| 1. |
- Katona, Gergely, 1975, et al.
(författare)
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Bayesian analysis of non-thermal structural changes induced by terahertz radiation in protein crystals
- 2016
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Ingår i: 2016 41ST INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ). - New York : IEEE conference proceedings. - 2162-2027 .- 2162-2035. - 9781467384858
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Konferensbidrag (refereegranskat)abstract
- We have periodically (25ms on - 25ms off) illuminated lysozyme crystals with 0.4 THz radiation and simultaneously monitored their X-ray diffraction intensity in order to study non-thermal structural changes in the protein. In this work we analyze the X-ray scaled and unmerged diffraction intensity observations using a multivariate Bayesian model in order to improve the accuracy of the intensity estimates. The diffraction intensity pairs of the illuminated and non-illuminated state show a predominantly positive correlation. The correlation decreases with increasing resolution suggesting that finer slicing and faster sampling of the rocking curve may further improve the accuracy and effect size of structure factor amplitude differences, making the interpretation of structural changes more straightforward. The improved analysis retains the most important structural features described previously (in helix 3) and provide addition details about the B-factor changes close to the substrate binding site.
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| 2. |
- Lundholm, Ida, 1986, et al.
(författare)
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Terahertz radiation induces non-thermal structural changes associated with Fröhlich condensation in a protein crystal
- 2015
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778 .- 2329-7778. ; 2:5
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Tidskriftsartikel (refereegranskat)abstract
- Whether long-range quantum coherent states could exist in biological systems, and beyond low-temperature regimes where quantum physics is known to be applicable, has been the subject to debate for decades. It was proposed by Fröhlich that vibrational modes within protein molecules can order and condense into a lowest-frequency vibrational mode in a process similar to Bose-Einstein condensation, and thus that macroscopic coherence could potentially be observed in biological systems. Despite the prediction of these so-called Fröhlich condensates almost five decades ago, experimental evidence thereof has been lacking. Here, we present the first experimental observation of Fröhlich condensation in a protein structure. To that end, and to overcome the challenges associated with probing low-frequency molecular vibrations in proteins (which has hampered understanding of their role in proteins’ function), we combined terahertz techniques with a highly sensitive X-ray crystallographic method to visualize low-frequency vibrational modes in the protein structure of hen-egg white lysozyme. We found that 0.4 THz electromagnetic radiation induces non-thermal changes in electron density. In particular, we observed a local increase of electron density in a long a-helix motif consistent with a subtle longitudinal compression of the helix. These observed electron density changes occur at a low absorption rate indicating that thermalization of terahertz photons happens on a micro- to milli-second time scale, which is much slower than the expected nanosecond time scale due to damping of delocalized low frequency vibrations. Our analyses show that the micro- to milli-second life time of the vibration can only be explained by Fröhlich condensation, a phenomenon predicted almost half a century ago, yet never experimentally confirmed.
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| 3. |
- Ahlberg Gagnér, Viktor, 1989, et al.
(författare)
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Clustering of atomic displacement parameters in bovine trypsin reveals a distributed lattice of atoms with shared chemical properties
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Low-frequency vibrations are crucial for protein structure and function, but only a few experimental techniques can shine light on them. The main challenge when addressing protein dynamics in the terahertz domain is the ubiquitous water that exhibit strong absorption. In this paper, we observe the protein atoms directly using X-ray crystallography in bovine trypsin at 100 K while irradiating the crystals with 0.5 THz radiation alternating on and off states. We observed that the anisotropy of atomic displacements increased upon terahertz irradiation. Atomic displacement similarities developed between chemically related atoms and between atoms of the catalytic machinery. This pattern likely arises from delocalized polar vibrational modes rather than delocalized elastic deformations or rigid-body displacements. The displacement correlation between these atoms were detected by a hierarchical clustering method, which can assist the analysis of other ultra-high resolution crystal structures. These experimental and analytical tools provide a detailed description of protein dynamics to complement the structural information from static diffraction experiments. © 2019, The Author(s).
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| 4. |
- Rodilla, Helena, 1982, et al.
(författare)
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Millimeter-wave sensor based on a λ/2-line resonator for identification and dielectric characterization of non-ionic surfactants
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Studies of biological and artificial membrane systems, such as niosomes, currently rely on the use of fluorescent tags, which can influence the system under investigation. For this reason, the development of label-free, non-invasive detection techniques is of great interest. We demonstrate an open volume label-free millimeter-wave sensing platform based on a coplanar waveguide, developed for identification and characterization of niosome constituents. A design based on a λ/2-line resonator was used and on-wafer measurements of transmission and reflection parameters were performed up to 110 GHz. Our sensor was able to clearly distinguish between common niosome constituents, non-ionic surfactants Tween 20 and Span 80, measuring a resonance shift of 3 GHz between them. The complex permittivities of the molecular compounds have been extracted. Our results indicate insignificant frequency dependence in the investigated frequency range (3 GHz – 110 GHz). Values of permittivity around 3.0 + 0.7i and 2.2 + 0.4i were obtained for Tween 20 and Span 80, respectively.
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| 5. |
- Jensen, Maja, 1978, et al.
(författare)
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High-resolution macromolecular crystallography at the FemtoMAX beamline with time-over-threshold photon detection
- 2021
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Ingår i: Journal of Synchrotron Radiation. - 1600-5775 .- 0909-0495. ; 28, s. 64-70
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Tidskriftsartikel (refereegranskat)abstract
- Protein dynamics contribute to protein function on different time scales. Ultrafast X-ray diffraction snapshots can visualize the location and amplitude of atom displacements after perturbation. Since amplitudes of ultrafast motions are small, high-quality X-ray diffraction data is necessary for detection. Diffraction from bovine trypsin crystals using single femtosecond X-ray pulses was recorded at FemtoMAX, which is a versatile beamline of the MAX IV synchrotron. The time-over-threshold detection made it possible that single photons are distinguishable even under short-pulse low-repetition-rate conditions. The diffraction data quality from FemtoMAX beamline enables atomic resolution investigation of protein structures. This evaluation is based on the shape of the Wilson plot, cumulative intensity distribution compared with theoretical distribution, I/σ, Rmerge /Rmeas and CC1/2 statistics versus resolution. The FemtoMAX beamline provides an interesting alternative to X-ray free-electron lasers when studying reversible processes in protein crystals.
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| 6. |
- Jayasankar, Divya, et al.
(författare)
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A 3.5-THz, ×6-Harmonic, Single-Ended Schottky Diode Mixer for Frequency Stabilization of Quantum-Cascade Lasers
- 2021
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - : IEEE Microwave Theory and Techniques Society. - 2156-342X .- 2156-3446. ; 11:6, s. 684-694
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Tidskriftsartikel (refereegranskat)abstract
- Efficient and compact frequency converters are essential for frequency stabilization of terahertz sources. In this article, we present a 3.5-THz, × 6-harmonic, integrated Schottky diode mixer operating at room temperature. The designed frequency converter is based on a single-ended, planar Schottky diode with a submicron anode contact area defined on a suspended 2-μ m ultra-thin gallium arsenide substrate. The dc-grounded anode pad was combined with the radio frequency E-plane probe, which resulted in an electrically compact circuit. At 200-MHz intermediate frequency, a mixer conversion loss of about 59 dB is measured resulting in a 40-dB signal-to-noise ratio for phase locking a 3.5-THz quantum-cascade laser. Using a quasi-static diode model combined with electromagnetic simulations, good agreement with the measured results was obtained. Harmonic frequency converters without the need of cryogenic cooling will help in the realization of highly sensitive space and air-borne heterodyne receivers.
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| 7. |
- Jayasankar, Divya, et al.
(författare)
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Design and development of 3.5 THz Schottky-based fundamental mixer
- 2021
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Ingår i: 2020 50th European Microwave Conference, EuMC 2020. - : Institute of Electrical and Electronics Engineers Inc.. - 9782874870590 ; , s. 595-598
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Konferensbidrag (refereegranskat)abstract
- Broadband Schottky diode mixers operating at room-temperature are crucial for terahertz heterodyne instrumentation in space-borne applications. In this paper, we present the design of a compact 3.5 THz fundamental single-ended Schottky diode mixer. The design is based on Schottky diodes with a sub-micron anode area, defined using nanolithography techniques, and integrated with suspended strip lines on an ultra-thin GaAs-membrane.
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| 8. |
- Jayasankar, Divya, et al.
(författare)
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Investigation of Hydrogel Skin Phantoms Using Terahertz Time-domain Spectroscopy
- 2022
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Ingår i: 2022 52nd European Microwave Conference, EuMC 2022. - : Institute of Electrical and Electronics Engineers Inc.. - 9782874870699 ; , s. 401-403
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Konferensbidrag (refereegranskat)abstract
- Human skin phantoms are essential to enable fast, label-free, and reliable testing of pharmaceutical and cosmetic products. We report the characterisation of polyvinyl alcohol-based hydrogel phantoms along with in-vivo skin measurements of three volunteers from 0.2 to 1 THz. The results indicate that frequency-dependent properties of hydrogel phantoms are similar to human skin and show promising prospects of being utilised as a skin equivalent.
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| 9. |
- Majdi, Saman, 1977-, et al.
(författare)
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Enhanced Hall mobility in graphene-on-electronic-grade diamond
- 2023
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 123:1
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Tidskriftsartikel (refereegranskat)abstract
- The outstanding electronic properties of graphene make this material a candidate for many applications, for instance, ultra-fast transistors. However, self-heating and especially the detrimental influence of available supporting substrates have impeded progress in this field. In this study, we fabricate graphene-diamond heterostructures by transferring graphene to an ultra-pure single-crystalline diamond substrate. Hall-effect measurements were conducted at 80 to 300 K on graphene Hall bars to investigate the charge transport properties in these devices. Enhanced hole mobility of 2750 cm(2) V-1 s(-1) could be observed at room-temperature when using diamond with reduced nitrogen (N-s(0)) impurity concentration. In addition, by electrostatically varying the carrier concentration, an upper limit for mobility is determined in the devices. The results are promising for enabling carbon-carbon (C-C) devices for room-temperature applications.
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| 10. |
- Stenarson, Jörgen, 1972, et al.
(författare)
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Sensitivity Analysis of TRL Calibration in Waveguide Integrated Membrane Circuits
- 2013
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 3:5, s. 558-565
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Tidskriftsartikel (refereegranskat)abstract
- We present a sensitivity analysis on TRL calibrated S-parameter measurements of membrane circuits in the WR-03 waveguide band (220-325 GHz). The impact of waveguide and membrane circuit misalignment, as well as waveguide dimension mismatch is investigated. The analysis is performed for the thru-reflect-line (TRL) calibration applied to E-plane split waveguide blocks carrying membrane circuits. The analysis shows a large influence of the waveguide width tolerance on transmission and reflection phase after the TRL calibration. For a 20 mm long rectangular waveguide with a ± 5 µm width tolerance a phase uncertainty as large as ± 45° for reflection and ± 30° for transmission measurements is observed.
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