Impedimetric genosensing of DNA polymorphism correlated to cystic fibrosis: A comparison among different protocols and electrode surfaces

In this work, a genosensor for the impedimetric detection of the triple base deletion in a cystic fibrosis-related DNA synthetic sequence is presented. Screen-Printed Carbon Electrodes containing Carboxyl functionalised multi-walled carbon nanotubes were used for the immobilization of an amino-modified oligonucleotide probe, complementary to the Cystic Fibrosis (CF) mutant gene. The complementary target (the mutant sequence) was then added and its hybridization allowed. The change of interfacial charge transfer resistance (Rct) between the solution and the electrode surface, experimented by the redox marker ferrocyanide/ferricyanide, confirmed the hybrid formation. A non-complementary DNA sequence and a three-mismatch sequence corresponding to the wild DNA gene (present in healthy people) were used as negative controls. A further step employing a signalling biotinylated probe was performed for signal amplification using streptavidin-modified gold nanoparticles (strept-AuNPs). In order to observe by SEM the presence and distribution of strept-AuNPs, a silver enhancement treatment was applied to electrodes already modified with DNA–nanoparticles conjugate. The developed protocol allowed the very sensitive detection of the triple base deletion in a label-free CF-related DNA sequence, achieving a LOD around 100 pM. Results were finally compared with those obtained using different protocols for immobilization of DNA capture probe.