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Highly Sensitive and Selective Nanogap-Enhanced SERS Sensing Platform
摘要： This paper reports a highly sensitive and selective surface-enhanced Raman spectroscopy (SERS) sensing platform. We used a simple fabrication method to generate plasmonic hotspots through a direct maskless plasma etching of a polymer surface and the surface tension-driven assembly of high aspect ratio Ag/polymer nanopillars. These collapsed plasmonic nanopillars produced an enhanced near-field interaction via coupled localized surface plasmon resonance. The high density of the small nanogaps yielded a high plasmonic detection performance, with an average SERS enhancement factor of 1.5 × 107. More importantly, we demonstrated that the encapsulation of plasmonic nanostructures within nanofiltration membranes allowed the selective filtration of small molecules based on the degree of membrane swelling in organic solvents and molecular size. Nanofiltration membrane-encapsulated SERS substrates do not require pretreatments. Therefore, they provide a simple and fast detection of toxic molecules using portable Raman spectroscopy.
关键词： hotspots,sensors,molecular filtration,surface-enhanced Raman spectroscopy,localized surface plasmon resonance
更新于2025-11-14 15:30:11
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The effect of second phase La0.67TiO2.87 on the phase structure and impedance spectroscopy of La2Ti2(1 + x)O7 piezoelectric ceramics
摘要： The Ti excess La2Ti2 (1 + x) O7 (x = 0, 0.005, 0.01, 0.02, 0.05, 0.1) piezoelectric ceramics have been prepared by sol-gel technology and solid state synthesis method. Through refinement analysis, the phase structure of the ceramics varies with Ti content. Most monoclinic phase (~ 93 %) and a handful of orthogonal phase (~ 7 %) coexist in La2Ti2 (1 + 0) O7 ceramics. Pure monoclinic phase La2Ti2O7 with space group P21 appears in La2Ti2 (1 + 0.005) O7 and La2Ti2 (1 + 0.01) O7 ceramics. Monoclinic phase La2Ti2 O7 and a certain proportion of tetragonal phase La0.67TiO2.87 coexist in La2Ti2 (1 + 0.02) O7, La2Ti2 (1 + 0.05) O7 and Ti2 (1 + 0.1) O7 ceramics. With the excess of Ti content, the monoclinic phase ratio and distortion angles in a-b projection plane of the ceramics increase first and then decrease, which is consistent with the variation tendency of piezoelectric constant d33. The excellent piezoelectric constant for Ti2 (1 + 0.01) O7 ceramics is 2.8 pC/N. Impedance analysis shows that the conductive mechanisms of all samples include both grain and grain boundary conductivity at temperature range T ≥ 500 ℃. The formation of tetragonal phase La0.67TiO2.87 derives from Ti excess in pure monoclinic phase La2Ti2O7. The existence of tetragonal phase La0.67TiO2.87 can obviously increase the capacitance of ceramics at x ≥ 0.05. All prepared piezoelectric La2Ti2 (1 + x) O7 ceramics have highly frequency stability and are candidates for ultrahigh temperature piezoelectric application.
关键词： La2Ti2(1 + x)O7 ceramics,phase structure,impedance spectroscopy
更新于2025-11-14 15:27:09
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Complex impedance, FT-Raman, and photoluminescence spectroscopic studies of pure and L-phenylalanine doped ammonium dihydrogen phosphate single crystals: the correlation with hydrogen bonding defect
摘要： Ammonium dihydrogen phosphate (ADP) is an important nonlinear optical (NLO) material used for electro-optical applications. The aromatic side chain contained dopant like L-phenylalanine causes defect in ADP. The pure and L-phenylalanine doped ADP crystals are grown using slow solvent evaporation technique at room temperature. The Powder XRD spectra suggest tetragonal crystal system and slit shifting of peak. The FT-Raman shows strong absorption peak at 922 cm?1 due to v1 group symmetry of P - OH for all grown crystals without shifting indicating the single phase nature of all the crystals. The photoluminescence study suggests the presence of defects in doped crystals compared to the pure one due to increase of Stokes shift and vibrational energy relaxation phenomena. The dielectric constant and dielectric loss have shown the usual behavior with respect to frequency and temperature. The calculated electro-optic coefficient is found to be in accordance with dielectric constant. The protonic conduction is prevailing for electric transport, and from Jonscher’s plot, the correlation barrier hopping (CBH) is confirmed. The Nyquist plot and modulus spectra of pure ADP show the presence of grain and grain boundary while the same plots for L-phenylalanine doped ADP show the presence of grain only. The stretch exponent exhibits non-Debye-type relaxation.
关键词： Photoluminescence,Protonic conductivity,Impedance spectroscopy,Dihydrogen phosphate,Raman spectroscopy
更新于2025-11-14 15:26:12
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Photo-physical properties of substituted 2,3-distyryl indoles: Spectroscopic, computational and biological insights
摘要： The structural dependence of the photo-physical properties of substituted 2,3-distyryl (23DSI) indoles were studied using several spectroscopic techniques including steady-state UV-VIS spectroscopy, steady-state fluorescence spectroscopy, steady-state excitation spectroscopy, time correlated single photon counting (TCSPC) spectroscopy, and time-resolved fluorescence upconversion spectroscopy (TRFLS). Each of 23DSI derivatives investigated showed distinct fluorescence emission and UV-VIS spectra, indicating strong structural dependence of the emission and the excitation. The UV-VIS spectra of the 23DSI derivatives showed three main identical absorption bands with minor deviations in the absorbance caused by substituent groups on the distyryl rings. The time-resolved fluorescence up-conversion studies indicated that the fluorescence undergoes a mono-exponential decay whereas the calculated fluorescence lifetime showed relatively short fluorescence lifetimes of approximately 1 ns. All of the 23DSI derivatives showed two-photon absorption upon direct excitation of 1.6 W laser pulses at 800 nm. These studies suggest that the substituents, attached to distyryl core, are capable of boosting or hindering fluorescence intensities by distorting the π-conjugation of the 23DSI molecule. Our studies showed that 23DSI (p-F) has the highest fluorescence emission quantum yield. Theoretical calculations for the ground state of 23DSI derivatives confirmed differences in electron densities in 23DSI derivatives in the presence of different substituent attachments. The excellent fluorescence emission, high fluorescence quantum yield and two-photon absorption properties of these 23DSI molecules make them attractive candidates for potential applications in the fields of biological imaging, biomedicine, fluorescent probes, and photodynamic inactivation (PDI). B. subtilis samples, treated with micro molar solutions of 23DSI (p-OCH3) and 23DSI (p-CH3), showed very effective photodynamic inactivation (PDI) upon irradiation with white light.
关键词： Two photon absorption,Time-resolved fluorescence upconversion laser spectroscopy,Photodynamic inactivation,Gaussian calculations,Photo-physical properties,Light-activation
更新于2025-11-14 15:26:12
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Thickness of sublimation grown SiC layers measured by scanning Raman spectroscopy
摘要： We have grown homoepitaxial high resistivity SiC layers on conducting SiC substrates. We develop a method to determine the thickness of grown layers by scanning confocal Raman spectroscopy (SCRS). We also grow epitaxial graphene on SiC layers to label the top sample surface, and, we correlate the top surface position with Rayleigh scattering (RS). The interface between the high resistivity SiC layer and conductive SiC substrate is probed by the transition from LO phonon to the coupled LO phonon-plasmon Raman mode. The layer thickness measurements are veri?ed by ellipsometry and Secondary Ion Mass Spectroscopy (SIMS). We show that the SCRS method provides superior lateral and vertical resolution, it is robust against errorneous conclusions based on ad-hoc models, and it is easy to implement.
关键词： SiC layer thickness,Graphene,Raman spectroscopy
更新于2025-11-14 15:19:41
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Sexing of chicken eggs by fluorescence and Raman spectroscopy through the shell membrane
摘要： In order to provide an alternative to day-old chick culling in the layer hatcheries, a noninvasive method for egg sexing is required at an early stage of incubation before onset of embryo sensitivity. Fluorescence and Raman spectroscopy of blood offers the potential for precise and contactless in ovo sex determination of the domestic chicken (Gallus gallus f. dom.) eggs already during the fourth incubation day. However, such kind of optical spectroscopy requires a window in the egg shell, is thus invasive to the embryo and leads to decreased hatching rates. Here, we show that near infrared Raman and fluorescence spectroscopy can be performed on perfused extraembryonic vessels while leaving the inner egg shell membrane intact. Sparing the shell membrane makes the measurement minimally invasive, so that the sexing procedure does not affect hatching rates. We analyze the effect of the membrane above the vessels on fluorescence signal intensity and on Raman spectrum of blood, and propose a correction method to compensate for it. After compensation, we attain a correct sexing rate above 90% by applying supervised classification of spectra. Therefore, this approach offers the best premises towards practical deployment in the hatcheries.
关键词： Raman spectroscopy,sexing,chicken eggs,fluorescence spectroscopy,shell membrane
更新于2025-11-14 15:18:02
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Full color carbon dots through surface engineering for constructing white light-emitting diodes
摘要： White light-emitting diodes (WLEDs) devices are replacing the filament lamp and they can provide a light close to the natural sunlight, which have thus drawn considerable attention in these recent years. It remains a scientific challenge to develop WLEDs using environmentally friendly, easy-to-process and cost-effective phosphors. Here we synthesized blue-, green- and red-carbon dots (denoted as B-, G- and R-CDs) by a facile solvothermal method with high dispersity both in aqueous and organic solvent. The quantum yield (QY) of the R-CDs achieved up to 24.7%. These CDs can be easily dissolved in polyvinylpyrrolidone (PVP) colloid, leading to the production of ultraviolet (UV)-excited LED devices to avoid the retinal damage caused by blue ray excitation. The fluorescence emission of the WLED has a wide band, covering the whole visible light region. Importantly, the influence of doping that gives rise to the change of emissive colors has been elucidated by X-ray photoelectron spectroscopy (XPS) combined with a computation method in order to provide a systematic controllable tuning on the functionalization of CDs. As such, WLEDs were demonstrated with color coordinates of (0.33, 0.33), a color temperature of 5612 K in the CIE chromaticity diagram with good anti-photobleaching and a color rendering index (CRI) of 89.
关键词： polyvinylpyrrolidone,White light-emitting diodes,solvothermal method,UV-excited LED devices,density functional theory,quantum yield,X-ray photoelectron spectroscopy,carbon dots
更新于2025-11-14 15:18:02
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Dependence of Mechanical Stresses in Silicon Nitride Films on the Mode of Plasma-Enhanced Chemical Vapor Deposition
摘要： Films of silicon nitride SiNx, obtained by plasma-enhanced chemical vapor deposition from the monosilane SiH4 and ammonia NH3 gases, are widely used in microelectronics and micro- and nanoelectromechanical systems. Residual mechanical stresses and film composition are important characteristics for many applications. The properties of SiNx films, particularly mechanical stresses and composition, depend largely on the conditions of production, e.g., the ratio of the reacting gas flow rates, the composition of the gas mixture, the power and frequency of the plasma generator, and the temperature and pressure during deposition. Despite the great volume of works on the subject, data regarding the dependence of the properties and composition of SiNx films on the conditions of production remain sparse. This work considers the effect the ratio of the reacting gas flow rates has on the mechanical stresses and composition of silicon nitride films SiNx obtained by plasma-enhanced chemical vapor deposition from gaseous mixtures of SiH4 monosilane and NH3 ammonia using low-frequency plasma. It is found that when the ratio of the gas flow rates of SiH4 and NH3 is raised from 0.016 to 0.25, the compressive mechanical stresses are reduced by 31%, the stoichiometric coefficient falls from 1.40 to 1.20, the refractive index rises from 1.91 to 2.08, the concentration of N–H bonds is reduced by a factor of 7.4, the concentration of Si–H bonds grows by a factor of 8.7, and the concentration of hydrogen atoms is reduced by a factor of 1.5. These results can be used for the controlled production of SiNx films with such specified characteristics as residual mechanical stresses, refractive index, stoichiometric coefficient, and the concentration of hydrogen-containing bonds.
关键词： mechanical stresses,optical profilometry,films of PECVD silicon nitride SiNx,IR Fourier spectroscopy
更新于2025-11-14 15:18:02
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Soil Particles and Phenanthrene Interact in Defining the Metabolic Profile of Pseudomonas putida G7: A Vibrational Spectroscopy Approach
摘要： In soil, organic matter and mineral particles (soil particles; SPs) strongly influence the bio-available fraction of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), and the metabolic activity of bacteria. However, the effect of SPs as well as comparative approaches to discriminate the metabolic responses to PAHs from those to simple carbon sources are seldom considered in mineralization experiments, limiting our knowledge concerning the dynamics of contaminants in soil. In this study, the metabolic profile of a model PAH-degrading bacterium, Pseudomonas putida G7, grown in the absence and presence of different SPs (i.e., sand, clays and humic acids), using either phenanthrene or glucose as the sole carbon and energy source, was characterized using vibrational spectroscopy (i.e., FT-Raman and FT-IR spectroscopy) and multivariate classification analysis (i.e., PLS-DA). The different type of SPs specifically altered the metabolic profile of P. putida, especially in combination with phenanthrene. In comparison to the cells grown in the absence of SPs, sand induced no remarkable change in the metabolic profile of the cells, whereas clays and humic acids affected it the most, as revealed by the higher discriminative accuracy (R2, RMSEP and sensitivity) of the PLS-DA for those conditions. With respect to the carbon-source (phenanthrene vs. glucose), no effect on the metabolic profile was evident in the absence of SPs or in the presence of sand. On the other hand, with clays and humic acids, more pronounced spectral clusters between cells grown on glucose or on phenanthrene were evident, suggesting that these SPs modify the way cells access and metabolize PAHs. The macromolecular changes regarded mainly protein secondary structures (a shift from α-helices to β-sheets), amino acid levels, nucleic acid conformation and cell wall carbohydrates. Our results provide new interesting evidences that SPs specifically interact with PAHs in defining bacteria metabolic profiles and further emphasize the importance of studying the interaction of bacteria with their surrounding matrix to deeply understand PAHs degradation in soils.
关键词： phenanthrene,FTIR spectroscopy,soil particles,multivariate classification analysis,bacteria,metabolic profile,FT-Raman spectroscopy
更新于2025-11-14 15:16:37
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Near-infrared (NIR) surface-enhanced Raman spectroscopy (SERS) study of novel functional phenothiazines for potential use in dye sensitized solar cells (DSSC)
摘要： Near-infrared (NIR) surface-enhanced Raman spectroscopy (SERS) is used to investigate the interaction between six novel phenothiazine-merocyanine dyes containing the three different functional groups rhodanine, 1,3-indanedione and cyanoacylic acid with plasmonic nanomaterials, to decide if the incorporation of plasmonic nanoparticles could enhance the efficiency of a Gr?tzel-type solar cell. The studies were carried out in the solution state using spherical and rod-shaped gold nanostructures. With KCl induced agglomerated spherical gold nanoparticles, forming SERS hot spots, the results showed low detection limits between 0.1 mmol L?1 for rhodanine containing phenothiazine dyes, because of the formation of Au–S bonds and 3 mmol L?1 for cyanoacrylic acid containing dyes, which formed H-aggregates in the watery dispersion. Results with gold nanorods showed similar trends in the SERS measurements with lower limits of detection, because of a shielding effect from the strongly-bound surfactant. Additional fluorescence studies were carried out to determine if the incorporation of nanostructures leads to fluorescence quenching. Overall we conclude that the addition of gold nanoparticles to rhodanine and 1,3-indanedione containing phenothiazine merocyanine dyes could enhance their performance in Gr?tzel-type solar cells, because of their strong interactions with plasmonic nanoparticles.
关键词： surface-enhanced Raman spectroscopy,plasmonic nanoparticles,dye sensitized solar cells,phenothiazine-merocyanine dyes,Near-infrared
更新于2025-11-14 15:16:37