Max Schütz

SERS Labels for Red Laser Excitation: Silica‐Encapsulated SAMs on Tunable Gold/Silver Nanoshells

In a glass house: Silica-encapsulated self-assembled monolayers (SAMs) on tunable gold/silver nanoshells were used as labels for surface-enhanced Raman scattering (SERS). This concept combines the spectroscopic advantages arising from maximum surface coverage and uniform molecular orientation of the Raman reporter molecules within the complete monolayer together with the high chemical and mechanical stability of the glass shell.

Fast and Cost-Effective Purification of Gold Nanoparticles in the 20–250 nm Size Range by Continuous Density Gradient Centrifugation

A multilayer quasi-continuous density gradient centrifugation method for separating 20-250 nm metal colloids with high size resolution while maintaining particle stability is presented. Colloidal mixtures containing monodisperse gold nanospheres and clusters thereof, in particular, gold dimers, are purified with yields up to 94%. The rapid method uses standard laboratory equipment.

3D self-assembled plasmonic superstructures of gold nanospheres: synthesis and characterization at the single-particle level.

The synthesis of 3D self-assembled plasmonic superstructures of gold nanospheres as well as the characterization of their structural and optical properties at the single-particle level is presented. This experimental work is complemented by FEM (finite element method) simulations of elastic scattering spectra and the spatial |E|(4) distribution for establishing structure-activity correlations in these complex 3D nanoclusters.

Synthesis of glass-coated SERS nanoparticle probes via SAMs with terminal SiO2 precursors.

Surface-enhanced Raman scattering (SERS) combines the benefits of vibrational Raman scattering with highest sensitivity, using nanostructures that can support localized plasmon resonances. [1‐4] The main application of SERS is the label-free detection of analytes. [5‐8] An alternative and more recent approach uses SERS as a readout method in bioanalytical applications: the selective detection of proteins and oligonucleotides is achieved by employing target-specific SERS nanoparticle probes. [7‐11] The central motivation for this strategy is the option to detect numerous target molecules within a single measurement (multiplexing). The basis of spectral multiplexing in SERS arises from the small linewidth of vibrational Raman bands compared with the significantly broader emission profiles of molecular fluorophores. [12,13] Further important advantages are quantification of target concentration and the extreme sensitivity of SERS, in particular SERRS (surface-enhanced resonance Raman scattering). [14,15] Additionally, the simultaneous excitation of spectrally distinct SERS nanoparticle probes requires only a single laser wavelength. Different designs for nanoparticle-based SERS probes (SERSlabels,SERSnanotags)areavailable,whichdifferinthe plasmonic nanostructure, the Raman reporter molecule, and the optional protective shell. [9,16‐18] Using a self-assembled monolayer(SAM)ofRamanreportermoleculesonthesurface of the nanoparticle has several advantages. [18‐22] Firstly,

Immuno-surface-enhanced coherent anti-stokes Raman scattering microscopy: immunohistochemistry with target-specific metallic nanoprobes and nonlinear Raman microscopy.

Immunohistochemistry (IHC) is one of the most widely used staining techniques for diagnostic purposes. The selective localization of target proteins in tissue specimens by conventional IHC is achieved with dye- or enzyme-labeled antibodies in combination with light microscopy. In this contribution, we demonstrate the proof-of-principle for IHC based on surface-enhanced coherent Raman scattering for contrast generation. Specifically, antibody-labeled metallic nanoshells in conjunction with surface-enhanced coherent anti-Stokes Raman scattering (SECARS) microscopy are employed for the selective, sensitive, and rapid localization of the basal cell protein p63 in normal prostate tissue. Negative control experiments were performed in order to confirm the selective binding of the target-specific metal nanoprobes and to disentangle the role of plasmonic (metal) and molecular (Raman reporter) resonances in this plasmon-assisted four-wave mixing technique.

Femtogram detection of cytokines in a direct dot-blot assay using SERS microspectroscopy and hydrophilically stabilized Au–Ag nanoshells

Rapid parallel detection of two cytokines (IL-6 and IL-8) with femtogram sensitivity in a simple direct dot-blot assay is demonstrated. The microspectroscopic SERS acquisition scheme employs rationally designed, hydrophilically stabilized Au-Ag nanoshells as SERS labels, which are optimized for signal enhancement upon red laser excitation.

Microspectroscopic SERS detection of interleukin-6 with rationally designed gold/silver nanoshells

Rationally designed gold/silver nanoshells (Au/Ag-NS) with plasmon resonances optimized for red laser excitation in order to minimize autofluorescence from clinical samples exhibit scattering cross-sections, which are ca. one order of magnitude larger compared with solid quasi-spherical gold nanoparticles (Au-NPs) of the same size. Hydrophilic stabilization and sterical accessibility for subsequent bioconjugation of Au/Ag-NS is achieved by coating their surface with a self-assembled monolayer (SAM) of rationally designed Raman reporter molecules comprising terminal mono- and tri-ethylene glycol (EG) spacers, respectively. The stability of the hydrophilically stabilized metal colloid was tested under different conditions. In contrast to metal colloids coated with a SAM without terminal EG spacers, the hydrophilically stabilized SERS particles do not aggregate under physiologically relevant conditions, i.e., buffer solutions with high ionic strength. Using these rationally designed SERS particles in conjunction with a microspectroscopic acquisition scheme, a sandwich immunoassay for the sensitive detection of interleukin-6 (IL-6) was developed. Several control experiments demonstrate the high specificity of the assay towards IL-6, with a lowest detectable concentration of ca. 1 pg mL(-1). The signal strength of the Au/Ag-NS is at least one order of magnitude higher compared with hydrophilically stabilized, non-aggregated solid quasi-spherical Au-NPs of the same size.

Design and synthesis of Raman reporter molecules for tissue imaging by immuno-SERS microscopy

The design and synthesis of Raman reporter molecules comprising olefin or alkyne moieties with strong and characteristic vibrational Raman bands is presented. Chemisorption onto the surface of colloidal Au/Ag shells yields a self-assembled monolayer. Hydrophilic stabilization of such SERS labels can be achieved by short terminal ethylene glycol units attached to the Raman reporter. Encapsulation by silica with subsequent functionalization of the glass surface allows the conjugation to biomolecules such as antibodies. We demonstrate the use of SERS-labeled antibodies for tissue imaging of the tumor suppressor p63 in prostate biopsies.

Direct Silica Encapsulation of Self‐Assembled‐Monolayer‐Based Surface‐Enhanced Raman Scattering Labels with Complete Surface Coverage of Raman Reporters by Noncovalently Bound Silane Precursors

Silica-coated surface-enhanced Raman scattering (SERS) labels with a self-assembled monolayer (SAM) on the entire surface of the metal colloid combine high chemical and mechanical stability with bright and reproducible Raman signals due to the complete surface coverage and uniform molecular orientation within the SAM. Currently available chemical syntheses are either based on the direct encapsulation of covalently bound silane precursors or comprise several steps, such as the sequential addition of noncovalently bound polyelectrolytes to render the surface vitreophilic. Here, a generic approach for the direct and fast silica encapsulation of commercially available Raman reporter molecules with polar head groups by noncovalently bound silane precursors is reported. The formation of highly SERS-active silica-coated clusters during silica encapsulation is determined by several parameters, in particular the type of Raman reporter molecule, the solvent, and the type and amount of the silane precursor.

SERS microscopy: plasmonic nanoparticle probes and biomedical applications

Nanoparticle probes for use in targeted detection schemes and readout by surface-enhanced Raman scattering (SERS) comprise a metal core, Raman reporter molecules and a protective shell. One design of SERS labels specifically optimized for biomedical applications in conjunction with red laser excitation is based on tunable gold/silver nanoshells, which are completely covered by a self-assembled monolayer (SAM) of Raman reporters. A shell around the SAM-coated metal core stabilizes the colloid and prevents particle aggregation. The optical properties and SERS efficiencies of these plasmonic nanostructures are characterized both experimentally and theoretically. Subsequent bioconjugation of SERS probes to ligands such as antibodies is a prerequisite for the selective detection of the corresponding target molecule via the characteristic Raman signature of the label. Biomedical imaging applications of SERS-labeled antibodies for tumor diagnostics by SERS microscopy are presented, using the localization of the tumor suppressor p63 in prostate tissue sections as an example.