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McKenna M.,Dublin City University | Soberon F.,Dublin City University | Ricco A.J.,Dublin City University | Daniels S.,Dublin City University | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2016

We compare immobilization methods for oligonucleotides on carboxylic acid surfaces with the goal of improving hybridization efficiency for single-stranded DNA (ssDNA) bioassays. When immobilized via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), ssDNA (either modified with a terminal amine or not) specifically binds to the surface; without EDC, binding is minimal. EDC-activated probes can, however, bind covalently to the surface through nucleobase as well as terminal amino groups. Unmatched base pairs from the former are detected via melting curve analysis: the target begins to unwind at ∼40 °C below the double-strand melting temperature of ∼64 °C. To eliminate such backbone binding, we immobilized azide-functionalized DNA via click chemistry, resulting in hybridization efficiencies 5 times higher than with EDC. This improvement, and the room-temperature hybridization of the click chemistry process, make it an important alternative to EDC for reliable DNA assays with maximum specificity and sensitivity. © 2016 Elsevier B.V. All rights reserved.

Yeates P.,National Center for Plasma Science and Technology | Costello J.T.,National Center for Plasma Science and Technology | Costello J.T.,Dublin City University | Kennedy E.T.,National Center for Plasma Science and Technology | Kennedy E.T.,Dublin City University
Review of Scientific Instruments | Year: 2010

Laser ion sources are used to generate and deliver highly charged ions of various masses and energies. We present details on the design and basic parameters of the DCU laser ion source (LIS). The theoretical aspects of a high voltage (HV) linear LIS are presented and the main issues surrounding laser-plasma formation, ion extraction and modeling of beam transport in relation to the operation of a LIS are detailed. A range of laser power densities (I∼ 108-1011 W cm-2) and fluences (F=0.1-3.9 kJ cm-2) from a Q-switched ruby laser (full-width half-maximum pulse duration ∼35 ns, λ=694 nm) were used to generate a copper plasma. In "basic operating mode," laser generated plasma ions are electrostatically accelerated using a dc HV bias (5-18 kV). A traditional einzel electrostatic lens system is utilized to transport and collimate the extracted ion beam for detection via a Faraday cup. Peak currents of up to I∼600 μA for Cu+ to Cu3+ ions were recorded. The maximum collected charge reached 94 pC (Cu2+). Hydrodynamic simulations and ion probe diagnostics were used to study the plasma plume within the extraction gap. The system measured performance and electrodynamic simulations indicated that the use of a short field-free (L=48 mm) region results in rapid expansion of the injected ion beam in the drift tube. This severely limits the efficiency of the electrostatic lens system and consequently the sources performance. Simulations of ion beam dynamics in a "continuous einzel array" were performed and experimentally verified to counter the strong space-charge force present in the ion beam which results from plasma extraction close to the target surface. Ion beam acceleration and injection thus occur at "high pressure." In "enhanced operating mode," peak currents of 3.26 mA (Cu2+) were recorded. The collected currents of more highly charged ions (Cu4+-Cu6+) increased considerably in this mode of operation. © 2010 American Institute of Physics.

Kavanagh D.,National Center for Plasma Science and Technology | Goodyear A.,Oxford Instruments | Cooke M.,Oxford Instruments | Daniels S.,National Center for Plasma Science and Technology
37th EPS Conference on Plasma Physics 2010, EPS 2010 | Year: 2010

The bulk plasma electron density and optical emission spectra are measured in a high density, high volume inductively coupled C4F8 plasma with a trace amount of Ar for actinometry purposes. The bulk plasma chemistry and electron density are measured and the influence of the bulk plasma properties on polymer deposition rates investigated. Fluorocarbon emissions are monitored across the experimental parameters. Electron density and polymer deposition rates scale linearly for all input parameters indicating the bulk electron density an effective measurement of C4F8 dissociation. It is found, that above other species emissions, the CF 202.4nm bulk emission scales with polymer deposition rates for all input parameters, indicating that the deposition of CF molecules on the silicon substrate to be the primary precursor for polymer film deposition.

O'Connor N.,National Center for Plasma Science and Technology | O'Connor N.,Dublin City University | Cahill O.,National Center for Plasma Science and Technology | Daniels S.,National Center for Plasma Science and Technology | And 3 more authors.
Journal of Hospital Infection | Year: 2014

Healthcare-associated infections (HCAIs) affect ~4.5 million patients in Europe alone annually. With the ever-increasing number of 'multi-resistant' micro-organisms, alternative and more effective methods of environmental decontamination are being sought as an important component of infection prevention and control. One of these is the use of cold atmospheric pressure plasma (CAPP) systems with clinical applications in healthcare facilities. CAPPs have been shown to demonstrate antimicrobial, antifungal and antiviral properties and have been adopted for other uses in clinical medicine over the past decade. CAPPs vary in their physical and chemical nature depending on the plasma-generating mechanism (e.g. plasma jet, dielectric barrier discharge, etc.). CAPP systems produce a 'cocktail' of species including positive and negative ions, reactive atoms and molecules (e.g. atomic oxygen, ozone, superoxide and oxides of nitrogen), intense electric fields, and ultraviolet radiation (UV). The effects of these ions have been studied on micro-organisms, skin, blood, and DNA; thus, a range of possible applications of CAPPs has been identified, including surface decontamination, wound healing, biofilm removal, and even cancer therapy. Here we evaluate plasma devices, their applications, mode of action and their potential role specifically in combating HCAIs on clinical surfaces. © 2014 The Healthcare Infection Society.

Vijayaraghavan R.K.,National Center for Plasma Science and Technology | McCoy A.P.,Dublin City University | Chauhan L.,Dublin City University | Chauhan L.,University of Petroleum and Energy Studies | And 5 more authors.
Journal of Physical Chemistry C | Year: 2014

p-type transparent conducting CuBr thin films were grown by thermal evaporation of CuBr followed by oxygen plasma treatment. Efficient incorporation of oxygen into the CuBr films was revealed, and the influence of plasma exposure on the electrical, structural, optical, and electronic properties of CuBr films was investigated. X-ray diffraction (XRD) analysis indicated the Zincblende structure of the oxygen plasma treated CuBr (OCB) films with the formation of nanocrystalline grains preferentially oriented along the (111) direction. p-type conducting OCB films show >85% average transmittance along with hole concentration, conductivity and Hall mobility values of ∼1019 cm-3, ∼1.5 S cm-1 and ∼0.45 cm2 V-1 s-1, respectively. The X-ray photoelectron spectra of the OCB films demonstrated that the plasma exposure resulted in a significant increase in the O 1s signal at the surface of OCB films. On the basis of the experimental results from the Hall measurements and X-ray photoemission, a possible explanation comprising the formation of a surface CuO layer is also proposed to elucidate the increase in the p-type conductivity of the OCB films. Strong room temperature emission of OCB films at around 416 nm was also observed, the intensity of which decreased with the increase of oxygen plasma exposure time. The results present oxygen plasma exposure as a simple and promising technique for the production of CuBr-based p-type materials for future transparent electronics. © 2014 American Chemical Society.

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