Silver nanoparticles: green synthesis, self-assembled nanostructures and their application as SERS substrates

In this paper, silver nanoparticles were synthesized using citrus peel extracts from species such as Citrus sinensis (orange fruit, AgNP-Ora), Citrus reticulata (tangerine fruit, AgNP-Tan), and Citrus aurantifolia (lemon fruit, AgNP-Lem). The absorption spectra of the AgNP-Ora and AgNP-Tan colloids show localized surface plasmon resonance (LSPR) bands at 445 and 423 nm, respectively. For the same synthesis method, a low intensity LSPR band for AgNP-Lem is observed, indicating a low yield of this reaction. However, the transmission electron microscopy images show that the colloid prepared using lemon extract also presents AgNP larger than 5 nm (5-55 nm), which exhibit plasmonic properties. The synthesized silver nanoparticles are spherical in shape and are highly crystalline, and they were self-assembled on NH2-modified glass slides, forming AgNP aggregate substrates for all the three prepared silver colloids. We also explored the SERS activity of the AgNP substrates using 10(-6) mol L-1 solutions of 4-aminobenzenethiol, rhodamine 6G, and methylene blue as Raman probe molecules. It was possible to detect with a high signal-to-noise ratio the SERS spectral pattern of all probe molecules on AgNP substrates. This simple, low cost, and greener method for synthesizing silver nanoparticles may be valuable in future studies about SERS sensor development and can be extended to catalytic applications.