Preparation of silver nanoparticles by photo-reduction for surface-enhanced Raman scattering

A substrate for surface-enhanced Raman scattering (SERS) has been developed. Based on the surface-catalyzed reduction of Ag⁺ by citrate on the silver nanoparticles surface under light irradiation, small silver seeds on a quartz slide can be enlarged. The optical properties and characteristics of the silver films have been investigated by ultraviolet-visible spectroscopy, scan electron microscope and atomic force microscopy (AFM). The results indicate that the particle size and shape are different at different reduction time. At the first 3 h, some triangular and hexagonal nanoparticles formed; with the reduction proceeding, the shape of the silver particles became irregular and the size became larger. The silver films obtained are very suitable as SERS active substrate. The relationship between SERS intensity and the reduction time has been investigated for 1,4-bis[2-(4-pyridyl)ethenyl]-benzene molecule adsorbed on the silver film. The SERS intensity reached a maximum at 8 h reduction. The AFM measurements indicate that roughness features with an average size of 100 nm are present on the surface, which yielded the strongest SERS signal. Pyridine was used as a probe molecule to investigate the enhancement factor (EF) of the silver films. According to the formalism of Tian and co-workers, the EF of the silver films is estimated to be 3.4 × 10⁵. The silver film that can remain active for more than 50 days would seem to be suitable for various analytical applications.     

Highly-ordered, 3D petal-like array for surface-enhanced Raman scattering

Despite the great potential of the application of surface-enhanced Raman scattering (SERS), the difficulty in fabricating suitable SERS substrates is still a problem. Based on the self-assembly of silica nanoparticles, a simple method is here proposed to fabricate a highly-ordered, 3D, petal-like arrayed structure (3D PLAS) that serves as a promising SERS substrate for both its high reproducibility and enormous SERS enhancement. Such a novel structure is easily achieved by anisotropically etching a self-assembly bilayer of silica nanoparticles, followed by metal deposition. The SERS performance of the 3D PLAS and its relationship with the main parameters, including the etching time, the diameter of silica nanoparticles, and the deposited metal film, are characterized using 632.8 nm incident light. With Rhodamine 6G as a probe molecule, the spatially averaged SERS enhancement factor is on the order of 5 × 10(7) and the local enhancement factor is much higher, both of which can be improved further by optimizing the parameters.     

Patterning nanoroads and quantum dots on fluorinated graphene

Using ab initio methods we have investigated the fluorination of graphene and find that different stoichiometric phases can be formed without a nucleation barrier, with the complete “2D-Teflon” CF phase being thermodynamically most stable. The fluorinated graphene is an insulator and turns out to be a perfect matrix-host for patterning nanoroads and quantum dots of pristine graphene. The electronic and magnetic properties of the nanoroads can be tuned by varying the edge orientation and width. The energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO) of quantum dots are size-dependent and show a confinement typical of Dirac fermions. Furthermore, we study the effect of different basic coverage of F on graphene (with stoichiometries CF and C₄F) on the band gaps, and show the suitability of these materials to host quantum dots of graphene with unique electronic properties.     

Facile synthesis of amine-functionalized graphene quantum dots with highly pH-sensitive photoluminescence

Graphene quantum dots (GQDs) as promising materials have gained increasing attention due to their optical and chemical properties, but the complicated synthetic procedures restrict their large-scale application. Here we report a novel one-pot hydrothermal method to synthesize the GQDs with bifunctional groups (-OH and -NH₂) using a polycyclic aromatic hydrocarbon as the precursor, in which 1,5-dinitronaphthalene was graphitized in aqueous ammonium solution. The as-synthesized GQDs with single-layer structures have a size distribution of 1–3 nm and an average value of 1.5 nm. The alkaline species play a crucial role in the formation of amine-functionalized GQDs. More importantly, the as-synthesized GQDs exhibit a distinct pH-sensitive photoluminescence and the fluorescence colors vary from bluish green to yellow with pH value from 5 to 10, which can be attributed to the protonation and deprotonation of the amine-groups in acid or alkaline solution.     

2D/3D growth of GaN by molecular beam epitaxy: towards GaN quantum dots

The first stages of the growth of strained GaN on AlN were studied using reflection high energy electron diffraction, atomic force microscopy and high resolution electron microscopy. It was shown that GaN grows in the Stranski–Krastanov mode, with three-dimensional islanding occuring after deposition of two monolayers. This 2D/3D transition was found to depend on the growth temperature. At low growth temperature, coalescence of 3D islands rapidly leads to a smooth surface. At high temperature, no smoothing process is observed. It is shown that the size of the 3D islands is controlable and that it is small enough to expect quantum effects.     

Preparation and enhanced properties of ZrMOF@CdTe nanoparticles with high-density quantum dots

ZrMOF@CdTe nanoparticles (NPs) with high fluorescence were synthesized by hydrothermal method. The morphology, particle size distribution, compositions, fluorescence properties and stability of the synthesized ZrMOF@CdTe were analyzed via the characterization by TEM, ICP-AES and fluorescence spectrophotometry, and the effects of the reaction time and pH value on the fluorescent property of ZrMOF@CdTe NPs were discussed. The results show that ZrMOFs could maintain its morphology and structure well during the process of loading CdTe quantum dots. With the increase of the loading reaction time, the red-shifted emission peaks of ZrMOF@CdTe NPs appear, and their fluorescence gradually changes from green to red color. With the increase of the pH value and temperature of the hydrothermal reaction, the fluorescence of ZrMOF@CdTe NPs was also consistent with the red-shifted change. The fluorescent property of ZrMOF@CdTe NPs could be remained for more than 3 months. Therefore, ZrMOF@CdTe NPs synthesized by the hydrothermal method have the characteristics of simple operation, adjustable fluorescent color and high stability, and the potential application in the fields of biological detection and sensing is expected.     

Tunable and highly reproducible surface-enhanced Raman scattering substrates made from large-scale nanoparticle arrays based on periodically poled LiNbO3 templates

Abstract

This work describes novel surface-enhanced Raman scattering (SERS) substrates based on ferroelectric periodically poled LiNbO₃ templates. The templates comprise silver nanoparticles (AgNPs), the size and position of which are tailored by ferroelectric lithography. The substrate has uniform and large sampling areas that show SERS effective with excellent signal reproducibility, for which the fabrication protocol is advantageous in its simplicity. We demonstrate ferroelectric-based SERS substrates with particle sizes ranging from 30 to 70 nm and present tunable SERS effect from Raman active 4-mercaptopyridine molecules attached to AgNPs when excited by a laser source at 514 nm.     

Diagnosis of breast cancer by analysis of sialic acid concentrations in human saliva by surface-enhanced Raman spectroscopy of silver nanoparticles

Breast cancer is the most common type of malignant tumor among women and their second leading cause of cancer-related deaths.The most common method for screening and diagnosis is mammography.Nonetheless,two main problems have been identified.First,the dose of radiation received during the test prevents the method from the use on women who are ＜ 40 years old.Second,there can be mammogram failure owing to the lack of tumor contrast with the fibrous tissue.Therefore,there is a need for screening methods that will help to identify high-risk cases.We developed a biological marker test that can help to identify them.Increased levels of sialic acid (SA) in saliva are known to correlated with breast cancer.In this study,we evaluated the feasibility of Raman spectroscopy as a method for quantification of SA in saliva,using citrate-reduced silver nanoparticles (cit-Ag-NPs) as a surface-enhanced Raman spectroscopy (SERS) substrate.Quantification of SA was accomplished by measuring its intensity in saliva and comparing it with a calibration curve of SA standards.The mean SA concentration in saliva was found to be significantly higher among 100 breast cancer patients (18.3 ± 9.4 mg·dL-1;mean ± SD) than among 106 healthy controls (3.5 ± 1.0 mg·dL-1).The SERS test showed sensitivity of 94％ and specificity 98％ for detection of patients with breast cancer,assuming that SA concentration ＞ 7 mg·dL-1 is a cutoff for positive test results.Our findings prove the usefulness of this SERS technique as a simple,convenient,and highly sensitive method of quantitative analysis of SA in saliva.The simplicity of this nanotechnological test may help to substantially reduce the mortality among patients with breast cancer by providing women with a simple,noninvasive screening test that can be applied regardless of age or density of breast tissue.     

Actinide-embedded gold superatom models: Electronic structure,spectroscopic properties,and applications in surface-enhanced Raman scattering

Actinide elements encaged in a superatomic cluster can exhibit unique properties due to their hyperactive valence electrons. Herein, the electronic and spectroscopic properties of Th@Au₁₄ are predicted and compared with that of the isoelectronic entities [Ac@Au₁₄]^? and [Pa@Au₁₄]⁺ using density functional theory. The calculation results indicate that these clusters all adopt a closedshell superatomic 18-electron configuration of the 1S²1P⁶1D¹⁰ Jellium state. The absorption spectrum of Th@Au₁₄ can be interpreted by the Jelliumatic orbital model. In addition, calculated spectra of pyridine-Th@Au₁₄ complexes in the blue laser band exhibit strong peaks attributable to charge transfer (CT) from the metal to the pyridine molecule. These charge-transfer bands lead to a resonant surface-enhanced Raman scattering (SERS) enhancement of ～10⁴. This work suggests a basis for designing and synthesizing SERS substrate materials based on actinide-embedded gold superatom models.

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Ultraviolet-visible and surface-enhanced Raman scattering spectroscopy studies on self-assembled films of ruthenium phthalocyanine on organic monolayer-modified silver substrates

A self-assembled film of ruthenium phthalocyanine (RuPc) fabricated on a silver substrate pre-modified with a monolayer of 4-mercaptopyridine (PySH) or 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BPENB) was studied by ultraviolet-visible (UV-Vis) and surface enhanced Raman scattering (SERS) spectroscopy. PySH or BPENB was used as a ligand to link RuPc since they not only modify the silver substrate, but also deliver a pyridyl group pointing out from the silver surface. Therefore, we can explore the relationship between the structure and orientation of metallophthalocyanine and the substrate modified by the two kinds of organic-monolayers with the different conjugates and molecular lengths. UV-Vis bands due to the organic-monolayer (PySH or BPENB) modified silver films shift to longer wavelengths and a new band arising from the metallophthlocyanine appears, suggesting the binding of RuPc to PySH/BPENB, as well as the interaction between the marcocycle of RuPc and the ring of PySH/BPENB. Vibrational bands arising from both the RuPc and PySH/BPENB moieties appear clearly in the SERS spectra of the RuPc-PySH/BPENB composite films, indicating that RuPc is successfully assembled on the top of PySH/BPENB film. The shifts and relative intensity changes of bands due to PySH or BPENB in the SERS spectra imply the binding of the metallophthalocyanine to the pyridyl group in the composite films. Furthermore, the comparison of the SERS spectra revealed that the orientations of PySH and BPENB in the two kinds of composite films are different; the BPENB moiety in the RuPc-BPENB composite film is more perpendicular to the silver surface compared with the PySH moiety in the RuPc-PySH composite film.     

Graphene oxide-Ag nanocomposite: In situ photochemical synthesis and application as a surface-enhanced Raman scattering substrate

In the present study, a facile method is developed for the synthesis of graphene oxide-Ag nanocomposite (GOAg). The method involves the application of in situ photochemical deposition and growth processes under certain alkaline environments in the absence of chemical reductants and surfactants. Silver nanoparticles with monodisperse size are well dispersed on the surface of graphene oxide (GO). The roles of GO and NaOH in the formation of GOAg are discussed. A corresponding formation mechanism of GOAg is proposed. Fluorescence quenching and Raman enhancement are examined as well.     

Surface-structured gold-nanotube mats: fabrication, characterization, and application in surface-enhanced Raman scattering

The fabrication and characterization of nanostructured fibrous gold mats having high specific surface areas is reported. Freestanding porous films of 6-20-μm thickness and density 0.43 ± 0.02 g cm(3) are prepared using e-beam evaporation of gold on an electrospun nanoporous polymer template and subsequent removal of the template polymer in a suitable solvent. Structural characterization using electron microscopy techniques shows a nanofiber diameter in the range of 300-6000 nm, and the size of the nanochannels on the fiber surface is ≈200-350 nm. Such surface structuring is achieved through fast evaporation of organic solvent and phase separation of polymers during the electrospinning process. The wedge thickness varies from a few nanometers to a few tens of nanometers. The freestanding films possess good mechanical integrity and robustness. The calculated Young's modulus based on the slope in the elastic region is ≈114 MPa and gives an ultimate breaking strength of 0.7-0.8 MPa at a percentage elongation of 1.5-2.0%. X-ray diffraction and transmission electron microscopy measurements demonstrate the formation of polycrystalline gold nanostructures. Electrical characterization performed on these gold nanotubes reveals pure metallic behavior. Raman spectroscopic characterization of the fibrous membrane is performed using crystal violet (CV) adsorbed on it. Well-defined spectral peaks are obtainable at concentrations as low as 10(-7) M of CV, which did not give spectral signals at this low concentration on its own.     

Facile synthesis of graphene quantum dots/ZSM-5 type metalosilicate composites and evaluating their performance in photocatalytic degradation of methylene blue and electrochemical water splitting

Graphene quantum dots (GQDs)/ZSM-5 type cobaltosilicate and GQDs/ZSM-5 type chromosilicate composites were prepared by two methods; direct and solid state dispersion (SSD) method. The composites were characterized using XRD, FT-IR, UV–vis absorption, and SEM techniques. The photocatalytic activities of composites were evaluated by degradation of methylene blue (MB) under both UV and vis light irradiation. The composites prepared by direct method showed better photocatalytic activity and the GQDs/chromosilicate composite had a superior performance. This composite could remove about 96 % and 87 % of MB at first 30 min under UV and vis light, respectively. The results of photocatalytic degradation kinetic studies revealed that the composites follow the pseudo-second-order kinetic model (R² = 0.99) with rate constants ranging from 0.295 to 0.581 g mg^?1 min^?1 for different composites prepared by direct method. The GQDs/metalosilicate composites were also examined for the electrochemical water splitting. The GQDs/cobaltosilicate composites required lower overpotentials for HER and OER in comparison to the pure GDQs and cobaltosilicate. Moreover, the charge transfer resistance and Warburg impedance was lower than the corresponding values obtained for the pure cobaltosilicate and GQDs. These new GQDs-based composites are expected to open new windows in materials science and electrocatalytic-related processes.     

The enhanced and polarized Raman spectra on the spherical aluminum powders encapsulated within graphene nanosheets

This article deals with the Raman spectroscopic research of aluminum–graphene (Al–Gr) composites obtained by aqueous suspension-based mixing to improve dispersion of graphene sheets in composite powders. Raman spectra of composite powders reflect encapsulated nanostructure of Al–Gr composite powders and chemical interaction of oxygen groups on graphene oxide (GO) with magnesium ions (Mg²⁺), depending on the added Mg²⁺ content. First, the enhanced Raman signal for our composite powders is an apparent evidence of that graphene sheets with uniform dispersion on Al matrix are in close contact with the spherical surface of Al powders. The polarization dependence of the Raman spectra, which are dependent on the incident laser spot, also confirms that the graphene sheets surrounded the spherical powder. SEM image, XPS and FT-IR spectra for the composite powders provide additional data to decipher the Raman analysis results.     

Cu-In-S三元量子点的合成及其性能调控

采用前驱体分解法制备了Cu-In-S量子点,研究了制备工艺对Cu-In-S量子点的形貌以及光学性能的影响。实验结果表明,反应时间和反应温度可影响Cu-In-S纳米颗粒的尺寸和光学性能。随时间增加,Cu-In-S粒径变大,同时会伴随着棒状晶体的出现,荧光发射谱的峰位发生红移。随反应温度升高,纳米晶的形核速率和长大速率增加,并且粒径也有增大,纳米晶的形状可以由单一的球形变为球形与棒状的混合,荧光谱峰位亦会发生红移。X射线光电子能谱分析表明,所制备颗粒为CuInS2纳米晶。为进一步制备无毒量子点发光器件(QLEDs)奠定了基础。     

Surface-enhanced Raman scattering substrate of silver nanoparticles depositing on AAO template fabricated by magnetron sputtering

In this report, we describe a fabrication process of low-cost and highly sensitive SERS substrates by using a simple anodizing setup and a low-energy magnetron sputtering method. The structure of the SERS substrates consists of silver nanoparticles deposited on a layer of anodic aluminum oxide (AAO) template. The fabricated SERS substrates are investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM), and a confocal Raman spectroscope. We have verified from the surface morphology that the fabricated SERS substrates consist of high-density round-shape silver nanoparticles where their size distribution ranges from 10 to 30 nm on the top and the bottom of nanopores. The surface-enhanced Raman scattering activities of these nanostructures are demonstrated using methylene blue (MB) as probing molecules. The detection limit of 10⁻⁸ M can be achieved from this SERS substrate.     

A novel method for the preparation of water-soluble and small-size CdSe quantum dots

A novel method for the preparation of water-soluble and small-size CdSe quantum dots has been reported under high-intensity ultrasonic irradiation. The as-prepared products have been characterized by absorption spectra, X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM).     

Mesoflowers: A new class of highly efficient surface-enhanced Raman active and infrared-absorbing materials

A method for the synthesis of a new class of anisotropic mesostructured gold material, which we call “mesoflowers”, is demonstrated. The mesoflowers, unsymmetrical at the single particle level, resemble several natural objects and are made up of a large number of stems with unusual pentagonal symmetry. The mesostructured material has a high degree of structural purity with star-shaped, nano-structured stems. The mesoflowers were obtained in high yield, without any contaminating structures and their size could be tuned from nano- to meso-dimensions. The dependence of various properties of the mesoflowers on their conditions of formation was studied. The near-infrared-infrared (NIR-IR) absorption exhibited by the mesoflowers has been used for the development of infrared filters. Using a prototypical device, we demonstrated the utility of the gold mesoflowers in reducing the temperature rise in an enclosure exposed to daylight in peak summer. These structures showed a high degree of surface-enhanced Raman scattering (SERS) activity compared to spherical analogues. SERS-based imaging of a single mesoflower is demonstrated. The high SERS activity and NIR-IR absorption property open up a number of exciting applications in diverse areas. Electronic Supplementary Material  Supplementary material is available in the online version of this article at http://dx.doi.org/ and is accessible free of charge.     

Synthesis and characterization of CdTe quantum dots embedded gelatin nanoparticles via a two-step desolvation method

Novel CdTe quantum dots (QDs) embedded gelatin nanoparticles (CdTe/gelatin nanoparticles) were synthesized via a two-step desolvation method. The morphology and size distribution of the nanoparticles were characterized by transmission electron microscope (TEM) and laser particle size analyzer. They are presented spherically and relatively uniform with a diameter of 150 nm. The luminescent properties of the nanoparticles were investigated by using fluorescence spectrophotometry and fluorescence microscopy. The fluorescence stability of nanoparticles was tested in vitro. It was found that the nanoparticles were stable in water and phosphate-buffered saline (PBS) solution (pH 7.4) for at least 15 days. A possible formation mechanism of the CdTe/gelatin nanoparticles was also proposed. The inherent stability and biocompatibility indicate that the nanoparticles are expected to be promising candidates for in vivo biological imaging studies.