Figure 4.

Mismatch detection with electrochemical readout at the secondary electrode. Constant-potential amperometry was conducted at the secondary electrodes with an applied potential of +0.35 V, while the primary-electrodes were held at −0.40 V in the presence of 4 μM MB and 300 μM Fe(CN)₆³⁻. The blue traces represent currents measured at readout electrodes complementary to well-matched DNA sequences (18-mers) on the primary array, while the red traces represent the analogous currents generated at electrodes complementary to mismatched duplexes. For comparison (dashed lines), the identical assay was carried out on a separate array in which the DNA duplexes were conjugated via copper(II) activation directly at the primary electrodes; clearly, greater signal differential between well- vs, mismatched sequences occurs when monolayers are formed by catalyst activation at the secondary electrode. In these experiments, all primary-array electrodes were first modified with an underlying 50/50 azide/phosphate monolayer before DNA conjugation.