ORCID Profile
0000-0003-1679-5410
Current Organisation
University of Leeds
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Publisher: American Chemical Society (ACS)
Date: 20-07-2017
DOI: 10.1021/ACS.ANALCHEM.7B01235
Abstract: Terahertz-frequency-range measurements can offer potential insight into the picosecond dynamics, and therefore function, of many chemical systems. There is a need to develop technologies capable of performing such measurements in aqueous and polar environments, particularly when it is necessary to maintain the full functionality of biological s les. In this study, we present a proof-of-concept technology comprising an on-chip planar Goubau line, integrated with a microfluidic channel, which is capable of low-loss, terahertz-frequency-range spectroscopic measurements of liquids. We also introduce a mathematical model that accounts for changes in the electric field distribution around the waveguide, allowing accurate, frequency-dependent liquid parameters to be extracted. We demonstrate the sensitivity of this technique by measuring a homologous alcohol series across the 0.1-0.8 THz frequency range.
Publisher: AIP Publishing
Date: 17-05-2005
DOI: 10.1063/1.1938255
Abstract: We report the operation of band-stop filters in the terahertz (THz) frequency range, working at a center frequency of 600GHz. The filters were characterized by embedding them in a microstrip line attached to photoconductive switches which act as THz emitters and detectors. The filters have applications in sensing and detection. The chosen filter design allows cascading of several filters along the same microstrip line, which is of particular importance for a proposed molecular sensing array.
Publisher: International Union of Crystallography (IUCr)
Date: 14-12-2010
DOI: 10.1107/S0021889810043372
Abstract: The application of terahertz time-domain spectroscopy and imaging to the study of proteins in crystalline form is demonstrated. Terahertz time-domain spectroscopy is particularly sensitive to the long-range ordering of molecules, with proven utility for the spectroscopy of crystalline biological small molecules. Here, the terahertz time-domain absorption response of a macromolecular protein single crystal is investigated for the first time. In particular, the effect of dehydration on the terahertz absorption coefficient of tetragonal hen egg white lysozyme crystals is reported.
Publisher: IEEE
Date: 09-2009
Publisher: AIP Publishing
Date: 03-04-2006
DOI: 10.1063/1.2191423
Abstract: We report on measurements of the excitation, propagation, and detection of picosecond duration electrical pulses at cryogenic (∼4K) temperatures in a microstrip circuit. A reduction is observed in the measured excitation and propagating pulse widths at low temperatures, compared with room temperature. The results indicate both that the electrical properties of low-temperature-grown GaAs make it suitable for photoconductive excitation and detection in cryogenic optoelectric circuits and that an organic polymer is a good transmissive medium for terahertz (THZ) frequency range excitations at low temperatures. This work will prove an invaluable starting point for future guided wave terahertz experiments at cryogenic temperatures.
Publisher: AIP Publishing
Date: 31-08-2009
DOI: 10.1063/1.3216579
Abstract: We have measured the picosecond time-domain response of Goubau-line waveguides, formed on quartz substrates, by integrating regions of low-temperature-grown gallium arsenide into the waveguides to act both as pulsed current emitters and detectors. Using one pair of photoconductive switches for excitation and a second pair for detection, pulsed signal propagation of a low dispersion electric field mode was demonstrated in the Goubau-lines, with the signal bandwidth extending beyond 800 GHz. Furthermore, it was demonstrated that terahertz bandstop filters can be integrated into a Goubau-line for removal of specific frequencies from the transmitted pulses.
Publisher: AIP Publishing
Date: 08-2013
DOI: 10.1063/1.4816736
Abstract: We present the self-aligned fabrication of on-chip devices in which waveguides, incorporating integrated photoconductive switches, are combined with two-dimensional electron systems to allow probing of the ultrafast (terahertz frequency range) properties of confined semiconductor systems, both at cryogenic temperatures and in high magnetic fields. We demonstrate the direct injection of on-chip terahertz pulses into the mesoscopic system by femtosecond, near infra-red laser excitation of in-plane photoconductive switches formed on an epitaxially grown, low-temperature GaAs layer, which is integrated monolithically with a GaAs/AlGaAs heterostructure containing a two-dimensional electron system. Both the input and output terahertz signals of an on-chip waveguide are s led by altering dynamically the photoconductive excitation/detection arrangement in situ on a single device. We also demonstrate a new method for sub-Kelvin excitation and detection of on-chip terahertz frequency radiation in a 3He/4He dilution refrigerator that allows the photocurrent and detected terahertz transient to be mapped as function of the near-infrared excitation position at the emitter and the detector, respectively. Furthermore, we demonstrate transmission of terahertz transients through a two-dimensional electron system in a coplanar waveguide under magnetic field at temperatures as low as 200 mK.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3LC50485A
Abstract: We investigate the effect of substrate thickness on the transmission bandwidth of on-chip terahertz-frequency-range planar Goubau lines both experimentally and theoretically. The bandwidth and frequency resolution are improved through substrate thinning and geometry modifications (reducing reflections arising from the THz photoconductive generators and detectors). We demonstrate that the enhanced bandwidth (2 THz) and resolution (3.75 GHz) allows this type of on-chip waveguide to be used for spectroscopic measurements of polycrystalline materials from cryogenic (4 K) to room temperature (292 K) by recording vibrational absorption spectra from overlaid s les of lactose monohydrate.
Publisher: IEEE
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 02-02-2017
DOI: 10.1038/SREP41872
Abstract: The ability to isolate specific, viable cell populations from mixed ensembles with minimal manipulation and within intra-operative time would provide significant advantages for autologous, cell-based therapies in regenerative medicine. Current cell-enrichment technologies are either slow, lack specificity and/or require labelling. Thus a rapid, label-free separation technology that does not affect cell functionality, viability or phenotype is highly desirable. Here, we demonstrate separation of viable from non-viable human stromal cells using remote dielectrophoresis, in which an electric field is coupled into a microfluidic channel using shear-horizontal surface acoustic waves, producing an array of virtual electrodes within the channel. This allows high-throughput dielectrophoretic cell separation in high conductivity, physiological-like fluids, overcoming the limitations of conventional dielectrophoresis. We demonstrate viable/non-viable separation efficacy of % in pre-purified mesenchymal stromal cells, extracted from human dental pulp, with no adverse effects on cell viability, or on their subsequent osteogenic capabilities.
Publisher: IEEE
Date: 08-2017
Publisher: IEEE
Date: 09-2008
Publisher: IEEE
Date: 08-2015
Publisher: AIP Publishing
Date: 05-2012
DOI: 10.1063/1.4711101
Abstract: We demonstrate that aqueous suspensions of microbubbles, formed into arrays using standing surface acoustic waves (SSAWs), can be transported by controlled modulation of the SSAW frequency. The array is repeatedly captured at a sequence of spatial positions along the acoustic beam path and long-range transportation is achieved by periodic cycling of the applied frequency across the transducer bandwidth. We also demonstrate that controllable alignment and transport can be achieved in a detachable microfluidic device, where the microfluidic channel, in which particle transport occurs, is separated from the piezoelectric substrate by an acoustic coupling gel. Proof-of-concept transport is first discussed using a test system of latex particles before the non-invasive manipulation technique is applied to arrays of microbubbles. We explore the role of acoustic radiation forces in the spatial control of particles by analysing the dynamics of particle manipulation by SSAWs. Our results highlight the exquisite control which we have over the position and transport of particles and we anticipate that this technique could find wide applications for the accurate and programmable, non-invasive ordering and transport of biological s les in microfluidic systems.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2016
Publisher: IEEE
Date: 08-2017
Publisher: IEEE
Date: 09-2013
Publisher: IEEE
Date: 08-2015
Publisher: SPIE
Date: 09-02-2006
DOI: 10.1117/12.660716
Publisher: IEEE
Date: 09-2013
Publisher: The Optical Society
Date: 11-11-2016
DOI: 10.1364/OE.24.026986
Publisher: IEEE
Date: 09-2006
Publisher: IEEE
Date: 10-2012
Publisher: IEEE
Date: 09-2010
Publisher: AIP Publishing
Date: 03-11-2008
DOI: 10.1063/1.3013349
Abstract: We demonstrate that terahertz microstrip-line waveguides can be used to measure absorption spectra of polycrystalline materials with a high frequency resolution (∼2 GHz) and with a spatial resolution that is determined by the microstrip-line dimensions, rather than the free-space wavelength. The evanescent terahertz-bandwidth electric field extending above the microstrip line interacts with, and is modified by, overlaid dielectric s les, thus enabling the characteristic vibrational absorption resonances in the s le to be probed. As an ex le, the terahertz absorption spectrum of polycrystalline lactose monohydrate was investigated the lowest lying mode was observed at 534(±2) GHz, in excellent agreement with free-space measurements. This microstrip technique offers both a higher spatial and frequency resolution than free-space terahertz time-domain spectroscopy and requires no contact between the waveguide and s le.
Publisher: IEEE
Date: 09-2012
Publisher: AIP Publishing
Date: 02-02-2009
DOI: 10.1063/1.3076127
Abstract: The two-dimensional concentration and manipulation of micron-scale particles by orthogonal, surface acoustic, standing waves is demonstrated. The particles are organized by liquid pressure waves in a microfluidic system over a piezoelectric substrate and form a uniform two-dimensional array with a spacing governed by the mechanical nodes of the two orthogonal, surface acoustic, standing waves. The nodal spacing can be controlled in each orthogonal direction independently by adjustment of the radio frequency applied to the separate acoustic wave transducers. This technique could be used to enhance the particle concentrations at sensing locations in DNA or protein array detectors.
Publisher: IEEE
Date: 06-2007
Publisher: AIP Publishing
Date: 10-05-2010
DOI: 10.1063/1.3427191
Abstract: We demonstrate the generation of broadband terahertz (THz) frequency radiation from photoconductive emitters formed from Fe-doped InGaAs (Fe:InGaAs), grown by metal-organic chemical vapor deposition, following pulsed (femtosecond) laser excitation at wavelengths ranging from 830 nm to 1.55 μm. The Fe is incorporated epitaxially during growth, giving precise control over the doping level. Using both single-crystal ZnTe and GaP electro-optic detectors over the same wavelength range, the emission spectra from several Fe:InGaAs wafers with different Fe content were measured, with THz emission from all wafers showing bandwidths in excess of 2.0 THz. The THz output power was found to be strongly dependant on the Fe content, the thickness of the Fe:InGaAs layer, and the excitation wavelength.
Publisher: IEEE
Date: 09-2009
Publisher: IEEE
Date: 09-2006
Publisher: Springer Science and Business Media LLC
Date: 04-2006
Publisher: IEEE
Date: 08-2017
Publisher: AIP Publishing
Date: 21-03-2011
DOI: 10.1063/1.3571289
Abstract: We report the detection of terahertz frequency radiation using photoconductive antennas fabricated from Fe-doped InGaAs, grown by metal-organic chemical vapor deposition. Coherent photoconductive detection is demonstrated using femtosecond laser pulses centered at either an 800 or a 1550 nm wavelength. The InGaAs resistivity and the sensitivity of photoconductive detection are both found to depend on the Fe-doping level. We investigate a wide range of probe laser powers, finding a peak in detected signal for ∼5 mW probe power, followed by a reduction at larger powers, attributed to screening of the detected THz field by photo-generated carriers in the material. The measured signal from Fe:InGaAs photoconductive detectors excited at 800 nm is four times greater than that from a low-temperature-grown GaAs photodetector with identical antenna design, despite the use of a ten times smaller probe power.
Publisher: AIP Publishing
Date: 15-09-2006
DOI: 10.1063/1.2335601
Abstract: We report on a numerical study of the sensitivity of electrical terahertz (THz) frequency range passive filters under conditions of dielectric loading. We investigate band-pass filters, ring resonators, and band-stop filters, all of which have been proposed as devices capable of measuring the hybridization state of overlaid DNA films, thereby acting as genetic sensors. The transmission characteristics of these filters are examined when loaded with s les of different relative permittivities and thicknesses, and these results are discussed in the context of recent experimental works. A comparative analysis of the three filter types is performed, and conclusions are drawn on the suitability of the various filters for the analysis of DNA films during genetic testing and other dielectric materials.
Publisher: International Union of Crystallography (IUCr)
Date: 25-12-2013
DOI: 10.1107/S1600576713029506
Abstract: 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 s le 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.
Publisher: IEEE
Date: 10-2011
Publisher: AIP Publishing
Date: 28-01-2008
DOI: 10.1063/1.2838748
Abstract: We report on the use of standing surface acoustic waves, formed on a single-crystal piezoelectric substrate, to organize micron-scale latex particles into an array comprising a series of lines in an adjacent microfluidic system. The lines of particles are formed parallel to the substrate surface and perpendicular to the surface acoustic wave vector. They extend across the width of the acoustic beam aperture, with a periodicity of one-half the surface acoustic wavelength. The position and spacing of the particle arrays can be altered by adjusting the acoustic wave frequency within the device passband. We discuss the mechanism responsible for the formation of the lines, which could be widely applicable to the alignment of microscopic objects held in suspension.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2018
End Date: 2020
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2017
End Date: 2021
Funder: Engineering and Physical Sciences Research Council
View Funded Activity