Plasmonic Microneedle Arrays for in Situ Sensing with Surface-Enhanced Raman Spectroscopy (SERS).

Surface-enhanced Raman spectroscopy (SERS) is a sensitive, chemically specific, and short-time response probing method with significant potential in biomedical sensing. This paper reports the integration of SERS with microneedle arrays as a minimally invasive platform for chemical sensing, with a particular view toward sensing in interstitial fluid (ISF). Microneedle arrays were fabricated from a commercial polymeric adhesive and coated with plasmonically active gold nanorods that were functionalized with the pH-sensitive molecule 4-mercaptobenzoic acid.

Physicochemical Trapping of Neurotransmitters in Polymer-Mediated Gold Nanoparticle Aggregates for Surface-Enhanced Raman Spectroscopy.

Because of the sharp distance dependence of surface-enhanced Raman spectroscopy (SERS), analyte molecules that do not exhibit strong affinity for Au/Ag often elude detection. New methods of integrating such analytes with SERS substrates are required to circumvent this limitation and expand the sensitivity of SERS to new molecules and applications. We communicate here a solution-phase, capture agent-free method of aggregating Au nanospheres in the presence of five neurotransmitters (dopamine, epinephrine, norepinephrine, serotonin, and histamine) and preventing sedimentation by encapsulating the aggregated nanospheres with polyvinylpyrrolidone, thereby trapping the neurotransmitters in close proximity to the Au nanospheres and enabling SER detection.

Spiers Memorial Lecture. Surface-enhanced Raman spectroscopy: from single particle/molecule spectroscopy to ångstrom-scale spatial resolution and femtosecond time resolution.

Four decades on, surface-enhanced Raman spectroscopy (SERS) continues to be a vibrant field of research that is growing (approximately) exponentially in scope and applicability while pushing at the ultimate limits of sensitivity, spatial resolution, and time resolution. This introductory paper discusses some aspects related to all four of the themes for this Faraday Discussion. First, the wavelength-scanned SERS excitation spectroscopy (WS-SERES) of single nanosphere oligomers (viz.

Single-Molecule Chemistry with Surface- and Tip-Enhanced Raman Spectroscopy.

Single-molecule (SM) surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) have emerged as analytical techniques for characterizing molecular systems in nanoscale environments. SERS and TERS use plasmonically enhanced Raman scattering to characterize the chemical information on single molecules. Additionally, TERS can image single molecules with subnanometer spatial resolution.

Ultrahigh-Vacuum Tip-Enhanced Raman Spectroscopy.

Molecule-surface interactions and processes are at the heart of many technologies, including heterogeneous catalysis, organic photovoltaics, and nanoelectronics, yet they are rarely well understood at the molecular level. Given the inhomogeneous nature of surfaces, molecular properties often vary among individual surface sites, information that is lost in ensemble-averaged techniques. In order to access such site-resolved behavior, a technique must possess lateral resolution comparable to the size of surface sites under study, analytical power capable of examining chemical properties, and single-molecule sensitivity.

Bisboronic Acids for Selective, Physiologically Relevant Direct Glucose Sensing with Surface-Enhanced Raman Spectroscopy.

This paper demonstrates the direct sensing of glucose at physiologically relevant concentrations with surface-enhanced Raman spectroscopy (SERS) on gold film-over-nanosphere (AuFON) substrates functionalized with bisboronic acid receptors. The combination of selectivity in the bisboronic acid receptor and spectral resolution in the SERS data allow the sensors to resolve glucose in high backgrounds of fructose and, in combination with multivariate statistical analysis, detect glucose accurately in the 1-10 mM range. Computational modeling supports assignments of the normal modes and vibrational frequencies for the monoboronic acid base of our bisboronic acids, glucose and fructose.

Surface-Enhanced Raman Spectroscopy Biosensing: In Vivo Diagnostics and Multimodal Imaging.

This perspective presents recent developments in the application of surface-enhanced Raman spectroscopy (SERS) to biosensing, with a focus on in vivo diagnostics. We describe the concepts and methodologies developed to date and the target analytes that can be detected. We also discuss how SERS has evolved from a "point-and-shoot" stand-alone technique in an analytical chemistry laboratory to an integrated quantitative analytical tool for multimodal imaging diagnostics.

High-Resolution Distance Dependence Study of Surface-Enhanced Raman Scattering Enabled by Atomic Layer Deposition.

We present a high-resolution distance dependence study of surface-enhanced Raman scattering (SERS) enabled by atomic layer deposition (ALD) at 55 and 100 °C. ALD is used to deposit monolayers of Al2O3 on bare silver film over nanospheres (AgFONs) and AgFONs functionalized with self-assembled monolayers. Operando SERS is used to measure the intensities of the Al-CH3 and C-H stretches from trimethylaluminum (TMA) as a function of distance from the AgFON surface.

Silver colloidal pastes for dye analysis of reference and historical textile fibers using direct, extractionless, non-hydrolysis surface-enhanced Raman spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) is an ideal tool for analyzing dyes on historical textiles because it requires very little sample compared to other available analytical methods and analysis can be done directly on the fiber. This paper reports on the first systematic study of the use of citrate-reduced silver colloidal pastes for the direct, extractionless, non-hydrolysis detection of dyes directly on wool, silk, cotton, and flax fibers. This type of study provides greater insight into the optimal conditions required for accurate analysis of dyes in historical samples.

Immobilized nanorod assemblies: fabrication and understanding of large area surface-enhanced Raman spectroscopy substrates.

We describe the fabrication of optimized plasmonic substrates in the form of immobilized nanorod assemblies (INRA) for surface-enhanced Raman spectroscopy (SERS). Included are high-resolution scanning electron micrograph (SEM) images of the surface structures, along with a mechanistic description of their growth. It is shown that, by varying the size of support microspheres, the surface plasmon resonance is tuned between 330 and 1840 nm.

Structure enhancement factor relationships in single gold nanoantennas by surface-enhanced Raman excitation spectroscopy.

Determining the existence of any direct spectral relationship between the far-field scattering properties and the near-field Raman-enhancing properties of surface-enhanced Raman spectroscopy (SERS) substrates has been a challenging task with only a few significant results to date. Here, we prove that hot spot dominated systems show little dependence on the far-field scattering properties because of differences between near- and far-field localized surface plasmon resonance (LSPR) effects as well as excitation of new plasmon modes via a localized emitter. We directly probe the relationship between the near- and far-field light interactions using a correlated LSPR-transmission electron microscopy (TEM) surface-enhanced Raman excitation spectroscopy (SERES) technique.

Creating, characterizing, and controlling chemistry with SERS hot spots.

In this perspective we discuss the roles of hot spots in surface-enhanced Raman spectroscopy (SERS). After giving background and defining the hot spot, we evaluate a variety of SERS substrates which often contain hot spots. We compare and discuss the differentiating properties of each substrate.

Surface-Enhanced Femtosecond Stimulated Raman Spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) and femtosecond stimulated Raman spectroscopy (FSRS) have revolutionized the Raman spectroscopy field. SERS provides spectroscopic detection of single molecules, and FSRS enables the acquisition of Raman spectra on the ultrafast time scale of molecular motion. Here, we present the first successful combination of these two techniques, demonstrating surface-enhanced femtosecond stimulated Raman spectroscopy (SE-FSRS) using gold nanoantennas with embedded reporter molecules.

Structure-activity relationships in gold nanoparticle dimers and trimers for surface-enhanced Raman spectroscopy.

Understanding the detailed relationship between nanoparticle structure and activity remains a significant challenge for the field of surface-enhanced Raman spectroscopy. To this end, the structural and optical properties of individual plasmonic nanoantennas comprised of Au nanoparticle assemblies that are coated with organic reporter molecules and encapsulated by a SiO(2) shell have been determined using correlated transmission electron microscopy (TEM), dark-field Rayleigh scattering microscopy, surface-enhanced Raman scattering (SERS) microscopy, and finite element method (FEM) calculations. The distribution of SERS enhancement factors (EFs) for a structurally and optically diverse set of nanoantennas is remarkably narrow.

Gold nanoparticle dimer plasmonics: finite element method calculations of the electromagnetic enhancement to surface-enhanced Raman spectroscopy.

Finite element method calculations were carried out to determine extinction spectra and the electromagnetic (EM) contributions to surface-enhanced Raman spectroscopy (SERS) for 90-nm Au nanoparticle dimers modeled after experimental nanotags. The calculations revealed that the EM properties depend significantly on the junction region, specifically the distance between the nanoparticles for spacings of less than 1 nm. For extinction spectra, spacings below 1 nm lead to maxima that are strongly red-shifted from the 600-nm plasmon maximum associated with an isolated nanoparticle.

Ellipsometric identification of collective optical properties of silver nanocrystal arrays.

The optical properties of silver nanocrystal arrays are investigated using spectroscopic ellipsometry in combination with polarized reflection measurements. Analysis of the ellipsometry and reflectometry spectra in terms of the "thin island film" theory enables a transparent identification of the contribution of collective effects to the optical response. Negligible image charge effects imply that only dipole contributions have to be considered.