Photonic application of proteins

The currently faced biggest challenge in integrated optics (IO) is finding or developing materials that can be used as active components for optical circuits. In order for a material to be considered for IO applications, it has to possess optimal non-linear optical (NLO) properties, such as a large light-induced refractive index change, but also mechanical stability. In my thesis, I investigated the photoactive yellow protein (PYP) with various experimental methods to assess the protein’s IO applicability. During the measurements, a glycerol-doped (GL) PYP film was used to maintain high mechanical stability and optical homogeneity of the investigated PYP-films. First, the kinetics of certain photocycle intermediates of PYP were monitored with absorption kinetics measurements to find the optimal environment to use the protein films in. This was followed by measuring the linear and non-linear refractive index of GL-PYP films. The NLO refractive index was investigated with the Z-scan technique as a function of excitation laser pulse parameters, i.e., average and peak intensities, and repetition rate of the pulses. For investigating the potential miniaturization and the possibility of creating homogeneous protein monolayers for further IO applications, PYP films were monitored with vibrational sum-frequency spectroscopy (VSFG). Finally, IO switching was demonstrated utilizing different photocycle intermediates. Mach- Zehnder interferometer was used for slow, while transient grating spectroscopy was applied to perform sub-ps optical switching. Based on the results, GL-PYP films are viable alternatives as IO active materials

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

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

All-Optical Switching Demonstrated with Photoactive Yellow Protein Films

Integrated optics (IO) is a field of photonics which focuses on manufacturing circuits similar to those in integrated electronics, but that work on an optical basis to establish means of faster data transfer and processing. Currently, the biggest task in IO is finding or manufacturing materials with the proper nonlinear optical characteristics to implement as active components in IO circuits. Using biological materials in IO has recently been proposed, the first material to be investigated for this purpose being the protein bacteriorhodopsin; however, since then, other proteins have also been considered, such as the photoactive yellow protein (PYP). In our current work, we directly demonstrate the all-optical switching capabilities of PYP films combined with an IO Mach-Zehnder interferometer (MZI) for the first time. By exploiting photoreactions in the reaction cycle of PYP, we also show how a combination of exciting light beams can introduce an extra degree of freedom to control the operation of the device. Based on our results, we discuss how the special advantages of PYP can be utilized in future IO applications

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

Spectrokinetic characterization of photoactive yellow protein films for integrated optical applications

In this paper, the photocycle of the dried photoactive yellow protein film has been investigated in different humidity environments, in order to characterize its nonlinear optical properties for possible integrated optical applications. The light-induced spectral changes of the protein films were monitored by an optical multichannel analyser set-up, while the accompanying refractive index changes were measured with the optical waveguide lightmode spectroscopy method. To determine the number and kinetics of spectral intermediates in the photocycle, the absorption kinetic data were analysed by singular value decomposition and multiexponential fitting methods, whose results were used in a subsequent step of fitting a photocycle model to the data. The absorption signals of the films were found to be in strong correlation with the measured light-induced refractive index changes, whose size and kinetics imply that photoactive yellow protein may be a good alternative for utilization as an active nonlinear optical material in future integrated optical applications. © 2019, The Author(s)

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

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

The interaction of chondroitin sulfate with a lipid monolayer observed by using nonlinear vibrational spectroscopy

The first vibrational sum-frequency generation (VSFG) spectra of chondroitin sulfate (CS) interacting with dipalmitoyl phosphatidylcholine (DPPC) at air-liquid interface are reported here, collected at a laser repetition rate of 100 kHz. By studying the VSFG spectra in the regions of 1050-1450 cm(-1), 2750-3180 cm(-1), and 3200-3825 cm(-1), it was concluded that in the presence of Ca2+ ions, the head groups together with the head-group-bound water molecules in the DPPC monolayer are strongly influenced by the interaction with CS, while the organization of the phospholipid tails remains mostly unchanged. The interactions were observed at a CS concentration below 200 nM, which exemplifies the potential of VSFG in studying biomolecular interactions at low physiological concentrations. The VSFG spectra recorded in the O-H stretching region at chiral polarization combination imply that CS molecules are organized into ordered macromolecular superstructures with a chiral secondary structure

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.Peer Reviewe

Photoactive yellow protein adsorption at hydrated polyethyleneimine and poly-L-glutamic acid interfaces

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 ß2-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 C-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 a-helixes, evidenced by a strongly blue-shifted chiral amide I band of the ß-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., ß-scaffold, but is also sensitive to tertiary protein structure