Label free electrochemical DNA hybridization discrimination effects at the binary and ternary mixed monolayers of single stranded DNA/diluent/s in presence of cationic intercalators

Abstract

Electrochemical label free DNA hybridization discrimination of the brain tumor sequence CK20 has been made at the gold–thiol and thiol diluent binary and ternary mixed monolayer interfaces in presence of the [Fe(CN) 6] 3− and double stranded DNA (dsDNA) specific cationic intercalators, proflavine (PF) and methylene blue (MB), respectively. Thiol hexane labeled single stranded DNA (HS-ssDNA) and thiol diluents such as 6-mercapto-1-hexanol (MCH) and 3-mercaptopropionic acid (MPA) are used to construct the mixed monolayers. Change in the peak-to-peak separation (Δ E p) for the [Fe(CN) 6] 3− redox reaction indicates the efficiency of the diluents in removing the randomly oriented HS-ssDNA. Smaller Δ E p 248 mV noticed for the HS-ssDNA/MPA compared to the HS-ssDNA/MCH mixed monolayers (812 mV) indicates the less influence of the MCH diluent on the arrangement of HS-ssDNA layer. However, the hybridization discrimination effect negotiated in presence of both the [Fe(CN) 6] 3− and PF intercalator showed zero effect for the HS-ssDNA/MPA interface, and ∼20–30% effect for the HS-ssDNA/MCH interface. The discrimination effect at the HS-ssDNA/MPA interface further increased to 80% by inserting the MCH at the local defects to form a multicomponent ternary HS-ssDNA/MPA/MCH layer interface. These differential discrimination effects are attributed to the formation of compact and/or defective layer structures, evidenced from their reductive desorption voltammetry in 0.5 M KOH. The presence of single base (C–A) mismatch in the hybrid is diagnosed by a decrease in coulometric charge compared to the perfect dsDNA. The target concentration of 10 pM is detected selectively and sensitively.