Preparation and SERS performance of silver nanowires arrays on paper by automatic writing method.

Silver nanowire ink was written on the surface of drawing paper by automatic writing method. Scanning electron microscopy was used to characterize the surface morphologies of the drawing paper before and after writing silver nanowires. The effects of fabrication parameters and measurement parameters on silver nanowires arrays were investigated. Crystal violet was selected as the probe molecule to study the SERS performance of silver nanowires arrays. The detection limit of crystal violet was as low as 10-15 mol/L. The uniformity and repeatability of the arrays were also explored, and the relative standard deviation values were about 10%. Moreover, silver nanowires arrays were also relatively stable that SERS signals were still observed after ten weeks. Detection of the crystal violet residue was further achieved on the substrates by continuously pressing nine times. In addition, silver nanowires arrays were also applied to the quantitative analyses of 2, 2'-bipyridyl.

Robotic written silver ink on photographic paper for detection of thiram residues in fruits.

With the widespread application of pesticide in agriculture, pesticide residues in food have posed serious health risks to human. There is an urgent requirement to detect pesticide residues in food. In this work, a sensitive and effective method was employed to measure thiram residues in fruit using surface-enhanced Raman scattering (SERS) technique. Silver ink was written on photographic paper (AgNPs-photographic paper) directly by robotic writing technique. The AgNPs-photographic paper substrates possessed good SERS activities and high stability among four months. A good linear response between the peaks intensities and the logarithmic concentrations of thiram was obtained with the limit of detection (LOD) of 0.024 ppb. The substrates also exhibited excellent reproducibility with relative standard deviation (RSD) value less than 10% from ten different substrates. SERS mapping was tested to characterize the uniformity of AgNPs-photographic paper, and the RSD value was calculated to be 14.34% at 1377 cm-1 measured by 120 points. The LOD values of apple and peach juice adulterated with thiram were 0.0024 and 0.024 ppm, respectively. The LOD values of thiram residues on apple and peach peels were both 0.25 ng/cm2. It was demonstrated that the substrates prepared by robotic writing technique had great potential for practical application in food safety inspection.

Efficient fabrication of highly sensitive AgNPs-drawing paper SERS substrates by robotic writing approach.

Inspired by hand writing approach for preparing surface-enhanced Raman scattering (SERS) substrates, silver nanoparticles (AgNPs) decorated drawing paper substrates were prepared by robotic writing technique. The wettabilities and surface morphologies of the drawing paper before and after the deposition of AgNPs were characterized by contact angle analyzer and scanning electron microscope, respectively. Malachite green was employed as a probe molecule to evaluate the SERS activities of the AgNPs-drawing paper substrates. The AgNPs-drawing paper substrates exhibited extremely high sensitivity that the detection limit for malachite green was down to 10-18 mol/L and the Raman enhancement factor was calculated to be 1015. The relative standard deviation (RSD) values of the Raman peaks intensities collected from twelve points on a single substrate and fifteen substrates were used to evaluate the uniformity and reproducibility of the AgNPs-drawing paper substrates. It was found that the substrates had good reproducibility and uniformity with RSD values of 7.29% and 9.70%, respectively. Furthermore, the prepared AgNPs-drawing paper substrates exhibited long-term stability among six months.

Inkjet printed silver nanoparticles on hydrophobic papers for efficient detection of thiram.

Silver nanoparticles coated paper (AgNPs-paper) substrates were prepared by inkjet printing Ag ink on four different wettability papers. Scanning electron microscope and contact angle analyzer were used to characterize their surface morphology and wettability. AgNPs-paper substrates were used to detect the surface-enhanced Raman scattering (SERS) spectra of thiram aqueous solution. Relationships between the surface wettability, surface morphology and SERS activities of the substrates were systematically studied. The silver nanoparticles deposited on the hydrophobic papers (photographic paper, graph paper, and weighing paper) were evenly and densely arranged. While in-homogeneous distribution was observed on the hydrophilic printing paper. It can be found that the AgNPs-photographic paper with the maximum contact angle exhibited the highest SERS enhancement. The detection limit for thiram adsorbed on the AgNPs-photographic paper was 10-10 mol/L, which was lower than the others. Good linear responses (R2 = 0.9918, 0.9897) between the SERS intensities and logarithmic concentrations were obtained from 104 to 10-10 mol/L. Moreover, the substrate had good uniformity and reproducibility with relative standard deviation values of 4.20% and 4.90% measured by eight points and ten substrates, respectively. The AgNPs-photographic paper exhibited high stability within eight months.

Fabrication and SERS performance of silver nanoarrays by inkjet printing silver nanoparticles ink on the gratings of compact disc recordable.

Silver nanoarrays were fabricated by inkjet printing silver nanoparticles ink on the gratings of compact disc recordable (CD-R). Rhodamine 6G (R6G) was chosen as a probe molecule to evaluate their surface-enhanced Raman scattering (SERS) performance. The finite-difference time domain (FDTD) solution was used to simulate local electric field distribution of silver nanoparticles on the grating surface and flat surface, respectively. It was found that the Ag/grating substrate possessed higher enhancement ability than the Ag/flat due to the high-density hot spots of periodic structure of the grating. The silver nanoarrays substrate exhibited high stability and the characteristic peaks of R6G can be still well observed after eight months. The substrate also exhibited a good spot-to-spot reproducibility with an RSD of 10.21% by eight points. SERS mappings of R6G adsorbed on silver nanoarrays were tested under the ultra-fast Raman imaging mode, and the relative standard deviation (RSD) values of uniformity were calculated to be 8.35% and 11.53% at 610 cm-1 band measured by 2500 and 6480 points, respectively. In addition, the as-prepared silver nanoarrays was successfully applied to the detection of melamine in adult milk powder solution directly. A good linear relationship with the correlation coefficient of 0.9968 between peak intensity and concentration was obtained from 1.2 to 100 mg/L.

Direct detection of melamine in infant formula milk powder solution based on SERS effect of silver film over nanospheres.

A direct and sensitive method to detect melamine in infant formula milk powder solution based on the SERS effect of silver film over nanospheres (AgFON) was developed. AgFON was prepared by vacuum magnetron sputtering and dip-coating methods. The surface morphology and roughness were characterized by using scanning electron microscope and atomic force microscope. AgFON was used as a substrate to detect the SERS spectra of melamine in infant formula milk powder solution directly without any pretreatments. Semi-quantitative analyses of melamine with various concentrations in milk powder solution were carried out. A good linearity with correlation coefficient of 0.9926 between peak intensity and concentration was obtained from 2 to 25 mg/L. Furthermore, the as-prepared AgFON substrate had good uniformity with relative standard deviation value of 5.56% collected from ten randomly selected positions. The electric field distribution of AgFON was simulated by finite difference time domain solution, which revealed that the huge enhancement of Raman signals was ascribed to the high-density hot spots of the substrate.

Tunable MoS2 modified hybrid surface plasmon waveguides.

The tunable propagation properties of MoS2 supported hybrid surface plasmon waveguides based on dielectric fiber-gap-metal substrate structures have been investigated by using the finite element method, including the effects of structural parameters, the dielectric fiber shape and carrier concentration of the MoS2 layer. The results reveal that as the dielectric fiber radius increases, the confinement of the hybrid mode increases, and the losses show a peak. The shape of the dielectric fiber affects the propagation properties obviously, with an optimum structural parameter (a large value of the elliptical parameter) the confinement and figure of merits increase, and the dissipation decreases simultaneously. In addition, as the carrier concentration of the MoS2 layer increases, the modulation depth of absorption reaches more than 40%, and the propagation constants manifest obvious double peaks at wavelengths of 610 nm (2.03 eV) and 660 nm (1.88 eV), coming from the excitons' absorption of the MoS2 layer. The results are very useful in helping one to understand the tunable mechanisms of hybrid mode waveguide structures and for the design of novel surface plasmonic devices in the future, e.g. absorbers, modulators, lasers, and resonators.

Fabrication and characterization of La2Zr2O7 films on different buffer architectures for YBa2Cu3O7-δ coated conductors by RF magnetron sputtering.

La2Zr2O7 (LZO) films were grown on different buffer architectures by radio frequency magnetron sputtering for the large-scale application of YBa2Cu3O7-x (YBCO)-coated conductors. The three different buffer architectures were cerium oxide (CeO2), yttria-stabilized zirconia (YSZ)/CeO2, and CeO2/YSZ/CeO2. The microstructure and surface morphology of the LZO film were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and atomic force microscopy. The LZO films prepared on the CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were preferentially c-axis-oriented and highly textured. The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°. All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks. The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.