Coupling Single-Drop Microextraction with SERS: A Demonstration Using p-MBA on Gold Nanohole Array Substrate

Single-drop microextraction (SDME) was coupled with surface-enhanced Raman scattering (SERS) to provide sample extraction and pre-concentration for detection of analyte at low concentrations. A gold nanohole array substrate (AuNHAS), fabricated by interference lithography, was used as SERS substrate and para-mercaptobenzoic acid (p-MBA) was tested as a probe molecule, in the concentration range 10^-8-10^-4 mol L^-1. With this approach, a limit of 10^-7 mol L^-1 was clearly detected. To improve the detection to lower p-MBA concentration, as 10^-8 mol L^-1, the SDME technique was applied. The p-MBA Raman signature was detected in two performed extractions and its new concentration was determined to be ~4.6 × 10^-5 mol L^-1. This work showed that coupling SDME with SERS allowed a rapid (5 min) and efficient pre-concentration (from 10^-8 mol L^-1 to 10^-5 mol L^-1), detection, and quantification of the analyte of interest, proving to be an interesting analytical tool for SERS applications.

Silver nanoflowers for single-particle SERS with 10 pM sensitivity

Surface-enhanced Raman scattering (SERS) has received considerable attention as a noninvasive optical sensing technique with ultrahigh sensitivity. While numerous types of metallic particles have been actively investigated as SERS substrates, the development of new SERS agents with high sensitivity and their reliable characterization are still required. Here we report the preparation and characterization of flower-shaped silver (Ag) nanoparticles that exhibit high-sensitivity single-particle SERS performance. Ag nanoflowers (NFs) with bud sizes in the range 220-620 nm were synthesized by the wet synthesis method. The densely packed nanoscale petals with thicknesses in the range 9-22 nm exhibit a large number of hot spots that significantly enhance their plasmonic activity. A single Ag NF particle (530-620 nm) can detect as little as 10^-11 M 4-mercaptobenzoic acid, and thus provides a sensitivity three orders of SERS magnitude greater than that of a spherical Ag nanoparticle. The analytical enhancement factors for single Ag NF particles were found to be as high as 8.0 × 10⁹, providing unprecedented high SERS detectivity at the single particle level. Here we present an unambiguous and systematic assessment of the SERS performances of the Ag NFs and demonstrate that they provide highly sensitive sensing platforms by single SERS particle.

In situ synthesis of Au-shelled Ag nanoparticles on PDMS for flexible, long-life, and broad spectrum-sensitive SERS substrates

A simple, fast, one-step fabrication of silver nanoparticles with atomically thin gold coatings on polydimethylsiloxane affords oxidation-resistant and highly sensitive surface enhanced Raman scattering (SERS) substrates.

Facile fabrication of a silver dendrite-integrated chip for surface-enhanced Raman scattering

A facile approach to fabricating a surface-enhanced Raman scattering (SERS)-active chip by integrating silver dendrites with copper substrate through a one-step process was explored. The structures of dendrites were synthesized and controlled by an AgNO3/PVP aqueous system, and the fabrication parameters amount of AgNO3/PVP and reaction time were systematically investigated. The optimized silver dendrites, closely aggregated on the surface of the copper chip, exhibited high SERS activity for detecting rhodamine 6G at a concentration as low as 3.2 × 10(-11) M. Meanwhile, the prepared SERS-active chip displayed a high thermal stability and good reproducibility. Moreover, the potential application for analysis of polycyclic aromatic hydrocarbons was demonstrated by detection of fluoranthene at a low concentration of 4.5 × 10(-10) M. This SERS-active chip prepared by the convenient and high-yield method would be a promising means for rapid detection under field conditions.

Sensitive and easily recyclable plasmonic SERS substrate based on Ag nanowires in mesoporous silica

Parallel aligned Ag nanowires in SBA-15 present high SERS sensitivity due to improved plasmonic coupling effect. The further utilization of reversible conversion reaction between Ag and AgCl makes this SERS substrate easily renewable.