A new dual-signalling electrochemical aptasensor with the integration of “signal on/off” and “labeling/label-free” strategies

The integration of “signal on/off” and “labeling/label-free” strategies was applied to the fabrication of a sensitive and selective dual-signalling electrochemical aptasensor. Ferrocene (Fc), being labeled on single stranded DNA as one signal indicator, could provide “turn on” signal through the DNA conformational changes resulted from target binding with aptamer. [Ru(NH 3 ) 6 ] 3+ (RuHex), as another signal indicator, could provide “turn off” signal through the electrostatic interaction between the anionic DNA phosphate backbones and the cationic RuHex, which is a label-free signal. Cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) were employed for monitoring the stepwise fabrication process of the biosensor. Under the optimized conditions, the dual signal changes were quantified using square wave voltammetry (SWV). Based on the superposition of the dual signal changes (|D I RuHex |   +   Δ I Fc ), the sensitivity of this aptasensor for lysozyme detection was improved compared to individual signal. The results indicated that lysozyme could be detected in a wide linear range (1.0   ×   10 −11 –1.0   ×   10 −7   M) with a low detection limit down to 0.8 pM. Moreover, the resulting biosensor exhibited good specificity, stability and reproducibility, indicating that the present strategy was promising for broad potential application in clinic assay.