Showing papers by "Sebastian Schlücker published in 2016"

Roadmap on biosensing and photonics with advanced nano-optical methods

Abstract: This roadmap, through the contributions of ten groups worldwide, contains different techniques, methods and materials devoted to sensing in nanomedicine. Optics is used in different ways in the detection schemes. Raman, fluorescence and infrared spectroscopies, plasmonics, second harmonic generation and optical tweezers are all used in applications from single molecule detection (both in highly diluted and in highly concentrated solutions) to single cell manipulation. In general, each optical scheme, through device miniaturization and electromagnetic field localization, exploits an intrinsic optical enhancement mechanism in order to increase the sensitivity and selectivity of the device with respect to the complex molecular construct. The materials used for detection include nanoparticles and nanostructures fabricated with different 2D and 3D lithographic methods. It is shown that sensitivity to a single molecule is already accessible whether the system under study is a single cell or a multitude of cells in a molecular mixture. Throughout the roadm

Metal Nanoparticle-Catalyzed Reduction Using Borohydride in Aqueous Media: A Kinetic Analysis of the Surface Reaction by Microfluidic SERS

Abstract: Hydrides are widely used in reduction reactions. In protic solvents, their hydrolysis generates molecular hydrogen as a second reducing agent. The competition between these two parallel reduction pathways has been overlooked so far since both typically yield the same product. We investigated the platinum-catalyzed reduction of 4-nitrothiophenol to 4-aminothiophenol in aqueous sodium borohydride solution as a prominent model reaction, by using label-free SERS monitoring in a microfluidic reactor. Kinetic analysis revealed a strong pH dependence. Surprisingly, only at pH>13 the reduction is driven exclusively by sodium borohydride. This study demonstrates the potential of microfluidics-based kinetic SERS monitoring of heterogeneous catalysis in colloidal suspension.

Towards quantitative multi‐color nanodiagnostics: spectral multiplexing with six silica‐encapsulated SERS labels

Abstract: Quantitative multiplexing experiments using mixtures of up to six spectrally distinct surface-enhanced Raman scattering (SERS) nanoparticle labels are demonstrated. The SERS labels comprise gold nanoparticles, Raman reporter molecules chemisorbed onto the metal surface, and a silica shell providing chemical and mechanical stability as well as spectral reproducibility. Spectral unmixing is performed with a simple least-square algorithm because the overall SERS signal of the mixtures can be represented as a linear combination of the known spectral signatures from the individual silica-protected labels. In contrast, simple spectral unmixing using unprotected SERS particles, i.e. without a silica shell, was not successful because of band shifts and alternating peak heights in the mixtures, which is indicative of perturbing interactions between the SERS labels. Copyright © 2016 John Wiley & Sons, Ltd.

Label-free SERS monitoring of hydride reduction catalyzed by Au nanostars

Abstract: Surface-enhanced Raman scattering (SERS) is a promising molecular spectroscopic technique to study chemical reactions catalyzed by nobel metal nanoparticles. Herein, the Au nanostar (NS)-catalyzed hydride reduction of 4-nitrothiophenol to 4-aminothiophenol chemisorbed at the metal/solution interface was followed by SERS. By developing a simple two-step route, we demonstrated shape-controlled synthesis and morphology-dependent catalytic activity of AuNSs. The kinetic SERS monitoring of the reaction on the Au surface indicates that the catalytic activity of the AuNSs correlates with the sharpness of their tips. This is consistent with the known size-dependent catalytic activity of small AuNPs. In contrast to the complex bifunctional nanostructures reported previously, this work shows that AuNSs are bifunctional nanostructures suitable for investigating Au-catalyzed reactions. A proposed electron transfer mechanism explains the reduction of 4-nitrothiophenol to 4-aminothiophenol on AuNS tips where –NO2 groups have no direct contact with the catalyst. Copyright © 2016 John Wiley & Sons, Ltd.

iSERS microscopy guided by wide field immunofluorescence: analysis of HER2 expression on normal and breast cancer FFPE tissue sections.

Abstract: Surface-enhanced Raman scattering (SERS) microscopy is an emerging imaging technique for tissue-based cancer diagnostics. Specifically, immuno-SERS (iSERS) microscopy employs antibodies labelled by molecularly functionalized noble metal colloids for antigen localization on tissue specimen. Spectrally resolved iSERS acquisition schemes are typically rather time-consuming when large tissue areas must be scanned. Here, we demonstrate the application of iSERS imaging guided by wide field immunofluorescence (IF) for localization of the human epidermal growth factor receptor 2 (HER2) on breast tissue sections. The addition of unlabelled anti-HER2 primary antibodies to the tissue is followed by the incubation with secondary antibodies labelled with both Alexa-647 (for IF) and hydrophilically stabilized gold nanostars coated with aromatic thiols (for iSERS). False-color iSERS images clearly reveal the different HER2 expression levels on normal and breast cancer tissue, respectively. A series of negative controls confirms that the binding specificity of the secondary antibody is maintained after conjugation to the SERS nanoparticles.

Plasmonic Hot Electron Transport Driven Site-Specific Surface-Chemistry with Nanoscale Spatial Resolution

Abstract: Nanoscale localization of electromagnetic fields near metallic nanostructures underpins the fundamentals and applications of plasmonics. The unavoidable energy loss from plasmon decay, initially seen as a detriment, has now expanded the scope of plasmonic applications to exploit the generated hot carriers. However, quantitative understanding of the spatial localization of these hot carriers, akin to electromagnetic near-field maps, has been elusive. Here we spatially map hot-electron-driven reduction chemistry with 15 nanometre resolution as a function of time and electromagnetic field polarization for different plasmonic nanostructures. We combine experiments employing a six-electron photo-recycling process that modify the terminal group of a self-assembled monolayer on plasmonic silver nanoantennas, with theoretical predictions from first-principles calculations of non-equilibrium hot-carrier transport in these systems. The resulting localization of reactive regions, determined by hot carrier transport from high-field regions, paves the way for hot-carrier extraction science and nanoscale regio-selective surface chemistry.