micro-Raman Spectrometer Research Articles

Thermally Induced Polymorphic Changes in Poly(vinylidene Fluoride) Thin Layer Investigated Using Micro-Raman Spectroscopy

Poly vinylidene fluoride (PVDF) is a versatile polymer that shows polymorphism, and most of its applications are based on its piezoelectric properties given by its polar crystalline phases. Increasing the polymer’s polar β-phase content has been a major pursuit in material science. We present the results on the evolution of induced polymorphic changes of PVDF through thermal treatment and the presence of the nano-ZnO with different morphologies. Three types of samples—a PVDF pure layer, PVDF:ZnO nanoparticles (NPs) and PVDF:ZnO nanorods (NRs)—were subjected to stress by heating at different temperatures from 50 °C close to melting temperature, 170 °C. The changes in PVDF–ZnO composite layers were investigated in situ using an experimental setup consisting of a high-resolution micro-Raman spectrometer and a thermo-electric cell. The ZnO NPs and NRs added in PVDF lead to obtaining a PVDF nanocomposite in which the intensity of the β phase is much higher than that of the α phase: intensities ratio Iβ(840.6 cm−1)/Iα(798.9 cm−1) > 5.56. The phase is stable up to 150 °C, and with the increase in temperature to 170 °C, the β phase passes to a lower crystallinity α phase with a large amorphous content highlighted by the 400–700 cm−1 and 800–1000 cm−1 regions without Raman peaks.

Multivariate analysis of Raman spectra for discriminating human collagens: In vitro identification of extracellular matrix collagens produced by an osteosarcoma cell line

BackgroundThe NHS spends £4.3 billion annually to address musculoskeletal conditions, encompassing age-related bone disorders like osteoarthritis and osteoporosis. Traditional X-ray diagnostic methods are commonly employed for bone disorder diagnosis, primarily assessing gross anatomical bone structure changes. However, these methods are unable to identify subtle biochemical alterations within the bone. More detailed information, particularly about protein changes, may lead to enhanced diagnostics and treatment. Raman spectroscopy is a non-invasive, laser-based technique capable of detecting changes in the collagen component of bone. Despite its long-standing application in discerning mineral and protein changes within bone, there is limited evidence on Raman spectral signatures of purified human collagens and their differentiation. This study aimed to test the hypothesis that Raman spectroscopy could detect different types of collagen in the human body. ResultsA Raman microspectrometer with a 785 nm laser was used to measure unmineralized human collagens types I – VI and collagenous extracellular matrix (ECM) secreted by MG63 osteoblast-like cells. The results demonstrated the efficacy of Raman spectroscopy and subsequent multivariate analysis in distinguishing human collagen types I – VI. This implies that Raman spectroscopy, coupled with multivariate analysis, can identify pure human collagens and offers reference spectra similar to natural human collagen in the bone extracellular matrix. SignificanceThis study establishes Raman spectroscopy as a tool for identifying and characterizing human collagens, aiding in the diagnosis of connective tissue disorders. The creation of a spectral reference library for pure human collagen types I – VI holds potential for medical diagnostics, analytical chemistry, and materials science applications.

Qualitative and Quantitative Analyses of Microplastics in Tap Water Supply Network in Iran

Background: Microplastics (MPs) exposure can affect humans in various ways, with tap water being one of the potential sources. Microplastics can absorb other pollutants and pose risks to both humans and the environment. Objectives: The aim of this study was to investigate the presence of MPs in tap water from the drinking water distribution system of Isfahan, Iran, and to determine the exposure to MPs from drinking tap water. Methods: Samples were collected from different points in the drinking water distribution system of Isfahan, Iran. Samples were prepared for analysis through filtration and chemical digestion. The MPs were counted using a scanning electron microscope (SEM), and the composition of MPs was analyzed using a micro-Raman spectrometer. Results: The concentration of MPs in tap water was found to be 287.0 ± 65.9 MPs/l. MPs ≤ 10 µm were the predominant sizes, and fibers were the predominant shape. Polyethylene terephthalate, polyethylene, and polypropylene were the most frequently identified MPs, respectively. Conclusions: Considering that the Iranian population consumes 7 - 15 liters of water daily for drinking and cooking, it is estimated that the average intake of MPs through cooking and drinking water is 2009 - 43,051 particles per day.

Production perspectives of a high-status polychrome jewellery set from the Hunnic period (mid-5th century AD) Carpathian Basin

Fifty years after the discovery of the Regöly grave, the emblematic Hunnic period archaeological assemblage from Hungary, an extensive scientific investigation was performed on the polychrome dress accessories of the high-status woman, often referred to as the “Princess of Regöly”, buried there. The multi-instrumental analyses aimed to characterise material and technological aspects of the gemstone-inlaid artefacts (a set of a pair of bow-brooches and a belt buckle), i.e., the manufacturing and decorative techniques as well as the chemical and mineralogical compositions. The non-destructive and non-invasive gemmological and geochemical analyses applied optical microscopes, handheld XRF, SEM-EDX and Raman microspectrometer. This study provides the first comprehensive examination of the Hunnic period polychrome jewellery, and highlights the potential of combining surface and subsurface analyses to specify garnet provenances. It presents the first evidence of use of antique and early medieval garnet sources during the early Migration period. The findings enhance understanding of the garnet supply chain and trade network, the production organisation and potential workshop connections. Significant differences of the brooches and the buckle reveal varying levels of luxury among the elite, providing insight into the social context of the polychrome jewellery associated with the “Princess of Regöly”.

Degradation of a Sauce-Glazed Ware from the Song Dynasty Salvaged Out of Water at the Dalian Island Wharf: Part II—The Effect of Surface-Attached Marine Organism Remains

Dalian Island, located in the northwest of Pingtan County, Fujian Province, China, has been an important junction on the Maritime Silk Road since the Tang dynasty. This study focuses on sauce-glazed ceramic ware from the Song dynasty salvaged from the waters near Dalian Island Wharf. The composition, phase attributes, and microstructures of the marine organism remains attached to the ceramic ware were analyzed using an optical microscope, scanning electron microscope, and micro-Raman spectrometer to investigate the influence of marine organisms on the degradation of the ceramic ware. Long-term abrasion by sea wave-borne debris led to the increased surface roughness and wettability of the ceramic ware, facilitating the attachment of marine organisms. Differences in surface roughness between the inner and outer walls led to varying levels of biomass. Coralline algae secreted inducers to attract the larvae of macrofoulers. The attachment of different types of marine organisms had varying effects on the degradation of the ceramic ware. Firmly attached unitary organisms could alleviate the scouring of sea wave-borne debris and hinder the intrusion of foreign pollutants, thereby playing a ‘bio-protective’ role. In contrast, the group skeletons of modular organisms could reinforce the mechanically damaged surface but failed to block the intrusion of iron rust and other pollutants, resulting in chemical alterations of the glaze. Therefore, the specific species of the attached marine organisms should be considered in subsequent conservation efforts.

Correlative morphological, elemental and chemical phase analyses at the micrometric scale of powdered materials: Application to nuclear forensics

To characterize a mixture of powders using several analytical techniques, it is necessary that successive analyses be carried out on well-identified and localized particles, so that each characterization corresponds to a given powder. In this publication, powdered nuclear materials are characterized at the morphological and elemental levels with a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and at the chemical level with a micro-Raman spectrometer (MRS). However, to avoid a time-consuming and insufficiently accurate microparticle relocation process between SEM/EDS and MRS, micro-Raman analyses are carried out inside the SEM using a coupling device. In this way, all three pieces of information are obtained for exactly the same micrometric spot, without moving the sample or relocating the microparticles analyzed. The information can therefore be combined to characterize each component of the mixture. In this article, we describe in detail the methodology we have developed and optimized for morphological, elemental and chemical analysis of microparticles using a combined SEM/EDS and SRM. This methodology has been applied to powdered nuclear materials in two international nuclear forensics exercises. In the first exercise, named CMX-6, the combined use of the two instruments identified the presence of PuO2 microparticles and several uranium compounds (UO2, U3O8, UO2F2) in both materials. In the second exercise, called CMX-7, the methodology developed enabled us to distinguish two chemical phases of uranium, a uranyl oxy-hydroxide and a uranyl nitrate, each characterized by specific morphologies and the detection or non-detection of a minor elemental constituent (calcium).

Low-frequency Raman spectrum of methamphetamine hydrochloride and its alterations induced by impurities

Methamphetamine is one of the most abused drugs worldwide. Forensic laboratories have developed various methods to analyze methamphetamine for identifying and comparing seizures. These methods basically focus on the physicochemical properties of the methamphetamine molecule. Because methamphetamine is commonly distributed in its hydrochloride salt form, information on the crystalline state of methamphetamine could give new insight for forensic drug analysis. To grasp this information, we applied low-frequency Raman spectroscopy to methamphetamine hydrochloride. A laboratory-built low-frequency Raman microspectrometer was used for measuring low-frequency Raman spectra of optically pure and racemic methamphetamine hydrochloride. A mixture of methamphetamine hydrochloride with dimethyl sulfone, which is frequently added as a diluent to illicit methamphetamines, was also measured. An ab initio calculation was performed to assign peaks in the low-frequency spectra. The phonon modes of methamphetamine hydrochloride, and their changes induced by impurities are discussed. To the best of our knowledge, this is the first reported application of low-frequency Raman spectroscopy technique to methamphetamine hydrochloride.

Diet composition and plastic ingestion in Poecilia reticulata from urban streams.

Fish are excellent bioindicators and can reveal the presence of plastic in the environment. Diagnosing the composition and abundance of polymers in the fish diet makes it possible to evaluate their point sources and possible trophic transfers. We aimed to use the gastrointestinal contents of Poecilia reticulata in subtropical urban streams to detect the occurrence, shape, color, size, and chemical composition of polymers. For this, the diet of 240 individuals was analyzed using the volumetric method, and the microplastics (MPs; < 5mm) recorded were characterized using Raman spectroscopy. Individuals predominantly consumed organic detritus and aquatic macroinvertebrates, with higher proportions of Diptera. A total of 111 plastic particles (< 0.5 to 12mm) were recorded, and a subset of 14.4% was subjected to a micro-Raman spectrometer (830nm excitation). The occurrence of polyethylene terephthalate (PET) and polypropylene (PP) with phthalocyanine dye was recorded. Some fragments could not be identified by Raman, but they contained indigo blue dye. Poecilia reticulata had a predominantly detritivorous diet with a record of plastic consumption, reflecting environmental pollution. Our results demonstrate that individuals of P. reticulata have ingested MPs in urban streams. This reinforces the need for future studies on the relationship between the presence of MPs in fish and the level of pollution in streams, comparisons with species of different feeding habits, and the potentially harmful effects on the entire biota.

Enhancing Micro-Raman Spectroscopy: A Variable Spectral Resolution Instrument Using Zoom Lens Technology.

Raman spectroscopy is a powerful analytical technique based on the inelastic scattering of photons. Conventional macro-Raman spectrometers are suitable for mass analysis but often lack the spatial resolution required to accurately examine microscopic regions of interest. For this reason, the development of micro-Raman spectrometers has been driven forward. However, even with micro-Raman spectrometers, high resolution is required to gain better insight into materials that provide low-intensity Raman signals. Here, we show the development of a micro-Raman spectrometer with implemented zoom lens technology. We found that by replacing a second collimating mirror in the monochromator with a zoom lens, the spectral resolution could be continuously adjusted at different zoom factors, i.e., high resolution was achieved at a higher zoom factor and lower spectral resolution was achieved at a lower zoom factor. A quantitative analysis of a micro-Raman spectrometer was performed and the spectral resolution was analysed by FWHM using the Gaussian fit. Validation was also performed by comparing the results obtained with those of a high-grade laboratory Raman spectrometer. A quantitative analysis was also performed using the ANOVA method and by assessing the signal-to-noise ratio between the two systems.

Concentration and Characterisation with Spectroscopic Technique of Microplastics in the Surface Sediment and Commercial Fish Species of Gemlik Bay (Marmara Sea)

In this study, we aimed to evaluate and characterise the microplastic pollution in the sediment and commercial fish species in the Gemlik Bay, the Marmara Sea. Our results showed that the highest concentration of microplastics in the sediment was at the station in the Gemport Harbour (9.73 pieces.kg-1) and the lowest concentration was at the Kurşunlu offshore (3.33 pieces.kg-1). The highest microplastic concentration per individual was in the gills of Synapturichthys kleinii (Risso, 1827) (14.5 pieces.ind-1) and the lowest in Diplodus annularis (Linnaeus, 1758) (0.33 pieces.ind-1). The highest concentration (8.75 pieces.ind-1) was indicated in the gastrointestinal tract of Chelidonichthys lucerna (Linnaeus, 1758), but the lowest concentration (0.88 pieces.ind-1) was in that of D. annularis species. The fiber-type particles were the most determined microplastics in both the sediment and fish samples. The Micro-Raman Spectrometer revealed that Polyvinyl chloride and polypropylene were dominant in the sediment, and polyoxymethylene and polyphenylene sulfone polymers were dominant in fish species.

Freezing of sessile water droplets on titanium alloy surfaces with various roughness: An in-situ experimental study

The threat of icing caused by supercooled water droplets on aircraft components such as wings and compressors is a serious concern for aviation safety, and the surface roughness of these components can experience alterations due to environmental corrosion or damage. However, the potential impact of surface roughness variation on their susceptibility to icing remains unclear. In this study, the freezing experiments of sessile water droplets on the surfaces of a typical aero-engine titanium alloy (ZTC4) with varying roughness were conducted using a laser confocal micro-Raman spectrometer with a heating/freezing stage. Three freezing stages were captured via an optical microscope, and the temperature changes of water droplet during the cooling process were explored through heat transfer simulation. In addition, the relationship between Raman peaks and temperatures of frozen droplets was quantified. The results of 200 repeated experiments demonstrated that the freezing temperatures of sessile water droplets exhibited a two-parameter Weibull distribution, and there was a nonlinear positive correlation between the mean freezing temperature and surface roughness, which implied that environmental corrosion or damage leading to an increase in surface roughness may significantly elevate the probability of component icing and safety issues.

Biochemical component analysis of human myopic corneal stroma using the Raman spectrum.

This study aimed to measure the Raman spectrum of the human corneal stroma lens obtained from small incision lenticule extraction surgery (SMILE) in Asian myopic eyes using a confocal Raman micro-spectrometer built in the laboratory. Forty-three myopic patients who underwent SMILE with equivalent diopters between - 4.00 and - 6.00 D were selected, and the right eye data were collected. Corneal stroma lenses were obtained during surgery, and the Raman spectra were measured after air drying. The complete Raman spectrum of human myopic corneal stroma lens tissue was obtained within the range of 700-4000cm-1. Thirteen characteristic peaks were found, with the stronger peaks appearing at 937cm-1, corresponding to proline, valine, and the protein skeleton of the human myopic corneal stroma lens; 1243cm-1, corresponding to collagen protein; 1448cm-1, corresponding to the collagen protein and phospholipids; and 2940cm-1, corresponding to the amino acid and lipids, which was the strongest Raman peak. These results demonstrated that Raman spectroscopy has much potential as a fast, cost-effective, and reliable diagnostic tool in the diagnosis and treatment of eye diseases, including myopia, keratoconus, and corneal infection.

Investigating the Middle Iron Age ceramics of Van Fortress through multi-analytical techniques

This work presents the characterization results of Middle Iron Age pottery fragments excavated in Van Fortress, the historical capital of the Urartu Kingdom, located on the eastern coast of Lake Van in Turkey. A multi-analytical approach combining optical microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR) has been employed to investigate the mineralogical composition of ceramics. Micro-Raman spectrometer was also used for the characterization of the pigments used for decoration. The data collected from the analyses offered information on the minerals that were discovered in the ceramics, as well as the temperature at which the ceramics were fired and the atmosphere that they were exposed to. The existence of hematite suggests that they were subjected to firing in an oxidizing environment, with the exception of one sample, which has a sandwich shape characterized by a red-edge and a black center, indicating exposure to both reducing and oxidative atmospheres during the fire process. The ceramics utilized in this investigation are hypothesized to have been crafted from elemental substances procured from two to three distinct clay origins.

Occurrence and fate of microplastics from a water source to two different drinking water treatment plants in a megacity in eastern China

The widespread presence of microplastics (MPs) contamination in drinking water has raised concerns regarding water safety and public health. In this study, a micro-Raman spectrometer was used to trace the occurrence of MP transport from a water source to a drinking water treatment plant (DWTP)1 with an advanced treatment process and DWTP2 with a conventional treatment process and the contributions of different processes to the risk reduction of MPs were explored. Six types of MPs were detected: polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyamide, and polyvinyl chloride. 2–5 μm (35.8–41.2%) and polyethylene terephthalate (27.1–29.9%) were the most frequently detected MP sizes and types of water source samples, respectively. The abundance of MPs in treated water decreased by 72.7–83.0% compared to raw water. Ozonation and granular activated carbon (52.7%), and sand filtration (47.5%) were the most effective processes for removing MPs from DWTP1 and DWTP2, respectively. Both DWTPs showed significant removal effects on polyethylene terephthalate, with 80.0–88.1% removal rates. The concentrations of polystyrene increase by 30.0–53.4% after chlorination. The dominant components in the treated water of DWTP1 and DWTP2 were polypropylene (24.7%) and polyethylene 27.7%, respectively, and MPs of 2–5 μm had the highest proportion (55.3–64.3%). Pollution load index and potential ecological risk index of raw water treated by DWTPs were reduced by 48.0–58.7% and 94.5–94.7%, respectively. The estimated daily intake of MPs in treated water for infants was 45.5–75.0 items/kg/d, respectively, approximately twice that of adults. This study contributes to the knowledge gap regarding MP pollution in drinking water systems.

Ultra-deep (>5 GPa) subduction of paragneiss and metagranite in the Dabie UHP Terrane, central China: Constraints from zircon inclusions, phase equilibrium modelling and U-Pb geochronology

In the Dabie orogen, central China, the ultrahigh pressure metamorphism (UHPM) was best recorded from meta-mafic and ultramafic rocks occurring as lenses within voluminous amphibolite-facies metafelsic rocks. However, whether or not these metafelsic rocks experienced ultra-deep subduction (>5 GPa) has been rarely quantified because of the rare preservation of peak diagnostic assemblages. In this study, we reconstruct the P-T-t paths for paragneisses and metagranites from the Dabie region to better elucidate their metamorphic evolution based on detailed petrological, mineralogical and Raman micro-spectrometer analysis of zircon inclusion combined with conventional geothermobarometry, phase equilibrium modelling and U-Pb dating. At least three stages of metamorphic evolution are identified for these lithologies. The UHPM is represented by the assemblages of coesite + garnet Ia/Ib + jadeite + phengite + K-feldspar + aragonite for paragneiss and diamond + aragonite + magnesite + phengite + rutile + garnet for metagranite, respectively. The paragneiss experienced peak conditions of 4.5–6.0 GPa/690–720 °C, followed by a decompression heating to 3.5–4.6 GPa/750–850 °C. Also, the diamond + aragonite + magnesite inclusions in zircon from the metagranite provide the first direct mineralogical evidences for ultra-deep subduction. Furthermore, the minimum peak pressure was defined at 5.4 GPa based on pseudosection for metagranite. As a result, this study provides the first mineralogical and modelling evidences of ultra-deep subduction for the metafelsic rocks in the Dabie orogen. The dating results suggest that the UHPM, anatexis and amphibolite-facies overprint occurred at 236 ± 3 Ma, 226 ± 1 Ma and 195 ± 4 Ma, respectively. The estimated average exhumation rate is 5.8–7.2 km/Ma from peak UHP to amphibolite-facies stages. Moreover, a comparison of different collisional orogens suggests that the preservation of UHP minerals in metafelsic rocks strongly depends on exhumation rate.

Distributed measurement of supercontinuum generation along a silica fiber taper using a confocal spectrometer

A highly sensitive distributed measurement technique is employed to map supercontinuum generation along a tapered silica optical fiber. This technique, which utilizes a confocal Raman micro-spectrometer, relies on analyzing far-field frequency-resolved Rayleigh scattering along the waveguide with micrometer-scale spatial resolution and high spectral resolution. Non-destructive and non-invasive, the mapping system enables observation of every stage of supercontinuum generation along the fiber cone, including cascade Raman scattering, four-wave mixing, and dispersive wave generation. Consequently, it unveils unique nonlinear spatial dynamics that are beyond the reach of standard spectral analyzers.

A Subpixel Calibration Strategy for Micro-Raman Spectrometer in Subvisible Particles Traceable Detection

A Subpixel Calibration Strategy for Micro-Raman Spectrometer in Subvisible Particles Traceable Detection

Effect of elemental substitution on transition threshold behaviours of Ge-As(Sb)-Se glasses

In this paper, We prepare two groups of glasses: one is Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;As&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; with x ranging from 5% to 32.5%, the other is Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sb&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; with x spanning from 5% to 25%, by using the conventional melt-quench method, and investigate the effect of the elemental substitution of Sb for As on the threshold behaviors in Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;As(Sb)&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; glasses. We are to understand to what extent the topological model and chemical order model can explain the correlation between physical properties and glass compositions, and how the chemical composition can affect the glass transition threshold. Glass transition temperature is measured by the differential scanning calorimeter (Mettler-Toledo, DSC1) with different scanning rates ranging from 5 K/min to 30 K/min under a uniform nitrogen gas flow of 50 mL/min, the glass density is measured by a Mettler H20 balance with a MgO crystal used as a reference. Samples of each glass composition are weighed five times and the average density is recorded. The refractive index of the glass at 1.5 um is measured by a Metricon Model 2010 prism coupler. Raman spectra are measured by a T64000 Jobin-Yvon-Horiba micro-Raman spectrometer equipped with a liquid-nitrogen-cooled CCD detector. The 830 nm laser line is used as an excitation source, and the laser power is kept as small as possible to avoid any photo-induced effects. The resolution of the spectrometer is about 0.5 cm&lt;sup&gt;–1&lt;/sup&gt;. The systematic measurements of these physical parameters show that while the transition thresholds at MCN = 2.4 and 2.67 are verified in the Ge-As-Se glasses with ideal covalent network, these two transitions represent the covalent network structure inside the glass from an under-constrained “floppy” network to an over-constrained “rigid” phase and from the two-dimensional to the three-dimensional “stressed rigid” phase respectively. However, when As is substituted by Sb, the the resulting Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sb&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; glass with non-ideal covalent network will change its transition threshold, changing into the chemically stoichiometric composition. We further deconvolve Raman scattering spectra into different structural units and the change of their respective intensity shows the same behavior, which is ascribed to the chemical effect induced by a large difference in atomic radius between As and Sb, and a relatively strong ionic feature of element Sb.

Ultrahigh sensitive SERS film of silver nanorods grown on nanohole array template by oblique angle deposition

To develop a highly sensitive silver nanorod (AgNR) array SERS film, anodic aluminum oxide (AAO) nanohole array templates were employed as seed substrates for oblique angle deposition (O.A.D.) by thermal evaporation. By pore broadening process, precise hole arrays of various diameters were fabricated from preliminarily prepared nanoholes of 30 nm diameter comprising equilateral triangle unit cells whose side length is 100 nm. Aligned silver nanorods of ∼1 μm length were fabricated on the several kinds of seed templates. The optical properties of the AgNR films were measured using thiophenol self-assembled monolayers on the film surfaces and a micro-Raman spectrometer employing a 785 nm pump laser. Out of the AgNR array samples, the AgNR array deposited on an 80-nm hole array substrate showed the highest SERS activity. The highest surface enhancement factor (E.F.) of Raman signal measured in this experiment was ∼7·107, which is ∼7 times higher than that of the AgNR array fabricated on a flat substrate. The main role of the nanopore array substrate was found to decrease the density of the grown nanorods, which is the key parameter determining the E.F. values of the AgNR arrays. From this and previous works, the optimum nanorod density is anticipated to be 8–9 rods/μm2, where E.F. of > 109 could be obtained. The nanorod density of the optimum AgNR array in this experiment was ∼10/μm2. The origin of the key role conducted by the nanorod density cannot be explained by hot spot effect and waits for understanding in the future studies. The ultrahigh sensitive AgNR array SERS film obtained in this work can be a very powerful medium for various chemical and biological sensors.

Direct photodegradation of internally mixed sodium chloride and malonic acid single aerosols: Impact of the photoproducts on the hygroscopic properties of the particles

Sea-salt aerosols (SSA) are one of the key natural aerosols in our atmosphere, consisting predominantly of sodium chloride (NaCl). Throughout their atmospheric transport, these aerosols undergo complex internal mixing, giving rise to a rich variety of inorganic and organic species, including dicarboxylic acids. This study investigates firstly the composition and deliquescence properties of coarse particles containing pure malonic acid (MA2, CH2(COOH)2) and internally mixed NaCl and MA2, by means of an acoustic levitation system coupled with a Raman microspectrometer. Secondly, we report here the first experimental observation and characterization of the products arising from photochemical reactions under UV–Visible irradiation (338 ≤ λ ≤ 414 nm) in the absence of an oxidant under acoustic levitation conditions in MA2 and NaCl/MA2 aerosols. Furthermore, the impact of photodegradation on the hygroscopic properties of these particles is examined. We confirmed the irreversible formation of monosodium malonate (NaMA, HOOCCH2COONa), which coexists with NaCl or MA2 on non-irradiated particles. We also demonstrated the formation of oxalic acid (OA2, HOOC–COOH) within irradiated MA2 droplets and the appearance of glyoxylic acid (GlyA, HCOCOOH) in NaCl containing droplets. The photolysis process exerts a marked effect on the hygroscopic properties of the particles, resulting in a shift in deliquescence transitions toward higher relative humidity (RH) values. This study contributes to the understanding of the intricate physicochemical processes involved in SSA during their atmospheric transport. Likewise, this work sheds light on the impacts of these types of aerosols on cloud formation and climate change.