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Impedimetric Detection of Microorgansims Using Platinum Nanowires

Fatih Nadi Gur

Master Thesis, TU Dresden, October 2012

The detection of microorganism is vital in terms of the prevention and identification of problems related to health and safety. Pathogenic microorganisms cause illness outbreaks, hospitalizations and even deaths. Although analytical detection techniques have been developed for a very long time they often still suffer from problems such as low sensitivity, long response time, high cost and low accuracy. Nanotechnology has been suggested as one of the solutions to these problems and one of the fields of particular interest for detection development is the impedimetric detection techniques based on sensitivity of impedance changes. Impedance-based detection methods provide high sensitivity, real time, label-free and fast detection response. In this thesis, a novel impedimetric detection technique developed and tested. Electrical impedance spectroscopy is studied for the detection of Escherichia coli bacteria. For the sensor element, gold microelectrodes are fabricated on a glass substrate with photolithography, platinum nanowires are deposited from an aqueous solution between the microelectrodes using dielectrophoresis. Nanoscale platinum electrodes are typically obtained by applying high bias and nanoscopic gaps in between nanowires are achieved. Escherichia coli bacteria in de-ionized water are captured in the nanogaps by apllying inhomogeneous electric field. Once bacteria are captured, the impedance changes are acquired by measuring the changes in the frequency response of the system. Bacteria attachment in between nanowires leads to high magnitude and phase shifts. As a proof of principle for the usefulness of this particular detection method, two different studies are carried out successfully. The first study is frequency response of captured bacteria in dry ambient and impedance spectra is used to analyze detection. Impedance profile shows detection depends on the applied frequency. Escherichia coli bacteria show response at certain frequency domain. The second study is real time detection of bacteria in liquid media. In this case, specific detectionfrequencies are investigated and captured bacteria lead high amplitude and phase shift at low frequency range.

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