Crystal Violet Molecules Research Articles

The Origin of Mo2C Films for Surface-Enhanced Raman Scattering Analysis: Electromagnetic or Chemical Enhancement?

The relatively weak Raman enhanced factors of semiconductor-based substrate limit its further application in surface-enhanced Raman scattering (SERS). Here, a kind of two-dimensional (2D) semimetal material, molybdenum carbide (Mo2C) film, is prepared via a chemical vapor deposition (CVD) method, and the origin of SERS is investigated for the first time. The detection limits of the prepared Mo2C films for crystal violet (CV) and rhodamine 6G (R6G) molecules are low at 10-6 M and 10-8 M, respectively. Our detailed theoretical analysis, based on density functional theory and the finite element method, demonstrates that the enhancement of the 2D Mo2C film is indeed CM in nature rather than the EM effects. Besides, the basic doping strategies are proposed to further optimize the SERS sensitivity of Mo2C for Fermi level regulation. We believe this work will provide a helpful guide for developing a highly sensitive semimetal SERS substrate.

Insight into adsorption mechanism, modeling, and desirability function of crystal violet and methylene blue dyes by microalgae: Box-Behnken design application

Herein, an environmentally friendly and efficient adsorbent of microalgae (MAG) was applied for the removal of crystal violet (CV) and methylene blue (MB) dyes from aqueous solutions. Multivariate modeling and optimization of CV and MB dyes removal onto MAG via Box-Behnken design (BBD) were investigated depending on three variables i.e. MAG dosage (20–100 mg), initial pH (4–10), and adsorption time (2–6 min). The adsorption kinetics and isotherm analyses revealed that the pseudo-second-order and Langmuir models governed the adsorption of CV and MB dyes onto MAG. The maximum adsorption capacity of MAG generated from the Langmuir equation was computed to be 243.0 mg/g for CV and 297.1 mg/g for MB. The determined thermodynamic parameters denoted that the adsorption mode of CV and MB dyes by MAG was spontaneous and endothermic. Several interactions like electrostatic forces, n-π stacking, and H-bonding caused the adsorption process of CV and MB molecules on the surface of MAG. The results showed that MAG could be an effective and locally available candidate adsorbent for removing dyestuffs from contaminated effluents. • Microalgae were applied for the removal of cationic dyes removal (crystal violet, CV) and (methylene blue, MB). • Box–Behnken design was applied to enhance the adsorption process. • The adsorption capacities for CV and MB were 243.0 mg/g and 297.1 mg/g, respectively. • The adsorption mechanism can be assigned to the electrostatic forces, n-π stacking, and H-bonding

Hydrothermal Synthesis and Photocatalytic Performance of Barium Carbonate/Tin Dioxide Nanoparticles

Background: Crystal violet dye is stable and difficult to be biodegraded owing to the existence of the multiple aromatic rings of the crystal violet molecules. Removing crystal violet dye from the wastewater is a major challenge. Objective: The aim of the research is to synthesize barium carbonate/tin dioxide nanoparticles and investigate the photocatalytic performance for the degradation of crystal violet. Methods: Barium carbonate/tin dioxide nanoparticles were synthesized via a facile hydrothermal route without any surfactants. The crystal structure, micro-morphology, size and optical performance of the barium carbonate/tin dioxide nanoparticles were investigated by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and solid ultraviolet-visible diffuse reflectance spectrum. Results : The size of the barium carbonate/tin dioxide nanoparticles is 20 nm to 200 nm with the band gap of 3.71 eV. The photocatalytic activity of the barium carbonate/tin dioxide nanoparticles was measured by the photocatalytic degradation of crystal violet. The crystal violet degradation efficiency reaches 92.1% with the ultraviolet-visible irradiation time of 8 h using 10 mg barium carbonate/tin dioxide nanoparticles. The crystal violet degradation ratio increases to 96.1% when the dosage of the barium carbonate/tin dioxide nanoparticles increases to 20 mg/10 mL crystal violet dye solution. Active species capture photocatalytic experiments showed that the holes, hydroxyl radicals and superoxide ion radicals are the main active species. Reusability experiments displayed that the barium carbonate/tin dioxide nanoparticles are stable for the crystal violet dye degradation. Conclusion: The barium carbonate/tin dioxide nanoparticles show good photocatalytic performance toward crystal violet under ultraviolet light irradiation.

Rapid and ultrasensitive solution-based SERS detection of drug additives in aquaculture by using polystyrene sulfonate modified gold nanobipyramids

In recent years, surface-enhanced Raman spectroscopy (SERS) has been widely used in various fields for the rapid detection of trace-level molecular targets. In this study, we have developed a simple and effective solution-based SERS protocol to improve the activity for the detection of cationic dye molecules in aquaculture. The polystyrene sulfonate functionalized gold nanobipyramids (PSS–Au BPs) were synthesized from the cetyltrimethylammonium bromide (CTAB) reaction system followed by the ligand exchange process. The halide ions-induced aggregation of PSS-Au BPs was carried out by using four type of different salts such as NaCl, NaBr, MgCl2 and MgSO4 to investigate their influence on the SERS activity. The results demonstrate that the ionic strength of the solution has an important impact on the colloidal stability and SERS activity. The PSS-Au BPs show an improved SERS sensitivity at lower concentrations of the aggregating agents in solution-based SERS by detecting the crystal violet (CV) molecules with a limit of detection (LOD) to 3.28 × 10−11 M. Furthermore, to demonstrate the generality of our proposed strategy, trace amounts of three more dyes such as malachite green (MG), methylene blue (MB), and rhodamine 6G (R-6G), as well as other molecules such as thiram and bisphenol-S were also detected. This protocol not only provides a method for rapid on-site detection of trace-level molecules but can also be applied to other SERS-based analysis.

Hierarchically rough CuO/Ag composite film with controlled morphology as recyclable SERS-active substrate

Oxide semiconductor combined with noble metal nanocomposites have attracted extensive attention because of its excellent surface-enhanced Raman scattering (SERS) effect and photocatalytic degradation ability which can be applied repeatedly to the detection of pollutants. In this work, hierarchically rough copper oxide (CuO) was first prepared on the surface of copper foil by anodic oxidation, and then loaded silver nanoparticles layer by magnetron sputtering method to obtain CuO/Ag composite film. Such CuO/Ag composite substrate exhibits good SERS performance and recyclability due to its efficient photocatalytic degradation ability. Using Rhodamine 6G (R6G) molecules as probe molecules, the influence of the surface hierarchically rough micro/nanostructures, and the amounts of Ag nanoparticles covered on the CuO film surface were both studied in detail. Using optimized CuO/Ag composite film as SERS active substrate, the detection limit of R6G molecules and crystal violet (CV) molecules were as low as 10−11 M and 10−10 M, respectively. The evolution diagram of Raman spectra shows that such substrate can use its own photocatalytic performance to degrade surface adsorbed molecules under light irradiation, so as to achieve self-cleaning and reusable. After repeated use, the SERS performance was only slightly degraded, showing excellent reusability. For the detection of thiram, we found a limit concentration of 10−8 M. In addition, on the basis of material surface morphology and charge transfer, the SERS enhanced mechanism and photocatalytic mechanism were proposed and discussed. The as-prepared hierarchically rough CuO/Ag composite film is expected to be applied to efficient SERS sensors.

Multiple valence states of Fe boosting SERS activity of Fe3O4 nanoparticles and enabling effective SERS-MRI bimodal cancer imaging

Developing novel nanoparticle-based bioprobes utilized in clinical settings with imaging resolutions ranging from cell to tissue levels is a major challenge for tumor diagnosis and treatment. Herein, an optimized strategy for designing a Fe3O4-based bioprobe for dual-modal cancer imaging based on surface-enhanced Raman scattering (SERS) and magnetic resonance imaging (MRI) is introduced. Excellent SERS activity of ultrasmall Fe3O4 nanoparticles (NPs) was discovered, and a 5 × 10−9 M limit of detection for crystal violet molecules was successfully obtained. The high-efficiency interfacial photon-induced charge transfer in Fe3O4 NPs was promoted by multiple electronic energy levels ascribed to the multiple valence states of Fe, which was observed using ultraviolet–visible diffuse reflectance spectroscopy. Density functional theory calculations were utilized to reveal that the narrow band gap and high electron density of states of ultrasmall Fe3O4 NPs significantly boosted the vibronic coupling resonances in the SERS system upon illumination. The subtypes of cancer cells were accurately recognized via high-resolution SERS imaging in vitro using the prepared Fe3O4-based bioprobe with high sensitivity and good specificity. Notably, Fe3O4-based bioprobes simultaneously exhibited T1-weighted MRI contrast enhancement with an active targeting capability for tumors in vivo. To the best of our knowledge, this is the first report on the use of pure semiconductor-based SERS-MRI dual-modal nanoprobes in tumor imaging in vivo and in vitro, which has been previously realized only using semiconductor–metal complex materials. The non-metallic materials with SERS–MRI dual-modal imaging established in this report are a promising cancer diagnostic platform, which not only showed excellent performance in early tumor diagnosis but also possesses great potential for image-guided tumor treatment.

Adsorption of a Cationic Dye Crystal Violet onto a Binary Mixture of Forest Waste Biopolymer: Advanced Statistical Physics Studies

An eco-friendly and low cost modified mixture of both Wild Carob and Cupressus sempervirens with H3PO4 (Cupcar-H3PO4) was prepared to extract a cationic dye (Crystal Violet) from an aqueous solution in a batch reactor at the laboratory of chemical engineering, Department of Process Engineering, Faculty of Technology, Farhat Abbas Setif University-1. The pH effect, contact time, initial concentration of dye, ionic strength and temperature were investigated in this study. The Maximum adsorption capacity was found to be 117.26 mg/g at 25°C for a natural pH (ph =6.22). The active functional groups of Cupcar-H3PO4. These peak shifts indicated that especially the bonded –OH groups, C–O stretching of ether groups, and C=C group played a major role in CV adsorption onto Cupcar-H3PO4. The new bands of low intensity which appeared at 890 cm−1 and 813 cm-1 after CV adsorption and which could be attributed to a υ (CV-biosorbent) constituted the most striking result. Kinetics of biosorption of crystal violet (CV) was analyzed and the results showed that both pseudo order (PSO) and the pseud nth-order model (PNO) models gave most accurate fit than the pseudo-first-order model (PFO). Isotherm data were analyzed by four classical models, Langmuir and Freundlich with two parameters, Sips and Redlich-Peterson with three parameters. And for more information on the mechanism of CV uptake on the Cupcar-H3PO4 material, three advanced models are applied to isothermal data, Monolayer with one energy (M1), Monolayer with two energies (M2), and Double layer with one energy (M3). For the classical models and in the case of the two parameters models the Langmuir one gives a better fit for the data isotherm according to the R2. In the case of three parameters models, both Sips and Redlich-Peterson accurately described experimental data. Monolayer with two energy sites model (M2) was shown to be the most appropriate advanced statistical physics model for fitting CV biosorption onto the Cupcar-H3PO4 biosorbent, this model suggested that the CV pollutant was adsorbed at two different Cupcar-H3PO4 biosorbent sites, and that a variable number of CV molecules could be adsorbed at each site; from this, the CV dye was adsorbed with 2 different adsorption energies. The changes in the enthalpy, the standard free energy and the entropy were also evaluated and the reaction was found to be spontaneous, endothermic and physical in nature.

UV excited enhanced Raman scattering on carbon-doped SnS2 nanoflowers

Chemically stable and biocompatible SnS2 nanostructures are excellent building blocks for semiconductor-based SERS applications. A comparative UV-SERS study of adsorbed crystal violet (CV) probe molecules on 2D-layered tin disulfide (SnS2) nanoplates and carbon-doped SnS2 nanoflowers is reported. The carbon doping in the SnS2 nanostructure plays a significant role in exciting electrons by UV laser and interfacial charge transfer (CT) process through a substantial reduction in the band-gap. The optimized carbon-doped SnS2 material acts as an excellent SERS substrate, exhibiting significant SERS activity with an enhancement of 2.9 × 102 and a low detection limit of 10−7 mol/L for CV molecules under UV excitation. This remarkable sensitivity and enhancement are attributed to surface defects caused by carbon doping. Energy band engineering on the above 2D semiconductor substrate is a new approach in the SERS field. It may pave the way for the development of novel SERS technology under UV excitation.

Effective adsorption of crystal violet dye on sugarcane bagasse–bentonite/sodium alginate composite aerogel: Characterisation, experiments, and advanced modelling

A novel sugarcane bagasse–bentonite/sodium alginate (SCB–Ben/SA) composite aerogel was prepared as an effective green adsorbent via blending–cross-linking for the removal of crystal violet (CV) dye from aqueous solution. The equilibrium adsorption capacity of SCB–Ben/SA for CV was 839.9 mg/g at 0.8 mg/mL adsorbent dosage, temperature 303 K, pH 4, and 800 mg/L initial CV concentration, and presented a removal rate of 85%. Adsorption kinetics studied using the novel pseudo-first-order and pseudo-second-order (PFO–PSO) combined model showed that CV adsorption by SCB–Ben/SA was a complex process and did not include a single mechanism, but involved both chemical and physical adsorption reactions; however, chemisorption was the dominant kinetic mechanism. The dynamic characteristics of CV adsorption process achieved through the liquid film around SCB–Ben/SA and the pores inside SCB–Ben/SA was described satisfactorily and conveniently using the novel film–pore mass transfer (FPMT) model. A multilayer adsorption model was applied to further understand the CV adsorption behaviour of SCB–Ben/SA. The number of linked CV molecules per functional group varied from 0.53 to 0.63 for SCB–Ben/SA. The CV molecules were adsorbed on SCB–Ben/SA via mixed orientation. The adsorption isotherms and thermodynamics revealed that the multilayer adsorption process was endothermic and spontaneous. Overall, SCB–Ben/SA was found to be an efficient, low-cost, green, and recyclable adsorbent for organic dye removal.

Verification and Analysis of Single-Molecule SERS Events via Polarization-Selective Raman Measurement.

We propose polarization-selective Raman measurement as a decent method for single-molecule surface-enhanced Raman scattering (SMSERS) verification. This approach features rapid acquisition of SMSERS events and appeals liberal requirements for analyte concentration. It is demonstrated as an efficient tool in sorting out dozens of SMSERS events from a large-scale plasmonic dimer array. In addition, it allows identification of a mixed SMSERS event containing two different individual molecules. In this article, the RPM method is employed to explore the underlying mechanisms of signal blinking, spectral wandering, and other unique characteristics in SMSERS. We observed synchronized blinking of different modes from one Rhodamine 6G (R6G) molecule, but a disagreement is found in a mixed SMSERS event containing one R6G molecule and one crystal violet molecule. Our approach offers a reliable means to interpret SMSERS events in statistical terms and facilitate the fundamental understanding of SMSERS.

Nanoscale engineering of ring-mounted nanostructure around AAO nanopores for highly sensitive and reliable SERS substrates

Surface-enhanced Raman scattering (SERS) is recognized as one of the most favored techniques for enhancing Raman signals. The morphology of the SERS substrate profoundly affects molecular Raman spectra. This study aimed to construct a ring-mounted nanostructured substrate via liquid–liquid two-phase self-assembly incorporated with anodic aluminum oxide (AAO) membrane transfer techniques. High-density nanoparticles (NPs) assembled on AAO membranes were ascribed to reduce the diameters of the nanopores, with Au–Ag alloy NPs to regulate the dielectric constant so as to reveal the local surface plasmon resonance tunability. SERS engineered in this way allowed for the fabrication of a ring-mounted nanostructured substrate where the distribution density of NPs and dielectric constant could be independently fine-tuned. High SERS activity of the substrate was revealed by detecting the enhanced factor of crystal violet and rhodamine 6G molecules, which was up to 1.56 × 106. Moreover, SERS of thiram target molecules confirmed the supersensitivity and repeatability of the substrate as a practical application. The results of this study manifested a low-cost but high-efficiency ring-mounted nanostructured SERS substrate that might be suitable in many fields, including biosensing, medical research, environmental monitoring, and optoelectronics.

Low temperature-promoted surface plasmon resonance effect and ultrasensitive surface-enhanced Raman scattering detection of creatinine

Creatinine is a key biomarker for diagnosing and monitoring kidney disease, so rapid and sensitive testing is very important. Raman spectroscopy is particularly suitable for quantitatively detecting the creatinine in the human environment because it is sensitive to subtle changes in the concentration of the analyte. In this work an effective strategy is provided to promote the activity of surface-enhanced Raman scattering spectroscopy by enhancing the photon-induced charge transfer efficiency at low temperature. The nano-gold icosahedron (Au<sub>20</sub>) is obtained by the seed-growing method, which is used as an active substrate for SERS. The ultra-low temperature (98 K) SERS detection technology is used to realize the rapid and sensitive detection of the dye molecule crystal violet (CV) and creatinine in normal saline. The experimental results show that at room temperature of 296 K, the detection limit of Au<sub>20</sub> substrate for CV molecules is as low as 10<sup>–12</sup> mol/L, and the signals are uniform; at a low temperature of 98 K, the detection limit of CV molecules can reach 10<sup>–14</sup> mol/L, which is two orders of magnitude lower than that at 296 K. As a result, the adopted cryogenic temperature can effectively weaken the lattice thermal vibration and reduce the release of phonons, then suppress phonon-assisted non-radiative recombination. So, it will increase the number of photo-induced electrons to participate in the photo-induced charge transfer efficiency. Finally, we perform the label-free detection of creatinine in saline by using an Au<sub>20</sub> substrate. The results show that the detection limit of the SERS substrate for creatinine is 10<sup>–6</sup> mol/L at 296 K, and the linear correlation coefficient of the 1619 cm<sup>–1</sup> peak is 0.9839. At a low temperature of 98 K, the detection limit of creatinine concentration is as low as 10<sup>–8</sup> mol/L, and the linear correlation coefficient of the 1619 cm<sup>–1</sup> peak becomes 0.9973. It can be seen that low temperature may further improve the detection limit of creatinine concentration and the linearity of characteristic peak. In summary, the current work provides a new idea for accurately detecting the creatinine concentration in the field of biomedicine.

Synthesis and Near-Field Enhancement of Composite Nanoarrays Based on Electrodeposition and in Situ Reaction

Since the morphology and element composition of metal nanostructures strongly affect the surface plasma oscillation characteristics, it has been widely concerned in surface enhanced Raman scattering (SERS). Herein, we proposed a novel route to fabricate composite Au/Ag nanoparticle arrays with synergistic effect for electromagnetic enhancement. Ag nanoparticles were electrodeposited onto a home-made template with highly ordered bowl-like pits. After a novel method of “confined annealing”, we further achieved well-regulated spherical Ag NP arrays, and the composite Au/Ag nanoparticle arrays were finally obtained via in situ replacement. The fabricated composite nanostructures showed stable and sensitive surface enhanced Raman scattering (SERS) performance mainly due to the synergistic effect and abundant “hot spots”, with the enhancement factor (EF) of [Formula: see text] for crystal violet (CV) molecules. In addition, this simple and effective preparation process greatly improved the uniformity of three-dimensional nanostructures, providing a new idea for further improving the stability of SERS signals.

Tip enrichment surface-enhanced Raman scattering based on the partial Leidenfrost phenomenon for the ultrasensitive nanosensors

Surface-enhanced Raman scattering (SERS) possesses the advantage that directly detects target analytes in solution with high specificity and sensitivity without complicated pretreatment procedures. It remains a challenge in most practical applications to achieve molecule sensitivity in any highly diluted solutions. Here, we develop a robust and practical molecular enrichment strategy that can effectively confine analyte molecules and Au nanoparticles together in a short time into a small-sized sensitive region on a needle tip, based on the Leidenfrost phenomenon and capillary force. In this strategy, the Leidenfrost evaporation phenomenon maintains the analytes droplet in a Cassie state based on a levitating force, and at the same time, a hung needle tip anchors the droplet based on the capillary force. After 1–2 min quick evaporation, more than 98% Au nanoparticles and analytes can be condensed into an around 0.5 mm small size area on the needle tip. Due to the significant enrichment capability and reproducibility, the SERS measurement enables to achieve the limit of detection (LOD) down to 0.08 nM (at an S/N ratio of 3) for crystal violet (CV) molecules and to nM level for several types of pesticide molecules (glyphosate, carbendazim, thiram and choline) in ethanol solution. The strategy was also applied to the detection of CV molecules in mixture pigments solution, thiram in spiked environment water samples, with good selectivity and sensitivity. In addition, using the high thermal conductivity substrate without additional surface modification, this enrichment SERS detection may open the possibility of universal applications due to its facile and cost-effective. The accurate site of the needle tip offers great practical potentials for on-site identification by using a handheld Raman spectrometer.

Classification of two species of Gram-positive bacteria through hyperspectral microscopy coupled with machine learning.

Gram stain is one of the most common techniques used to visualize bacteria under microscopy and classify bacteria into two large groups (Gram-positive and Gram-negative). However, such an inaccurate classification is unfavorable for bacterial research. For instance, soil-rhizosphere bacteria, Bacillus megaterium (B. megaterium) and Bacillus cereus (B. cereus) have different effects on plants, nonetheless, they are both Gram-positive and difficult to be differentiated. Here, we present a method to precisely classify Gram-positive bacteria via hyperspectral microscopy. The pH-value differences in the intracellular environment of various types of bacteria can lead to different ionization of the auxochrome of crystal violet (CV) molecules during the Gram stain process. Consequently, there is a subtle difference in the absorption peak of Gram-stained bacteria. Harnessing hyperspectral microscopy can capture this subtle difference and enable precise classification. Besides the spectral features, the spatial features were also used to improve the quality of bacterial identification. The results show that the classification accuracy of two species of Gram-positive bacteria, B. megaterium and B. cereus, is up to 98.06%. We believe this method can be used for other Gram-positive bacteria and Gram-negative bacteria, realizing a more elaborate classification for Gram-stained bacteria.

Polymer-nanoimprinting route for the construction of large-area Au@Ag plasmonic arrays using as highly-uniform SERS platforms

Metallic plasmonic nanostructures have been widely investigated due to their unique optical controllability. In particular, the construction of large-area and uniform multi-metallic plasmonic nanoarrays with low cost has been a persistent pursuit. Herein, we proposed a simple method for the preparation of [email protected] plasmonic arrays via polymer-nanoimprinting. Polycarbonate （PC） were reprinted with the pore structure of anodic aluminum oxide (AAO) template by hot melt embossed to form regular array of PC nanopillars. Then, a series of metallic plasmonic nanoarrays were obtained by depositing Au and Ag films with different thickness ratios on the top of the PC nanopillar. The uniform nanoarrays showed controllable near-field enhancing properties, and were employed as active surface-enhanced Raman Scattering (SERS) substrates, exhibiting good signal homogeneity (RSD ≈ 3.33%) for crystal violet (CV) molecules. This paper provides a simple, low-cost, and popularizing method for the preparation of SERS substrate with stable performance, having a good application prospect.

Co-Quenching Effect between Lanthanum Metal-Organic Frameworks Luminophore and Crystal Violet for Enhanced Electrochemiluminescence Gene Detection.

Exploring new electrochemiluminescence (ECL) luminophores to construct high-efficiency sensing systems is always a hot direction for developing ECL sensors. Compared with other luminophores, metal-organic frameworks (MOFs) exhibit high mass transfer ability for accelerating the reactivity in its pore channels, which is conducive to improving the performance of ECL sensors. In this work, La3+ -BTC MOFs (LaMOFs) are prepared as the highly active reactor and novel ECL luminophore. On this basis, a novel co-quenching effect mechanism is proposed based on double-stranded DNA (dsDNA) triggered cooperation between LaMOFs and crystal violet (CV) molecules. Under the confined pore channels of LaMOFs, CV can play an important role as the photon-acceptor due to the matched absorption spectrum with the ECL spectrum of LaMOFs, and the electron-acceptor on account of its lowest unoccupied molecular orbital level. Based on the proposed co-quenching effect mechanism, a constructed ECL gene sensor shows good assay performance toward p53 gene in the detection range of 1 pm to 100nm with a detection limit of 0.33 pm. The co-quenching effect integrating LaMOFs with CV is expected to be a versatile approach in the construction of ECL gene sensor, which has good prospect in expanding the application range of ECL technology.

Amorphous Ni(OH)2 nanocages as efficient SERS substrates for selective recognition in mixtures

Surface-enhanced Raman scattering (SERS) technology has become one of the most powerful tools for identifying trace analytes due to its outstanding merit of fingerprint spectrum. It has been found that noble metal (Ag, Au) materials can produce obvious surface plasmon resonance under visible light illumination, which can bring out a strong SERS effect. However, due to poor stability and non-selectivity, its practical applications are seriously hindered, especially for the detection of polluted water contaminating mixture organic pollutants. Herein, we designed an amorphous Ni(OH)2 nanocages (a-Ni(OH)2 NCs) substrate that exhibits an excellent SERS performance with good spectral stability and selectivity, which is attributed to the strong interfacial photo-induced charge transfer (PICT) mechanism between a-Ni(OH)2 NCs and molecules. Due to the effective vibrational coupling of a-Ni(OH)2 NCs and molecule under laser irradiation, the PICT transitions between a-Ni(OH)2 NCs and molecules evidently increase the molecular polarizability tensor and magnify molecular Raman scattering cross-section, resulting in a remarkable SERS activity. Besides, in wastewater containing several nitrogen and phosphorus pollutants, we successfully identified methylene blue and crystal violet molecules by using a-Ni(OH)2 NCs due to their selective recognition function. This research points out a new application direction for SERS technology in water pollution detection based on non-metal substrates, which widely broadens application prospects of SERS spectroscopy.

Highly Sensitive and Spatially Homogeneous Surface-Enhanced Raman Scattering Substrate under Plasmon–Nanocavity Coupling

We fabricated a plasmon–nanocavity coupling structure composed of Au nanoparticles (Au-NPs), titanium dioxide, and Au-film (ATA) as a highly sensitive and spatially homogeneous surface-enhanced Raman scattering (SERS) substrate. The SERS intensity of the ATA was ∼11 times higher than that of the Au-NPs/TiO2 substrates without cavity enhancement. This SERS enhancement was attributed to the remarkable near-field enhancement of Au-NPs under coupling with cavity resonance. Under the present experimental conditions, crystal violet (CV) molecule decorated ATA prepared from a concentration as low as 10–7 mol/L could be detected, which is 1 order of magnitude higher sensitivity than the samples without cavities. More importantly, a spatially homogeneous SERS signal distribution of Raman mapping on the ATA was demonstrated over a 20 × 20 μm2 area on the sample, attributed to the homogeneous near-field distribution over the Au-NPs under coherent coupling between plasmon resonance and cavity resonance. We envision that this plasmon–nanocavity coupling SERS structure with high sensitivity, repeatability, and spatial homogeneity can be practically used in chemical and biomolecule detection devices.

Cost-effective large-area Ag nanotube arrays for SERS detections: effects of nanotube geometry

This study demonstrated highly-ordered metallic nanotube arrays (MeNTAs) with a precisely controlled geometric shape to promote surface-enhanced Raman scattering (SERS). Using both simulation and experimental methods, we designed and fabricated MeNTAs with nanotube geometries that possess a large surface area to absorb probe molecules as well as geometric features capable of inducing hot spots for SERS enhancement. The proposed top-down wafer-scale lithographic and sputter-deposition process is a simple and cost-effective approach to the fabrication of 1 mm × 1 mm MeNTA at room temperature. Simulation results of nanotubes with various materials (Au, Ag, and Cu), diameters (100–1500 nm), geometric shapes (circle, equilateral triangle and square) and triangle corner curvatures (ranging from 0 to 300 nm) identified Ag triangles with sharp tips as the geometry best suited to SERS enhancement. The SERS spectra of crystal violet molecules generated from the Ag MeNTAs verified the patterns observed in computational simulations, wherein the effects of MeNTA on SERS decreased with an increase in the size of the nanotubes. Enhancement factor of 1.06 × 109 was obtained from our triangular Ag MeNTA, confirming its efficacy as an ultrahigh sensitivity SERS-active substrate.