Characteristic Raman Peak Research Articles

Detecting the saddling deformations in nickel meso-phenyl substituted porphyrins using low-frequency Raman characteristic peaks.

The out-of-plane (OOP) deformations of metalloporphyrins macrocycle are closely related to their biological functions, and Raman spectroscopy is a powerful tool for investigating OOP deformations. However, due to the interplay of electronic structure, substituents, porphyrin macrocycle in-plane (IP) and OOP deformations, it is challenging to measure the OOP deformations directly, or, establish a confirmative correlation between the frequency shifts of characteristic peaks and specific OOP deformation changes. In this work, we first selected the model porphyrin Ni-P and employed DFT calculations to explore the relationship between the ruffling and saddling deformation changes and their corresponding Raman spectral differences. Subsequently, we focused on nickel meso-tetraphenyl porphyrin (NiTPP), nickel meso-tetrachlorophenylporphyrin (NiTClP), and nickel meso-tetramethoxyphenyl porphyrin (NiTMeOP), which are structurally similar in nature, and investigated the relationship between their OOP deformations and Raman spectra bands based on both experiments and DFT calculations. The results indicate that the ruffling deformation magnitudes of the three nickel porphyrins are almost identical, while the saddling deformation magnitudes differ remarkably. The frequency change of the characteristic peak γ18 in relation to saddling deformation of the three porphyrins is 7.7cm-1/Å, which is close to that of the model porphyrin Ni-P 10.6cm-1/Å. Therefore, the characteristic peak γ18 can be used as a "reporter" for the change in saddling deformation. As such, this work demonstrates how to utilize the frequency shifts of low-frequency Raman characteristic peaks to identify the OOP deformation changes of the porphyrin macrocycle caused by variations in the external environment, thereby providing a theoretically assisted tool for revealing the reasons for their biological function variations.

Ultrafast Microwave-Synthesized 2D/1D MnO2/Carbon Nanotube Hybrid for Bilirubin Detection in Simulated Blood Serum.

Hybridization of carbon nanotubes (CNTs) and manganese dioxide (MnO2) integrates the biocompatibility and outstanding electrocatalytic activity of MnO2 with the exceptional conductivity of CNTs, thus providing a superior synergistic sensing platform for the detection of biomolecules. However, the existing methods for synthesizing MnO2/CNT hybrids are complex and inefficient, resulting in low yields and limited surface functionalities. Hence, in this study, we present a low-cost and ultrafast solid-phase synthesis of the MnO2/CNT hybrid using a facile microwave technique to detect a crucial biomolecule bilirubin. The successful synthesis of the MnO2/CNT hybrid is confirmed through characteristic Raman and X-ray diffraction peaks, while morphology is analyzed by imaging techniques such as FESEM and HRTEM. The MnO2/CNT/nickel foam (NF) sensor is thereafter used for the electrochemical detection of bilirubin. The sensor demonstrates a wide linear detection range from 10 nM to 1 mM, with a sensitivity of 6.87 mA nM-1 cm-2 toward bilirubin, as determined through the differential pulse voltammetry technique. The lower limit of detection is noted at 3.3 nM (=3.3 S/m). Furthermore, the as-fabricated sensor showcases high selectivity against the interfering species. Real-time analysis conducted in simulated blood serum using the standard addition method reveals an outstanding recovery percentage of approximately 98%. The conductive MnO2/CNT hybrid interacts robustly with bilirubin, aided by the porous NF substrate for stability, catalytic activity, and rapid electron transfer, enabling sensitive bilirubin detection. The work provides an ultrafast, low-cost, and high-yield solid-phase microwave synthesis of MnO2/CNT hybrid material and broadens its application in the detection of biological specimens for clinical diagnosis and biomedical research.

Synthesis of UiO-66/Ag/TiO2 composite as reusable SERS substrate

Substrate materials with high sensitivity, uniformity and reusability are crucial for the practical application of surface-enhanced Raman scattering (SERS) spectral technique. The solvothermal method was employed to synthesize a novel octahedral UiO-66/Ag composite in this study, which serves as an excellent SERS-active substrate for the detection of rhodamine 6 G (R6G) at concentrations as low as 10−10 M and thiram at 10−6 M. Moreover, it exhibits a strong linear relationship between SERS intensities and logarithmic concentration. By incorporating TiO2 nanoparticles, the UiO-66/Ag/TiO2 composite demonstrates comparable SERS activity to that of UiO-66/Ag composite while also exhibiting remarkable photocatalytic degradation abilities towards dye molecules such as R6G and crystal violet (CV). Notably, after three cycles of "SERS detection-degradation", the Raman characteristic peaks of CV or R6G molecules retain an intensity over 83 %, highlighting its excellent reusability. This MOF-based composite substrate combines the exceptional adsorption performance of UiO-66 for trace molecules, abundant hot spots provided by Ag nanoparticles, and good photocatalytic ability of TiO2 nanoparticles. Therefore, this sensitive, uniform, and reusable substrate holds significant potential in practical applications for detecting food contamination and environmental pollution.

Development and validation of an analytical method for the simultaneous quantitation of posaconazole Form I and Form-S in oral suspensions

Any polymorphic conversion of an active pharmaceutical ingredient (API), even if partial, is likely to lead to changes in its efficiency and safety. Posaconazole, an antifungal drug, is detected as Form-S in the commercially available oral suspensions. However, a mixture of Form-S and the initial Form I is likely to coexist depending either on the manufacturing process of the suspensions and/or to the storage conditions of the suspension. The simultaneous quantitation of these crystal forms in suspensions is challenging because of the dose inhomogeneity and the instability of Form-S at ambient conditions. Although X-ray Powder Diffraction (XRPD) was initially employed, preferred orientation issues in the suspension inhibited the successful quantitative determination of the polymorphs. In order to circumvent the problem Raman spectroscopy was selected for addressing this challenge, while the additional application of a home-made rotation system reduced the inhomogeneity problems. A separate calibration curve was generated for each polymorph using a conventional linear regression. The combination of these two relations led to the formation of a comprehensive equation relating the characteristic Raman peak intensities of posaconazole Form-S and Form I with the concentrations thereof. The method was validated and the results were confirmed through a partial least square regression (PLSR). The detection limits for Form-S and Form I were determined equal to 1.9 mg/mL and 2.2 mg/mL, respectively.

A study on the changes in rice composition under reduced fertilization conditions using Raman spectroscopy technology

The substitution of microbial fertilizer for chemical fertilizer can not only improve soil fertility but also effectively enhance rice quality. To investigate the effect of different amounts of combined application of chemical fertilizer and microbial fertilizer on the amylose content of rice, this study adopts theoretical calculations to compare the preprocessed Raman spectroscopy information of rice with reduced fertilization and establishes a recognition model for the amylose content of rice, which is used to detect the amylose content in rice. Based on the amylose spectral values measured by Raman spectroscopy and the known starch structure and functional groups, the Raman peaks are mainly distributed in the range of 400 cm− 1 to 1400 cm− 1. The Raman characteristic peaks at 483 cm− 1, 869 cm− 1, 933 cm− 1, 1082 cm− 1, 1126 cm− 1, 1335 cm− 1, 1385 cm− 1, and 1455 cm− 1 exhibit strong vibration modes, which are consistent with its main nutrient component of amylose. By comparing the measured amylose content in the regions treated with microbial fertilizer combined with different amounts of reduced fertilization and the spectral intensity values of amylose measured by Raman spectroscopy, the results show that the treatment of combining conventional amounts of microbial fertilizer with different amounts of reduced chemical fertilizer exhibits a decreasing trend in the amylose content of rice.

Fabrication of high performance 2D flexible SERS substrate based on cellulose nanofibrils and its application for pesticide residue detection

Cellulose nanofibrils (CNFs) can serve as an efficient surface enhanced Raman scattering (SERS) platform for in situ detection of trace targets. In this study, a highly reproducible SERS platform based on TEMPO-oxidized CNFs (T-CNFs) was fabricated by the ion-exchange. Self-assembly of silver nanoparticles (AgNPs) was accomplished in only 120 s. The abundant carboxylate groups and good hydrophilicity of T-CNFs facilitated uniform and dense loading of AgNPs over the surface area. The obtained SERS substrate greatly enhanced the Raman signal of different pesticides, and the detection limits of thiram and thiabendazole were 5.81 × 10−8 M and 9.63 × 10−8 M, respectively. SERS substrate could produce homogeneous Raman-enhanced signals (relative standard deviation (RSD) = 6.59 %). In addition, due to the good flexibility, SERS substrate could collect and detect pesticide residues from the surface of apples. The intensities of Raman characteristic peak at 1384 cm−1 showed a good linear relationship with the analyte concentrations (0.96 ng/cm2–9600 ng/cm2). The constructed SERS substrate provided a theoretical basis for the preliminary rapid screening of hazardous chemical residues in food, which was of great value for the SERS technique to become a routine on-site analysis method for pesticide residues.

A magnetic SERS-imprinted sensor for the determination of cardiac troponin I based on proteolytic peptide technology

Acute myocardial infarction is a sudden and high-mortality disease that can be accurately diagnosed by measuring the level of cardiac troponin I in the blood. Currently, cTnI commonly used clinical detection methods usually have excellent sensitivity and are suitable for large-scale sample detection analysis. However, most of these methods are operated through multiple steps of fixation, incubation, reaction and separation, and most of them require professionals to operate complex instruments, which greatly limits their applicability in real-time rapid detection. Therefore, a method that requires low professional skills and can perform rapid detection is necessary. We presents an alternative strategy to quantify cTnI in clinical serum samples using a combination of SERS and magnetic molecularly imprinted polymers (MMIP). MMIPs was synthesized under Polyvinyl Pyrrolidone (PVP) conditions without vinyl modification using characteristic peptide as template, MAA and DMAm as functional monomers. The internal Raman probe 4-MBA was connected through Ag-SH bonds in MMIPs to solve the problem that the target object had no Raman characteristic peak. MMIPs with high magnetic and adsorptive properties showed characteristic absorption peaks at the Raman shift of 1582 cm−1 after specific capture of the target templates. The Raman signals of the 4-MBA were reduced due to shielding effects and the detection range of this method was 0.001–100 ng mL−1. The recoveries and relative standard deviations (RSDs) of the spiked experiments were 103.1%–106.3 % and 3.54 %–7.38 %, respectively. In summary, this work had appropriate sensitivity and specificity, and there was no significant difference in detection results after ELISA verification. It provided a flexible and practical analysis method for detecting cTnI based on SERS technology. In addition, the imprinting materials of other disease markers can be prepared by changing the template molecules, which provides a new idea for the detection of other biomarkers.

Role of growth temperature on microstructural and electronic properties of rapid thermally grown MoTe2 thin film for infrared detection

In the field of electronic and optoelectronic applications, two-dimensional materials are found to be promising candidates for futuristic devices. For the detection of infrared (IR) light, MoTe2possesses an appropriate bandgap for which p-MoTe2/n-Si heterojunctions are well suited for photodetectors. In this study, a rapid thermal technique is used to grow MoTe2thin films on silicon (Si) substrates. Molybdenum (Mo) thin films are deposited using a sputtering system on the Si substrate and tellurium (Te) film is deposited on the Mo film by a thermal evaporation technique. The substrates with Mo/Te thin films are kept in a face-to-face manner inside the rapid thermal-processing furnace. The growth is carried out at a base pressure of 2 torr with a flow of 160 sccm of argon gas at different temperatures ranging from 400 °C to 700 °C. The x-ray diffraction peaks appear around 2θ= 12.8°, 25.5°, 39.2°, and 53.2° corresponding to (002), (004), (006), and (008) orientation of a hexagonal 2H-MoTe2structure. The characteristic Raman peaks of MoTe2, observed at ∼119 cm-1and ∼172 cm-1, correspond to the in-plane E1gand out-of-plane A1gmodes of MoTe2, whereas the prominent peaks of the in-plane E12gmode at ∼234 cm-1and the out-of-plane B12gmode at ∼289 cm-1are also observed. Root mean square (RMS) roughness is found to increase with increasing growth temperature. The bandgap of MoTe2is calculated using a Tauc plot and is found to be 0.90 eV. Electrical characterizations are carried out using current-voltage and current-time measurement, where the maximum responsivity and detectivity are found to be 127.37 mA W-1and 85.21 × 107Jones for a growth temperature of 600 °C and an IR wavelength illumination of 1060 nm.

Synthesis and physical characterization of novel Ag2S-CdS /Ag /GNP ternary nanocomposite

A new type of Ag2S-CdS/Ag/GNP nanocomposite material was successfully synthesized in the presented work. The structural and physical properties of compounds were studied separately and together. Ag2S-CdS/Ag/GNP nanocomposite materials were studied by Xray diffraction (XRD), Ultraviolet-Visible (UV-Vis), Fourier Transform Infrared (FTIR), Raman spectroscopy and Scanning Electron Microscopy (SEM). Based on the results, Ag nanowires (NWs) were successfully synthesized, and then it was determined that during the hybridization process, two phases of acanthite Ag2S and the cubic crystal system of Ag2O were formed. Then, Ag2S-CdS NWs were formed from mixed monoclinic Ag2S and hexagonal CdS. In the absorption spectrum of Ag NWs, the main absorbance peaks were observed at 357.3 nm and 380.2 nm. The energy gap (Eg) values of the Ag sample are 3.8 eV. The band gap value of Ag2S (2.5, 3.8, 4.6 eV) and Ag2S-CdS (2.5, 3.8, 4.8 eV) have a triple value due to the formation of a hybrid structure. The Raman spectrum of Ag2S-CdS belongs to longitudinal-optical (LO) phonon modes of zinc-blende phase CdS and for the 1, 2, and 3 times spin-coated samples on the surface of GNP/PVA have observed all characteristic Raman peaks, which belong to NWs at 485.13 cm-1, and 960.22 cm-1.

Study of the relationship among biomarkers, cell and tissue of glioma through Raman spectroscopy

Glioma is the most common brain tumors with high mortality and recurrence rates. Currently, the diagnosis methods for glioma are mainly based on tissue level, cellular level and biomarker level. In this paper, the characteristics of biomarkers (γ-aminobutyric acid and matrix mtalloproteinses-2), U87MG glioma cell and tissue were studied based on Raman spectroscopy, respectively. The results showed that the γ-aminobutyric acid concentration exhibited a linear relation with the intensity of characteristic peaks in 800–1600 cm−1 region, whereas the spectral baseline increased with the increasing of sample concentration in 200–700 cm−1 region. The Raman characteristics of matrix mtalloproteinses-2 in 20–1800 cm−1 region was investigated. Especially, it is demonstrated that the matrix mtalloproteinses-2 showed sixteen low-wavenumber Raman peaks in the range of 20–300 cm−1. Moreover, the U87MG glioma cell showed seven different Raman characteristic peaks in 600–1800 cm−1 region. Compared with the normal tissue, the Raman intensity of tumor tissue showed apparent intensity differences in 300–1800 cm−1, where the intensity changes of these Raman peaks were related to the reducing of the lipid metabolic pathways, and increase of the RNA in tumor tissue region. Furthermore, it is found that the Raman spectra of U87MG glioma cell and tumor tissue had corresponding peaks in the Raman spectra of the liquid γ-aminobutyric acid and matrix mtalloproteinses-2. It is suggested that the γ-aminobutyric acid and matrix mtalloproteinses-2 contributed to the formation and growth of glioma cell and tissue. Thus, Raman spectroscopy not only can diagnose glioma at the biomarkers, cellular and tissue level, but also analyze the relationship among the three. Furthermore, the results provided a physical marker for the detection of glioma in clinically.

Artificial shock wave impact studies on Olivine single crystal - A Raman spectroscopic approach

After the invention of indoor tabletop shock tubes, studies on the impact of low-pressure acoustic shock waves on materials have been sufficiently conducted and found several spectacular phase transitions. However, the acoustic shock wave impact studies on minerals remain unexplored. The floodgates are to be opened by streamlining a systematic approach in bringing out a new era of spectacular findings as more and more minerals are involved in the investigation. Hence, in the present investigation, we have chosen one of the most prominent upper mantle earth minerals of α-Olivine (forsterite-Mg2SiO4) single crystal for the ex-situ shock wave recovery experiment with 2.0 MPa transient pressure. Raman spectroscopic technique has been utilized to examine the crystallographic stability of the title mineral. The observed shock-wave impact results demonstrate that the forsterite remains to be in the crystallized state maintaining the same space group of Pbnm, however, significant changes have been witnessed in the normalized intensity ratio of the characteristic doublet Raman peaks of the forsterite (asymmetry stretching SiO4 (824 cm−1)/symmetry stretching SiO4 (855 cm−1) such that the values are found to be 2.17, 2.27, 1.38, 0.51, and 2.43 against the number of shock pulses of 0, 1, 2, 3 and 4, respectively. It is to be noted that, we have found more pronounced changes in the doublet Raman peak intensity compared to the flat plate accelerator shock compression experiment on forsterite (Tielke et al., J. Geophys. Res. Planets (2022)) and the observed values are 0.8, 0.3, 0.6, 0.8 and 0.52 for 0, 21.3, 22.4, 38.9 and 41.8 GPa, respectively without undergoing any structural transitions towards the high-pressure phases. Based on the assessment of comparative results, tabletop shock-tubes can be strongly considered for mineralogical research to expand the current knowledge on the behaviors of the earth and space minerals under extreme-conditions.

Super-Spectral-Resolution Raman spectroscopy using angle-tuning of a Fabry-Pérot etalon with application to diamond characterization

Raman spectroscopy is an extremely powerful laser-based method for characterizing materials based on their unique inelastic scattering spectrum. Ultimately, the power of the technique is limited by the resolution of the spectrometer. Here we introduce a new method for achieving Super-Spectral-Resolution Raman Spectroscopy (SSR-RS), by angle-tuning a Fabry–Pérot (F-P) etalon filter that we incorporated in a micro-Raman setup. A monolithically coated F-P etalon structure, only 1.686 mm in thickness, was mounted onto an angle-tunable motorized stage, and Raman spectra were automatically acquired for many different angles of the etalon. Using a low-resolution grating of 150 g/mm by itself, without the F-P etalon, we obtained a best-case regular Raman spectral linewidth of 44 cm−1 for the characteristic Raman peak from a diamond sample. When we applied the SSR-RS technique to diamond, we obtained a super-spectral resolution peak that was 27x narrower, namely 1.63 cm−1, and a Raman shift of 1331.3 cm−1. To baseline SSR-RS, we applied the super-spectral-resolution method to extract the linewidth and peak wavelength of the laser excitation itself and obtained a laser linewidth of better than 0.014 cm−1, with a laser wavelength centered at 531.962 nm, close to the stated wavelength of 532 nm. This extracted laser linewidth is 3300x times narrower compared to its measured linewidth of 46 cm−1. Thus, our work suggests that SSR-RS can be very generally applied to greatly improve the resolution and precision of Raman instrumentation, and potentially lower the cost of obtaining high-resolution Raman spectroscopic capabilities.

SERS-active core-satellite nanostructures in a membrane filter-integrated microfluidic device for sensitive and continuous detection of trace molecules

We developed a surface-enhanced Raman scattering (SERS)-active plasmonic core-satellite nanostructure and incorporated it into a membrane filter-integrated microfluidic device for continuous monitoring of molecules in solution. The core-satellite nanostructures were fabricated by immobilizing a high number density of gold nanoparticles (AuNPs) on silica beads.to create many nanogaps among the AuNPs. The sizes of the nanogaps were fine-tuned by adding a silver (Ag) shell to optimize the SERS activity. In addition, citrate molecule, the capping agent of the nanoparticles, was displaced by alkali halides. The displacement not only reduced the SERS signals of citrate but also enhanced the adsorption of target molecules. The alkali halide-treated core-satellite nanostructures were accumulated onto a membrane filter integrated into a microfluidic device, serving as a uniform and sensitive SERS substrate. By increasing the volume of the sample solution flowing through the membrane filter, we increased the number of molecules adsorbed to the nanostructures, amplifying the intensities of their characteristic Raman peaks. Our microfluidic SERS device demonstrated continuous SERS detection of malachite green at a concentration as low as 500 fM. In summary, while various core-satellite nanostructures and microfluidic SERS devices have been reported, the integration of the membrane filter-containing microfluidic device with the core-satellite nanostructures facilitated sensitive and continuous molecule detection in our study.

Analysis of structural composition and antioxidant activity of traditional fermented sour meat peptides

Chinese traditional fermented sour meat has a unique flavor and nutritional value. The antioxidant activity of sour meat peptides is related to their molecular weights, amino acid compositions, and structural characteristics. Therefore, this study explores the relationships between them. The results indicate that sour meat peptides with molecular weights <1 kDa exhibit significant antioxidant properties both in vitro and in vivo. The smaller the molecular weights, the higher the content of typical amino acids with antioxidant activity (p <0.05), and the characteristic peaks of ultraviolet absorption decrease. The absorption peak at 284.5 nm blue-shifted, and the polarity of the microenvironment increased. The peak intensity and peak area of the Raman characteristic peaks of tyrosine residues and aliphatic amino acids were enhanced. In the secondary structure, there is a high content of β-turns and a low content of α-helix, which are closely related to the enhancement of antioxidant activity.

Temporal metabolic dynamics and heterogeneity of viable but nonculturable Pseudomonas aeruginosa induced by chlorine disinfection at single-cell resolution

Characterizing the metabolic network and dynamics of Viable But Nonculturable (VBNC) bacteria is crucial for their identification and control. In this study, single-cell Raman spectroscopy was used to explore the metabolic intricacies of VBNC P. aeruginosa induced by chlorine disinfection over 24 h. VBNC P. aeruginosa exhibited significant reductions of 75.98 %, 84.26 % and 81.07 % in carbohydrate, protein and nucleic acid Raman peaks, signaling decreased metabolic activity in these crucial components. Intriguingly, lipid metabolism in VBNC P. aeruginosa remained robust, indicating a potential adaptation to environmental stress. Furthermore, this study analyzed Raman characteristic peaks to examine metabolic conversion in these bacteria. VBNC P. aeruginosa displayed distinct phase-specific metabolic conversion patterns compared to culturable ones. These findings shed light on the temporal dynamics of metabolic processes, such as lipid-carbohydrate conversion, which appeared to be ongoing throughout the incubation period in VBNC P. aeruginosa. Compared to the culturable state, VBNC P. aeruginosa exhibited reduced isotopic assimilation rates for carbon, nitrogen and hydrogen by 40.57 %, 44.62 % and 39.45 %, indicating decreased substrate uptake for biomolecular synthesis. Additionally, the metabolic heterogeneity index of the VBNC bacterial population increased by 37.28 %, with this heterogeneity displaying a progressive increase with the duration of the culture. This observation suggests VBNC P. aeruginosa differentiation into distinct subpopulations, believed crucial for survival in challenging environments. These findings reveal the metabolic dynamics of VBNC state bacteria, providing insights into their adaptive strategies and implications for environmental health risk assessment and precise control technologies.

Identification of Cortex Cercis chinensis Decoction Pieces from Different Growth Origins Using Raman Spectroscopy

The complexity of traditional Chinese medicine (TCM) components and the time-consuming of traditional detection methods make it necessary and meaningful to establish rapid and efficient identification techniques. This study explores the potential of Raman spectroscopy, a non-destructive technique offering details of molecular structure, for rapid and accurate identification. Cortex Cercis chinensis (CCC) decoction pieces from diverse geographical origins, Anhui, Sichuan, Zhejiang, and Hubei, were collected and analyzed using Raman spectroscopy at 785 nm, and the Raman characteristic peaks were analyzed. MATLAB software was employed to analyze the similarity between the spectra of CCC decoction pieces, and the original Raman spectral data were transformed into first and second derivative spectra. The results revealed distinct Raman spectral characteristics of carbohydrates and glycosidic bonds (characteristic peaks at 480, 531, 549, 873, 946 and 1086 cm−1). The correlation coefficients of the all the four samples from different origins ranged from 0.9625 to 0.9912, while the coincidence coefficients ranged from 0.9602 to 0.9934. The first and second derivative demonstrated significantly different peaks within specific ranges, 180–200, 280–380, and 680–740 cm−1 for first derivatives, 160–300, 340–400 and 420–480 cm−1 for second derivatives. These obvious differences in first and second derivative spectra of Raman spectra of CCC decoction pieces demonstrated the different growth origins. In conclusion, the study demonstrated the ability of Raman spectroscopy to accurately differentiate CCC decoction pieces from different geographical growth origin. These findings provided a basis for further application of Raman spectra characteristic fingerprints to be used in quality control for rapid identification of the quality and origin of TCM raw materials.

Monolayer graphene oxide-Au loaded compound (GO-Au) as a flexible, stable and sensitive SERS active substrate for detection of stonehouse clam toxin (STX)

Stonehouse clam toxin (STX) is a prevalent neuroparalytic toxin found among shellfish toxins. When consumed by humans, it disrupts neuronal conduction, potentially leading to quadriplegia, headache, shock, and even respiratory failure-induced death. This study introduces a highly sensitive and specific method for detecting shellfish toxins. The approach involves utilizing graphene gold-loaded compounds alongside stone house clam toxin aptamers and their complementary chains. The layered structure of graphene creates numerous hot spots among nanoparticles, while its arched spatial configuration offers an enhanced specific surface area, resulting in improved Surface-Enhanced Raman Scattering (SERS). By combining the signaling molecule Bodipy R6G-modified Apt with GO-Au loading compounds, distinctive Raman characteristic peaks emerge. Due to the strong affinity between Apt and STX, the Apt carrying the signaling molecule migrates away from the SERS aptamer probe's surface, thereby attenuating the original SERS signal intensity and facilitating ultra-sensitive shellfish toxin detection. The detection limit for the toxin was determined to be 5.47 nM, with a recovery rate ranging from 97.60 % to 108.32 %, affirming the applicability of this design for quantitative and specific shellfish toxin detection, signifying its considerable practical significance.

Defect induced Raman shifts and bandgap engineering in layered SnSe2+δ bulks

In the context of the extensive application prospect of two-dimensional (2D) chalcogenides, we synthesized layered SnSe2+δ bulks with defects employing a hybrid chemical vapor transport-melt approach. Both the Eg and A1g Raman characteristic peaks in SnSe2+δ are dominated by cubic anharmonicity, coupled with nonlinear temperature dependencies below 140 K. Notably, the reduction in phonon energy observed in these vibrational modes can be ascribed to defect-mediated Raman scattering, irrespective of deficient or excess Se defects. However, the lower consistency in the Raman shifts of the in-plane Eg vibrations compared to the out-of-plane A1g modes suggests that the defects predominantly entail the absence of Se atoms and the substitutions of Sn by Se, delineating a continuum of Se-deficient and Se-enriched compositions. Furthermore, Se defects induce the contraction of the indirect bandgaps, facilitating a transition from medium to narrow bandgap semiconductors in SnSe2+δ, which underscores the tunable nature of the bandgaps through the incorporation of Se defects. These discoveries present an avenue for bandgap engineering and foster a deeper comprehension of the phonon and thermal properties of layered chalcogenides for further advanced technologies.

Formation of macroscopic black dots in transparent alumina ceramics prepared by pulsed electric current sintering

Transparent alumina ceramics produced by pulsed electric current sintering (PECS) include black dots, which can be observed with the naked eye. These black dots have porous structures caused by the aggregates in the raw powder. In order to investigate the detailed mechanism of black dot formation, transparent alumina ceramics were prepared by sintering α-alumina granules to produce large pseudo-aggregates and introducing them into α-alumina powder for PECS. Macroscopic black dots were formed in the sample. Characteristic Raman peaks of graphite were detected in porous parts of these macroscopic black dots. Analysis of gas phases generated from graphite sheets for PECS suspected to be involved in carbon contamination showed CO and CO2 generation. In thermodynamic calculations on carbon activity during PECS, gas phase including CO and CO2 generated from the hot graphite mold/sheet permeates the porous part of the cold sample, and the carbon activity of gases including CO and CO2 on the porous surface theoretically exceeds unity. Then, CO is adsorbed and decomposed on the porous surface, resulting in carbon contamination. The formation of macroscopic black dots is caused by carbon deposition in agglomerates of the raw powder from CO generated by graphite sheets during PECS.

Effect of process parameters on microstructure and Raman characteristics of magnesium doped ZnO thin films

MgxZn1-xO thin films were prepared on glass substrates by radio frequency magnetron sputtering under different sputtering processes. The surface morphology, microstructure, and Raman characteristics of the films were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman Spectrometer. The results show that an increase in the O/Ar ratio decreases the surface smoothness of the thin film and worsens the particle uniformity. The particles of undoped Magnesium doped Zinc Oxide (ZnO) films are small and uniform, and the uniformity of the particles in the films becomes worse after doping. Moreover, there are multiple diffraction peaks in the magnesium doped Zinc Oxide films, presenting a polycrystalline state, but the diffraction peak positions do not significantly change with the concentration and intensity of magnesium doped. The Raman characteristic peak undergoes a blue shift with the increase of magnesium doping concentration, and the peak position shifts from 573 cm−1 to 607 cm−1.