explained by the fact that the enzyme is now wired through the redox hydrogel of the Os-polymer onto the CNTP electrode surface.
The hydrogel allows the immobilisation of the enzyme without suffering major structural changes or loss of activity but at the
same time the high surface area of the SWCNTs allows a bigger exposure of the enzyme’s catalytic sites as well as a high loading of FDH with a possible enhancement of the resulting signal. Fig. 5 shows the calibration curve for fructose registered by the optimised biosensor and in the inset it is possible to see the linear part of the calibration curve. It shows a good linearity over the range of 0.1–5 mM. At higher fructose concentrations the curve becomes nonlinear approaching a saturation value (K = 3.66 mM). Statistical analysis gave the following equation y = 0.14x + 5.24 10 M (r = 0.9992, n = 6), where y indicates the current (lA) and x the fructose concentration (mM). The sensitivity was found to be 1.95 lAcm 2 mM and the detection limit was found to be about 1 lM, calculated using the relation 3S.D.a/b, where S.D.a is the absolute standard deviation of the intercept and b the slope of the calibration curve. The biosensor showed also a fast response time of about 4 s. In the literature several FDH biosensors based on platinum, glassy carbon and carbon paste electrodes have been reported. The comparison of some analytical characteristics of the previously reported FDH biosensors and the proposed biosensor was given in Table 1