Excellent SERS Activity Research Articles

Electric field-induced assembly of Au-Ag alloy nanoparticles into nano-reticulation for ultrasensitive SERS.

This paper discusses a method for assembling Au-Ag alloy nanoparticles (NPs) using direct current (DC) electric field to fabricate highly active SERS substrates. Different nanostructures could be obtained by regulating the intensity and action time of DC electric field. Under the condition of 5mA*10 min, we obtained Au-Ag alloy nano-reticulation (ANR) substrate with excellent SERS activity (Enhancement factor on order of magnitude of 106). ANR substrate has excellent SERS performance due to the resonance matching between its LSPR mode and excitation wavelength. The uniformity of the Raman signal on ANR is greatly improved than bare ITO glass. ANR substrate also has the ability to detect multiple molecules: ANR substrate can respectively detect Rh6G and CV molecules with a concentration as low as 10-10 M and 10-9 M and the Raman spectral intensity of the probe molecules on the surface of the ANR substrate has good linear correlation with the molecular concentration (R2 > 0.95). In addition, ANR substrate can detect both thiram and aspartame (APM) molecules far below (thiram for 0.0024 ppm and APM for 0.0625 g/L) the safety standard, which demonstrate its practical application potential.

Multi-dimensional plasmonic coupling system for efficient enrichment and ultrasensitive label-free SERS detection of bilirubin based on graphene oxide-Au nanostars and Au@Ag nanoparticles

Rapid and sensitive detection of free bilirubin (BR) is essential for early diagnosis of jaundice and other hepatobiliary diseases. Inspired by sandwich immunoassay strategy, a multi-dimensional plasmonic coupling SERS platform composed of graphene oxide-Au nanostars nanocomposites (GANS NCs) and Au@Ag nanoparticles (NPs) was designed for label-free detection of BR. Specifically, GANS NCs were first prepared, and their excellent SERS activity was ascribed to synergistic enhancement effect of electromagnetic enhancement and chemical enhancement. Furthermore, SERS spectroscopy was used to monitor the adsorption process of BR. Subsequently, secondary reinforcing Au@Ag NPs were directly added, ultimately resulting in a multi-dimensional plasmonic coupling effect. The SERS enhancing mechanism of coupled system was discussed through electromagnetic field simulations. Interestingly, the high-density hotspots generated by strong plasmonic coupling in GANS-Au@Ag substrate could lead to more extraordinary SERS enhancing behavior compared to GANS NCs. Sensing efficiency of the SERS platform was examined by BR with a detection limit down to 10−11 M. Besides, GANS-Au@Ag NCs performed high uniformity and reproducibility. This work not only opens up a new avenue for construction of multi-dimensional plasmonic coupling system, but also offers a new biosensing technology for label-free diagnosis of BR-related diseases, thereby expecting to be applied in clinical diagnosis.

Casting liquid PDMS on self-assembled bilayer polystyrene nanospheres to prepare a SERS substrate with two layers of nanopits for detection of p-nitrophenol.

p-Nitrophenol (PNP) is widely used in pesticides, pharmaceuticals, and dyestuffs. It is vital to detect trace PNP in the environment, because it poses significant environmental hazards due to its high toxicity. In this paper, a new method was reported for preparing a SERS substrate with excellent SERS activity by combining self-assembly techniques and flexible materials. First, the three-dimensional (3D) polystyrene (PS) photonic crystal (PC) structural master was fabricated by stacking two layers of self-assembled PS nanospheres with different diameters. Polydimethylsiloxane (PDMS) with a complementary structure to the master was obtained by casting, curing and peeling off. Finally, the PDMS-Ag substrate was fabricated by sputtering a thin Ag layer on the PDMS structure. The enhancement factor (EF) of the PDMS-Ag substrate was calculated to be 2.90 × 109 by using 4-amino thiophenol (ATP) as the probe molecule, and the limit of detection (LOD) for ATP can reach 10-11 M. And the RSD of the SERS intensity for the peak at 1078 cm-1 on the PDMS-Ag substrates from batch to batch was within 2%, indicating the high reproducibility of the as-prepared substrate. The quantitative analysis of PNP was achieved with a LOD of 10-8 M. Therefore, the PDMS-Ag substrate exhibits high sensitivity and reproducibility, and it can detect PNP in trace amounts, with great potential for detecting other contaminants.

WO3 Nanopores Array Modified by Au Trisoctahedral NPs: Formation, Characterization and SERS Application

The WO3 nanopores array was obtained by an anodization method in aqueous solution with addition of F- ions. Several factors affecting the final morphology of the samples were tested such as potential, time, and F- concentrations. The morphology of the formed nanopores arrays was examined by SEM microscopy. It was found that the optimal time of anodization process is in the range of 0.5-1 h. The nanopores size increased with the increasing potential. The XPS measurements do not show any contamination by F- on the surface, which is common for WOx samples formed by an anodization method. Such a layer was successfully modified by anisotropic gold trisoctahedral NPs of various sizes. The Au NPs were obtained by seed-mediated growth method. The shape and size of Au NPs was analysed by TEM microscopy and optical properties by UV-VIS spectroscopy. It was found that the WO3-Au platform has excellent SERS activity. The R6G molecules could be detected even in the range of 10-9 M.

Simultaneous determination of three food contaminants in shrimp paste by hollow porous pentagonal Au/Ag alloy nanotubes with excellent SERS activity

Herein, we reported a robust and sensitive SERS sensing platform based on hollow porous pentagonal Au/Ag alloy nanotubes (Au/AgANTs) for simultaneous determination of three food contaminants. With the increase amount of etching agent, the morphology of the nanoparticles changed from solid to hollow porous structures, and then the disappearance of pores, accompanied by a trend of first increasing and then decreasing SERS activity. The Au/AgANTs with pentagonal cross section, hollow and pore structure provide stronger local electric field. Under optimized experimental conditions, they were utilized to achieve the simultaneous determination of rhodamine B (RhB), methylene blue (MB) and malachite green (MG) in shrimp paste with low detection limit (5.3 ×10−11 M for RhB, 1.27 ×10−10 M for MB and 4.07 ×10−12 M for MG), wide linear detection range (1.0 ×10−8∼1.0 ×10−4 M for RhB, 1.0 ×10−9∼1.0 ×10−5 M for MB, and 1.0 ×10−9∼1.0 ×10−5 M for MG) and satisfactory recoveries (97.24–102.66%), suggesting that the developed method is a promising tool for accurate quantification of the three food contaminants at trace level.

Fe3O4@m-ZrO2@Ag ternary magnetic nanocomposites for sensitive SERS sensing and photocatalytic removal of Cr(VI) and organic dyes

In this study, a crystalline mesoporous ZrO2 interlayer allowing for enrichment capability and photocatalytic activity was introduced to develop a novel magnetic Fe3O4/m-ZrO2/Ag nanocomposite combined with excellent SERS activity and photocatalytic property. The coverage of Ag nanoparticles on Fe3O4/m-ZrO2/Ag was well controlled to tune their SERS sensitivity by varying the feed amount of AgNO3. Several characterization methods were utilized to investigate their composition, morphology and crystal structure. The SERS experiments demonstrated Fe3O4/m-ZrO2/Ag nanocomposites possessed markedly SERS sensitivity, exceptional signal reproducibility and excellent storing stability. They could sense R6G and Cr (VI) at the concentrations of 10−9 and 5 × 10−8 M, respectively. Beyond that, the Fe3O4/m-ZrO2/Ag nanocomposites effectively accomplished recyclable detecting R6G and Cr (VI) in 5 cycles through facile photocatalytic removal of pollutants under UV irradiation. Altogether, the novel Fe3O4/m-ZrO2/Ag nanocomposites prepared in this study have high SERS sensitivity and good photocatalytic performance, which is of great significance for environmental detection and ecological restoration.

Simultaneous Determination of Three Food Contaminants in Shrimp Paste by Hollow Porous Pentagonal Au/Ag Alloy Nanotubes with Excellent Sers Activity

Simultaneous Determination of Three Food Contaminants in Shrimp Paste by Hollow Porous Pentagonal Au/Ag Alloy Nanotubes with Excellent Sers Activity

Dual-functional porous copper films modulated via dynamic hydrogen bubble template for in situ SERS monitoring electrocatalytic reaction

Dual-functional porous copper films were prepared by dynamic hydrogen bubble template (DHBT) technique to achieve in situ SERS monitoring of electrocatalytic reaction. The morphology and SERS activity of porous copper films were effectively modulated by electrolyte additive, current density, and deposition time. The interfacial evolution behaviors of porous copper films were monitored by in situ synchrotron radiation X-ray imaging. The three-dimensional porous copper films in the presence of CTAB additive present a thinner leaf-like dendritic structure and excellent SERS activity. Although the diverse morphologies of porous copper films are obtained with inorganic additives including (NH4)2SO4, Na2SO4, or NaCl, they are deleterious to the SERS activity due to the microstructural changes of copper films, even significantly lower than that of the additive-free condition. The obtained porous copper films exhibit high sensitivity (10−9 mol/L) and good reproducibility for efficient SERS detection. Furthermore, the electrocatalytic reduction process of 4-nitrophenol on the porous copper films was successfully in situ monitored based on their excellent SERS activity.

Controlled synthesis of Au–Fe3O4 hybrid hollow spheres with excellent SERS activity and catalytic properties

Au-Fe3O4 hybrid hollow spheres have been successfully synthesized by a one-pot process via the hydrothermal treatment of FeCl3, HAuCl4, citrate, urea, and polyacrylamide (PAM). The amount of Au nanoparticles located in the hybrid hollow spheres can be tuned by changing the molar ratio of Au/Fe precursors. A possible synthetic mechanism of the Au-Fe3O4 hybrid hollow spheres has been proposed. The obtained hybrids exhibit not only a superior surface-enhanced Raman scattering (SERS) sensitivity, but also an excellent catalytic activity. The detection limit of the Au-Fe3O4 hybrid hollow spheres (the Au/Fe molar ratio is 0.2, Au-Fe3O4-0.2) for R6G can reach up to 10(-10) M, which can meet the required concentration level for ultratrace detection of analytes using SERS. Furthermore, the catalytic experiments of the Au-Fe3O4-0.2 hybrid hollow spheres demonstrate that the model of 4-nitrophenol (4-NP) molecules can be degraded within 3 min and the catalytic activity can be recovered without sharp activity loss in six runs, which indicates their superior catalytic degradation activity. The reason may be due to the highly efficient partial charge transfer between Au and Fe3O4 at the nanoscale interface. The results indicate that the bifunctional Au-Fe3O4 hybrid hollow spheres can serve as promising materials in trace detection and industrial waste water treatment.

Preparation of High SERS-Active Silver Films in an Aqueous Solution of Room Temperature Ionic Liquids

A very simple method for preparation of high SERS-active silver films was reported in the paper. The process is performed by reduction of silver nitrate with glucose on a borosilicate cover glass in an aqueous solution of 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4). The silver film shows excellent SERS activity in the presence of adsorbed 4-mercaptobenzoic acid (4-MBA) with excitation at 632.8 nm, and the enhancement factor reaches ∼3 × 105. Moreover, there exists a synergistic effect on SERS signals for BMIMBF4 and NaCl. The synthetic method reported here suggests a very promising route for preparation of sensitive SERS-active substrates.