Label-free electrochemical immunosensor for ultrasensitive detection of neuron-specific enolase based on enzyme-free catalytic amplification

Enzyme-free catalytic amplification is of great significance for sensitive label-free electrochemical immunosensors. In this study, an enzyme-free catalytic amplification based label-free amperometric immunosensor was developed for sensitive detection of neuron-specific enolase (NSE) by use of a AuPd nanoparticle–multiwalled carbon nanotube (AuPd-MWCNT) composite, ferrocenecarboxaldehyde (Fc-CHO), and chitosan hybrid hydrogel. The intrinsic virtues of chitosan not only resulted in bioactivity of the attached antibodies and made the other component of the immunosensor easier to fix on the electrode, but also imparted abundant binding sites to the hydrogel to condense Fc-CHO to achieve the initial signal amplification. Fc-CHO, which served as an electroactive species to generate a redox response, also exhibits excellent electrocatalytic activity toward H2O2. AuPd-MWCNT composite, with enhanced peroxidase-like catalytic activity, could catalyze H2O2 to accelerate electron transfer. When H2O2 was present in the detection solution, synergetic catalysis of Fc-CHO and AuPd-MWCNT composite toward H2O2 was achieved, thus realizing enzyme-free signal amplification. On the basis of this enzyme-free signal amplification, the electrochemical immunosensing platform provided a wide linear range from 1 pg mL-1 to 100 ng mL-1, a low detection limit of 0.483 pg mL-1, and high sensitivity of 7.22 μA (log10CNSE)-1. Moreover, the immunosensor showed enormous potential in clinical application.