Mapping the Inhomogeneity in Plasmonic Catalysis on Supported Gold Nanoparticles Using Surface-Enhanced Raman Scattering Microspectroscopy

The characterization of a catalyst often occurs by averaging over large areas of the catalyst material. On the other hand, optical probing is easily achieved at a resolution at the micrometer scale, specifically in microspectroscopy. Here, using surface-enhanced Raman scattering (SERS) mapping of larger areas with micrometer-sized spots that contain tens to hundreds of supported gold nanoparticles each, the photoinduced dimerization of <i>p</i>-aminothiophenol (PATP) to 4,4′-dimercaptoazobenzene (DMAB) was monitored. The mapping data reveal an inhomogeneous distribution of catalytic activity in the plasmon-catalyzed reaction in spite of a very homogeneous plasmonic enhancement of the optical signals in SERS. The results lead to the conclusion that only a fraction of the nanostructures may be responsible for a high catalytic activity. The high spot-to-spot variation in catalytic activity is also demonstrated for DMAB formation by the plasmon-catalyzed reduction from <i>p</i>-nitrothiophenol (PNTP) and confirms that an improvement of the accuracy and reproducibility in the characterization of catalytic reactions can be achieved by microspectroscopic probing of many positions. Using SERS micromapping during the incubation of PATP, we demonstrate that the reaction occurs during the incubation process and is influenced by different parameters, leading to the conclusion of dimerization in a gold-catalyzed, nonphotochemical reaction as an alternative to the plasmon-catalyzed process. The results have implications for the future characterization of new catalyst materials as well as for optical sensing using plasmonic materials

Surface Enhanced Hyper-Raman Scattering of the Amino Acids Tryptophan, Histidine, Phenylalanine, and Tyrosine

In this work, we report nonresonant surface-enhanced hyper-Raman (SEHRS) spectra of the amino acids tryptophan, histidine, phenylalanine, and tyrosine using silver nanoparticles. The spectra are obtained at an excitation wavelength of 1064 nm and compared to the corresponding surface-enhanced Raman scattering (SERS) spectra measured at 532 nm excitation. The majority of the bands in the SEHRS spectra are assigned. Important hallmarks of the spectra include strongly diminished or absent bands from the ring breathing modes. SEHRS and SERS spectra obtained from histidine and tyrosine indicate changes at slightly varied amino acid concentration. Small changes in the SEHRS spectra were more pronounced than variation in the corresponding SERS data, supporting the high sensitivity of the SEHRS spectra with respect to structural changes due to small variations in surface environment. The possibility to measure nonresonant SEHRS spectra of amino acids in solution and the complementary information obtained from the spectra demonstrates the potential of this method for future investigations of proteins and more complicated biological structures and their interaction with nanostructures

Infrared spectroscopy across scales in length and time at BESSY II

The infrared beamline at BESSY II storage ring was upgraded recently to extend capabilities of infrared microscopy. The end-stations available at the beamline are now facilitating improved characterization of molecules and materials at different length scales and time resolution. We report the current outline of the beamline and give an overview of the end-stations available. In particular, presented here are first results obtained with using a new microscope for nano-spectroscopy that was implemented. We demonstrate the capabilities of the scattering-type near-field optical microscope (s-SNOM) by investigation of cellulose microfibrils, representing nanoscopic objects of a hierarchical structure. It is shown that the s-SNOM coupled to the beamline allows to perform imaging with spatial resolution less than 30 nm and to collect infrared spectra from effective volume of less than 30x30x12 $nm^3$. Potential steps for a further optimization of the beamline performance are discussed

Surface-Enhanced Hyper-Raman Spectra of Adenine, Guanine, Cytosine, Thymine, and Uracil

Using picosecond excitation at 1064 nm, surface-enhanced hyper-Raman scattering (SEHRS) spectra of the nucleobases adenine, guanine, cytosine, thymine, and uracil with two different types of silver nanoparticles were obtained. Comparing the SEHRS spectra with SERS data from the identical samples excited at 532 nm and with known infrared spectra, the major bands in the spectra are assigned. Due to the different selection rules for the one- and two-photon excited Raman scattering, we observe strong variation in relative signal strengths of many molecular vibrations obtained in SEHRS and SERS spectra. The two-photon excited spectra of the nucleobases are found to be very sensitive with respect to molecule–nanoparticle interactions. Using both the SEHRS and SERS data, a comprehensive vibrational characterization of the interaction of nucleobases with silver nanostructures can be achieved

samples

List of the pollen sample

wavenumbers

FTIR wavenumbers for spectral dat

README

Main info on dat

Near-Infrared-Emitting Nanoparticles for Lifetime-Based Multiplexed Analysis and Imaging of Living Cells

The increase in information content from bioassays and bioimaging requires robust and efficient strategies for the detection of multiple analytes or targets in a single measurement, thereby addressing current health and security concerns. For fluorescence techniques, an attractive alternative to commonly performed spectral or color multiplexing presents lifetime multiplexing and the discrimination between different fluorophores based on their fluorescence decay kinetics. This strategy relies on fluorescent labels with sufficiently different lifetimes that are excitable at the same wavelength and detectable within the same spectral window. Here, we report on lifetime multiplexing and discrimination with a set of nanometer-sized particles loaded with near-infrared emissive organic fluorophores chosen to display very similar absorption and emission spectra, yet different fluorescence decay kinetics in suspension. Furthermore, as a first proof-of-concept, we describe bioimaging studies with 3T3 fibroblasts and J774 macrophages, incubated with mixtures of these reporters employing fluorescence lifetime imaging microscopy. These proof-of-concept measurements underline the potential of fluorescent nanoparticle reporters in fluorescence lifetime multiplexing, barcoding, and imaging for cellular studies, cell-based assays, and molecular imaging

ZHTS

FTIR spectra (Absorbance values) of pollen sample

Specific Interaction of Tricyclic Antidepressants with Gold and Silver Nanostructures as Revealed by Combined One- and Two-Photon Vibrational Spectroscopy

We report two-photon excited nonresonant surface-enhanced hyper Raman scattering (SEHRS) spectra of tricyclic antidepressant (TCA) molecules during their interaction with biocompatible gold nanostructures and with silver nanostructures. The SEHRS spectra of amitriptyline, desipramine, and imipramine are compared with surface-enhanced Raman scattering (SERS) spectra on both kinds of nanoparticles, obtained with excitation at 532 and 785 nm. The SEHRS spectra of the TCA molecules show several intense contributions by infrared-active vibrations. Combining SEHRS with SERS therefore enables a comprehensive vibrational characterization of the interaction of the molecules with the nanostructures. SEHRS and SERS data indicate that the molecules interact with the silver nanostructures mainly via their ring moiety. In contrast, in the interaction with gold, the methylaminopropyl side chain plays a very important role, along with parts of the ring system. It is possible to obtain the spectra of the molecules with near-infrared excitation and with gold nanoparticles in cell culture media. The spectral signatures of the drug molecules collected at low pH values characteristic of late endosomal stages or of acidified tissues are very stable and show only small changes in the interaction of the TCA with the gold nanoparticles. The results will help to develop tools for the characterization of new nanoparticle-based drug delivery platforms in real biological environments