Development of a new electrochemical glycosensor for the detection of the Vibrio cholerae toxin

Guillén Posteguillo, Carlos ORCID: 0000-0003-3635-4081 (2022). Development of a new electrochemical glycosensor for the detection of the Vibrio cholerae toxin. University of Birmingham. Ph.D.

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Abstract

Scarcity was during millennia the main concern to humans regarding food and water. Hunger and malnutrition are still a shameful reality of humankind but over 90% of the world’s population has left this blight behind and human attention has shifted towards food quality. The most important feature of food quality is its safeness. And although most of us take the safety of what we eat and drink for granted, the World Health Organization estimates that every year hundreds of millions of people worldwide fall ill and near half a million die after ingesting poisoned food or water.

Pathogens are responsible for a majority of cases of foodborne diseases. Many species of bacteria, capable of surviving outside the host for long periods of time, are especially dangerous. Phenomena like climate change, increase in the consumption of processed food, world trade and the aging of the world population have only increased the risks of food/water biocontamination. Current methods to detect bacteria in food matrices have significant drawbacks, especially in the face of the challenges mentioned above. Electrochemical biosensors are an excellent alternative thanks to combining their high sensitivity with other features like simplicity, fastness, and portability.

Cholera, the illness caused by the bacterium Vibrio cholerae, is still a prevalent foodborne disease in some regions of the world. This thesis describes the efforts to develop a new electrochemistry biosensor based on saccharides to detect in water the toxin produced by V. cholerae and prevent cholera disease.

Chapter 1 lays down the problem caused by cholera and the need to improve the detection of V. cholerae. It also explains the concept of electrochemical biosensors and includes examples of this technology to detect bacteria, in particular V. cholerae. Chapter 2 sets the objectives of the thesis, while Chapter 3 describes the principles of the experimental techniques used in this project.

The following four chapters constitute the experimental sections of the thesis per se. Chapter 4 reports on the experimental procedures implemented and the chemicals used through the project. Chapter 5 is devoted to synthesising small sulphur- containing hydrazide molecules to work as linkers between the sensor’s transducer, a Au(poly) electrode, and the biorecognition element (BRE), a sugar. It also explains the difficulties of using these linkers to integrate both elements. In Chapter 6 sulphur- containing polyhydrazides are employed as alternative linkers: following glycosylation with Gal and Lac, cyclic voltammetry (CV) demonstrates their successful adsorption on Au(poly) electrodes. Finally, Chapter 7 describes the detection of cholera toxin subunit B (CTB) using Au(poly) electrodes modified with glycosylated polyhydrazides and different electrochemical techniques (i.e., electrochemical impedance spectroscopy, EIS; and square-wave voltammetry, SWV). According to the preliminary results shown in this chapter, SWV would allow a qualitative detection of CTB in water whilst EIS also a quantitative analysis.

This text is completed with Chapter 8, which draws conclusions from the results obtained in previous chapters and discusses the next steps and future perspectives.

This thesis demonstrates that polyhydrazides can be used as linkers to immobilise sugars on Au electrodes. It also shows some promising results to use this platform in electrochemical biosensors to detect the cholera toxin (CT).

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):