Two strategies were followed for the preparation of cholesterol biosensors. The first one was based on the immobilization of cholesterol oxidase (ChOx) enzyme on the AuNPs/PDDA/CNTs/GCE and the detection of hydrogen peroxide formed in the enzyme reaction. The analytical characteristics of this biosensor (Table 1) were better than those from other cholesterol biosensors with similar configurations. However, the selectivity was low because of the relatively high potential of detection used, +0.6 V. The second strategy was based on the immobilization of two enzymes, ChOx and peroxidase (HRP), using hydroquinone as the redox mediator. At these conditions, a potential of detection as low as -50 mV was applied, this consequently improving selectivity. Table 1 compares the analytical characteristics of HRP/ChOx/AuNPs/ PDDA/CNTs/GCE and HRP/ChOx/GA/MNPs/PDDA/CNTs/GCE biosensors with those from monoenzymatic biosensor. As can be observed, higher slopes of the calibration plots, lower limits of detection, and longer life times were obtained.
The developed designs were validated by application to the analysis of human serum spiked with cholesterol at physiological concentration levels. The results obtained are shown in Table 2.
It can be concluded that cholesterol biosensors based on wrapped carbon nanotubes and gold or magnetic nanoparticles exhibit suitable analytical characteristics for the fast, simple and accurate determination of free cholesterol in human serum.
