Broadband vibrational sum-frequency generation spectrometer at 100 kHz in the 950-1750 cm−1 spectral range utilizing a LiGaS2 optical parametric amplifier

We present a 100 kHz broadband vibrational sum-frequency generation (VSFG) spectrometer operating in the 5.7-10.5 µm (950-1750 cm−1) wavelength range. The mid-infrared beam of the system is obtained from a collinear, type-I LiGaS2-crystal-based optical parametric amplifier seeded by a supercontinuum and pumped directly by 180 fs, ~32 µJ, 1.03 µm pulses from an Yb:KGd(WO4)2 laser system. Up to 0.5 µJ mid-infrared pulses with durations below 100 fs were obtained after dispersion compensation utilizing bulk materials. We demonstrate the utility of the spectrometer by recording high-resolution, low-noise vibrational spectra of Langmuir-Blodgett supported lipid monolayers on CaF2. The presented VSFG spectrometer scheme offers superior signal-to-noise ratios and constitutes a high-efficiency, low-cost, easy-to-use alternative to traditional schemes relying on optical parametric amplification followed by difference frequency generation.Peer Reviewe

Ultrafast all-optical switching using doped chromoprotein films

Next-generation communication networks require > Tbit/s single-channel data transfer and processing with sub-picosecond switches and routers at network nodes. Materials enabling ultrafast all-optical switching have high potential to solve the speed limitations of current optoelectronic circuits. Chromoproteins have been shown to exhibit a fast light-controlled refractive index change much larger than that induced by the optical Kerr effect due to a purely electronic nonlinearity, alleviating the driving energy requirements for optical switching. Here, we report femtosecond transient grating experiments demonstrating the feasibility of < 200-fs all-optical switching by hydrated thin films of photoactive yellow protein, for the first time, and compare the results with those obtained using bacteriorhodopsin. Possibilities for the practical utilization of the scheme in extremely high-speed optical modulation and switching/routing with nominally infinite extinction contrast are discussed.Comment: 12 pages, 3 Schemes, 4 Figures. The following article has been submitted to APL Photonics. After it is published, it will be found at https://aip.scitation.org/journal/ap

Vibrational sum-frequency generation spectroscopy of lipid bilayers at repetition rates up to 100 kHz

Broadband vibrational sum-frequency generation (BB-VSFG) spectroscopy has become a well-established surface analytical tool capable of identifying the orientation and structure of molecular layers. A straightforward way to boost the sensitivity of the technique could be to increase the laser repetition rate beyond that of standard BB-VSFG spectrometers, which rely on Ti:sapphire lasers operating at repetition rates of 1-5 kHz. Nevertheless, possible thermally induced artifacts in the vibrational spectra due to higher laser average powers are unexplored. Here, we discuss laser power induced temperature accumulation effects that distort the BB-VSFG spectra of 1,2-diacyl-sn-glycero-3-phosphocholine at an interface between two transparent phases at repetition rates of 5, 10, 50, and 100 kHz at constant pulse energy. No heat-induced distortions were found in the spectra, suggesting that the increase in the laser repetition rate provides a feasible route to an improved signal-to-noise ratio or shorter data acquisition times in BB-VSFG spectroscopy for thin films on transparent substrates. The results have implications for future BB-VSFG spectrometers pushing the detection limit for molecular layers with low surface coverage

Photoactive Yellow Protein Adsorption at Hydrated Polyethyleneimine and Poly-l-Glutamic Acid Interfaces

This article was supported by the German Research Foundation (DFG) and the Open Access Publication Fund of Humboldt-Universität zu Berlin.Chiral and achiral vibrational sum-frequency generation (VSFG) spectroscopy was performed in the 1400–1700 and 2800–3800 cm−1 range to study the interfacial structure of photoactive yellow protein (PYP) adsorbed on polyethyleneimine (PEI) and poly-l-glutamic acid (PGA) surfaces. Nanometer-thick polyelectrolyte layers served as the substrate for PYP adsorption, with 6.5-pair layers providing the most homogeneous surfaces. When the topmost material was PGA, it acquired a random coil structure with a small number of β2-fibrils. Upon adsorption on oppositely charged surfaces, PYP yielded similar achiral spectra. However, the VSFG signal intensity increased for PGA surfaces with a concomitant redshift of the chiral Cα-H and N–H stretching bands, suggesting increased adsorption for PGA compared to PEI. At low wavenumbers, both the backbone and the side chains of PYP induced drastic changes to all measured chiral and achiral VSFG spectra. Decreasing ambient humidity led to the loss of tertiary structure with a re-orientation of α-helixes, evidenced by a strongly blue-shifted chiral amide I band of the β-sheet structure with a shoulder at 1654 cm−1. Our observations indicate that chiral VSFG spectroscopy is not only capable of determining the main type of secondary structure of PYP, i.e., β-scaffold, but is also sensitive to tertiary protein structure.National Research, Development and Innovation Office, HungaryEotvos Lorand Research NetworkDeutsche ForschungsgemeinschaftGerman Academic Exchange Service (DAAD)Eotvos Hungarian State Scholarship of Tempus Public Foundation funded by the Hungarian GovernmentPeer Reviewe

Dominant immunosuppression of dendritic cell function by prostate-cancer-derived exosomes

Exosomes are a distinct population of extracellular vesicles of endocytic origin with a protein repertoire similar to the parent cell. Although tumour-derived exosomes harbour immunosuppressive characteristics, they also carry tumour antigens and thus potentially contribute to immune activation. The aim of this study was to examine the impact of prostate cancer exosomes on tumour antigen cross-presentation. DU145 cells, transduced with shRNA to knockdown Rab27a (DU145KD) that inhibits exosome secretion, triggered significantly stronger tumour-antigen-specific T cell responses when loaded onto dendritic cells (DC) than control DU145 cells. Enhanced T cell response was prevented by adding purified exogenous DU145 exosomes to DU145KD cells, demonstrating that the dominant effect of tumour exosomes is immunosuppression and not antigen delivery. CD8+ T cell responses were impaired via exosomal regulation of DC function; exosomes triggered the expression of CD73, an ecto-5-nucleotidase responsible for AMP to adenosine hydrolysis, on DC. CD73 induction on DC that constitutively express CD39 resulted in an ATP-dependent inhibition of TNFα- and IL-12-production. We identified exosomal prostaglandin E2 (PGE2) as a potential driver of CD73 induction, as inhibition of PGE2 receptors significantly reduced exosome-dependent CD73 induction. The results reveal a hitherto unknown suppression of DC function via exosomal PGE2, adding a new element to tumour exosome–immune cell cross-talk

Nonlinear Optical Investigation of Microbial Chromoproteins

Membrane-bound or cytosolic light-sensitive proteins, playing a crucial role in energy- and signal-transduction processes of various photosynthetic microorganisms, have been optimized for sensing or harvesting light by myriads of years of evolution. Upon absorption of a photon, they undergo a usually cyclic reaction series of conformations, and the accompanying spectro-kinetic events assign robust nonlinear optical (NLO) properties for these chromoproteins. During recent years, they have attracted a considerable interest among researchers of the applied optics community as well, where finding the appropriate NLO material for a particular application is a pivotal task. Potential applications have emerged in various branches of photonics, including optical information storage and processing, higher-harmonic and white-light continuum generation, or biosensorics. In our earlier work, we also raised the possibility of using chromoproteins, such as bacteriorhodopsin (bR), as building blocks for the active elements of integrated optical (IO) circuits, where several organic and inorganic photonic materials have been considered as active components, but so far none of them has been deemed ideal for the purpose. In the current study, we investigate the linear and NLO properties of biofilms made of photoactive yellow protein (PYP) and bR. The kinetics of the photoreactions are monitored by time-resolved absorption experiments, while the refractive index of the films and its light-induced changes are measured using the Optical Waveguide Lightmode Spectroscopy (OWLS) and Z-scan techniques, respectively. The nonlinear refractive index and the refractive index change of both protein films were determined in the green spectral range in a wide range of intensities and at various laser repetition rates. The nonlinear refractive index and refractive index change of PYP were compared to those of bR, with respect to photonics applications. Our results imply that the NLO properties of these proteins make them promising candidates for utilization in applied photonics, and they should be considered as valid alternatives for active components of IO circuits. © Copyright © 2020 Krekic, Zakar, Gombos, Valkai, Mero, Zimányi, Heiner and Dér

Efficient generation of few-cycle pulses beyond 10 μm from an optical parametric amplifier pumped by a 1-µm laser system

Nonlinear vibrational spectroscopy profits from broadband sources emitting in the molecular fingerprint region. Yet, broadband lasers operating at wavelengths above 7 μm have been lacking, while traditional cascaded parametric frequency down-conversion schemes suffer from exceedingly low conversion efficiencies. Here we present efficient, direct frequency down-conversion of femtosecond 100-kHz, 1.03-μm pulses to the mid-infrared from 7.5 to 13.3 μm in a supercontinuum-seeded, tunable, single-stage optical parametric amplifier based on the wide-bandgap material Cd0.65Hg0.35Ga2S4. The amplifier delivers near transform-limited, few-cycle pulses with an average power > 30 mW at center wavelengths between 8.8 and 10.6 μm, at conversion efficiencies far surpassing that of optical parametric amplification followed by difference-frequency generation or intrapulse difference-frequency generation. The pulse duration at 10.6 μm is 101 fs corresponding to 2.9 optical cycles with a spectral coverage of 760–1160 cm−1. CdxHg1−xGa2S4 is an attractive alternative to LiGaS2 and BaGa4S7 in small-scale, Yb-laser-pumped, few-cycle mid-infrared optical parametric amplifiers and offers a much higher nonlinear figure of merit compared to those materials. Leveraging the inherent spatial variation of composition in CdxHg1−xGa2S4, an approach is proposed to give access to a significant fraction of the molecular fingerprint region using a single crystal at a fixed phase matching angle.Peer Reviewe

Comparison of ESTs from juvenile and adult phases of the giant unicellular green alga Acetabularia acetabulum

BACKGROUND: Acetabularia acetabulum is a giant unicellular green alga whose size and complex life cycle make it an attractive model for understanding morphogenesis and subcellular compartmentalization. The life cycle of this marine unicell is composed of several developmental phases. Juvenile and adult phases are temporally sequential but physiologically and morphologically distinct. To identify genes specific to juvenile and adult phases, we created two subtracted cDNA libraries, one adult-specific and one juvenile-specific, and analyzed 941 randomly chosen ESTs from them. RESULTS: Clustering analysis suggests virtually no overlap between the two libraries. Preliminary expression data also suggests that we were successful at isolating transcripts differentially expressed between the two developmental phases and that many transcripts are specific to one phase or the other. Comparison of our EST sequences against publicly available sequence databases indicates that ESTs from the adult and the juvenile libraries partition into different functional classes. Three conserved sequence elements were common to several of the ESTs and were also found within the genomic sequence of the carbonic anhydrase1 gene from A. acetabulum. To date, these conserved elements are specific to A. acetabulum. CONCLUSIONS: Our data provide strong evidence that adult and juvenile phases in A. acetabulum vary significantly in gene expression. We discuss their possible roles in cell growth and morphogenesis as well as in phase change. We also discuss the potential role of the conserved elements found within the EST sequences in post-transcriptional regulation, particularly mRNA localization and/or stability