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- Asif, Muhammad, 1978-
(författare)
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Electrochemical Biosensors Based on Functionalized Zinc Oxide Nanorods
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The semi-conductor zinc oxide (ZnO), a representative of group II-VI has gained substantial interest in the research community due to its novel properties and characteristics. ZnO a direct band gap (3.4eV) semi-conductor has a stable wurtzite structure. Recently ZnO have attracted much interest because of its unique piezoelectric, semiconducting, catalytic properties and being biosafe and biocompatible morphology combined with the easiness of growth. This implies that ZnO has a wide range of applications in optoelectronics, sensors, transducers, energy conversion and medical sciences. This thesis relates specifically to biosensor technology and pertains more particularly to novel biosensors based on multifunctional ZnO nanorods for biological, biochemical and chemical applications.The nanoscale science and engineering have found great promise in the fabrication of novel nano-biosensors with faster response and higher sensitivity than of planar sensor configurations. This thesis aims to highlight recent developments in materials and techniques for electrochemical biosensing, design, operation and fabrication. Rapid research growths in biomaterials, especially the availability and applications of a vast range of polymers and copolymers associated with new sensing techniques have led to remarkable innovation in the design and fabrication of biosensors. Specially nanowires/nanorods and due to their small dimensions combined with dramatically increased contact surface and strong binding with biological and chemical reagents will have important applications in biological and biochemical research. The diameter of these nanostructures is usually comparable to the size of the biological and chemical species being sensed, which intuitively makes them represent excellent primary transducers for producing electrical signals. ZnO nanostructures have unique advantages including high surface to volume ratio, nontoxicity, chemical stability, electrochemical activity, and high electron communication features. In addition, ZnO can be grown as vertical nanorods and has high ionic bonding (60%), and they are not very soluble at biological pH-values. All these facts open up for possible sensitive extra/intracellular ion measurements. New developments in biosensor design are appearing at a high rate as these devices play increasingly important roles in daily life. In this thesis we have studied calcium ion selectivity of ZnO nanorods sensors using ionophore membrane coatings in two research directions: first, we have adjusted the sensor with sufficient selectivity especially for Ca2+, and the second is to have enough sensitivity for measuring Ca2+ concentrations in extra and intracellular media. The sensor in this study was used to detect and monitor real changes of Ca2+ across human fat cells and frog cells using changes in the electrochemical potential at the interface in the intracellular microenvironment.The first part of the thesis presents extracellular studies on calcium ions selectively by using ZnO nanorods grown on the surface of a silver wire (250 μm in diameter) with the aim to produce proto-type electrochemical biosensors. The ZnO nanorods exhibited a Ca2+-dependent electrochemical potentiometric behavior in an aqueous solution. The potential difference was found to be linear over a large logarithmic concentration range (1μM to 0.1M) using Ag/AgCl as a reference electrode. To make the sensors selective for calcium ions with sufficient selectivity and stability, plastic membrane coatings containing ionophores were applied. These functionalized ZnO nanorods sensors showed a high sensitivity (26.55 mV/decade) and good stability.In the second part, the intracellular determination of Ca2+ was performed in two types of cells. For that we have reported functionalized ZnO nanorods grown on the tip of a borosilicate glass capillary (0.7 μm in diameter) used to selectively measure the intracellular free Ca2+ concentration in single human adipocytes and frog oocytes. The sensor exhibited a Ca2+ linear electrochemical potential over a wide Ca2+ concentration range (100 nM to 10 mM). The measurement of the Ca2+ concentration using our ZnO nanorods based sensor in living cells were consistent with values of Ca2+ concentration reported in the literature.The third and final part, presents the calcium ion detection functionalized ZnO nanorods coupled as an extended gate metal oxide semiconductor field effect transistor (MOSFET). The electrochemical response from the interaction between the ZnO nanorods and Ca2+ in an aqueous solution was coupled directly to the gate of a MOSFET. The sensor exhibited a linear response within the range of interest from 1 μM to 1 mM. Here we demonstrated that ZnO nanorods grown on a silver wire can be combined with conventional electronic component to produce a sensitive and selective biosensor.
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| 2. |
- Asif, Muhammad, 1978-, et al.
(författare)
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Selective calcium ion detection with functionalized ZnO nanorods-extendedgate MOSFET
- 2009
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Ingår i: Biosensors & bioelectronics. - : ELSEVIER. - 0956-5663 .- 1873-4235. ; 24:11, s. 3379-3382
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Tidskriftsartikel (refereegranskat)abstract
- Zinc oxide nanorod-extended gate field effect transistor (MOSFET) is demonstrated for the detection of calcium (Ca2+) ions. ZnO nanorods were grown on the surface of a silver wire to produce an electrochemical nanosensor for selectively detecting Ca2+. The electrochemical response from the interaction between the ZnO nanorods and Ca2+ in an aqueous solution is coupled directly to the gate of a field effect transistor (MOSFET). The induced voltage change on the gate results in a measureable current response. In order to adapt the sensors for Ca2+ ions measurements in biological fluids with sufficient selectivity and stability, a plastic membrane coating containing ionophores was applied on the nanorods. The sensor exhibited a linear response within the range of interest from 1 μM to 1 mM. This work demonstrates a simple technique for sensitive detection of Ca2+ ions by efficient transfer of the chemical response directly to a standard electronic component producing a low impedance signal.
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| 3. |
- Asif, Muhammad, 1978-, et al.
(författare)
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Studies on Calcium Ion Selectivity of ZnO Nanowire Sensors Using Ionophore Membrane Coatings
- 2008
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Ingår i: Research Letters in Nanotechnology. - : Hindawi Publishing Corporation. - 1687-6849 .- 1687-6857. ; 2008:Article ID 701813
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Tidskriftsartikel (refereegranskat)abstract
- Zinc oxide nanorods with 100nm diameter and 900nm length were grown on the surface of a silver wire (0.25mm in diameter) with the aim to produce electrochemical nanosensors. It is shown that the ZnO nanorods exhibit a Ca2+-dependent electrochemical potentiometric behavior in an aqueous solution. The potential difference was found to be linear over a large logarithmic concentration range (1 μM to 0.1 M) using Ag/AgCl as a reference electrode and the response time was less than one minute. In order to adapt the sensors for calcium ion measurements in biological fluids with sufficient selectivity and stability, plastic membrane coatings containing ionophores were applied. These functionalized ZnO nanorods sensors showed a high sensitivity (26.55 mV/decade) and good stability.
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| 5. |
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| 6. |
- Fulati, Alimujiang, et al.
(författare)
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Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods
- 2009
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Ingår i: SENSORS. - : MDPI AG. - 1424-8220. ; 9:11, s. 8911-8923
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Tidskriftsartikel (refereegranskat)abstract
- ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells.
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| 7. |
- Israr, Muhammed Qadir, et al.
(författare)
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Trimming of aqueous chemically grown ZnO nanorods into ZnO nanotubes and their comparative optical properties
- 2009
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Ingår i: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:7, s. 073114-
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Tidskriftsartikel (refereegranskat)abstract
- Highly oriented ZnO nanotubes were fabricated on a silicon substrate by aqueous chemical growth at low temperature (andlt; 100 degrees C) by trimming of ZnO nanorods. The yield of nanotubes in the sample was 100%. Photoluminescence spectroscopy of the nanotubes reveals an enhanced and broadened ultraviolet (UV) emission peak, compared with the initial nanorods. This effect is attributed to whispering gallery mode resonance. In addition, a redshift of the UV emission peak is also observed. Enhancement in the deep defect band emission in the nanotubes compared to nanorods was also manifested as a result of the increased surface area.
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| 8. |
- Klason, Peter, 1977, et al.
(författare)
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Electrical characteristics and stability of gold and palladium Schottky contacts on ZnO nanorods
- 2008
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:47, s. 475202-
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Tidskriftsartikel (refereegranskat)abstract
- The electrical characteristics and stability of Pd and Au Schottky contacts on ZnO nanorods grown on glass substrate have been investigated. The nanorods were grown using the aqueous chemical growth method. The nanorods were characterized with scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL). Prior to the metal contact deposition, an insulating PMMA layer was deposited between the nanorods. The best-produced Schottky contact was an as-deposited Pd/ ZnO contact with an ideality factor of 1.7 +/- 0.43 and a barrier height of 0.67 +/- 0.09 eV. The relatively high ideality factor indicates that the current transport cannot be described by pure thermionic transport. The presence of surface states due to the high evaporation pressure is probably the reason for the high ideality factor. Post metal deposition annealing at 150 degrees C for 30 min in air lowered the barrier height and decreased the Au/ ZnO ideality factor but increased it for Pd/ ZnO. The current follows ohmic behavior when the applied forward bias, V-forward, is lower than 0.1 V, whereas for Vforward between 0.1 and 0.45 V the current follows I similar to exp(cV), and at higher forward biases the current-voltage characteristics follow the relation I similar to V-2, indicating that the space-charge current-limiting mechanism is dominating the current transport.
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| 9. |
- Klason, P, et al.
(författare)
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Fabrication and characterization of p-Si/n-ZnO heterostructured junctions
- 2009
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Ingår i: MICROELECTRONICS JOURNAL. - : Elsevier BV. - 0026-2692. ; 40:4-5, s. 706-710
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Tidskriftsartikel (refereegranskat)abstract
- In this paper ZnO nanorods and nanodots (with and without a SiO2 buffer layer) were grown on p-Si, forming p-n heterojunctions. The nanorod devices showed no visible electroluminescence (EL) emission but showed rectifying behavior. Covering around 60% of the length of the nanorods with PMMA produced an ideality factor of 3.91 +/- 0.11 together with a reverse saturation current of 6.53 +/- 4.2 x 10(-8) A. Up to two orders of magnitude rectification was observed for the current at bias -3 and 3 V. The nanodot devices showed EL emission under forward bias conditions. It seems that the buffer layer increased both the stability and efficiency of the devices, since the buffer layer device could operate at larger applied voltage and showed EL emission under reverse bias.
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