Browsing by Subject "Polymers--Electric properties"
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Item Amperometric DNA sensing using wired enzyme based electrodes(2003) Zhang, Yongchao; Heller, AdamA water soluble copolymer of acrylamide and 4-vinylpyridine complexed with [Os(bpy)2Cl]+/2+ (bpy = 2,2’-bipyridine), was synthesized. An electrodeposition method of making redox polymer films on electrodes was developed. This method was also shown to be effective in incorporating enzymes and amine-terminated DNA sequences in the redox polymer film. A 38-base DNA sequence was detected at 20 pM concentration in 15-35 μL droplets by an electrochemical enzyme-amplified sandwich-type assay on a mass-manufacturable screen printed carbon electrode with a diameter of 3.5 mm. A DNA-capturing oligonucleotide was attached to the pre-deposited redox polymer film using the electrodeposition method. The electrode was exposed to the droplet containing the tested DNA sample, and was then treated with a droplet containing horseradish peroxidase-labeled detection sequence. Formation of the capture-target-detection sandwich brought the horseradish peroxidase-label of the detection sequence in electrical contact with the redox polymer, making the sandwich an electrocatalyst for the reduction of hydrogen peroxide to water at + 0.2 V (Ag/AgCl). The radial diffusion of electrons through the redox polymer film on the microelectrode allowed the electrodeposition of a thicker film of the redox polymer, an increase in the loading of the capture sequence, and increased the collection efficiency of the electron vacancies originating in the electroreduced H2O2. With a 10-μm diameter carbon fiber microelectrode, as few as 3000 copies of the 38-basse DNA sequence were detected at 0.5 fM concentration in a 10 μL sample. A biofuel cell operating at a power density of 50 μW cm–2 at 0.5 V under physiological conditions (air saturated, pH 7.4, 0.14 M NaCl, 37.5°C, 15 mM glucose) was developed. The cell had a glucose electro-oxidizing anode and an O2 electro-reducing cathode. The anode and the cathode were 7 μm diameter, 2 cm long carbon fibers, on which the catalytic enzyme-redox polymer adducts were cross-linked. When the miniature cell operated at 0.5 V, the power output dropped to about 60% of its initial value after 2 days of continuous operation at 37.5°C.Item Charge transport in polymer semiconductors(2007) Basu, Debarshi, 1980-; Dodabalapur, Ananth, 1963-This work is focused on the electrical characterization of polymer field effect transistors. Conventional method of characterizing organic polymeric semiconductors includes field-effect mobility measurement and optical time-of-flight measurement of drift mobility. In this dissertation we have introduced a new method that combines the advantages of both these methods. It involves the injection of carriers at the source of a transistor using a voltage pulse followed by their subsequent extraction at the drain. The delay between the two events is used to extract the velocity of carriers. The electronic time-of-flight method is a fast, simple and direct method to determine the charge transport properties of the semiconductor. In addition it also presents itself as a source of information for understanding injection into the semiconductor and determining the trap distribution. Theoretical modeling of transport was performed. Simulation was also done to include effect of non-idealities that are forbiddingly difficult to be solved analytically. Time of flight measurements of drift mobility were performed in organic transistors with varying semiconductors and dielectrics. It was observed that the electronic time-of-flight mobility lies in the range of the field-effect mobility. Variation in drift mobility was also observed with the applied pulse voltage. This was explained to be caused due to a combination of the increase in mobility with gate voltage and the increase in drift mobility at high lateral fields. Finally mobility measurements were done on transistors with varying channel length and it was concluded that the mobility increases proportional to the exponential square root of the electric field. Finally a derivation of the pulse voltage method is discussed that involves the use of a small signal electronic impulse instead of a large signal voltage pulse. It was shown that this method could not be used to calculate the drift velocity in a polymer transistor as it is valid only for low conductivity materials whose dielectric relaxation time is lower that the transit time of the carriers injected.