Publications by authors named "Volker Deckert"

92 Publications

Supramolecular Reorientation During Deposition Onto Metal Surfaces of Quasi-Two-Dimensional Langmuir Monolayers Composed of Bifunctional Amphiphilic, Twisted Perylenes.

Langmuir 2021 Sep 10. Epub 2021 Sep 10.

Leibniz Institute of Photonic Technology (Leibniz-IPHT), Albert-Einstein-Str. 9, 07745 Jena, Germany.

Supramolecular dye structures, which are often ruled by π-π interactions between planar chromophores, crucially determine the optoelectronic properties of layers and interfaces. Here, we present the interfacial assembly of perylene monoanhydride and monoimide that do not feature a planar chromophore but contain chlorine substituents in the bay positions to yield twisted chromophores and hence modified π-stacking. The assembly of the twisted perylene monoanhydride and monoimide is driven by their amphiphilicity that ensures proper Langmuir layer formation. The shielding of the hydrophilic segment upon attaching an alkyl chain to the imide moiety yielded a more rigid Langmuir layer, even though the degrees of freedom were increased due to this modification. For the characterization of the Langmuir layer's supramolecular structure, the layers were deposited onto glass, silver, and gold substrates via Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques and were investigated with atomic force microscopy and surface-enhanced resonance Raman spectroscopy (SERRS). From the similarity between all SERR spectra of the LS and LB layers, we concluded that the perylenes have changed their orientation upon LB deposition to bind to the silver surface of the SERRS substrate via sulfur atoms. In the Langmuir layer, the perylenes, which are π-stacked with half of the twisted chromophores, must already be inclined and cannot achieve full parallel alignment because of the twisting-induced steric hindrance. However, upon rotation, the energetically most favorable antiparallel aligned structures can be formed and bind to the SERRS substrate. Thus, we present, to the best of our knowledge, the first fabrication of quasi-two-dimensional films from twisted amphiphilic perylene monoimides and their reassembly during LB deposition. The relation between the molecular structure, supramolecular interfacial assembly, and its adoption during adsorption revealed here is crucial for the fabrication of defined functionalizations of metal surfaces, which is key to the development of organic (opto)electronic devices.
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http://dx.doi.org/10.1021/acs.langmuir.1c01525DOI Listing
September 2021

Unveiling the interaction of protein fibrils with gold nanoparticles by plasmon enhanced nano-spectroscopy.

Nanoscale 2021 Sep 2;13(34):14469-14479. Epub 2021 Sep 2.

Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Str. 9, 07745 Jena, Germany.

The development of various degenerative diseases is suggested to be triggered by the uncontrolled organisation and aggregation of proteins into amyloid fibrils. For this reason, there are ongoing efforts to develop novel agents and approaches, including metal nanoparticle-based colloids, that dissolve amyloid structures and prevent pathogenic protein aggregation. In this contribution, the role of gold nanoparticles (AuNPs) in degrading amyloid fibrils of the model protein lysozyme is investigated. The amino acid composition of fibril surfaces before and after the incubation with AuNPs is determined at the single fibril level by exploiting the high spatial resolution and sensitivity provided by tip-enhanced and surface-enhanced Raman spectroscopies. This combined spectroscopic approach allows to reveal the molecular mechanisms driving the interaction between fibrils and AuNPs. Our results provide an important input for the understanding of amyloid fibrils and could have a potential translational impact on the development of strategies for the prevention and treatment of amyloid-related diseases.
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http://dx.doi.org/10.1039/d1nr03190bDOI Listing
September 2021

pH-dependent disintegration of insulin amyloid fibrils monitored with atomic force microscopy and surface-enhanced Raman spectroscopy.

Spectrochim Acta A Mol Biomol Spectrosc 2021 Jul 8;256:119672. Epub 2021 Mar 8.

Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Str. 9, 07745 Jena, Germany; Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich-Schiller-University Jena, Helmholtzweg 4, 07743 Jena, Germany; Institute of Quantum Science and Engineering, Texas A&M University, College Station, TX 77843-4242, USA. Electronic address:

Aggregation of insulin into amyloid fibrils is characterized by the conversion of the native secondary structure of the peptide into an enriched ß-sheet conformation. In vitro, the growth or disintegration of amyloid fibrils can be influenced by various external factors such as pH, temperature etc. While current studies mainly focus on the influence of environmental conditions on the growth process of insulin fibrils, the present study investigates the effect of pH changes on the morphology and secondary structure of mature fibrils. In the experiments, insulin is fibrillated at pH 2.5 and the grown mature fibrils are suspended in pH 4-7 solutions. The obtained structures are analyzed by atomic force microscopy (AFM) and surface-enhanced Raman spectroscopy (SERS). Initially grown mature fibrils from pH 2.5 solutions show a long and intertwined morphology. Increasing the solution pH initiates the gradual disintegration of the filamentous morphology into unordered aggregates. These observations are supported by SERS experiments, where the spectra of the mature fibrils show mainly a β-pleated sheet conformation, while the amide I band region of the amorphous aggregates indicate exclusively α-helix/unordered structures. The results demonstrate that no complex reagent is required for the disintegration of insulin fibrils. Simply regulating the pH of the environment induces local changes in the protonation state within the peptide chains. This effectively disrupts the well-ordered β-sheet structure network based on hydrogen bonds.
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http://dx.doi.org/10.1016/j.saa.2021.119672DOI Listing
July 2021

The impact of episporic modification of on virulence and interaction with phagocytes.

Comput Struct Biotechnol J 2021 20;19:880-896. Epub 2021 Jan 20.

Leibniz Institute for Natural Product Research and Infection Biology - Hans Knöll Institute (HKI), Jena, Germany.

Fungal infections caused by the ancient lineage Mucorales are emerging and increasingly reported in humans. Comprehensive surveys on promising attributes from a multitude of possible virulence factors are limited and so far, focused on and . This study addresses a systematic approach to monitor phagocytosis after physical and enzymatic modification of the outer spore wall of , one of the major causative agents of mucormycosis. Episporic modifications were performed and their consequences on phagocytosis, intracellular survival and virulence by murine alveolar macrophages and in an invertebrate infection model were elucidated. While depletion of lipids did not affect the phagocytosis of both strains, delipidation led to attenuation of LCA strain but appears to be dispensable for infection with LCV strain in the settings used in this study. Combined glucano-proteolytic treatment was necessary to achieve a significant decrease of virulence of the LCV strain in during maintenance of the full potential for spore germination as shown by a novel automated germination assay. Proteolytic and glucanolytic treatments largely increased phagocytosis compared to alive resting and swollen spores. Whilst resting spores barely (1-2%) fuse to lysosomes after invagination in to phagosomes, spore trypsinization led to a 10-fold increase of phagolysosomal fusion as measured by intracellular acidification. This is the first report of a polyphasic measurement of the consequences of episporic modification of a mucormycotic pathogen in spore germination, spore surface ultrastructure, phagocytosis, stimulation of Toll-like receptors (TLRs), phagolysosomal fusion and intracellular acidification, apoptosis, generation of reactive oxygen species (ROS) and virulence.
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http://dx.doi.org/10.1016/j.csbj.2021.01.023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7851798PMC
January 2021

Laser spectroscopic technique for direct identification of a single virus I: FASTER CARS.

Proc Natl Acad Sci U S A 2020 11 22;117(45):27820-27824. Epub 2020 Oct 22.

Institute for Quantum Science and Engineering, Texas A&M University, College Station, TX 77843;

From the famous 1918 H1N1 influenza to the present COVID-19 pandemic, the need for improved viral detection techniques is all too apparent. The aim of the present paper is to show that identification of individual virus particles in clinical sample materials quickly and reliably is near at hand. First of all, our team has developed techniques for identification of virions based on a modular atomic force microscopy (AFM). Furthermore, femtosecond adaptive spectroscopic techniques with enhanced resolution via coherent anti-Stokes Raman scattering (FASTER CARS) using tip-enhanced techniques markedly improves the sensitivity [M. O. Scully, , 99, 10994-11001 (2002)].
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http://dx.doi.org/10.1073/pnas.2013169117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7668096PMC
November 2020

Enhancing sensitivity of lateral flow assay with application to SARS-CoV-2.

Appl Phys Lett 2020 Sep;117(12):120601

Texas A&M University, College Station, Texas 77843, USA.

Lateral flow assay (LFA) has long been used as a biomarker detection technique. It has advantages such as low cost, rapid readout, portability, and ease of use. However, its qualitative readout process and lack of sensitivity are limiting factors. We report a photon-counting approach to accurately quantify LFAs while enhancing sensitivity. In particular, we demonstrate that the density of SARS-CoV-2 antibodies can be quantified and measured with an enhanced sensitivity using this simple laser optical analysis.
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http://dx.doi.org/10.1063/5.0021842DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7518548PMC
September 2020

Surface characterization of nanoscale co-crystals enabled through tip enhanced Raman spectroscopy.

Nanoscale 2020 May;12(18):10306-10319

Nanomatériaux pour les Systèmes Sous Sollicitations Extrêmes (NS3E), ISL-CNRS-UNISTRA UMR 3208, French-German Research Institute of Saint-Louis, 5, rue du Général Cassagnou, B.P. 70034, 68301 Saint-Louis, France.

Atomic Force Microscopy coupled with Tip Enhanced Raman Spectroscopy (AFM-TERS) was applied to obtain information about the structure and surface composition of single nano co-crystals. For this purpose, a co-crystalline system consisting of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo-[5.5.0.03,11.05,9]-dodecane (CL-20) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) in a molar ratio of 2 : 1 (CL-20/HMX) was chosen. CL-20/HMX nano-plates were prepared by spray flash evaporation. To ensure co-crystallinity and nanostructures, powder X-ray diffraction and AFM investigations were performed. The results demonstrate that coherence lengths and particle dimensions are on a similar level though coherence lengths appear shorter than measured particle dimensions. According to this fact, defects inside the nano co-crystals are minimized. The co-crystallinity was additionally proven by confocal Raman spectroscopy. Here, marker bands for pristine CL-20 and HMX were chosen which appear in the CL-20/HMX spectrum in an intensity ratio of ∼2.5 : 1 (CL-20 : HMX). Afterwards surface investigations of single CL-20/HMX nano-plates were performed by AFM-TERS. Due to the surface sensitivity of TERS, these experiments reveal that the ratio of the Raman intensities between CL-20 and HMX inverts at CL-20/HMX nano-plate surfaces. Therefore, it is concluded that nano co-crystal surfaces consist of molecular layers of HMX. A theoretical approximation of the normal coordinates of the investigated marker vibrations supports this conclusion since it can exclude the occurrence of the intensity ratio inversion because of the given orientation between CL-20/HMX nano-plates and the Raman scattering system. Based on this finding, an impact ignition mechanism is proposed, enabling explanation of the close impact sensitivity values of β-HMX and CL-20/HMX.
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http://dx.doi.org/10.1039/d0nr00397bDOI Listing
May 2020

Multimodal Characterization of Resin Embedded and Sliced Polymer Nanoparticles by Means of Tip-Enhanced Raman Spectroscopy and Force-Distance Curve Based Atomic Force Microscopy.

Small 2020 04 29;16(17):e1907418. Epub 2020 Mar 29.

Leibniz Institute of Photonic Technologies (IPHT) Jena, Albert-Einsteinstraße 9, 07745, Jena, Germany.

Understanding the property-function relation of nanoparticles in various application fields involves determining their physicochemical properties, which is still a remaining challenge to date. While a multitude of different characterization tools can be applied, these methods by themselves can only provide an incomplete picture. Therefore, novel analytical techniques are required, which can address both chemical functionality and provide structural information at the same time with high spatial resolution. This is possible by using tip-enhanced Raman spectroscopy (TERS), but due to its limited depth information, TERS is usually restricted to investigations of the nanoparticle surface. Here, TERS experiments are established on polystyrene nanoparticles (PS NPs) after resin embedding and microtome slicing. With that, unique access to their internal morphological features is gained, and thus, enables differentiation between information obtained for core- and shell-regions. Complementary information is obtained by means of transmission electron microscopy (TEM) and from force-distance curve based atomic force microscopy (FD-AFM). This multimodal approach achieves a high degree of discrimination between the resin and the polymers used for nanoparticle formulation. The high potential of TERS combined with advanced AFM spectroscopy tools to probe the mechanical properties is applied for quality control of the resin embedding procedure.
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http://dx.doi.org/10.1002/smll.201907418DOI Listing
April 2020

Direct molecular-level near-field plasmon and temperature assessment in a single plasmonic hotspot.

Light Sci Appl 2020 9;9:35. Epub 2020 Mar 9.

1Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Strasse 9, D-07745 Jena, Germany.

Tip-enhanced Raman spectroscopy (TERS) is currently widely recognized as an essential but still emergent technique for exploring the nanoscale. However, our lack of comprehension of crucial parameters still limits its potential as a user-friendly analytical tool. The tip's surface plasmon resonance, heating due to near-field temperature rise, and spatial resolution are undoubtedly three challenging experimental parameters to unravel. However, they are also the most fundamentally relevant parameters to explore, because they ultimately influence the state of the investigated molecule and consequently the probed signal. Here we propose a straightforward and purely experimental method to access quantitative information of the plasmon resonance and near-field temperature experienced exclusively by the molecules directly contributing to the TERS signal. The detailed near-field optical response, both at the molecular level and as a function of time, is evaluated using standard TERS experimental equipment by simultaneously probing the Stokes and anti-Stokes spectral intensities. Self-assembled 16-mercaptohexadodecanoic acid monolayers covalently bond to an ultra-flat gold surface were used as a demonstrator. Observation of blinking lines in the spectra also provides crucial information on the lateral resolution and indication of atomic-scale thermally induced morphological changes of the tip during the experiment. This study provides access to unprecedented molecular-level information on physical parameters that crucially affect experiments under TERS conditions. The study thereby improves the usability of TERS in day-to-day operation. The obtained information is of central importance for any experimental plasmonic investigation and for the application of TERS in the field of nanoscale thermometry.
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http://dx.doi.org/10.1038/s41377-020-0260-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7061098PMC
March 2020

The chemical effect goes resonant - a full quantum mechanical approach on TERS.

Nanoscale 2020 Mar 5;12(11):6346-6359. Epub 2020 Mar 5.

Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany.

Lately, experimental evidence of unexpectedly extremely high spatial resolution of tip-enhanced Raman scattering (TERS) has been demonstrated. Theoretically, two different contributions are discussed: an electromagnetic effect, leading to a spatially confined near field due to plasmonic excitations; and the so-called chemical effect originating from the locally modified electronic structure of the molecule due to the close proximity of the plasmonic system. Most of the theoretical efforts have concentrated on the electromagnetic contribution or the chemical effect in case of non-resonant excitation. In this work, we present a fully quantum mechanical description including non-resonant and resonant chemical contributions as well as charge-transfer phenomena of these molecular-plasmonic hybrid systems at the density functional and the time-dependent density functional level of theory. We consider a surface-immobilized tin(ii) phthalocyanine molecule as the molecular system, which is minutely scanned by a plasmonic tip, modeled by a single silver atom. These different relative positions of the Ag atom to the molecule lead to pronounced alterations of the Raman spectra. These Raman spectra vary substantially, both in peak positions and several orders of magnitude in the intensity patterns under non-resonant and resonant conditions, and also, depending on, which electronic states are addressed. Our computational approach reveals that unique - non-resonant and resonant - chemical interactions among the tip and the molecule significantly alter the TERS spectra and are mainly responsible for the high, possibly sub-Angstrom spatial resolution.
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http://dx.doi.org/10.1039/c9nr09814cDOI Listing
March 2020

Plasmon induced deprotonation of 2-mercaptopyridine.

Analyst 2020 Mar 4;145(6):2106-2110. Epub 2020 Feb 4.

Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, 07745 Jena, Germany.

Surface plasmons can provide a novel route to induce and simultaneously monitor selective bond formation and breakage. Here pH-induced protonation, followed by plasmon-induced deprotonation of 2-mercaptopyridine was investigated using surface- and tip-enhanced Raman scattering (SERS and TERS). A large difference in the deprotonation rate between SERS and TERS will be demonstrated and discussed with respect to hot-spot distribution.
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http://dx.doi.org/10.1039/c9an01970gDOI Listing
March 2020

Present and Future of Surface-Enhanced Raman Scattering.

ACS Nano 2020 01 8;14(1):28-117. Epub 2019 Oct 8.

Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371 , Singapore.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.
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http://dx.doi.org/10.1021/acsnano.9b04224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6990571PMC
January 2020

Organic acids, siderophores, enzymes and mechanical pressure for black slate bioweathering with the basidiomycete Schizophyllum commune.

Environ Microbiol 2020 04 31;22(4):1535-1546. Epub 2019 Jul 31.

Friedrich Schiller University, Institute of Microbiology, Microbial Communication, Neugasse 25, D-07743, Jena, Germany.

Although many fungi are known to be able to perform bioweathering of rocks and minerals, little information is available concerning the role of basidiomycetes in this process. The wood-rotting basidiomycete Schizophyllum commune was investigated for its ability to degrade black slate, a rock rich in organic carbon. Mechanical pressure of hyphae and extracellular polymeric substances was investigated for biophysical weathering. A mixed ß1-3/ß1-6 glucan, likely schizophyllan that is well known from S. commune, could be identified on black slate surfaces. Secretion of siderophores and organic acids as biochemical weathering agents was shown. Both may contribute to biochemical weathering in addition to enzymatic functions. Previously, the exoenzyme laccase was believed to attack organic the matter within the black slate, thereby releasing metals from the rock. Here, overexpression of laccase showed enhanced dissolution of quartz phases by etching and pitting. At the same time, the formation of a new secondary mineral phase, whewellite, could be demonstrated. Hence, a more comprehensive understanding of biophysical as well as biochemical weathering by S. commune could be reached and unexpected mechanisms like quartz dissolution linked to shale degradation.
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http://dx.doi.org/10.1111/1462-2920.14749DOI Listing
April 2020

Tip-Enhanced Raman Imaging of Single-Stranded DNA with Single Base Resolution.

J Am Chem Soc 2019 01 31;141(2):753-757. Epub 2018 Dec 31.

Texas A&M University , College Station , Texas 77843 , United States.

Tip-enhanced Raman scattering (TERS) is a promising optical and analytical technique for chemical imaging and sensing at single molecule resolution. In particular, TERS signals generated by a gap-mode configuration where a silver tip is coupled with a gold substrate can resolve a single-stranded DNA (ssDNA) molecule with a spatial resolution below 1 nm. To demonstrate the proof of subnanometer resolution, we show direct nucleic acid sequencing using TERS of a phage ssDNA (M13mp18). M13mp18 provides a known sequence and, through our deposition strategy, can be stretched (uncoiled) and attached to the substrate by its phosphate groups, while exposing its nucleobases to the tip. After deposition, we scan the silver tip along the ssDNA and collect TERS signals with a step of 0.5 nm, comparable to the bond length between two adjacent DNA bases. By demonstrating the real-time profiling of a ssDNA configuration and furthermore, with unique TERS signals of monomeric units of other biopolymers, we anticipate that this technique can be extended to the high-resolution imaging of various nanostructures as well as the direct sequencing of other important biopolymers including RNA, polysaccharides, and polypeptides.
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http://dx.doi.org/10.1021/jacs.8b11506DOI Listing
January 2019

Uptake of fatty acids by a single endothelial cell investigated by Raman spectroscopy supported by AFM.

Analyst 2018 Feb;143(4):970-980

Jagiellonian Centre for Experimental Therapeutics (JCET), Jagiellonian University, Bobrzynskiego 14, 30-348 Krakow, Poland.

In this work, confocal Raman imaging was used to study the formation of lipid droplets (LDs) in vitro in a single endothelial cell upon incubation with polyunsaturated fatty acids (10 or 25 μM) including arachidonic acid (AA) and its deuterated analog (AA-d), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Based on the Raman spectra obtained from a single endothelial cell, it was possible to investigate biochemical changes induced by addition of polyunsaturated fatty acids. In particular, the content of lipids in the formed LDs and the unsaturation degree were identified by Raman spectroscopy by marker bands at 1660 cm due to the C[double bond, length as m-dash]C stretching and at ∼3015 cm due to the stretching mode of [double bond, length as m-dash]C-H associated with C[double bond, length as m-dash]C double bonds (except for a deuterated form where these bands are shifted respectively). To establish if the exogenous fatty acid was taken up by the cell and stored in LDs, a deuterium labelled polyunsaturated fatty acid was used. AA-d shows characteristic bands at around 2200-2300 cm assigned to the [double bond, length as m-dash]C-D stretching modes. We established the uptake of AA and the accumulation of EPA into newly formed LDs in the endothelial cells. In contrast, no accumulation of DHA in LDs was observed even though LDs were formed upon DHA incubation. Furthermore, using AFM we demonstrated that the presence of LDs in the endothelium affected endothelial stiffness which could have pathophysiological significance. In summary, the results suggest that the formation of LDs in the endothelium involves exogenous and endogenous polyunsaturated fatty acids, and their relative contribution to the LD formation seems distinct for AA, EPA and DHA.
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http://dx.doi.org/10.1039/c7an01043eDOI Listing
February 2018

Protein Handshake on the Nanoscale: How Albumin and Hemoglobin Self-Assemble into Nanohybrid Fibers.

ACS Nano 2018 02 12;12(2):1211-1219. Epub 2018 Jan 12.

Chair of Materials Science (CMS), Otto Schott Institute of Materials Research, Faculty of Physics and Astronomy, Friedrich Schiller University Jena , Löbdergraben 32, 07743 Jena, Germany.

Creating and establishing proof of hybrid protein nanofibers (hPNFs), i.e., PNFs that contain more than one protein, is a currently unsolved challenge in bioinspired materials science. Such hPNFs could serve as universal building blocks for the bottom-up preparation of functional materials with bespoke properties. Here, inspired by the protein assemblies occurring in nature, we introduce hPNFs created via a facile self-assembly route and composed of human serum albumin (HSA) and human hemoglobin (HGB) proteins. Our circular dichroism results shed light on the mechanism of the proteins' self-assembly into hybrid nanofibers, which is driven by electrostatic/hydrophobic interactions between similar amino acid sequences (protein handshake) exposed to ethanol-triggered protein denaturation. Based on nanoscale characterization with tip-enhanced Raman spectroscopy (TERS) and immunogold labeling, our results demonstrate the existence and heterogenic nature of the hPNFs and reveal the high HSA/HGB composition ratio, which is attributed to the fast self-assembling kinetics of HSA. The self-assembled hPNFs with a high aspect ratio of over 100 can potentially serve as biocompatible units to create larger bioactive structures, devices, and sensors.
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http://dx.doi.org/10.1021/acsnano.7b07196DOI Listing
February 2018

On the Control of Chromophore Orientation, Supramolecular Structure, and Thermodynamic Stability of an Amphiphilic Pyridyl-Thiazol upon Lateral Compression and Spacer Length Variation.

ACS Appl Mater Interfaces 2017 Dec 11;9(50):44181-44191. Epub 2017 Dec 11.

Institute of Physical Chemistry, Friedrich Schiller University Jena , Helmholtzweg 4, 07743 Jena, Germany.

The supramolecular structure essentially determines the properties of organic thin films. Therefore, it is of utmost importance to understand the influence of molecular structure modifications on supramolecular structure formation. In this article, we demonstrate how to tune molecular orientations of amphiphilic 4-hydroxy thiazole derivatives by means of the Langmuir-Blodgett (LB) technique and how this depends on the length of an alkylic spacer between the thiazole chromophore and the polar anchor group. Therefore, we characterize their corresponding supramolecular structures, thermodynamic, absorption, and fluorescence properties. Particularly, the polarization-dependence of the fluorescence is analyzed to deduce molecular orientations and their possible changes after annealing, i.e., to characterize the thermodynamic stability of the individual solid state phases. Because the investigated thiazoles are amphiphilic, the different solid state phases can be formed and be controlled by means of the Langmuir-Blodgett (LB) technique. This technique also allows to deduce atomistic supramolecular structure motives of the individual solid phases and to characterize their thermodynamic stabilities. Utilizing the LB technique, we demonstrate that subtle molecular changes, like the variation in spacer length, can yield entirely different solid state phases with distinct supramolecular structures and properties.
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http://dx.doi.org/10.1021/acsami.7b13042DOI Listing
December 2017

Plasmon induced polymerization using a TERS approach: a platform for nanostructured 2D/1D material production.

Faraday Discuss 2017 12;205:213-226

Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, 07745 Jena, Germany.

Plasmon-induced chemical reactions have recently attracted great attention as a promising method for high efficiency light-energy conversion and proved to be useful in a wealth of different domains of chemistry and physics. One of the interesting and, so far, less explored avenues of such reactions is their potential for efficient, highly localized and controlled polymer production. Here, we present the first example of a localized, directed plasmon catalyzed polymerization process of a self-assembled monolayer on both silver and gold surfaces monitored by surface- and tip-enhanced Raman spectroscopy (SERS and TERS). As a proof-of-concept, a bi-functionalized dibenzo(1,2)dithiine-3,8-diamine (D3ATP) molecule that undergoes a well-known plasmon-induced coupling via the amino group into an azo group has been used. Initial dimerization is demonstrated using established marker bands associated with the formation of the azo group. A subsequent indicator for a polymerization reaction, the appearance of a new characteristic band, is monitored by time-dependent SERS and TERS experiments. We demonstrate that the dimerization reaction and hence, the subsequent polymerization, can be induced by a plasmonic feature, e.g. a TERS tip, at specific nanoscale locations and, at a much larger micron scale, by continuously scanning the plasmonic probe. The presented results provide the basis for designing further plasmonic catalysis experiments in general, and offer a new platform for producing ultra-thin polymer films with a defined structural dimension.
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http://dx.doi.org/10.1039/c7fd00157fDOI Listing
December 2017

Tip-enhanced Raman scattering for tracking of invasomes in the stratum corneum.

Biochim Biophys Acta Gen Subj 2017 Nov 6;1861(11 Pt A):2630-2639. Epub 2017 Jul 6.

Institute of Physical Chemistry and Abbe Center of Photonics, University of Jena, Helmholtzweg 4, 07743 Jena, Germany; Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, 07745 Jena, Germany. Electronic address:

Stratum corneum is the primary skin barrier to percutaneous absorption. Since 1980, topical liposomal formulations have been proposed and successfully employed for increasing the drug penetration through the skin. There is no clear consensus on the drug penetration mechanism from topically applied liposomes, despite a vast amount of research. One of the reasons for the ambiguity is that the interactions between the stratum corneum and liposomes are in nanoscale, which makes them difficult to probe. In this study, we employed tip-enhanced Raman scattering (TERS) to gain a better understanding of the interactions between the human stratum corneum and topically applied liposomal system called invasomes. TERS is capable of imaging at nanometer spatial resolution and can provide structural information at the nanometer scale. A sample preparation technique was developed and calibrated to enable TERS on complex stratum corneum samples. Invasomes prepared from a head deuterated phospholipid were employed to aid identification of topically applied liposomal phospholipid in the stratum corneum. Results presented in this study give for the first time a strong spectroscopic evidence along with high-resolution images to show intact invasome vesicles deep in the stratum corneum upon topical application.
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http://dx.doi.org/10.1016/j.bbagen.2017.07.003DOI Listing
November 2017

Mastering high resolution tip-enhanced Raman spectroscopy: towards a shift of perception.

Chem Soc Rev 2017 Jul;46(13):3922-3944

Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Straße 9, D-07745 Jena, Germany.

Recent years have seen tremendous improvement of our understanding of high resolution reachable in TERS experiments, forcing us to re-evaluate our understanding of the intrinsic limits of this field, but also exposing several inconsistencies. On the one hand, more and more recent experimental results have provided us with clear indications of spatial resolutions down to a few nanometres or even on the subnanometre scale. Moreover, lessons learned from recent theoretical investigations clearly support such high resolutions, and vice versa the obvious theoretical impossibility to evade high resolution from a purely plasmonic point of view. On the other hand, most of the published TERS results still, to date, claim a resolution on the order of tens of nanometres that would be somehow limited by the tip apex, a statement well accepted for the past 2 decades. Overall, this now leads the field to a fundamental question: how can this divergence be justified? The answer to this question brings up an equally critical one: how can this gap be bridged? This review aims at raising a fundamental discussion related to the resolution limits of tip-enhanced Raman spectroscopy, at revisiting our comprehension of the factors limiting it both from a theoretical and an experimental point of view and at providing indications on how to move the field ahead. It is our belief that a much deeper understanding of the real accessible lateral resolution in TERS and the practical factors that limit them will simultaneously help us to fully explore the potential of this technique for studying nanoscale features in organic, inorganic and biological systems, and also to improve both the reproducibility and the accuracy of routine TERS studies. A significant improvement of our comprehension of the accessible resolution in TERS is thus critical for a broad audience, even in certain contexts where high resolution TERS is not the desired outcome.
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http://dx.doi.org/10.1039/c7cs00203cDOI Listing
July 2017

Tip-enhanced Raman spectroscopy - from early developments to recent advances.

Chem Soc Rev 2017 Jul;46(13):4077-4110

Leibniz Institute of Photonic Technology, Jena, Germany.

An analytical technique operating at the nanoscale must be flexible regarding variable experimental conditions while ideally also being highly specific, extremely sensitive, and spatially confined. In this respect, tip-enhanced Raman scattering (TERS) has been demonstrated to be ideally suited to, e.g., elucidating chemical reaction mechanisms, determining the distribution of components and identifying and localizing specific molecular structures at the nanometre scale. TERS combines the specificity of Raman spectroscopy with the high spatial resolution of scanning probe microscopies by utilizing plasmonic nanostructures to confine the incident electromagnetic field and increase it by many orders of magnitude. Consequently, molecular structure information in the optical near field that is inaccessible to other optical microscopy methods can be obtained. In this general review, the development of this still-young technique, from early experiments to recent achievements concerning inorganic, organic, and biological materials, is addressed. Accordingly, the technical developments necessary for stable and reliable AFM- and STM-based TERS experiments, together with the specific properties of the instruments under different conditions, are reviewed. The review also highlights selected experiments illustrating the capabilities of this emerging technique, the number of users of which has steadily increased since its inception in 2000. Finally, an assessment of the frontiers and new concepts of TERS, which aim towards rendering it a general and widely applicable technique that combines the highest possible lateral resolution and extreme sensitivity, is provided.
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http://dx.doi.org/10.1039/c7cs00209bDOI Listing
July 2017

High resolution spectroscopy reveals fibrillation inhibition pathways of insulin.

Sci Rep 2016 12 23;6:39622. Epub 2016 Dec 23.

Leibniz Institute of Photonic Technology (IPHT), Albert-Einsteinstr. 9, D-07745 Jena, Germany.

Fibril formation implies the conversion of a protein's native secondary structure and is associated with several neurodegenerative diseases. A better understanding of fibrillation inhibition and fibril dissection requires nanoscale molecular characterization of amyloid structures involved. Tip-enhanced Raman scattering (TERS) has already been used to chemically analyze amyloid fibrils on a sub-protein unit basis. Here, TERS in combination with atomic force microscopy (AFM), and conventional Raman spectroscopy characterizes insulin assemblies generated during inhibition and dissection experiments in the presence of benzonitrile, dimethylsulfoxide, quercetin, and β-carotene. The AFM topography indicates formation of filamentous or bead-like insulin self-assemblies. Information on the secondary structure of bulk samples and of single aggregates is obtained from standard Raman and TERS measurements. In particular the high spatial resolution of TERS reveals the surface conformations associated with the specific agents. The insulin aggregates formed under different inhibition and dissection conditions can show a similar morphology but differ in their β-sheet structure content. This suggests different aggregation pathways where the prevention of the β-sheet stacking of the peptide chains plays a major role. The presented approach is not limited to amyloid-related reasearch but can be readily applied to systems requiring extremely surface-sensitive characterization without the need of labels.
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http://dx.doi.org/10.1038/srep39622DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5180225PMC
December 2016

High-resolution Raman Spectroscopy for the Nanostructural Characterization of Explosive Nanodiamond Precursors.

Chemphyschem 2017 Jan 27;18(2):175-178. Epub 2016 Dec 27.

Leibniz Institute of Photonic Technology (IPHT), Albert-Einsteinstr. 9, 07745, Jena, Germany.

The specific attributes of nanodiamonds have attracted increasing interest for electronics or biomedical applications. An efficient synthetic route towards nanodiamonds is via detonation of hexolite (i.e. a mixture of TNT [2,4,6-trinitrotoluene] and RDX [1,3,5-trinitro-1,3,5-triazine]). In particular, detonation of hexolite crystallized by spray flash evaporation (SFE) yields extremely small diamonds (<4 nm). To unravel the detonation mechanism, a structural characterization of the explosives is required but is challenging due to their thermal instability. We demonstrate a combination of conventional Raman spectroscopy and tip-enhanced Raman spectroscopy (TERS) for resolving morphological and structural differences of differently prepared hexolite nanocomposites. The experiments allow for the first time a structural differentiation of individual TNT and RDX crystals and 15-20 nm sized core-shell structures, consequently providing a general approach to investigate the actual composition of mixtures on the nanometer scale.
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http://dx.doi.org/10.1002/cphc.201601276DOI Listing
January 2017

Secondary Structure and Glycosylation of Mucus Glycoproteins by Raman Spectroscopies.

Anal Chem 2016 12 11;88(23):11609-11615. Epub 2016 Nov 11.

Wellcome Trust Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester , Manchester M13 9PL, United Kingdom.

The major structural components of protective mucus hydrogels on mucosal surfaces are the secreted polymeric gel-forming mucins. The very high molecular weight and extensive O-glycosylation of gel-forming mucins, which are key to their viscoelastic properties, create problems when studying mucins using conventional biochemical/structural techniques. Thus, key structural information, such as the secondary structure of the various mucin subdomains, and glycosylation patterns along individual molecules, remains to be elucidated. Here, we utilized Raman spectroscopy, Raman optical activity (ROA), circular dichroism (CD), and tip-enhanced Raman spectroscopy (TERS) to study the structure of the secreted polymeric gel-forming mucin MUC5B. ROA indicated that the protein backbone of MUC5B is dominated by unordered conformation, which was found to originate from the heavily glycosylated central mucin domain by isolation of MUC5B O-glycan-rich regions. In sharp contrast, recombinant proteins of the N-terminal region of MUC5B (D1-D2-D'-D3 domains, NT5B), C-terminal region of MUC5B (D4-B-C-CK domains, CT5B) and the Cys-domain (within the central mucin domain of MUC5B) were found to be dominated by the β-sheet. Using these findings, we employed TERS, which combines the chemical specificity of Raman spectroscopy with the spatial resolution of atomic force microscopy to study the secondary structure along 90 nm of an individual MUC5B molecule. Interestingly, the molecule was found to contain a large amount of α-helix/unordered structures and many signatures of glycosylation, pointing to a highly O-glycosylated region on the mucin.
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http://dx.doi.org/10.1021/acs.analchem.6b03095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5218386PMC
December 2016

Spatially resolved spectroscopic differentiation of hydrophilic and hydrophobic domains on individual insulin amyloid fibrils.

Sci Rep 2016 09 21;6:33575. Epub 2016 Sep 21.

Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Str. 9, 07745 Jena, Germany.

The formation of insoluble β-sheet-rich protein structures known as amyloid fibrils is associated with numerous neurodegenerative diseases, such as Alzheimer's and Parkinson's disease. A detailed understanding of the molecular structure of the fibril surface is of interest as the first contact with the physiological environment in vivo and plays a decisive role in biological activity and associated toxicity. Recent studies reveal that the inherent sensitivity and specificity of tip-enhanced Raman scattering (TERS) renders this technique a compelling method for fibril surface analysis at the single-particle level. Here, the reproducibility of TERS is demonstrated, indicating its relevance for detecting molecular variations. Consequently, individual fibrils are systematically investigated at nanometer spatial resolution. Spectral parameters were obtained by band-fitting, particularly focusing on the identification of the secondary structure via the amide III band and the differentiation of hydrophobic and hydrophilic domains on the surface. In addition multivariate data analysis, specifically the N-FINDR procedure, was employed to generate structure-specific maps. The ability of TERS to localize specific structural domains on fibril surfaces shows promise to the development of new fibril dissection strategies and can be generally applied to any (bio)chemical surface when structural variations at the nanometer level are of interest.
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http://dx.doi.org/10.1038/srep33575DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5030623PMC
September 2016

Tip-Enhanced Raman Spectroscopy of Atmospherically Relevant Aerosol Nanoparticles.

Anal Chem 2016 10 21;88(19):9766-9772. Epub 2016 Sep 21.

Institute of Chemical Technologies and Analytics, TU Wien , Getreidemarkt 9, 1060 Vienna, Austria.

Atmospheric aerosol nanoparticles play a major role in many atmospheric processes and in particular in the global climate system. Understanding their formation by homogeneous or heterogeneous nucleation as well as their photochemical aging and atmospheric transformation is of utmost importance to evaluate their impact on atmospheric phenomena. Single particle analysis like tip-enhanced Raman spectroscopy (TERS) opens access to a deeper understanding of these nanoparticles. Atmospherically relevant nanoparticles, formed above a simulated salt lake inside an aerosol smog-chamber, were analyzed using TERS. TERS spectra of 11 nanoparticles were studied in detail. First results of TERS on atmospherically relevant aerosol nanoparticles reveal the presence of inorganic seed particles, a chemical diversity of equally sized particles in the nucleation mode, and chemical transformation during photochemical aging. Therefore, single particle analysis by optical near-field spectroscopy such as TERS of atmospheric nanoparticles will significantly contribute to elucidate atmospheric nucleation, photochemical aging, and chemical transformation processes by uncovering single particle based properties.
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http://dx.doi.org/10.1021/acs.analchem.6b02760DOI Listing
October 2016

Multimodal Spectroscopic Study of Amyloid Fibril Polymorphism.

J Phys Chem B 2016 09 17;120(34):8809-17. Epub 2016 Aug 17.

FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.

Amyloid fibrils are a large class of self-assembled protein aggregates that are formed from unstructured peptides and unfolded proteins. The fibrils are characterized by a universal β-sheet core stabilized by hydrogen bonds, but the molecular structure of the peptide subunits exposed on the fibril surface is variable. Here we show that multimodal spectroscopy using a range of bulk- and surface-sensitive techniques provides a powerful way to dissect variations in the molecular structure of polymorphic amyloid fibrils. As a model system, we use fibrils formed by the milk protein β-lactoglobulin, whose morphology can be tuned by varying the protein concentration during formation. We investigate the differences in the molecular structure and composition between long, straight fibrils versus short, wormlike fibrils. We show using mass spectrometry that the peptide composition of the two fibril types is similar. The overall molecular structure of the fibrils probed with various bulk-sensitive spectroscopic techniques shows a dominant contribution of the β-sheet core but no difference in structure between straight and wormlike fibrils. However, when probing specifically the surface of the fibrils with nanometer resolution using tip-enhanced Raman spectroscopy (TERS), we find that both fibril types exhibit a heterogeneous surface structure with mainly unordered or α-helical structures and that the surface of long, straight fibrils contains markedly more β-sheet structure than the surface of short, wormlike fibrils. This finding is consistent with previous surface-specific vibrational sum-frequency generation (VSFG) spectroscopic results ( VandenAkker et al. J. Am. Chem. Soc. , 2011 , 133 , 18030 - 18033 , DOI: 10.1021/ja206513r ). In conclusion, only advanced vibrational spectroscopic techniques sensitive to surface structure such as TERS and VSFG are able to reveal the difference in structure that underlies the distinct morphology and rigidity of different amyloid fibril polymorphs that have been observed for a large range of food and disease-related proteins.
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http://dx.doi.org/10.1021/acs.jpcb.6b05339DOI Listing
September 2016
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