Immobilization of ssDNA over carbon electrodes

Several strategies of DNA immobilization have been described onto screen-printed carbon electrodes (SPCEs). 

Although it is frequently used [58, 59], direct ssDNA immobilization over bare carbon surface happens in a random and untidy way due to the multiple interactions between the carbon surface and the phosphate structure of DNA. DNA strands immobilized by physical adsorption are not orientated and present a limited mobility, so the hybridization reaction is hampered by stearic impediments Fig. 9.6. 

Adsorption at controlled potential is generally carried out on pretreated SPCEs [13, 15, 60, 61]. Nevertheless, in these cases the probe strands are not totally accessible for their hybridization, diminishing the genosensor efficiency. 

Avidin [24], neutravidin [51], and streptavidin [54] have been used to immobilize biotinylated DNA strands onto carbon electrodes Fig. 9.7, but before immobilizing the probe the surface must be blocked to avoid unspecific adsorptions like that of the components of the genosensor. 

Other strategies are based on the formation of a polymer, by means of the electropolymerization of the probe modified with the 

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