Phenoxazine Functionalized, Exfoliated Graphite Based Electrodes for NADH Oxidation and Ethanol Biosensing

Abstract

Exfoliated graphite (EG) particles covalently functionalized with phenoxazine-based molecules have been used to prepare bulk-modified electrodes. The electrodes are of two types: 1) binder-less covalently modified EG pellets and 2) sol-gel derived composites of silicate and modified EG particles. The covalent modification is confirmed by infrared spectroscopy. The electrochemistry of attached molecules has been carried out to decipher the catalytic activity of immobilized phenoxazines towards NADH oxidation. Fast response time of about 4 ± 6 seconds and a low detection limit of 20 mM have been achieved using these electrodes. The sensor is found to yield a linear range of current response versus concentration between 0.02 and 1 mM of NADH. Biosensing in presence of alcohol dehydrogenase enzyme and NAD shows a linear response between 1 and 13 mM and the response time for alcohol sensing is found to be 20 ± 30 s. These electrodes are found to be very stable during operation and can be stored without any deterioration over a period of several months.

Modification of expanded graphite resulting in enhancement of electrochemical activity in the process of phenol oxidation

“…As can be seen in this figure, the used modification of EG brought about the appearance of a new band at 1,107 cm -1 (spectrum b). According to the literature data, the regarded signal may be assigned to the stretching vibrations of C-O bands pertaining to ether groups [5,8,9]. The above observation agrees also with aforementioned conclusions derived from both CV measurements performed in the electrolyte free of phenol and the XPS data.…”

“…Until now it is difficult to explain comprehensively the reasons for such a behavior. However, based on the literature one can assume that chemical treatment of EG in the mixture of H 2 SO 4 /HNO 3 gives rise to enrichment of the expanded graphite surface with some types of functional groups [8,9]. It is also known that the oxidative treatment of graphitic materials in concentrated H 2 SO 4 admix with oxidant (e.g.…”

“…The formation of EG-graphite oxide compound of enriched amount of surface oxygen groups may have a great influence on the improvement of electrochemical activity noted during the process of phenol oxidation. On the other hand, the mixture of H 2 SO 4 and HNO 3 with volume ratio of 3:1 is widely applied for the chemical preparation of graphite intercalation compound with sulfuric acid (H 2 SO 4 -GIC) [8,9,25]. The product of such a process can easily be transformed into expanded graphite by heat treatment at elevated temperature.…”

“…Among them, the oxidative treatment resulting in the enrichment of existing functional groups as well as the formation of novel ones on the EG surface seems to be the most useful. In practice, the processes of oxidative modification of chemical composition of the EG surface is realized by chemical [7][8][9], thermal [10], and electrochemical methods [11]. The advanced oxidation of graphite materials including expanded graphite in some cases leads to the formation of graphite oxide (GO).…”

Versatile bioelectronic interfaces based on heterotrifunctional linking molecules

“…This problem can be circumvented by using electron mediators, such as toluidine blue O (TBO) (Lu et al, 2004), meldola blue (MB) (Serban and El Murr, 2004), neutral red (NR) Zeikus, 1999, 2000) and nile blue A (NBA) (Ramesh et al, 2003), to shuttle electrons between the electrode and cofactor at moderate voltages. Several approaches have been developed to achieve mediated electron exchange between an electrode and a dehydrogenase enzyme, including the use of diffusional mediators to shuttle electrons between the electrode and cofactor (Barlett et al, 1991), immobilization of the enzymes in conductive polymers (Emr and Yacynych, 1995;Heller, 1990), and construction of a redox relay which conducts electrons between the enzyme and electrode (Degani and Heller, 1987;Schuhmann et al, 1991).…”