Target-inspired Zn2+-dependent DNAzyme for ultrasensitive impedimetric aptasensor based on polyacrylic acid nanogel as amplifier.

In general, the traditional impedimetric aptasensor for detecting protein is based on its high molecular weight and low dielectric constant. Yet, the efficiency of these aptasensors is hindered by the slight resistance change in the trace concentration range because of the high initial resistance (the electrostatic repulsion between the compact negatively charged DNA on the electrode and [Fe(CN)6]3-/4-). To effectively and simply circumvent this issue and improve the detection sensitivity, we design an impedimetric aptasensor by reducing the substrate DNA's density on the electrode through the target-inspired recycling DNA cleavage. In order to enlarge the differences in resistance, the polyacrylic acid (PAA) nanogel is implemented as amplifier due to its poor conduction and negative charge that can hinder electron transfer and repulse the mediator [Fe(CN)6]3-/4-, respectively. Based on the target-inspired DNAzyme and PAA nanogel as amplifier, the ultrasensitive impedimetric aptasensor of carcinoembryonic antigen (CEA) in the buffer solution possesses a wide dynamic range of 10 fg mL-1 to 10 ng mL-1 and ultra-low detection limit of 7.9 fg mL-1 (10-fold relative to equivalent aptasensors). When tested in human serum, the proposed aptasensor exhibits good performance with an ultra-low detection limit of 1.4 fg mL-1, which is slightly higher than that in buffer solution.