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Electrochemically reduced graphene oxide to support glucose oxidase electrocatalysis

Quinones Weiss, Graciela

[Thesis]. Manchester, UK: The University of Manchester; 2017.

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Abstract

A number of glucose biosensor configurations were produced to evaluate their performance in detecting the range of glucose concentrations they are submitted to. Five different modifications were produced, the first being a replica of the electrode modification studied in the work done by Unnikrishnan et al. and the other four consisted of alterations in the deposition of graphene oxide and the enzyme glucose oxidase from Aspergillus niger. Graphene oxide was used as the enzyme support material between the glassy carbon electrode used for the measurements and the glucose oxidase that carries out the bioelectrocatalytic conversion of glucose into gluconic acid. Effective characterization of graphene oxide before and after the electrochemical reduction was executed through Raman spectroscopy to quantify the level of defects and identify the loss of oxygen groups attached to the surface of graphene oxide. From the studied electrode modification, one produced predictable behavior where the concentrations were in agreement with the resulting currents, suggesting that glucose oxidase when present in the reduction of glucose oxidase is not only immobilized on the surface of the reduced graphene oxide but also contributes to easier reduction. This can be observed from the peak intensities in the Raman spectra where the ID/IG ratios for electrochemically reduced graphene in the absence of glucose is of 1.0656 and 1.031 ± 0.005 in the presence of glucose. The presence of glucose delivers 3.1% enhancement of the reduction process over its absence for oxygen group liberation. The obtained biosensors were subjected to three different glucose concentrations (10mM, 1mM, and 5μM). The most reliable as to its predictable behavior was the biosensor where graphene oxide was deposited on the electrode surface followed by glucose oxidase suspended in pH 7 PBS buffer and subsequently submitted to reduction potentials. This modification delivered expected current ranges and presented redox peaks for glucose oxidase in the anticipated potential range. This study delivers insight to other configurations, the effect of scan rate, pH and how the fabrication of electrode modification may also affect repeatability.

Layman's Abstract

Glucose biosensors fabricated with reduced graphene oxide are of great interest for improvement of accurate glucose detection and reduction of costs in their fabrication. Graphene is a carbon-based material which possesses superlative characteristics including electronic, allowing accurate signal detection in glucose biosensors. This work studies the possibility to use reduced graphene oxide as the signal transmitter between the glucose oxidase FAD group and the electrode on which it is deposited. It also delivers insight to other configurations, the effect of scan rate, pH and how the fabrication of electrode modification may also affect repeatability.