Electrochemical mediator material for glucose biosensors
Al-waeel, Majid Ali Saad (2022)
Al-waeel, Majid Ali Saad
2022
Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2022091258345
https://urn.fi/URN:NBN:fi-fe2022091258345
Tiivistelmä
During the day, the blood glucose levels of healthy humans change following the food intake or fasting and are regulated by insulin release. In diabetic or prediabetic patients, this regulation is disrupted; therefore, these patients need to control their blood glucose levels to avoid hypoglycaemia or prolonged hyperglycaemia. Electrochemical biosensors provide a means of actively measuring glucose blood levels. However, to accurately follow blood glucose changes, patients require frequent measurements. From that arises the need for continuous monitoring. Typically, continuous monitoring devices are worn on the body and therefore are subject to additional biocompatibility requirements. Not all conventionally used mediators in second-generation glucose biosensors are harmless. Hence the need arises for a mediator that is non-toxic when in contact with bodily fluids. Depending on the type of the body fluid, the glucose concentration range may vary by several orders of magnitude. This put already known biocompatible mediators under even more scrutiny. This thesis project studies different enzyme/mediator options to find a workaround for this issue.
As glucose oxidase is the golden standard enzyme used in blood glucose monitoring devices, in this work, the enzyme is tested with two mediators, TTF and TTF-TCNQ. The TTF-TCNQ system showed an adequate linear response to glucose. Glucose oxidase is further tested by modifying it with the redox mediator ferrocenecarboxylic acid to form a molecular relay system. This system can permit direct electron exchange between the enzyme and the electrode.
The enzyme GDH-PQQ is tested as a bioreceptor in a glucose biosensor. GDH-PQQ is remarkable as a bioreceptor as its working principle is independent of the presence of oxygen, which is one of the main issues facing GOx. GDH-PQQ is tested with the mediator PMS. The linear range and the magnitude of the response to glucose and biological interferants, such as dopamine and ascorbic acid, are measured.
Then the enzymes were tested with the conducting polymer PEDOT: PSS. PEDOT: PSS is crosslinked with PEGDE and immobilized together with the enzyme on the working electrode. The conducting polymer helps with the immobilization and the shuttling of electrons from the enzyme active site to the surface of the electrode. Adding the external mediator PMS to the GDH-PQQ/PEDOT: PSS biosensor system provided the highest obtained current response among the tested systems.
As glucose oxidase is the golden standard enzyme used in blood glucose monitoring devices, in this work, the enzyme is tested with two mediators, TTF and TTF-TCNQ. The TTF-TCNQ system showed an adequate linear response to glucose. Glucose oxidase is further tested by modifying it with the redox mediator ferrocenecarboxylic acid to form a molecular relay system. This system can permit direct electron exchange between the enzyme and the electrode.
The enzyme GDH-PQQ is tested as a bioreceptor in a glucose biosensor. GDH-PQQ is remarkable as a bioreceptor as its working principle is independent of the presence of oxygen, which is one of the main issues facing GOx. GDH-PQQ is tested with the mediator PMS. The linear range and the magnitude of the response to glucose and biological interferants, such as dopamine and ascorbic acid, are measured.
Then the enzymes were tested with the conducting polymer PEDOT: PSS. PEDOT: PSS is crosslinked with PEGDE and immobilized together with the enzyme on the working electrode. The conducting polymer helps with the immobilization and the shuttling of electrons from the enzyme active site to the surface of the electrode. Adding the external mediator PMS to the GDH-PQQ/PEDOT: PSS biosensor system provided the highest obtained current response among the tested systems.