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

Abstract

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.

Green Synthesis of Asymmetrically Textured Silver Meso-Flowers (AgMFs) as Highly Sensitive SERS Substrates

“…The disagrement of SERS signals indicated the feasible conversion of neighboring ATPs on the silver surface into 4−4′-dimercaptoazobenzen (DMAB) under high power laser (633 nm of He−Ne laser, 12 mW). 65 The chemical dimerization of 4-aminothiophenol (ATP) adsorbed on a roughened silver surface into DMAB was recently observed in SERS signals under continuous laser exposure or increasing the power density of a laser. 31,32,65 The chemical reaction was attributed to the hot electrons generated from the surface plasmon excitation or the local plasmon heating on silver nanoparticles in coexistence with O 2 /H 2 O.…”

“…65 The chemical dimerization of 4-aminothiophenol (ATP) adsorbed on a roughened silver surface into DMAB was recently observed in SERS signals under continuous laser exposure or increasing the power density of a laser. 31,32,65 The chemical reaction was attributed to the hot electrons generated from the surface plasmon excitation or the local plasmon heating on silver nanoparticles in coexistence with O 2 /H 2 O. 32 Although the reaction mechanism is not fully understood yet, the crucial role of silver nanoparticle as a surface plasmonassisted catalyst is undoubted.…”

In Situ Surface‐Enhanced Raman Spectroscopy Study of Plasmon‐Driven Catalytic Reactions of 4‐Nitrothiophenol under a Controlled Atmosphere

“…The successful synthesis of monodispersed Au nanotriangles leads to extended self‐assembly at the air–liquid interface, which allows the development of a promising surface‐enhanced Raman scattering (SERS) substrate 6. Uniform Ag microspheres with a nanoscale surface roughness have been synthesized as SERS substrates by the addition of poly(vinylpyrrolidone),7 small molecular acids,8 or amino acids9 as capping agents. The development of nanomaterials for practical applications requires synthetic methods to shift gradually from what it is to what we design.…”

Mechanistic understanding of surface plasmon assisted catalysis on a single particle: cyclic redox of 4-aminothiophenol

“…SERS and TERS not only induce chemical reactions at a metal surface through surface plasmon resonance, they also act as sensitive spectroscopic probes for monitoring the structural change of the adsorbed reactants34. SPAC reactions were first discovered on 4-aminothiophenol (4ATP) using SERS, where 4ATP was observed to gradually convert (dimerize) to 4,4′-dimercaptoazobenzene (DMAB) upon continuous laser excitation25678910. Recently, 4-nitrothiophenol (4NTP) has also been shown to dimerize into DMAB by this direct surface plasmon assisted technique1111213.…”