## 3 Results and Discussion  
Cyclic Voltammetric Studies of Linoleic and \(\alpha\)-Linolenic Hydroperoxides, Generated Using LOX in Free Solution, Using Plain SPECs and CoPC-SPECs  
Initial studies were performed using cyclic voltammetry to deduce the electrochemical behaviour of the fatty acid hydroperoxides, enzymatically generated by the action of LOX on linoleic and \(\alpha\)-linolenic acid. Two different types of working electrode were employed, namely a plain screen-printed carbon electrode (SPCE) and a SPCE which had been modified with the electrocataly cobalt phthalocyanine (CoPC), the latter is designated a CoPC-SPCE. The two test solutions initially contained either linoleic acid or \(\alpha\)-linolenic acid, at a concentration of 0.1 mM and 5K units/mL of the enzyme LOX. Figure 1, shows the resulting voltammograms obtained for the two types transducers with these solutions, and with a blank solution comprised of 0.1 M phosphate buffer containing 0.1 M NaCl.  
Figure 1a (blue) shows the cyclic voltammogram obtained with linoleic hydroperoxide, using a plain SPCE; this exhibits an oxidative current from about +1V that increases rapidly up to +1.5 V. The blank obtained with this electrode (dotted black) showed a considerably smaller current over the same voltage range. Although this anodic behaviour, resulting from direct oxidation of the hydroperoxide, is potentially analytically useful, the applied potential needed to operate an amperometric biosensor would be rather high. However, as seen in Figure 1b (red), when the SPCE is modified with the electrocataly cobalt phthalocyanine, the resulting CoPC-SPCE produces a well-defined voltammetric response at a much lower potential (plateau at about +0.75 V vs. Ag/AgCl). Consequently, better selectivity would be expected with this working electrode, than with the former.  
The cyclic voltammetric behaviour obtained with \(\alpha\)-linolenic hydroperoxide, with the same two working electrodes, showed similar behaviour (Figure 1c,d) to that found with linoleic hydroperoxide (Figure 1a,b). In this case, the CoPC-SPCE again produced the more analytically useful anodic response.  
The anodic responses obtained with the plain SPCEs are considered to result from the direct oxidation of the hydroperoxide functional group at the carbon surface. In the case of linolenic hydroperoxide, one hydroperoxide group is believed to be present at position-13 of the carbon chain [17], which has a chain length of 18 carbons; the electrode reaction is considered to be that shown in Equation (1):  
\[\text{ROOH}\rightarrow\text{R}+\text{O}_{2}+\text{H}^{+}+\text{e}^{-}\text{ (SPCE surface)} \tag{1}\]  
The free radicals (R\(\cdot\)) formed during the reaction may be expected to dimerise.  
In the case of linoleic hydroperoxide, there are believed to be two hydroperoxide groups formed at position-9 and position-13 of the 18-carbon chain [17]. If both of these hydroperoxide groups were to undergo electrochemical oxidation at the SPCE surface, the magnitude of the anodic current should be larger than that observed with the linolenic hydroperoxide. If one compares the magnitude of the anodic currents at a potential of +1.5 V vs. Ag/AgCl, for these two species shown in Figure 1a,b (both blue voltammograms), this does seem to be the case.  
The anodic responses obtained with the CoPC-SPCEs are considered to result from the electrocatalytic oxidation of the hydroperoxide groups, which involves redox reactions of the central cobalt ion (Co+/Co2+) of cobalt phthalocyanine; this is discussed more fully in the following section. As mentioned above, the lower oxidation potential obtained with this working electrode offered better selectivity, consequently we decided to explore the possibility of exploiting this device as a platform in the design of an amperometric fatty acid biosensor.