On-chip terahertz spectroscopic techniques for measuring mesoscopic quantum systems

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 sampled 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 (3)He∕(4)He 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.

SLO-2 isoforms with unique Ca(2+) - and voltage-dependence characteristics confer sensitivity to hypoxia in C. elegans

Slo channels are large conductance K (+) channels that display marked differences in their gating by intracellular ions. Among them, the Slo1 and C. elegans SLO-2 channels are gated by calcium (Ca ( 2+) ), while mammalian Slo2 channels are activated by both sodium (Na (+) ) and chloride (Cl (-) ). Here, we report that SLO-2 channels, SLO-2a and a novel N-terminal variant isoform, SLO-2b, are activated by Ca ( 2+) and voltage, but in contrast to previous reports they do not exhibit Cl (-) sensitivity. Most importantly, SLO-2 provides a unique case in the Slo family for sensing Ca ( 2+) with the high-affinity Ca ( 2+) regulatory site in the RCK1 but not the RCK2 domain, formed through interactions with residues E319 and E487 (that correspond to D362 and E535 of Slo1, respectively). The SLO-2 RCK2 domain lacks the Ca ( 2+) bowl structure and shows minimal Ca ( 2+) dependence. In addition, in contrast to SLO-1, SLO-2 loss-of-function mutants confer resistance to hypoxia in C. elegans. Thus, the C. elegans SLO-2 channels possess unique biophysical and functional properties.

Terahertz time-domain spectroscopy of glucose and uric Acid

We report the use ofterahertz time-domain spectroscopy for thestudy of two therapeutic bio-molecules:glucose and uric acid. Terahertztransmission spectra of crystalline samplesof both molecules were measured between 0.1-3.0 THz using an evacuated spectroscopysystem. We propose that the stereo-isomersof glucose show spectral featuresoriginating from intermolecular vibrationalmodes, as do uric acid and its derivativemolecule, allantoin. In addition, wepresent a full temperature dependence ofthe terahertz absorption of L-glucose.

Light-induced Difference Terahertz Spectroscopy

Visible/near-infraredlaser-induced difference spectroscopy basedon a time-domain terahertz system has beendeveloped, and used to study copperpathancyonine. We find that the absorptionpeak of this molecule at 1.08 THz changessignificantly under 790 nm laserexcitation, suggesting that we haveobserved the first evidence of vibrationalmode changes in the THz range induced byvisible/near-infrared light.

Determination of Glucose Concentration in Whole Blood using Fourier-Transform Infrared Spectroscopy

Fourier-transform infrared(FTIR) transmission spectroscopy has beenused for the determination of glucoseconcentrations in whole blood samples fromtwenty-eight patients. A four-vectorpartial least squares calibration model,using the spectral range 950-1200 cm(-1),yielded a standard error of prediction of0.59 mM for an independent test set. Forblood samples from a single patient, wefound that the glucose concentration wasproportional to the difference between thevalues of the second derivative spectrum at1082 cm(-1) and 1093 cm(-1), suggestingthat these two specific wavelengths can beused for determining glucose concentrationsin blood.

Fabrication and characterization of gold nano-wires templated on virus-like arrays of tobacco mosaic virus coat proteins

The rod-shaped plant virus tobacco mosaic virus (TMV) is widely used as a nano-fabrication template, and chimeric peptide expression on its major coat protein has extended its potential applications. Here we describe a simple bacterial expression system for production and rapid purification of recombinant chimeric TMV coat protein carrying C-terminal peptide tags. These proteins do not bind TMV RNA or form disks at pH 7. However, they retain the ability to self-assemble into virus-like arrays at acidic pH. C-terminal peptide tags in such arrays are exposed on the protein surface, allowing interaction with target species. We have utilized a C-terminal His-tag to create virus coat protein-templated nano-rods able to bind gold nanoparticles uniformly. These can be transformed into gold nano-wires by deposition of additional gold atoms from solution, followed by thermal annealing. The resistivity of a typical annealed wire created by this approach is significantly less than values reported for other nano-wires made using different bio-templates. This expression construct is therefore a useful additional tool for the creation of chimeric TMV-like nano-rods for bio-templating.

Multi-species data integration and gene ranking enrich significant results in an alcoholism genome-wide association study

BACKGROUND

A variety of species and experimental designs have been used to study genetic influences on alcohol dependence, ethanol response, and related traits. Integration of these heterogeneous data can be used to produce a ranked target gene list for additional investigation.

RESULTS

In this study, we performed a unique multi-species evidence-based data integration using three microarray experiments in mice or humans that generated an initial alcohol dependence (AD) related genes list, human linkage and association results, and gene sets implicated in C. elegans and Drosophila. We then used permutation and false discovery rate (FDR) analyses on the genome-wide association studies (GWAS) dataset from the Collaborative Study on the Genetics of Alcoholism (COGA) to evaluate the ranking results and weighting matrices. We found one weighting score matrix could increase FDR based q-values for a list of 47 genes with a score greater than 2. Our follow up functional enrichment tests revealed these genes were primarily involved in brain responses to ethanol and neural adaptations occurring with alcoholism.

CONCLUSIONS

These results, along with our experimental validation of specific genes in mice, C. elegans and Drosophila, suggest that a cross-species evidence-based approach is useful to identify candidate genes contributing to alcoholism.

Nanoscale programmable sequence-specific patterning of DNA scaffolds using RecA protein

Molecular self-assembly inherent to many biological molecules, in conjunction with suitable molecular scaffolds to facilitate programmable positioning of nanoscale objects, offers a promising approach for the integration of functional nanoscale complexes into macroscopic host devices. Here, we report the use of the protein RecA as a means of highly efficient programmable patterning of double-stranded (ds)DNA molecules with molecular-scale precision at specific locations along the DNA strand. RecA proteins form nucleoprotein filaments with single-stranded (ss)DNA molecules, which are chosen to be of sequence homologous to the desired binding region on the dsDNA scaffold. We show that the patterning yield can be in excess of 85% and we demonstrate that concurrent patterning of multiple locations on the same dsDNA scaffold can be achieved with separation between the assembled nucleoprotein filaments of less than 4 nm. This is an important prerequisite for this programmable and flexible DNA scaffold patterning technique to be employed in molecular- and nanoscale assembly applications.

Mode-locking of a terahertz laser by direct phase synchronization

A novel scheme to achieve mode-locking of a multimode laser is demonstrated. Traditional methods to produce ultrashort laser pulses are based on modulating the cavity gain or losses at the cavity roundtrip frequency, favoring the pulsed emission. Here, we rather directly act on the phases of the modes, resulting in constructive interference for the appropriated phase relationship. This was performed on a terahertz quantum cascade laser by multimode injection seeding with an external terahertz pulse, resulting in phase mode-locked terahertz laser pulses of 9 ps duration, characterized unambiguously in the time domain.

Lipid environment modulates the development of acute tolerance to ethanol in Caenorhabditis elegans

The development of tolerance to a drug at the level of the neuron reflects a homeostatic mechanism by which neurons respond to perturbations of their function by external stimuli. Acute functional tolerance (AFT) to ethanol is a fast compensatory response that develops within a single drug session and normalizes neuronal function despite the continued presence of the drug. We performed a genetic screen to identify genes required for the development of acute functional tolerance to ethanol in the nematode C. elegans. We identified mutations affecting multiple genes in a genetic pathway known to regulate levels of triacylglycerols (TAGs) via the lipase LIPS-7, indicating that there is an important role for TAGs in the development of tolerance. Genetic manipulation of lips-7 expression, up or down, produced opposing effects on ethanol sensitivity and on the rate of development of AFT. Further, decreasing cholesterol levels through environmental manipulation mirrored the effects of decreased TAG levels. Finally, we found that genetic alterations in the levels of the TAG lipase LIPS-7 can modify the phenotype of gain-of-function mutations in the ethanol-inducible ion channel SLO-1, the voltage- and calcium-sensitive BK channel. This study demonstrates that the lipid milieu modulates neuronal responses to ethanol that include initial sensitivity and the development of acute tolerance. These results lend new insight into studies of alcohol dependence, and suggest a model in which TAG levels are important for the development of AFT through alterations of the action of ethanol on membrane proteins.

Ethanol metabolism and osmolarity modify behavioral responses to ethanol in C. elegans

BACKGROUND

Ethanol (EtOH) is metabolized by a 2-step process in which alcohol dehydrogenase (ADH) oxidizes EtOH to acetaldehyde, which is further oxidized to acetate by aldehyde dehydrogenase (ALDH). Although variation in EtOH metabolism in humans strongly influences the propensity to chronically abuse alcohol, few data exist on the behavioral effects of altered EtOH metabolism. Here, we used the nematode Caenorhabditis elegans to directly examine how changes in EtOH metabolism alter behavioral responses to alcohol during an acute exposure. Additionally, we investigated EtOH solution osmolarity as a potential explanation for contrasting published data on C. elegans EtOH sensitivity.

METHODS

We developed a gas chromatography assay and validated a spectrophotometric method to measure internal EtOH in EtOH-exposed worms. Further, we tested the effects of mutations in ADH and ALDH genes on EtOH tissue accumulation and behavioral sensitivity to the drug. Finally, we tested the effects of EtOH solution osmolarity on behavioral responses and tissue EtOH accumulation.

RESULTS

Only a small amount of exogenously applied EtOH accumulated in the tissues of C. elegans and consequently their tissue concentrations were similar to those that intoxicate humans. Independent inactivation of an ADH-encoding gene (sodh-1) or an ALDH-encoding gene (alh-6 or alh-13) increased the EtOH concentration in worms and caused hypersensitivity to the acute sedative effects of EtOH on locomotion. We also found that the sensitivity to the depressive effects of EtOH on locomotion is strongly influenced by the osmolarity of the exogenous EtOH solution.

CONCLUSIONS

Our results indicate that EtOH metabolism via ADH and ALDH has a statistically discernable but surprisingly minor influence on EtOH sedation and internal EtOH accumulation in worms. In contrast, the osmolarity of the medium in which EtOH is delivered to the animals has a more substantial effect on the observed sensitivity to EtOH.

Different genes influence toluene- and ethanol-induced locomotor impairment in C. elegans

BACKGROUND

The abused volatile solvent toluene shares many behavioral effects with classic central nervous system depressants such as ethanol. Similarities between toluene and ethanol have also been demonstrated using in vitro electrophysiology. Together, these studies suggest that toluene and ethanol may be acting, at least in part, via common mechanisms.

METHODS

We used the genetic model, Caenorhabditis elegans, to examine the behavioral effects of toluene in a simple system, and used mutant strains known to have altered responses to other CNS depressants to examine the involvement of those genes in the motor effects induced by toluene.

RESULTS

Toluene vapor brings about an altered pattern of locomotion in wild-type worms that is visibly distinct from that generated by ethanol. Mutants of the slo-1, rab-3 and unc-64 genes that are resistant to ethanol or the volatile anesthetic halothane show no resistance to toluene. A mutation in the unc-79 gene results in hypersensitivity to ethanol, halothane and toluene indicating a possible convergence of mechanisms of the three compounds. We screened for, and isolated, two mutations that generate resistance to the locomotor depressing effects of toluene and do not alter sensitivity to ethanol.

CONCLUSIONS

In C. elegans, ethanol and toluene have distinct behavioral effects and minimal overlap in terms of the genes responsible for these effects. These findings demonstrate that the C. elegans model system provides a unique and sensitive means of delineating both the commonalities as well as the differences in the neurochemical effects of classical CNS depressants and abused volatile inhalants.

Integrated injection seeded terahertz source and amplifier for time-domain spectroscopy

We used a terahertz (THz) quantum cascade laser (QCL) as an integrated injection seeded source and amplifier for THz time-domain spectroscopy. A THz input pulse is generated inside a QCL by illuminating the laser facet with a near-IR pulse from a femtosecond laser and amplified using gain switching. The THz output from the QCL is found to saturate upon increasing the amplitude of the THz input power, which indicates that the QCL is operating in an injection seeded regime.

Chloride intracellular channels modulate acute ethanol behaviors in Drosophila, Caenorhabditis elegans and mice

Identifying genes that influence behavioral responses to alcohol is critical for understanding the molecular basis of alcoholism and ultimately developing therapeutic interventions for the disease. Using an integrated approach that combined the power of the Drosophila, Caenorhabditis elegans and mouse model systems with bioinformatics analyses, we established a novel, conserved role for chloride intracellular channels (CLICs) in alcohol-related behavior. CLIC proteins might have several biochemical functions including intracellular chloride channel activity, modulation of transforming growth factor (TGF)-β signaling, and regulation of ryanodine receptors and A-kinase anchoring proteins. We initially identified vertebrate Clic4 as a candidate ethanol-responsive gene via bioinformatic analysis of data from published microarray studies of mouse and human ethanol-related genes. We confirmed that Clic4 expression was increased by ethanol treatment in mouse prefrontal cortex and also uncovered a correlation between basal expression of Clic4 in prefrontal cortex and the locomotor activating and sedating properties of ethanol across the BXD mouse genetic reference panel. Furthermore, we found that disruption of the sole Clic Drosophila orthologue significantly blunted sensitivity to alcohol in flies, that mutations in two C. elegans Clic orthologues, exc-4 and exl-1, altered behavioral responses to acute ethanol in worms and that viral-mediated overexpression of Clic4 in mouse brain decreased the sedating properties of ethanol. Together, our studies demonstrate key roles for Clic genes in behavioral responses to acute alcohol in Drosophila, C. elegans and mice.

Assessment of coronary stent deployment using computer enhanced x-ray images-validation against intravascular ultrasound and best practice recommendations

OBJECTIVE

To investigate the accuracy of stent measurements using coronary x-ray angiograms with a computer based stent enhancement algorithm applied (StentBoost, SB). To derive recommendations for best practice when using such systems.

BACKGROUND

Computer enhancement algorithms allow better visualization of intracoronary stents to assist in ensuring adequate stent deployment. Factors that affect the accuracy of measurements taken on such systems are yet to be fully understood.

METHODS

We analysed stent deployment of 43 stents in 33 patients measuring minimum stent diameter and cross sectional area (CSA) using intravascular ultrasound (IVUS), SB enhanced x-ray images, and quantitative coronary angiography (QCA). We investigated if the use of two projections and method of calibration influenced correlation between IVUS and SB measurements.

RESULTS

Using two views and performing calibration via the guide catheter improved agreement between SB and IVUS measurements. For example, minimum stent diameter assessed with SB using one view and balloon markers for calibration produced a correlation coefficient, r, of 0.21, whereas using two views and the guide catheter for calibration increased agreement to r = 0.62. Relative measures of stent deployment, such as the ratio of minimum to maximum CSA, produced good correlation between IVUS and SB (r = 0.74).

CONCLUSIONS

When using the SB system, two projection angles should be used to image the stent. For absolute measurements, the guide catheter should be used for calibration purposes. Relative measures of stent size, which are probably sufficient for assessment of deployment, also give good agreement with similar measures on IVUS, and require no calibration.

Terahertz ambipolar dual-wavelength quantum cascade laser

Terahertz frequency quantum cascade lasers (THz QCLs) are compact solid-state sources of terahertz radiation that were first demonstrated in 2002. They have a broad range of potential applications ranging from gas sensing and non-destructive testing, through to security and medical imaging, with many polycrystalline compounds having distinct fingerprint spectra in the terahertz frequency range. In this article, we demonstrate an electrically-switchable dual-wavelength THz QCL which will enable spectroscopic information to be obtained within a THz QCL-based imaging system. The device uses the same active region for both emission wavelengths: in forward bias, the laser emits at 2.3 THz; in reverse bias, it emits at 4 THz. The corresponding threshold current densities are 490 A/cm(2) and 330 A/cm(2), respectively, with maximum operating temperatures of 98K and 120 K.

An assay for evoked locomotor behavior in Drosophila reveals a role for integrins in ethanol sensitivity and rapid ethanol tolerance

BACKGROUND

Ethanol induces similar behavioral responses in mammals and the fruit fly, Drosophila melanogaster. By coupling assays for ethanol-related behavior to the genetic tools available in flies, a number of genes have been identified that influence physiological responses to ethanol. To enhance the utility of the Drosophila model for investigating genes involved in ethanol-related behavior, we explored the value of an assay that measures the sedative effects of ethanol on negative geotaxis, an evoked locomotor response.

METHODS

We established eRING (ethanol Rapid Iterative Negative Geotaxis) as an assay for quantitating the sedative effects of ethanol on negative geotaxis (i.e., startle-induced climbing). We validated the assay by assessing acute sensitivity to ethanol and rapid ethanol tolerance in several different control strains and in flies with mutations known to disrupt these behaviors. We also used eRING in a candidate screen to identify mutants with altered ethanol-related behaviors.

RESULTS

Negative geotaxis measured in eRING assays was dose-dependently impaired by ethanol exposure. Flies developed tolerance to the intoxicating effects of ethanol when tested during a second exposure. Ethanol sensitivity and rapid ethanol tolerance varied across 4 control strains, but internal ethanol concentrations were indistinguishable in the 4 strains during a first and second challenge with ethanol. Ethanol sensitivity and rapid ethanol tolerance, respectively, were altered in flies with mutations in amnesiac and hangover, genes known to influence these traits. Additionally, mutations in the beta integrin gene myospheroid and the alpha integrin gene scab increased the initial sensitivity to ethanol and enhanced the development of rapid ethanol tolerance without altering internal ethanol concentrations.

CONCLUSIONS

The eRING assay is suitable for investigating genetic mechanisms that influence ethanol sensitivity and rapid ethanol tolerance. Ethanol sensitivity and rapid ethanol tolerance depend on the function of alpha and beta integrins in flies.

Predictable surface emission patterns in terahertz photonic-crystal quantum cascade lasers

We demonstrate a framework to understand and predict the far-field emission in terahertz frequency photonic-crystal quantum cascade lasers. The devices, which employ a high-performance three-well active region, are lithographically tunable and emit in the 104-120 microm wavelength range. A peak output power of 7 mW in pulsed mode is obtained at 10 K, and the typical device maximum operating temperature is 136 K. We identify the photonic-crystal band-edge states involved in the lasing process as originating from the hexapole and monopole modes at the G point of the photonic band structure, as designed. The theoretical far-field patterns, obtained via finite-difference time-domain simulations, are in excellent agreement with experiment. Polarization measurements further support the theory, and the role of the bonding wires in the emission process is elucidated.

Generation of Bessel beams using a terahertz quantum cascade laser

We report the generation of Bessel beams using polytetrafluoroethene conical lenses and a quantum cascade laser emitting at 2.8 THz. The formation of a central beam spot that retains its size over distances exceeding the characteristic Rayleigh range is demonstrated, and the power transport properties of these beams are compared with those obtained using parabolic reflectors. These lenses could provide an attractive alternative to parabolic reflectors for terahertz imaging applications where a large depth of focus and/or efficient and controllable coupling of radiation onto a small target are desirable.

The design and imaging characteristics of dynamic, solid-state, flat-panel x-ray image detectors for digital fluoroscopy and fluorography

Dynamic, flat-panel, solid-state, x-ray image detectors for use in digital fluoroscopy and fluorography emerged at the turn of the millennium. This new generation of dynamic detectors utilize a thin layer of x-ray absorptive material superimposed upon an electronic active matrix array fabricated in a film of hydrogenated amorphous silicon (a-Si:H). Dynamic solid-state detectors come in two basic designs, the indirect-conversion (x-ray scintillator based) and the direct-conversion (x-ray photoconductor based). This review explains the underlying principles and enabling technologies associated with these detector designs, and evaluates their physical imaging characteristics, comparing their performance against the long established x-ray image intensifier television (TV) system. Solid-state detectors afford a number of physical imaging benefits compared with the latter. These include zero geometrical distortion and vignetting, immunity from blooming at exposure highlights and negligible contrast loss (due to internal scatter). They also exhibit a wider dynamic range and maintain higher spatial resolution when imaging over larger fields of view. The detective quantum efficiency of indirect-conversion, dynamic, solid-state detectors is superior to that of both x-ray image intensifier TV systems and direct-conversion detectors. Dynamic solid-state detectors are playing a burgeoning role in fluoroscopy-guided diagnosis and intervention, leading to the displacement of x-ray image intensifier TV-based systems. Future trends in dynamic, solid-state, digital fluoroscopy detectors are also briefly considered. These include the growth in associated three-dimensional (3D) visualization techniques and potential improvements in dynamic detector design.

Loss of RAB-3/A in Caenorhabditis elegans and the mouse affects behavioral response to ethanol

The mechanisms by which ethanol induces changes in behavior are not well understood. Here, we show that Caenorhabditis elegans loss-of-function mutations in the synaptic vesicle-associated RAB-3 protein and its guanosine triphosphate exchange factor AEX-3 confer resistance to the acute locomotor effects of ethanol. Similarly, mice lacking one or both copies of Rab3A are resistant to the ataxic and sedative effects of ethanol, and Rab3A haploinsufficiency increases voluntary ethanol consumption. These data suggest a conserved role of RAB-3-/RAB3A-regulated neurotransmitter release in ethanol-related behaviors.

Terahertz quantum cascade lasers with copper metal-metal waveguides operating up to 178 K

We report terahertz quantum cascade lasers operating in pulsed mode at an emission frequency of 3 THz and up to a maximum temperature of 178 K. The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding material in the metal-metal waveguides.