Probing temperature- and solvent-dependent protein dynamics using terahertz time-domain spectroscopy

The effect of temperature on the terahertz-frequency-range material properties of lyophilized and single-crystal hen egg-white lysozyme has been measured using terahertz time-domain spectroscopy, with the results presented and discussed in the context of protein and solvent dynamical and glass transitions. Lyophilized hen egg-white lysozyme was measured over a temperature range from 4 to 290 K, and a change in the dynamical behaviour of the sample at around 100 K was observed through a change in the terahertz absorption spectrum. Additionally, the effect of cryoprotectants on the temperature-dependent absorption coefficient is studied, and it is demonstrated that terahertz time-domain spectroscopy is capable of resolving the true glass transition temperature of single-crystal hen egg-white lysozyme at 150 K, which is in agreement with literature values measured using differential scanning calorimetry

On-chip Terahertz Spectroscopy of Liquid Mixtures

We demonstrate 'through-substrate' sensing of fluids for application in the terahertz spectroscopy of biological materials. This technique employs planar Goubau lines with integrated photoconductive material, formed on a flexible, thin polyimide substrate, and bonded to a microfluidic channel. Few-picosecond pulses are used to probe liquid samples confined within the channel, over a total interaction length of 4 mm, overcoming water-absorption limitations of free-space terahertz transmission measurements

Focusing THz radiation in μm-scale waveguides

THz coplanar waveguides were fabricated on quartz wafers with integrated epitaxially transferred low temperature grown gallium arsenide photoconductive switches. THz radiation was excited on-chip and transmitted through a tapering of the coplanar waveguide structure where it was focused down to ~ 1.66μm. Theoretical modelling of the device confirms high E-field confinement and concentration

Accurate Parameter Extraction From Liquids Measured Using On-chip Terahertz Spectroscopy

We introduce a method for estimating the permittivity of liquid samples measured using integrated microfluidic/planar Goubau line terahertz waveguides, in which simulation results are incorporated with measurement data to enable accurate frequency-dependent analysis

THz-TDS of liquids in a temperature-controlled transmission flowcell

Precise temperature-control is necessary for many spectroscopic measurements. We present the temperature-dependent complex THz refractive index of liquid samples measured in a flowcell, analysed by a numerical method that allows simultaneous extraction of the sample's thickness to verify the temperature-stability of the cell

Spatially Resolved On-Chip Picosecond Pulse Detection Using Graphene

We present an on-chip time domain terahertz (TD-THz) system in which picosecond pulses are generated in low-temperature-grown gallium arsenide (LT-GaAs) and detected in graphene. The detected pulses were found to vary in amplitude, full width at half maximum (FWHM), and DC offset when sampled optically at different locations along a 50-μm-long graphene photoconductive (PC) detector. The results demonstrate the importance of detection location and switch design in graphene-based on-chip PC detectors

GMR at THz frequencies in coplanar waveguides

Tapered THz coplanar waveguides (CPWs) formed from Co/Cu multilayers with embedded low-temperature-grown gallium arsenide photoconductive switches were designed in order to observe giant magnetoresistance (GMR). Pulsed THz radiation was excited using the switches, and was transmitted through both straight and tapered CPWs. GMR-induced changes in the transmitted THz pulse amplitude were demonstrated

Free-space terahertz radiation from a LT-GaAs-on-quartz large-area photoconductive emitter

We report on large-area photoconductive terahertz (THz) emitters with a low-temperature-grown GaAs (LT-GaAs) active layer fabricated on quartz substrates using a lift-off transfer process. These devices are compared to the same LT-GaAs emitters when fabricated on the growth substrate. We find that the transferred devices show higher optical-to-THz conversion efficiencies and significantly larger breakdown fields, which we attribute to reduced parasitic current in the substrate. Through these improvements, we demonstrate a factor of ~8 increase in emitted THz field strength at the maximum operating voltage. In addition we find improved performance when these devices are used for photoconductive detection, which we explain through a combination of reduced parasitic substrate currents and reduced space-charge build-up in the device

Investigation into free-space terahertz radiation from a LT-GaAs-on-quartz photoconductive emitter

We report on large-area photoconductive THz emitters and detectors with an LT-GaAs active region fabricated on quartz substrates using a lift-off transfer process. These devices are compared to the same LT-GaAs emitters when fabricated on the growth substrate. We find that the transferred devices show higher optical-to-THz conversion efficiencies and significantly larger breakdown fields

An extracellular steric seeding mechanism for Eph-ephrin signaling platform assembly

Erythropoetin-producing hepatoma (Eph) receptors are cell-surface protein tyrosine kinases mediating cell-cell communication. Upon activation, they form signaling clusters. We report crystal structures of the full ectodomain of human EphA2 (eEphA2) both alone and in complex with the receptor-binding domain of the ligand ephrinA5 (ephrinA5 RBD). Unliganded eEphA2 forms linear arrays of staggered parallel receptors involving two patches of residues conserved across A-class Ephs. eEphA2-ephrinA5 RBD forms a more elaborate assembly, whose interfaces include the same conserved regions on eEphA2, but rearranged to accommodate ephrinA5 RBD. Cell-surface expression of mutant EphA2s showed that these interfaces are critical for localization at cell-cell contacts and activation-dependent degradation. Our results suggest a 'nucleation' mechanism whereby a limited number of ligand-receptor interactions 'seed' an arrangement of receptors which can propagate into extended signaling arrays