearest Neighbors, Adaptive Boosting, Random Forest, Principal Component Analysis-Linear Discriminant Analysis, and Support Vector Machine (SVM). Among them, SVM shows the highest accuracy (88.61 %) in classifying the esophageal tumor and normal tissues. The portable Raman system demonstrates robust measurements with an acceptable focal plane shift of up to 3 mm, which enables large-area Raman mapping on resected tissues. Based on this, we finally achieve successful Raman visualization of tumor boundaries on surgical margin specimens, and the Raman measurement time is less than 5 min. This work provides a robust, convenient, accurate, and cost-effective tool for the diagnosis of esophageal cancer tumors, advancing toward Raman-based clinical intraoperative applications.