Amino Acid-Assisted Synthesis of Hierarchical Silver Microspheres for Single Particle Surface-Enhanced Raman Spectroscopy

We demonstrate the use of amino acids as directing agents to synthesize hierarchical silver microspheres assembled by nanosheets with well-defined morphologies, in the absence of any other surfactants or capping agents. This fabrication method avoids the absorption of macromolecules and enables clean surface on the Ag microspheres. The chemical nature of the amino acids plays a vital role in the hierarchical structure of the Ag microspheres. As found, amino acids with simple structures and 2–3 carbon atoms like alanine and glycine lead to more loosely packed Ag microspheres, and those with more complicated structures and more carbon atoms, e.g. glycine, glutamine, and asparagine, result in close-packed Ag particles assembled by thinner nanosheets. By adjusting the concentration of AgNO₃ solution, size as well as the surface roughness of the Ag microspheres can be well controlled. Individual particles of the constructed hierarchical Ag microspheres with highly roughened surface can act as sensitive SERS platforms. Detection of chemical molecules and monitoring of the plasmon-driven chemical reactions have been carried out through a single particle SERS technique

Highly Sensitive Surface-Enhanced Raman Spectroscopy (SERS) Platforms Based on Silver Nanostructures Fabricated on Polyaniline Membrane Surfaces

Here, we demonstrate a facile synthesis of homogeneous Ag nanostructures fully covering the polyaniline (PANI) membrane surface simply by introducing organic acid in the AgNO₃ reaction solution, as an improved technique to fabricate well-defined Ag nanostructures on PANI substrates through a direct chemical deposition method [<i>Langmuir</i> <b>2010</b>, <i>26</i>, 8882]. It is found that the chemical nature of the acid is crucial to create a homogeneous nucleation environment for Ag growth, where, in this case, homogeneous Ag nanostructures that are assembled by Ag nanosheets are produced with the assistance of succinic acid and lactic acid, but only scattered Ag particles with camphorsulfonic acid. Improved surface wettability of PANI membranes after acid doping may also account for the higher surface coverage of Ag nanostructures. The Ag nanostructures fully covering the PANI surface are extremely sensitive in the detection of a target analyte, 4-mercaptobenzoic acid (4-MBA), using surface-enhanced Raman spectroscopy (SERS), with a detection limit of 10^–12 M. We believe the facilely fabricated SERS-active substrates based on conducting polymer-mediated growth of Ag nanostructures can be promising in the trace detection of chemical and biological molecules