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Scanning probe microscopy investigations of organic transistors

Thomas, Suzanne ORCID: 2019. Scanning probe microscopy investigations of organic transistors. PhD Thesis, Cardiff University.

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Delays in obtaining medical results from laboratory testing facilities is a well recognised bottleneck in the medical community. Employing methods that utilise real time electronic sensing could recover this potentially life-saving lost time. Such sensors have many applications within the medical field including detection of infectious diseases, biological or chemical weaponry, glucose sensors for diabetic patients, and many more. However we are approaching a time in human history when antibiotics may no longer be an effective way to treat bacterial infections, and as such we have chosen to pursue a bio-sensing device for antibiotic resistant enzymes. Due to the rise of antibiotic resistance in so called super-bugs compounded with the well documented medical bottleneck that results in long waiting times for test results, there is a call for real time bio-sensing devices that can detect antibiotic resistance. Presented in this thesis is work towards a real time bio-sensing device designed to detect the enzyme TEM-1 beta-lactamase (TEM-1), an enzyme found in bacteria resistant to beta-lactam based antibiotics. The work presented here begins from the base of the proposed device up, beginning with electrostatic characterisation and investigations of field-effect transistors (FET). Firstly an exploration of dinaptho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (DNTT) based organic field-effect transistor (OFET) devices using scanning Kelvin probe microscopy (SKPM) to evaluate contact resistance and mobility of three de vice conformations. Using the skills developed from these experiments, SKPM was further applied to four organic semiconductor (OSC) and polymer blends. Although these devices behaved in a different manner to the DNTT devices, and therefore investigations of contact resistance and mobility were not possible, producing maps of the magnitude of the gradient of the potential provided insight into the blending of the OSC and polymer in the device channel. Using the experience gained working with atomic force microscopy (AFM) and SKPM, the second element of the proposed devices was explored. By covalently binding a detector protein to single wall carbon nanotubes (SWCNT), the electrostatics of the two become interlinked, i.e. changes to the protein result in a change to the whole carbon nanotube (CNT)-protein system [1]. This is proposed as the sensing mechanism of the bio-sensor with the FET base allowing measurements of these changes to be recorded. A series of experiments were conducted using various proteins to ensure binding to the carbon nano-materials, as well as monitoring changes in height, and orientation of the bound protein structures. Finally the work culminates in the production, and preliminary testing, of a prototype bio-sensing device. CNTs were suspended across a nano-gap electrode device. The detector protein BLIP 41 azF was then covalently bound to the carbon nanotubes. Using a four point probe system to monitor changes in electrical characteristics, the analyte protein, TEM-1, was drop-cast onto the sensing device. While these tests proved inconclusive at this time it is hoped that further work will yield meaningful results.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: Scanning probe microscopy, atomic force microscopy, Scanning Kelvin probe microscopy, bio-sensing, carbon nanotubes, graphene, GFP, protein binding, EFM-phase.
Date of First Compliant Deposit: 25 March 2020
Last Modified: 07 Nov 2022 09:54

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