Glycogen and PHB are important intracellular biopolymers for carbon and energy storages. In addition to the central roles of glycogen and PHB as key branch points in carbohydrate metabolism, both might be used as indicators for the statuses of intracellular and extracellular environments, such as the levels of intermediate metabolites or biocatalysts (G6P, PGM, ATP, NAD(P)H), or the existences of inhibition substances (nitrate, azide)....[ Read more ]

Glycogen and PHB are important intracellular biopolymers for carbon and energy storages. In addition to the central roles of glycogen and PHB as key branch points in carbohydrate metabolism, both might be used as indicators for the statuses of intracellular and extracellular environments, such as the levels of intermediate metabolites or biocatalysts (G6P, PGM, ATP, NAD(P)H), or the existences of inhibition substances (nitrate, azide).

Due to the importance of these compounds, various non-biosensor methods have been developed for their determinations. However, these methods are time consuming, labor-intensive, expensive, or need to be performed by skilled personnel.

The importance of amperometric enzyme-based biosensors has increased considerably in recent years thanks to the advantages of being highly sensitive, rapid, accurate, economical and easy-to-handle for specific measurement of target analyte in complex matrices such as blood, food products and environmental samples. However, the already widely developed biosensors based on the combinations of enzymes or the combinations of enzymes with mediators easily encounter mediator leakage or inhibition, or are not sensitive enough.

Thus, in this thesis, focusing on glycogen, PHB, and their metabolic related compounds (G6P, PGM, ATP, NAD(P)H, L-glutamate, nitrate, azide), we report the developments of a number of new biosensor approaches by using or new enzyme matrix structures (chapter 3), new enzyme combinations on electrodes (chapter 5, 6, 7 and 9), new enzymatic reactions on electrodes (chapter 8), and new combinations of existing biosensor technologies with pretreatments (chapter 3 and 4).

Compared with other types of biosensors which were developed previously, the biosensor methods developed in this work are free from mediators, and thus being free from mediator leakage or inhibition, and they also have the advantages of being more sensitive, or more rapid, or more easy-to-handle, or free from electroactive substances.

Besides, we report new applications for the measurements of intracellular glycogen and PHB in pure and mixed cell cultures by using existing or currently developed biosensor methods (chapter 3 and 4).

Moreover, the work provides methodologies for the developments of other types of new biosensors and also provides potentials for new applications of the biosensors in various types of samples.