Portable Raman Spectrometer Research Articles

Additive Manufacturing‐Enabled Architected Nanocomposite Lattices Coated with Plasmonic Nanoparticles for Water Pollutants Detection

AbstractNovel low‐cost materials to uptake and detect vestigial amounts of pesticides are highly desirable for water quality monitoring. Herein, are demonstrated, for the first time, surface‐enhanced Raman scattering (SERS) sensors enabled via additively manufactured lattices coated with plasmonic nanoparticles (NPs) for detecting pesticides in real water samples. The architected lattices comprising polypropylene (PP) and multiwall carbon nanotubes (MWCNTs) are realized via fused filament fabrication (FFF). In the first stage, the SERS performance of the PP/MWCNT filaments coated with distinct metallic NPs (Ag NPs and Au NPs) is evaluated using methylene blue (MB) as molecular probe. Thereafter, distinctly architected hybrid SERS sensors with periodic porous and fully dense geometries are investigated as adsorbents to uptake MB from aqueous solutions and subsequent detection using SERS. The spatial distribution of MB and Ag NPs on the FFF‐printed lattices is accomplished by SERS imaging. The best hybrid composite is used as SERS probing system to detect low amounts of pesticides (thiram and paraquat) and offers a detection limit of 100 nm for both pesticides. As a proof‐of‐concept, FFF‐enabled test strips are used to detect in loco paraquat molecules spiked on real water samples (Estuary Aveiro water and tap water) using a portable Raman spectrometer.

Wafer-scale fibrous SERS substrates allow label-free, portable detection of food adulteration and diagnosis of pesticide poisoning

Herein, a method for constructing three-dimensional (3D) fibrous surface-enhanced Raman scattering (SERS) substrates was developed. This strategy enables the wafer-scale, direct formation of monolayer gold nanoparticles (Au NPs) on filter paper. The process begins with coating of the fiber surface with perfluorooctyltrichlorosilane (FOS) to manipulate the surface energy. During subsequent sputter deposition, the large difference in surface energy between the Au atoms and the FOS-modified fibers leads to the thermodynamically driven formation of discrete Au NPs, thereby generating an abundance of hotspots. Moreover, the Au NP–decorated paper maintained its great hydrophobicity, condensing the analyte molecules nearby hot spots after solvent evaporation. In addition, the 3D fibrous structure provided a large detection space to efficiently utilize the large depth of field of a portable Raman spectrometer. These features resulted in the as-designed SERS paper having high sensitivity, with the enhancement factor reaching 1.63 × 108 and the detection limit reaching the nanomolar level when using a portable 785-nm Raman spectrometer. We used this approach for the trace-level, label-free detection of a diverse range of substances as well as their practical on-site detection in multiple-component systems, including illegal rhodamine B in commercial beverages and lethal paraquat in poisoning patients.

Non-Destructive Screening of Sodium Metabisulfite Residue on Shrimp by SERS with Copy Paper Loaded with AgNP.

In order to prompt the appearance of the shrimp color, sodium metabisulfite is frequently added in shrimp processing, which is, however, prohibited in China and many other countries. This study aimed to establish a surface-enhanced Raman spectroscopy (SERS) method for screening sodium metabisulfite residues on shrimp surfaces, in a non-destructive manner. The analysis was carried out using a portable Raman spectrometer jointly with copy paper loaded with silver nanoparticles as the substrate material. The SERS response of sodium metabisulfite gives two fingerprint peaks at 620 (strong) and 927 (medium) cm-1, respectively. This enabled unambiguous confirmation of the targeted chemical. The sensitivity of the SERS detection method was determined to be 0.1 mg/mL, which was equal to residual sodium metabisulfite on the shrimp surface at 0.31 mg/kg. The quantitative relationship between the 620 cm-1 peak intensities and the concentrations of sodium metabisulfite was established. The linear fitting equation was y = 2375x + 8714 with R2 = 0.985. Reaching an ideal balance in simplicity, sensitivity, and selectivity, this study demonstrates that the proposed method is ideally suitable for in-site and non-destructive screening of sodium metabisulfite residues in seafood.

Toward rapid and sensitive point‐of‐care diagnosis with surface‐enhanced Raman scattering‐based optofluidic systems

AbstractWith the recent global outbreaks of infectious diseases such as coronavirus disease 2019, developing a detection system capable of quickly and accurately diagnosing diseases on‐site has become a pressing need. The ability to diagnose patients in the field is crucial for the prompt isolation and treatment of infected individuals and the prevention of the spread of the disease. Our research group has recently developed a surface‐enhanced Raman scattering optofluidic system that enables rapid and accurate point‐of‐care diagnostics. This account will introduce the principle and configuration of the fluidic devices, such as lateral flow assay strips or microfluidic channels, and the portable Raman spectrometer. We will also highlight the challenges that must be addressed for using this system in clinical settings. Rapid and accurate diagnosis is critical for effective disease management and control, and developing this system can significantly improve our ability to respond to outbreaks of infectious diseases.

MoS2 nanosheets decorated plasmonic silicon nanowires as SERS substrates for ultra-sensitive multiple analyte detection

We report the fabrication of hybrid SERS-active substrates for ultra-sensitive detection of diverse analyte molecules such as explosives, dyes, and bio-proteins. Vertically aligned (12-µm long, 250-nm diameter) Si nanowires (SiNWs) were prepared by a facile silver-assisted electroless (SAE) etching process. Ag and Au nanoparticles (NPs) were initially decorated on SiNWs using a simple immersion bath method. A hybrid SERS substrate was designed by encapsulating the 2D material (MoS2) on bi-metallic (Ag-Au nanoparticles) functionalized SiNWs. The synergetic effect from MoS2 nano-sheets and bi-metallic NPs produced superior detection of analytes down to ultra-trace levels. The versatility of hybrid substrate was tested extensively by detecting (i) malachite green (MG), (ii) melamine, (iii) naphthalene, (iv) bovine serum albumin (BSA), (v) adenine, (vi) L-Cysteine, (vii) Escherichia coli (E. coli), and (viii) tetryl (an explosive) molecules. We have observed excellent signal reproducibility with very low RSD values (3–5%). The analytic enhancement factors were estimated to be 3.6 × 108 for MG, 1.2 × 107 for melamine, and 6.4 × 105 for BSA, respectively. The estimated ‘limits of detection’ (LOD) for MG, melamine, naphthalene, adenine, and BSA were 216 pM, 42 nM, 78 nM, 5 nM, 7 nM, respectively. Furthermore, the durability of the substrate was studied extensively by evaluating the signal strength of 100 µM melamine for a prolonged duration in an ambient atmosphere. These established novel, robust, versatile, and potentially practical SERS-active hybrid substrates facilitate easy molecular detection in the field in conjunction with a portable or hand-held Raman spectrometer.

Evaluation of carbonification of coals using a portable Raman spectrometer

AbstractThe estimation of the degree of carbonification of coals can be investigated using the Raman microspectroscopy applied for the analysis of grains of selected macerals (altered remains of organic particles). This approach allows for the best control of the analyses such as precise selection and orientation of the maceral grains to be analysed. On the other hand, the miniaturized, especially handheld Raman spectrometers typically offer a significantly less controlled environment with the issues including large laser spot sizes and the focusing issues. However, the advantages of the miniaturized spectrometers include fast analyses and the possibility of in situ analyses. This study illustrates that it is possible to discriminate among the coals of different degrees of maturation of the carbonaceous matter and other types of carbonaceous matter using the data acquired with a portable Raman spectrometer using spectroscopic parameters: D and G band widths and wavenumber positions. The issues inherent to the analyses of such heterogeneous materials such as coals using a portable spectrometer were addressed. Moreover, the variability in the Raman spectroscopic backgrounds of a wide range of coals from lignite to anthracite necessitated the utilization of a robust background removal function. This study shows that modern portable Raman spectrometers with the appropriate excitation are capable of basic discrimination among the different types of carbonaceous matter, with implications towards fast in situ analyses of carbonaceous matter in rocks as an additional tool for a geologist.

Suite of Aptamer-Based Sensors for the Detection of Fentanyl and Its Analogues.

Fentanyl and its analogues are potent synthetic opioids that are commonly abused and are currently the number one cause of drug overdose death in the United States. The ability to detect fentanyl with simple, rapid, and low-cost tools is crucial for forensics, medical care, and public safety. Conventional on-site testing options for fentanyl detection─including chemical spot tests, lateral-flow immunoassays, and portable Raman spectrometers─each have their own unique flaws that limit their analytical utility. Here, we have developed a series of new aptamer-based assays and sensors that can detect fentanyl as well as several of its analogues in a reliable, accurate, rapid, and economic manner. These include colorimetric, fluorescent, and electrochemical sensors, which can detect and quantify minute quantities of fentanyl and many of its analogues with no response to other illicit drugs, cutting agents, or adulterants─even in interferent-ridden binary mixtures containing as little as 1% fentanyl. Given the high performance of these novel analytical tools, we foresee the potential for routine use by medical and law enforcement personnel as well as the general public to aid in rapid and accurate fentanyl identification.

Coupling Bifunctional Nanozyme-Mediated Catalytic Signal Amplification and Label-Free SERS with Immunoassays for Ultrasensitive Detection of Pathogens in Milk Samples.

Rapid and sensitive detection of foodborne bacteria is of great significance in guaranteeing food safety and preventing foodborne diseases. A bifunctional Au@Pt core-shell nanozyme with excellent catalytic properties and high surface-enhanced Raman scattering (SERS) activity was developed for the highly sensitive detection of Salmonella typhimurium based on a label-free SERS strategy. The ultrathin Pt shell (about 1 nm) can catalyze Raman-inactive molecules into Raman-active reporters, greatly amplifying the amount of signal molecules. Moreover, the Au core serves as an active SERS substrate to enhance the signal of reporter molecules, further significantly improving the detection sensitivity. Benefiting from the excellent properties, such a bifunctional Au@Pt nanozyme was integrated with a magnetic immunoassay to construct a label-free SERS platform for the highly sensitive detection of S. typhi with a low detection limit of 10 CFU mL-1. Also, the Au@Pt-based SERS platform exhibited excellent selectivity and was successfully utilized for the detection of S. typhi in milk samples by a portable Raman spectrometer. Our demonstration of the bifunctional nanozyme-based SERS strategy provides an efficient pathway to improve the sensitivity of label-free SERS detection of pathogens and holds great promise in food safety, environmental analysis, and other biosensing fields.

Ultrasensitive detection of SARS-CoV-2 antigen using surface-enhanced Raman spectroscopy-based lateral flow immunosensor.

The fast spread and transmission of the coronavirus 2019 (COVID-19) has become one of serious global public health problems. Herein, a surface enhanced Raman spectroscopy-based lateral flow immunoassay (LFA) was developed for the detection of SARS-CoV-2 antigen. Using uniquely designed core-shell nanoparticle with embedded Raman probe molecules as the indicator to reveal the concentration of target protein, excellent quantitative performance with a limit of detection (LOD) of 0.03 ng/mL and detection range of 10-1000 ng/mL can be achieved within 15 min. Besides, the detection of spiked virus protein in human saliva was also performed with a portable Raman spectrometer, proposing the feasibility of the method in practical applications. This easy-to-use, rapid and accurate method would provide a point-of-care testing way as the ideal alternative for current detection requirement of virus-related biomarkers.

Rapid and Robust Analysis of Coumatetralyl in Environmental Water and Human Urine Using a Portable Raman Spectrometer.

The widespread use and exposure of coumatetralyl (CMTT) has led to its accumulation in the environment and organisms, causing damage to ecosystems and adverse health effects in humans. Unfortunately, achieving fast detection of CMTT remains challenging. Herein, a rapid and robust surface-enhanced Raman spectroscopy (SERS) method was developed for rapid on-site detection of CMTT in environmental water and human urine. Clear trends were observed between the signal intensity and the logarithmic concentration of CMTT, ranging from 0.025 to 5.0 μg/mL with high reproducibility. The detection limits in water and human urine were as low as 1.53 and 13.71 ng/mL, respectively. The recoveries of CMTT for environmental water and urine samples were 90.2-98.2 and 82.0-87.5%, respectively, satisfactory for practical applications. The quantitative results of this approach were highly comparable to those obtained by high-performance liquid chromatography. Most importantly, it is cost-effective, operationally simple, and without a complicated sample preparation step. Detecting CMTT in water samples took only 5 min, and the detection of urine samples was completed within 8 min. This simple yet practical SERS approach offers a reliable application prospect for on-site CMTT detection in environmental water and point-of-care monitoring of poisoned patients.

Direct Thermal Growth of Gold Nanopearls on 3D Interweaved Hydrophobic Fibers as Ultrasensitive Portable SERS Substrates for Clinical Applications.

Surface-enhanced Raman spectroscopy (SERS)-based biosensors have attracted much attention for their label-free detection, ultrahigh sensitivity, and unique molecular fingerprinting. In this study, a wafer-scale, ultrasensitive, highly uniform, paper-based, portable SERS detection platform featuring abundant and dense gold nanopearls with narrow gap distances, are prepared and deposited directly onto ultralow-surface-energy fluorosilane-modified cellulose fibers through simple thermal evaporation by delicately manipulating the atom diffusion behavior. The as-designed paper-based SERS substrate exhibits an extremely high Raman enhancement factor (3.9× 1011 ), detectability at sub-femtomolar concentrations (single-molecule level) and great signal reproductivity (relative standard deviation: 3.97%), even when operated with a portable 785-nm Raman spectrometer. This system is used for fingerprinting identification of 12 diverse analytes, including clinical medicines (cefazolin, chloramphenicol, levetiracetam, nicotine), pesticides (thiram, paraquat, carbaryl, chlorpyrifos), environmental carcinogens (benzo[a]pyrene, benzo[g,h,i]perylene), and illegal drugs (methamphetamine, mephedrone). The lowest detection concentrations reach the sub-ppb level, highlighted by a low of 16.2 ppq for nicotine. This system appears suitable for clinical applications in, for example, i) therapeutic drug monitoring for individualized medication adjustment and ii) ultra-early diagnosis for pesticide intoxication. Accordingly, such scalable, portable and ultrasensitive fibrous SERS substrates open up new opportunities for practical on-site detection in biofluid analysis, point-of-care diagnostics and precision medicine.

Multi-Analytical Investigation on a Renaissance Polychrome Earthenware Attributed to Giovanni Antonio Amadeo

This research aimed to characterise pigments used to decorate a polychrome earthenware bas-relief of the 15th century entitled “Madonna with Child, Saint Catherine of Siena, and a Carthusian Prior”, attributed to Giovanni Antonio Amadeo (Pavia, 1447–Milan, 1522) and owned by the Sforzesco Castle Museum of Milan. The artwork underwent a cleaning procedure whose aims were the removal of the dark coating that obscured its surface and restoration work that could bring back its original features. Before the cleaning, six microsamples were collected and analysed using optical microscopy (OM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDXS), and Fourier-transform infrared microspectroscopy in ATR mode (ATR-FTIR), providing the restorers with decisive information on the materials underlying the coating. After the cleaning, the terracotta appeared vibrantly coloured, mainly with bright red, blue, green, black, and white tones. Then, some in situ, non-destructive, spectroscopic measurements were performed by a portable Raman spectrometer on some of the areas that could not otherwise have been sampled. The analyses revealed the presence of natural pigments, including lead white, azurite, yellow ochre, carbon black, calcite, cinnabar, and gypsum. For Madonna’s mantle, cobalt and Prussian blue were employed. Furthermore, the presence of barium sulphate was widely evidenced on the bas-relief. Albeit cobalt blue is of synthetic origin, its presence is compatible with the 15th-century palette, whereas Prussian blue and barium sulphate could be imputed to a previous restoration. Finally, the use of true gold for the background of the earthenware attests to the artwork’s importance and value.

Au nanocakes as a SERS sensor for on site and ultrafast detection of dioxins

Dioxin is a highly toxic and carcinogenic pollutant created during industrial production and waste incineration. Pollutant monitoring has made extensive use of surface-enhanced Raman spectroscopy (SERS) as a quick, non-destructive, sensitive, and affordable analytical method. However, the fabrication of a SERS substrate with ultrahigh sensitivity is a challenging task, the detection cost is expensive. Currently, these are the challenges faced by SERS technique for the detection of dioxin pollutants. In this paper, we present Au nanocakes (Au NCs) as an easy-to-build SERS substrate for sensitive SERS detection of dioxins in real samples. Based on three-dimensional finite-difference time-domain (3D-FDTD) calculations, the enhancement factor of the substrate following aggregation is approximately 1010. Using a portable Raman spectrometer, the limit of detection for dioxins such as 1-chloro-dibenzo-p-dioxin (1-CDD), 2,8-dichloro-dibenzo-p-dioxin (2,8-DCDD), and 2,3,7-trichloro-dibenzo-p-dioxin (2,3,7-TrCDD) in clean water reached as low as 5, 5, and 10 ng/mL, respectively. As a real-world application, the same toxic pollutants were detected in sewage water samples. Our findings could lead to the development of novel SERS-based sensors for the rapid detection of dioxins in real-world scenarios. Moreover, a portable Raman spectrometer is used to detect the pollutants, which is easy to use and inexpensive.

Low-cost, mass-producible nanostructured surface on flexible substrate with ultra-thin gold or silver film for SERS applications

Surface Enhanced Raman Spectroscopy has emerged as a powerful analytical technique for fingerprint recognition of molecular samples with high sensitivity. The Surface Enhanced Raman Scattering (SERS) effect has been extensively studied for the past few decades. However, only recently the commercialization of portable Raman spectrometers has taken SERS a step closer to real-world applications. Swift and convenient testing of analytes for point-of-care, environmental as well as food quality control and safety applications, is very lucrative. This can be realized with the use of low-cost, mass producible and environmentally friendly SERS active substrates in combination with portable Raman spectrometers. In this study, we demonstrate one approach to accomplish such a SERS-active substrate using nanostructured latex coated paperboard as a base substrate. The nanostructure is accomplished by applying a reverse gravure coater in combination with a short-wavelength infrared (IR) heater. The whole process is easily up-scalable. The SERS functionality is then obtained by physical vapor deposition of an ultra-thin layer of Au or Ag. The surface nanostructure was confirmed by atomic force microscopy, showing an additional nanoscale graininess after the deposition of Au or Ag. The successful metal deposition was confirmed by X-ray photoelectron spectroscopy and deposition homogeneity was also analyzed. To confirm the SERS effect, two model compounds; crystal violet and rhodamine 6G were tested in the concentration range of 1–1000 μM. The results confirmed that the nanostructured, flexible, paper-based substrate can perform as a SERS-active substrate with negligible background noise.

Lithography-free fabrication of scalable 3D nanopillars as ultrasensitive SERS substrates

Surface-enhanced Raman spectroscopy (SERS) detection of analyte molecules at ultra-low concentrations requires highly-efficient plasmonic nanostructures enabling a high hot-spot density. However, a facile and cost-effective strategy toward large-area fabrication of efficient nanostructures with significant electromagnetic field enhancement remains a great challenge. Further, SERS faces reliability issues with the molecular fingerprint at ultra-low concentrations. This work shows a one-step rapid fabrication technique utilizing glancing angle deposition for growing 3D nanopillars of Ag or Au, which is facile, scalable and cost-effective. The 3D nanopillar substrates can reliably detect analyte molecules with concentrations as low as 10-18 M with a high signal-to-noise ratio molecular fingerprint proven for Cresyl violet, p-aminothiophenol and Rhodamine 6G. The ultra-high enhancement is realized in conjunction with the formation of a high hot-spot density due to localized surface plasmons and surface plasmons at metal/air interface. A portable handheld Raman spectrometer is used to evaluate the potential application of the nanopillars for on-site diagnostics. It avoids the need for sophisticated tabletop instruments yet provides high-precision molecular specificity outside specialized laboratories. The 3D nanopillar substrates show excellent molecular detection limits at 10−15 M concentrations when tested with a handheld Raman spectrometer. The uniqueness of the 3D nanopillar features with the formation of a high density of hot-spots and one-step nanofabrication methods provide a platform to unravel on-site diagnostics with cost-effective approaches.

On-chip Raman spectrometers using narrow band filter array combined with CMOS image sensors

Recent advancements in nanotechnology raise the feasibility of a miniaturized, portable Raman spectrometer with promising applications such as material identification, food safety monitoring, and health care. Miniaturizing Raman spectrometers has remained a challenge owing to the inevitable weakness of Raman signals and the conflict between small size and spectral resolution. In this study, we present a portable mini-Raman spectrometer comprising a complementary metal–oxide semiconductor (CMOS) image sensor (CIS) integrated with an array of filter sets, a confocal probe, and a laser diode that successfully meets the miniaturization challenge. We also report successful measurement of Raman spectra using the CIS-based mini-spectrometer, measuring cyclohexane liquid, tylenol pills, and vitamin-C pills with high spectral resolution. Our mini-Raman spectrometer, which can measure Raman signals in a two-dimensional (2D) image format in a single-shot, can be embedded into commercial mobile phones and transformed into a promising Raman camera.

Comparative assessment of two portable Raman spectrometers for the characterisation of historical natural dye lakes

AbstractThis paper explores the use of portable Raman instruments to characterise natural dye lakes in paint mixtures, as an alternative approach to other Raman techniques (e.g. SERS). Raman spectroscopy has indeed been used extensively to study natural dyes as pure substances or as artistic pigments (dye lakes). However, the examination of these compounds with Raman spectroscopy is particularly challenging because of a strong fluorescence, a relatively weak Raman signal and their occurrence at low concentrations in artefacts. Because of these challenges, the typical way of analysing these materials is through either surface‐enhanced Raman spectroscopy (SERS) or Fourier‐transform (FT) Raman spectroscopy, yet those approaches are not always desirable in art analysis, especially as they often require micro‐sampling. Therefore, this study explores the potential of using commercial mobile instruments, which would open the possibilities for direct in situ analysis. Two dispersive instruments, one using a fibre‐optic probe and a 1064‐nm excitation laser and the other using the subtracted‐shifted excitation (SSE) post‐processing algorithm, have been tested in their feasibility to characterise dye lakes. Raman spectra were acquired from a set of laboratory reproductions of paint mixtures prepared with a chosen set of common lakes, three red (brazilwood, cochineal and madder) and one yellow (weld), mixed with natural proteinaceous and polysaccharide binders. The feasibility has been evaluated, and it is shown that these lakes produce a detectable Raman signal, in spite of the strong interference of the painting support (parchment) and that the two instruments provide significantly different information.

Correlation between Graphitic Carbon and Elemental Carbon in Diesel Particulate Matter in Workplace Atmospheres.

We investigated the suitability of the graphitic carbon (GC) content of diesel particulate matter (DPM), measured using Raman spectroscopy, as a surrogate measure of elemental carbon (EC) determined by thermal optical analysis. The Raman spectra in the range of 800-1800 cm-1 (including the D mode at ∼1322 cm-1 and the G mode at ∼1595 cm-1) were used for GC identification and quantification. Comparison of the Raman spectra for two certified DPM standards (NIST SRM 1650 and SRM 2975), two types of diesel engine exhaust soot, and three types of DPM-enriched workplace aerosols show that the uncertainty of GC quantification based on the D peak height, G peak height, and the total peak area below D and G peaks was about 6.0, 6.7, and 6.9%, respectively. The low uncertainty for different aerosol types suggested possible use of GC as a surrogate measure of EC in workplace atmospheres. A calibration curve was constructed using two laboratory-aerosolized DPM standards to describe the relationship between GC measured by a portable Raman spectrometer and the EC concentration determined by NIOSH Method 5040. The calibration curve was then applied to determine GC-based estimates of the EC contents of diesel engine exhaust samples from two vehicles and seven air samples collected at a hydraulic fracturing worksite. The GC-EC estimates obtained through Raman measurements agreed well with those found by NIOSH Method 5040 for the same samples at EC filter loadings below 2.86 μg/cm2. The study shows that using an appropriate sample collection method that avoids high filter mass loadings, onsite measurement of GC by a portable or hand-held Raman spectrometer can provide a useful indicator of EC in workplace aerosol.

μ-Raman Determination of Essential Oils' Constituents from Distillates and Leaf Glands of Origanum Plants.

A novel, inexpensive and simple experimental setup for collecting μ-Raman spectra of volatile liquids in very small quantities was developed. It takes advantage of capillary forces to detain minute volatile liquid volumes. Spectra of volatile and even scattering or absorbing media can be measured more effectively. The method is used to facilitate the collection of intensity-consistent Raman spectra from a series of reference compounds present in Origanum essential oils, in order to quantify their constituents by multiple linear regression. Wild grown Origanum plants, collected from five different regions in Greece and taxonomically identified as O. onites, O. vulgare subsp. hirtum and O. vulgare subsp. vulgare, were appropriately distilled to acquire their essential oils. Comparison of the Raman results with those from headspace gas chromatography-mass spectrometry (HS GC-MS) confirmed the successful relative quantification of the most abundant essential oil constituents, highlighting the similarities and differences of the three Origanum taxa examined. Finally, it is demonstrated that directly measuring the leaf peltate glandular hairs yields exploitable results to identify the main components of the essential oil they contain, underlining the potential of in situ (field or industry) measurements utilizing microscope-equipped portable Raman spectrometers.

Rapid identification and quantification of diquat in biological fluids within 30 s using a portable Raman spectrometer

Rapid detection of diquat (DQ) is essential in clinical diagnosis and rescue. Here, we developed a fast, simple-yet-practical detection strategy for the reliable identification and quantification of DQ in biological fluids. Based on surface-enhanced Raman spectroscopy (SERS), point-of-care detection was realized under the acidic condition with gold nanoparticles as the substrate. Under optimal experimental conditions, the detection limits of the strategy were 17.5 ppb and 1.99 ppm in human urine and gastric juice, respectively. High specificity and selectivity of the SERS strategy were demonstrated using common pesticides and coexisting biological substances. The method was also used to detect biofluids from 5 patients and urine samples from 10 healthy volunteers. The results were in high agreement with spectrophotometric and clinical liquid chromatography-mass spectrometry methods. The volume of urine samples required for this technique is merely 20 μL, and no preparation of the samples is required. Compared to traditional methods used in clinical settings, SERS-based methods are capable of real-time measurements that accurately provide rapid detection and response in non-laboratory settings, with great potential for on-site and point-of-care testing.