Fractal theory and controllable preparation of centimeter level silver nanowire arrays and their application in melamine detection as SERS substrates.

Silver nanowire arrays as surface-enhanced Raman scattering (SERS) substrates were prepared by a solid-state ionics method under the direct current electric field (DCEF) and used to rapidly detect melamine in aqueous solutions. The arrangement density and surface roughness of the prepared silver nanowire arrays are significantly different upon a change in the impressed current intensity. The growth mechanism of silver nanowire arrays was associated with the apical growth advantage and the irregular electrode interface. When the current intensity was 4 μA and 10 μA, the fractal dimension of silver nanowire arrays was 1.66 and 1.49, the diameters of nanowires ranged from 90 to 130 nm and 90 to 170 nm, and many densely arranged and regularly arranged silver nanoparticles lie in the prepared nanowire arrays, respectively. The result shows that there were more silver nanostructures and surface roughness under 4 μA DCEF. The Raman signal intensity of melamine molecule shows that the prepared SERS substrate exhibited a high sensitivity. The proposed method allow us detect melamine with a limit of 10 ^-15  mol/L and 10 ^-12  mol/L, which are lower than the safety limit estimated by the US food and Drug Administration. With its facile material synthesis, simple detection procedure and low detection concentration, this silver nanowire arrays with high surface roughness indicates a strong potential detection technique in the field of food safety.
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