Immobilization of hairpin deoxyribose nucleic acid aptamers on gold: surface folding dictated analyte-binding performance and electron transfer kinetics

The performance of hairpin aptamer-based electrochemical sensors is highly dependent on the structural nature of the DNA aptamer monolayer immobilized on the electrode surface. It was discovered in this study that an increase of the surface density of aptamers on the electrode does not improve the sensor’s sensitivity, but in fact diminishes its response to the analyte. The electron transfer kinetics between the redox centre (methylene blue) and the gold electrode strongly depend on the surface density (and thus the folding state) of the hairpin DNA aptamers, and shows a unique two-stage behaviour, i.e., a relatively fast process (irrespective of the surface density) at low surface density followed by a sharp decrease in the apparent rate constants (when the surface density increases).