Spectroscopy Research Articles

Aerosol-based multihollow surface DBD: a promising approach for nitrogen fixation

Nonthermal plasma reactors, which enable electrical discharges to be generated in various gases and both liquid and gaseous water, have attracted considerable attention as an alternative method for producing ammonia and fixing nitrogen. In this work, we investigated the basic performance of multihollow surface dielectric barrier discharge (MSDBD) to generate plasma in synthetic air and nitrogen-containing admixtures of water aerosols. The MSDBD in combination with the aerosol stream represents a rather complex geometry for generating the discharge; the plasma is significantly affected by the physicochemical properties of water aerosols on the one hand, on the other hand, this system facilitates the solvation of gaseous plasma products in water and the production of plasma-activated nitrogen-rich water (PAW). The plasma interaction with the water aerosols was studied using optical emission spectroscopy and a scanning mobility particle sizer to provide information about the size and distribution of the water particles entering and exiting the plasma reactor. The gas exiting the plasma reactor was analyzed using Fourier-transform infrared spectroscopy, and the PAW collected in an ice-cooled vessel was analyzed for nitrates (NO2 −), nitrites (NO3 −), and ammonia (NH3). MSDBD shows promise as a catalyst- and H2-free method for fixing nitrogen in water. Additionally, given the low energy consumption (<5 W) of MSDBD and the straightforward construction of the plasma unit, the suggested approach for PAW production offers a viable route for advancing a decentralized sustainable economy.

Anodic oxidation of wireless niobium electrode in bipolar electrochemistry

The anodic oxidation of a wireless niobium substrate serving as a bipolar electrode (BPE) in a direct or alternating current electric field was investigated in detail via spectrophotometry, electrochemical measurement, glow discharge–optical emission spectroscopy, and direct microscopic observation. Niobium oxide was a suitable material for the experiment because it is amorphous and can be evaluated through conventional electrochemical methods. It also has a clear interference color, enabling easy optical evaluation. The effect of the BPE configuration (e.g., vertical and horizontal alignments) in the cell on the anodic oxidation area was also investigated visually using the interference color. Transmission electron microscopy observation was also performed for an accurate measurement of the thickness of the anodic film formed on the niobium BPE. Although the basic film formation behavior and film composition were consistent with those in conventional anodization, even in wireless operation, the effective voltage directly contributing to film formation was found to be lower than the applied voltage (30%–70% of the applied voltage), depending on the electrolysis conditions.

Dual responsive behaviors in fluorescence of molecular crystals based on naphthalene pyridyl derivatives

Three compounds based on naphthalene and pyridine structures with different nitrogen positions (NP-2, NP-3, and NP-4) were synthesized. Except for displaying aggregation-induced emission (AIE) properties, the solution and crystals of these compounds show reversible fluorescence changes under alternative acid and base treatments. Experimental results, including X-ray diffraction, optical spectroscopy measurements, and cross-polarized microscope characterization, suggested that compounds might undergo reversible crystal-to-crystal transition upon external acid and base stimuli. It also revealed that the position of the heteroatom nitrogen in the pyridine unit significantly affected the intra- and intermolecular interactions, leading to restricted-intermolecular motions (RIMs) that caused the AIE effect. Besides, computational calculations indicated significant changes in molecular geometries and electronic interactions between the initial states and the protonated states. An information encryption system involving activation and operation codes was established based on the multiple stimuli-responsive properties. Our work not only presents a facile way to develop multiple responsive properties in molecular crystal systems but also explores their potential as highly emissive functional dyes for future applications.

Experimental Research on the Study of Мéntha Piperíta Makro- and Microelement Composition Growing in Goris, Syunik Region

The purpose of our work was to study the qualitative and quantitative composition of the mineral elements of peppermint (Méntha piperíta) leaves. The relevance of the study is revealed by the fact that, though some trace elements in low concentrations are necessary for plant growth, their excess can lead to plant death. This effect depends both on the nature of the element and on the type of plant. To achieve this goal, we used the method of optical emission spectroscopy with inductively coupled plasma on an Agilent 5110 ICP-OEC equipment. The object of research was the dried aerial part of peppermint (Méntha piperíta) growing in Goris region of Armenia. The content of 30 elements was determined, for five of which the biological absorption coefficient is greater than unity. This means that these elements accumulate in plants. These include strontium and molybdenum, which are toxic elements. Based on the data presented, it is certainly necessary to control the maximum permissible concentrations of molybdenum and strontium in peppermint (Méntha piperita) collections before using it in cooking and for the creation of medicinal products.

Potentially toxic metals in road dust: An assessment of ecological and health risks at Woldia and Kobo towns in North Wollo, Ethiopia

ABSTRACT The accumulation of heavy metals (HMs) in the environment threatens the ecosystem and human well-being. This study investigated the amounts of Mn, Fe, Ni, Co, Cu, Zn, Cd, Hg, Pb, As, and Cr, as well as the associated health and ecological risks. Thirty samples of roadside dust were collected in the northern Ethiopian towns of Woldia and Kobo. The collected samples were digested using acid digestion method and the levels of heavy metals were analysed using inductively coupled plasma optical emission spectroscopy. The results showed that the average concentrations of HMs were 0.103 (As)-7.6 (Cd) and 0.083 (Cd)-3.80 (Fe) mg/kg in Woldia and Kobo, respectively. All the HM concentrations investigated in this study were lower than the average global concentration, except for Hg in both towns and Cd in Woldia town. Analysis of variance (ANOVA) for the heavy metal concentration showed a significant difference across each sampling site, while Ni and Hg did not show a significant difference. The hazard quotient (HQ) and hazard index (HI) values of all HMs for adults and children through the three exposure routes were lower than 1, which means that they had a low likelihood of noncarcinogenic risks. The pollution index, geoaccumulation index, ecological risk index, integrated pollution index and risk index parameters were used to estimate the ecological risk. The results demonstrated that the pollution level mainly varied between low and moderate levels, except in Woldia, which is highly polluted by Cd metal that further detailed research is highly recommended to find out the sources of this metal.

Advanced Defect Spectroscopy in Wide Bandgap Semicondutors: Review and Recent Results

Abstract The study of deep level defects in semiconductors has always played a strategic role for the development of electronic and optoelectronic devices. In fact, deep levels have a strong impact on many of the device properties, including the efficiency, stability, and reliability because they can drive several physical process. Despite the advancements in crystal growth, wide and ultrawide bandgap semiconductors (such as gallium nitride and gallium oxide) are still strongly affected by the formation of defects that in general can act as carrier traps or generation-recombination centers. Conventional techniques used for deep level analysis in silicon need to be adapted for identifying and characterizing defects in wide bandap materials. This topical review paper presents an overview of reviews the theory of deep levels in semiconductor; in addition, we present a review and original results and on the application, limits and perspectives of two widely adopted most common deep -levels detection techniques, namely capacitance deep level transient spectroscopy and deep level optical spectroscopy, with specific focus on wide bandgap semiconductors. Finally, the most common traps of GaN and β-Ga2O3 are reviewed.

Machine learning-driven SERS analysis platform for rapid and accurate detection of precancerous lesions of gastric cancer.

A novel approach is proposed leveraging surface-enhanced Raman spectroscopy (SERS) combined with machine learning (ML) techniques, principal component analysis (PCA)-centroid displacement-based nearest neighbor (CDNN). This label-free approach can identify slight abnormalities between SERS spectra of gastric lesions at different stages, offering a promising avenue for detection and prevention of precancerous lesion of gastric cancer (PLGC). The agaric-shaped nanoarray substrate was prepared using gas-liquid interface self-assembly and reactive ion etching (RIE) technology to measure SERS spectra of serum from mice model with gastric lesions at different stages, and then a SERS spectral recognition model was trained and constructed using the PCA-CDNN algorithm. The results showed that the agaric-shaped nanoarray substrate has good uniformity, stability, cleanliness, and SERS enhancement effect. The trained PCA-CDNN model not only found the most important features of PLGC, but also achieved satisfactory classification results with accuracy, area under curve (AUC), sensitivity, and specificity up to 100%. This demonstrated the enormous potential of this analysis platform in the diagnosis of PLGC.

Label-free single-vesicle based surface enhanced Raman spectroscopy: A robust approach for investigating the biomolecular composition of small extracellular vesicles.

Small extracellular vesicles (sEVs) are cell-released vesicles ranging from 30-150nm in size. They have garnered increasing attention because of their potential for both the diagnosis and treatment of disease. The diversity of sEVs derives from their biological composition and cargo content. Currently, the isolation of sEV subpopulations is primarily based on bio-physical and affinity-based approaches. Since a standardized definition for sEV subpopulations is yet to be fully established, it is important to further investigate the correlation between the biomolecular composition of sEVs and their physical properties. In this study, we employed a platform combining single-vesicle surface-enhanced Raman spectroscopy (SERS) and machine learning to examine individual sEVs isolated by size-exclusion chromatography (SEC). The biomolecular composition of each vesicle examined was reflected by its corresponding SERS spectral features (biomolecular "fingerprints"), with their roots in the composition of their collective Raman-active bonds. Origins of the SERS spectral features were validated through a comparative analysis between SERS and mass spectrometry (MS). SERS fingerprinting of individual vesicles was effective in overcoming the challenges posed by EV population averaging, allowing for the possibility of analyzing the variations in biomolecular composition between the vesicles of similar and/or different sizes. Using this approach, we uncovered that each of the size-based fractions of sEVs contained particles with predominantly similar SERS spectral features. Indeed, more than 84% of the vesicles residing within a particular group were clearly distinguishable from that of the other EV sub-populations, despite some spectral variations within each sub-population. Our results suggest the possibility that size-based EV fractionation methods produce samples where similarly eluted sEVs are correlated with their respective biochemical contents, as reflected by their SERS spectra. Our findings therefore highlight the possibility that the biogenesis and respective biological functionalities of the various sEV fractions may be inherently different.

Empirical line ratios for optical emission spectroscopy in low-temperature, low-density, magnetised Ar plasmas

Spectroscopic evaluation of electron temperature and density in low-temperature, low-density, magnetized plasmas can be difficult, but necessary in situations where chemical erosion and physical sputtering prevent the use of other diagnostics, such as Langmuir probes (LP). Further, in such cases, because of the low densities and temperatures, the vessel and environment involved, theoretical line ratios derived from Collisional-Radiative models may not be easily applicable. This is the case, for example, of low-temperature (<15 eV), low-density (<1011 cm−3), magnetised plasma used for plasma-material interaction studies where chemical erosion and physical sputtering can be significant. The aim of the present work is to define an empirical line ratio (ELR) method derived from an extensive calibration campaign with the two diagnostics, using LP measurements as a reference. The ELR method is useful to permit the use of optical emission spectroscopy independent of LP in conditions that are critical for the latter, resulting in an effective instrument for the evaluation of plasma parameters. Further, the use of two different lines of sight and the influence of the magnetic field intensity on the measurements are also discussed. The proposed ELR method is demonstrated here for pure Ar linear plasmas and is in principle applicable also to other similar cases.

SERS as a tool for determination of structurally related compounds: The case of sulfanilamide class antibiotics

Analysis of real objects based on surface-enhanced Raman spectroscopy (SERS) often utilizes new SERS substrates and/or complex analysis procedures, and they are optimized for only the determination of a single analyte. Moreover, analysis simplicity and selectivity are often sacrificed for maximum (sometimes unnecessary) sensitivity. Consequently, this trend limits the versatility of SERS analysis and complicates its practical implementation. Thus, we have developed a universal, but simple SERS assay suitable for the determination of structurally related antibiotics (five representatives of the sulfanilamide class) in complex objects (human urine and saliva). The assay involves only mixing of acidified analyzed solution with co-activating agent (polydiallyldimethylammonium chloride – PDDA) and SERS substrate (standard colloidal silver nanoparticles). Acidification promotes the generation of SERS spectra with maximum similarity and intensity, which is explained by the favorable enhancement of the protonated sulfanilamide moiety (a structurally similar part of the studied antibiotics) as a result of its strong electrostatic interaction with the SERS-active surface. Meanwhile, the addition of PDDA improves analysis selectivity by reducing background signal from body fluids, enabling to simplify sample pretreatment (dilution for urine; mucin removal and dilution for saliva). Therefore, the assay allows for rapid (≤10 min), precise, and accurate class-specific determination of sulfanilamides within concentration ranges suitable for non-invasive therapeutic drug monitoring in urine (40–600 μM) and saliva (10–30 μM). We also believe that thorough investigation of structurally related analytes and accompanying effects (e.g., high spectral similarity) is a promising direction to improve the understanding of SERS in general and expand its capabilities as an analytical tool.

Metal-Organic Frameworks in Surface Enhanced Raman Spectroscopy-Based Analysis of Volatile Organic Compounds.

Volatile Organic Compounds (VOC) are a major class of environmental pollutants hazardous to human health, but also highly relevant in other fields including early disease diagnostics and organoleptic perception of aliments. Therefore, accurate analysis of VOC is essential, and a need for new analytical methods is witnessed for rapid on-site detection without complex sample preparation. Surface-Enhanced Raman Spectroscopy (SERS) offers a rapidly developing versatile analytical platform for the portable detection of chemical species. Nonetheless, the need for efficient docking of target analytes at the metallic surface significantly narrows the applicability of SERS. This limitation can be circumvented by interfacing the sensor surface with Metal-Organic Frameworks (MOF). These materials featuring chemical and structural versatility can efficiently pre-concentrate low molecular weight species such as VOC through their ordered porous structure. This review presents recent trends in the development of MOF-based SERS substrates with a focus on elucidating respective design rules for maximizing analytical performance. An overview of the status of the detection of harmful VOC is discussed in the context of industrial and environmental monitoring. In addition, a survey of the analysis of VOC biomarkers for medical diagnosis and emerging applications in aroma and flavor profiling is included.

Effect of tin doping on the structural, optical, and dielectric properties of unintentionally β-Ga2O3 single crystal

This paper studied the structural, optical, electrical, and dielectric properties of the undoped and 0.05 mol% Sn-doped β-Ga2O3 single crystals through comprehensive characterizations by x-ray diffraction (XRD), Raman scattering, Optical transmittance spectroscopy, x-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron (UPS) spectroscopy, and dielectric measurements. The optical bandgap decreases as Sn content increases. The results of XPS showed that Sn atoms were successfully added to the host β-Ga2O3 crystal. The position of the Fermi level of 0.05 mol% Sn-doped β-Ga2O3 is calculated to be 2.56 eV above the valence band and 1.85 eV beneath the conduction band. Also, the computed value of the work function of 0.05% mole Sn-doped β-Ga2O3 is 4.53 eV. AC conductivity increases, while dielectric loss and dielectric constant decrease with increasing frequency.

Alkyne Cyclotrimerisation, Acyclic Oligomerisation, and Transfer Hydrogenation Catalysed by a Titanium(IV) Phosphinoaryloxide Complex and its Redox Chemistry

AbstractThe reaction of sodium 2,4‐di‐tert‐butyl‐6‐(diphenylphos‐phino)phenolate (1, NaOArP) with TiIVCl4(THF)2 in a 2 : 1 molar ratio yielded TiIV(OArP)2Cl2 (2). The reduction of 2 with magnesium gave the dimeric titanium(III) compound [TiIII(OArP)2Cl]2 (3). In the presence of magnesium, compound 2 was found to catalyse the cyclotrimerization, acyclic oligomerisation, and hydrogenation of terminal alkynes. The complexes were characterised by single‐crystal X‐ray diffraction, optical spectroscopy, elemental analysis, and NMR or EPR spectroscopy, respectively.

Diffuse reflectance spectroscopy for optical characterizations of orthotopic head and neck cancer models in vivo

We demonstrated an easy-to-build, portable diffuse reflectance spectroscopy device along with a Monte Carlo inverse model to quantify tissue absorption and scattering-based parameters of orthotopic head and neck cancer models in vivo. Both tissue-mimicking phantom studies and animal studies were conducted to verify the optical spectroscopy system and Monte Carlo inverse model for the accurate extraction of tissue optical properties. For the first time, we reported the tissue absorption and scattering coefficients of mouse normal tongue tissues and tongue tumor tissues. Our in vivo animal studies showed reduced total hemoglobin concentration, lower tissue vascular oxygen saturation, and increased tissue scattering in the orthotopic tongue tumors compared to the normal tongue tissues. Our data also showed that mice tongue tumors with different sizes may have significantly different tissue absorption and scattering-based parameters. Small tongue tumors (volume was ∼60 mm3) had increased absorption coefficients, decreased reduced-scattering coefficients, and increased total hemoglobin concentrations compared to tiny tongue tumors (volume was ∼18 mm3). These results demonstrated the potential of diffuse reflectance spectroscopy to noninvasively evaluate tumor biology using orthotopic tongue cancer models for future head and neck cancer research.

A dual-signaling surface-enhanced Raman spectroscopy ratiometric strategy for ultrasensitive Hg2+ detection based on Au@Ag/COF composites

Heavy metal ion pollution poses significant risks to human health and ecological systems, and its monitoring is important. A sensitive and accurate surface-enhanced Raman spectroscopy (SERS) detection assay for Hg2+ was developed using Au@Ag/COF substrates and Y-shaped DNA labeled with two Raman reporters. The Au@Ag NPs in the COF produced robust and uniform E-fields, improving their detection reproducibility. The Y-shaped DNA design increased sensitivity with a low detection limit of 5.0 × 10−16 M by bringing the Raman reporter closer to the substrate surface. Additionally, the use of two Raman reporters allowed for a ratiometric method, improving detection accuracy by detecting both “signal-off” and “signal-on” signals. This selective sensor exhibited excellent recovery in river water, tap water, and milk samples, showcasing its robust biosensing capability for the detection of Hg2+ and its potential for sensing other heavy-metal ions in food and environmental applications.

Biosorption of copper, nickel, and manganese as well as the production of metal nanoparticles by Bacillus species isolated from soils contaminated with electronic wastes.

Improper electronic waste management in the world especially in developing countries such as Iran has resulted in environmental pollution. Copper, nickel, and manganese are from the most concerned soil contaminating heavy metals which found in many electronic devices that are not properly processed. The aim of this study was to investigate the biological removal of copper, nickel, and manganese by Bacillus species isolated from a landfill of electronic waste (Zainal Pass hills located in Isfahan, Iran) which is the and to produce nanoparticles from the studied metals by the isolated bacteria. The amounts of copper, nickel, and manganese in the soil was measured as 1.9 × 104 mg/kg, 0.011 × 104 mg/kg and 0.013 × 104 mg/kg, respectively based on ICP-OES analysis, which was significantly higher than normal (0.02 mg/kg, 0.05 mg/kg, and 2 mg/kg, respectively. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of metals on the bacterial isolates was determined. The biosorption of metals by the bacteria was evaluated by inductively coupled plasma optical emission spectroscopy (ICP-OES). The metal nanoparticles were synthetized utilizing the isolates in culture media containing the heavy metals with the concentrations to which the isolates had shown resistance. X ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used for the evaluation of the fabrication of the produced metal nanoparticles. Based on the findings of this study, a total of 15 bacterial isolates were obtained from the soil samples. The obtained MICs of copper, nickel, and manganese on the isolates were 40-300 mM, 4-10 mM, and 60-120 mM, respectively. The most resistant isolates to copper were FM1 and FM2 which were able to bio-remove 79.81% and 68.69% of the metal, respectively. FM4 and FM5 were respectively the most resistant isolate to nickel and manganese and were able to bio-remove 86.74% and 91.96% of the metals, respectively. FM1, FM2, FM4, and FM5 was molecularly identified as Bacillus cereus, Bacillus thuringiensis, Bacillus paramycoides, and Bacillus wiedmannii, respectively. The results of XRD, SEM and EDS showed conversion of the copper and manganese into spherical and oval nanoparticles with the approximate sizes of 20-40 nm. Due to the fact that the novel strains in this study showed high resistance to copper, nickel, and manganese and high adsorption of the metals, they can be used in the future, as suitable strains for the bio-removal of these metals from electronic and other industrial wastes.

Spectroscopic Manifestations Of (Anti)Aromaticity In Oxidized And Reduced Porphyrin And Norcorrole.

Aromaticity and antiaromaticity are foundational principes in organic chemistry, regularly invoked to explain stability, structure, and magnetic and electronic properties. There are ongoing challenges in assigning molecules as aromatic or antiaromatic using optical spectroscopy. Here we report spectroelectrochemical and computational analyses of porphyrin (18π neutral, aromatic) and norcorrole (16π neutral, antiaromatic), and their oxidized (16π porphyrin dication) and reduced (norcorrole 18π dianion) forms. Our results show that while the visible spectra are characteristic of (anti)aromaticity consistent with Hückel's rules, the IR spectra are much less informative, owing to the relative rigidity of norcorrole. The results have implications for the assignment of (anti)aromaticity in both ground-state and time-resolved excited-state spectra.

All-in-One Electrokinetic Strategy Coupled with a Miniaturized Chip for SERS Detection of Multipesticides.

Complexed and tiresome pretreatment processes have significantly impeded in-field analysis of environmental specimens. Herein, an all-in-one sample separation and enrichment strategy based on a compact charge-selective capture/nanoconfined enrichment (CSC/NCE) device is exploited for marker-free surface-enhanced Raman spectroscopy (SERS) detection of charged pesticides in matrix specimens. This tactic incorporating in situ separations, seizing, and nanoconfined enhancement can greatly elevate the effectiveness of sample pretreatment. Importantly, CSC/NCE with excellent adsorption performances and excellent plasmonic features facilitates concentration and signal amplification of electrically charged pesticides. With the introduction of an electric field on this integrated CSC/NCE, the matrix effect in samples could be significantly eradicated, and a distinct SERS response is witnessed for targeted analytes. Accurate quantification of multipesticides is achieved by synergizing the CSC/NCE chip and chemometrics, and the contents found by the CSC/NCE-based sensing strategy agree with those obtained from chromatography assays with relative deviations lower than 10%. The facile and versatile all-in-one tactic infused in a compact chip exhibits enormous potential for field-test application in chemical measurement and food safety.

Physicochemical analysis of deterioration affecting the darkening of rock art in Maros-Pangkep, South Sulawesi, Indonesia

This study investigates the darkening processes affecting Maros-Pangkep rock art through a comprehensive multianalytical approach. We integrate in-situ color index measurements using Nix color Pro 2 with various physicochemical characterization techniques, including optical microscopy, XRF, SEM-EDS, Raman spectroscopy, and FTIR. By examining microbial, geochemical, and anthropogenic factors on rock art pigment samples, we establish a clear correlation between the formation of blackish-gray layers and reduced chromaticity values, indicating a significant darkening process. The shift in pigment color from vibrant red or purple to a prevailing blackish-gray hue is attributed to surface accumulation. Surface morphology analysis reveals distinct blackish deposits and delicate white fibrous structures on darkened rock art. Elemental composition analysis demonstrates heightened blackish deposit formation and increased phosphorus content in darkened samples. SEM-EDS characterization exposes gypsum morphology, with filament-like structures prevailing in heavily darkened samples, highlighting the role of both geochemical and microbial factors in deposit layer formation. FTIR spectra results confirm the presence of gypsum minerals, which are attributed to the substrate minerals and/or mineral weathering product, and unveil the existence of organic compounds, indicating microbial activity. Additionally, Raman spectroscopy reveals the anthropogenic contribution, notably soot deposition produced by human activities, to the darkening of rock art. This study underscores the need for a holistic preservation approach addressing natural, human, and microbial impacts on cultural heritage sites. Further research is also needed to conduct cross-sectional stratigraphical analysis to understand the accurate mechanism of the deterioration process on the rock art. Moreover, excavation measures regarding the possible relationship of soot deposition with human activities are also important to be carried out at the sites.

Distinguishing methane from other hydrocarbons using machine learning and atmospheric pressure plasma optical emission spectroscopy

The ability to detect gas molecule and assign a concentration offers an inventive solution in the field of plasma integrated with machine learning. The most important finding of this work is firstly, to develop an algorithm for gas-molecule identification using three different hydrocarbons (CH4, C2H2, C2H6) and secondly, organize a model for detecting gas concentration (classification). For this reason, initially eight different gases evaluated. The study confirms the present of the unique emission lines as a gas indicator, i.e., a wavelength peak related to hydrocarbons identified via increasing in C x H y concentration. By means of unique variable important in projection, hydrocarbons can be distinguished. Our proposed Chemometric analysis strategy examined on >1000 samples and results development of suitable techniques that are sufficiently rapid, accurate and innovative. This demonstrates the potential for real-time, portable, and continuous monitoring of trace gases with potential applications in medical, environmental, and industrial gas sensing.