Electrochemiluminescence biosensor for folate receptor based on terminal protection of small-molecule-linked DNA

Owning to the characteristics such as high sensitivity and simplicity of apparatus, electrochemiluminescence (ECL) has become a powerful analytical technique and has been widely used. Ru(phen)32+ can be intercalated into the grooves of dsDNA and act as an ECL probe efficiently, which has been applied to develop a sensitive ECL biosensor for folate receptor in this study. One ssDNA with a thiol group at its 3′ termini had been modified on the Au electrode first, and the other ssDNA with folic acid at its 3′ termini hybridized with the former one being modified on the electrode surface to form a dsDNA. In the absence of folate receptor, the 3′-terminus in the dsDNA region can be specificity hydrolyzed into mononucleotides by ExoIII and on dsDNA presents on the electrode surface, leading to the lower of ECL intensity detected. However, in the presence of the target (folate receptor), ExoIII failed to hydrolyze the dsDNA since the one 3′-terminus had been protected by the target and the other protected by the Au electrode, resulting in the enhancement of ECL intensity. The enhanced ECL intensity has a linear relationship with the logarithm of folate receptor concentration in the range of 0.66 nmol/L and 26.31 nmol/L with a detection limit of 0.1204 nmol/L. The proposed biosensor had been applied to detect HeLa cells concentration with satisfied results.