Because of their perfect geometrical symmetry, spherical metal nanoparticles have attracted much attention for various applications, including fundamental studies and construction of plasmonic devices. In this work, monodisperse silver nanospheres (Ag NSs) in aqueous solution were directly prepared by a continuous process of seed-mediated growth followed by oxidative etching. Silver nanocubes (Ag NCs) were synthesized by a seed-mediated growth method and subsequently were transformed to Ag NSs by simple injection of Cu to the freshly prepared Ag NCs solution. Not requiring any centrifugation steps at both growth and etching stages makes this procedure convenient and efficient. The etching process and morphology evolution of silver nanostructure were monitored by UV-vis spectromater, SEM, and XRD. Monodisperse Ag NSs with broadly tunable diameters (from 37 to 68 nm) have been successfully prepared. The optical property of Ag NSs has been studied and the experimental results show fairly good consistency with simulation results. Furthermore, these Ag NSs prepared by our approach could be constructed into ordered superlattice by self-assembly technique based on their high monodispersity and sphericity.

Self-assembled Au@Ag nanocubes embedded with 4-MBA as an internal reference were applied for quantitative SERS measurements of aspartame in drinks.

A paper-based surface-enhanced Raman spectroscopy (SERS) substrate was prepared by assembling Au@Ag nanocubes onto a patterned paper with the assistance of a mask paper by liquid-liquid interface self-assembly techniques. The paper-based SERS substrate was glued to the glass slide to construct a novel lab-on-paper SERS platform. This paper-based SERS sensor possesses a sample injecting zone together with a SERS detection zone in order that sample pretreatment and detection could be performed simultaneously.The SERS performance of this paper-based sensor was investigated by using 4-MBA as a probe molecule, and its enhancement factor as high as 0.56 × 10 5 could be obtained. Additionally, the SERS sensor demonstrated an excellent repeatability with the relative standard deviation for the variation from the spot-to-spot Raman intensity as low as 12.8%. Based on the superiority and functionality of this paper-based SERS platform, sensitive SERS quantitative analysis of thiram in soil could be achieved, which suggests its significant application prospects for the measurement of pesticides in soil without any pretreatment.

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