The shape of GSK1120212 in vivo redox peaks for the direct electron transfer of GOD dramatically changed in the presence of O2 (Figure 4 (curve b)) as the reduction peak current increases, whereas the oxidation peak current decreased. The

changes in anodic and cathodic peaks confirmed that GOD in the GOD/PtAuNP/ss-DNA/GR modified electrode catalyzed the reduction of O2[35]. The electrocatalytic process of GOD/PtAuNP/ss-DNA/GR modified electrode is expressed as follows [36]: (1) (2) where GOD (FAD) and GOD (FADH2) represent the oxidized and reduced form of GOD, respectively. Figure 4 Cyclic voltammograms of GOD/PtAuNP/ss-DNA/GR modified electrode. They are in (curve a) N2-saturated and O2-saturated PBS (pH 7.0) in the (curve b) absence and (curve c) presence of 1.0 mM glucose at 100 mV s-1. Upon addition of 1.0 mM glucose into the PBS (Figure 4 (curve c)), the reduction peak current decreased. This can be attributed to the decrease in O2 content of the solution as it is consumed during the oxidation of glucose by the immobilized GOD. The mechanism for the electrode response process could JAK activation be expressed as the following reaction [37]: (3) According to the reaction above, there is a linear relationship between the amount of

glucose increase and the dissolved O2 decrease, that is, a model of the glucose amperometric biosensor could be constructed by detecting the decrease of the reduction peak current of dissolved O2 to indicate the concentration of glucose. Optimization of experimental conditions The pH value is one of the parameters

that affect the response of GOD/PtAuNP/ss-DNA/GR modified electrode to glucose. Figure 5A presents the pH dependence of the amperometric response of 0.1 mM glucose in the pH range of 5.0 to 9.0 at the potential of -0.2 V. It NADPH-cytochrome-c2 reductase can be seen that the current increased as the pH changed from 5.0 to 7.0 and then decreased above pH 7.0. The maximum response was obtained at pH 7.0, which was consistent with the previously reported GOD-based modified electrode [37, 38]. Therefore, a pH 7.0 PBS was used as the electrolyte in subsequent experiments. Figure 5 Effects of (A) pH, (B) applied potential, and (C) temperature. These are effects on amperometric response of the GOD/PtAuNP/ss-DNA/GR modified electrode to 0.1 mM glucose in 0.1 M PBS (pH 7.0). The applied potential is an important parameter that affects the sensitivity of the biosensor. Figure 5B displays the dependence of applied potential on the amperometric response of the biosensor to 0.1 mM glucose in PBS (pH 7.0). When the applied potential was changed from 0 to -0.35 V, the maximum response current was observed at -0.2 V. To obtain high sensitivity and to minimize possible interferences, -0.2 V was chosen as the optimum applied potential for further investigations. The effect of temperature on the amperometric response of glucose was also studied.