Dual-signal aptamer sensor based on polydopamine-gold nanoparticles and exonuclease I for ultrasensitive malathion detection

A highly sensitive dual-signal aptamer sensor based on polydopamine-gold nanoparticles (PDA-AuNPs) and exonuclease I (Exo I) was developed for detection of malathion. Compared with traditional sensing elements, aptamer has many advantages, such as high affinity, superior specificity, strong stability and easy modification. The electrodeposition synthesis of PDA-AuNPs gave excellent biocompatibility and electrical conductivity on the sensor. With the addition of malathion, the specific interaction between malathion and its aptamer forced the aptamer to detach from the electrode surface and induced the capture probe to form a hairpin structure on the electrode surface. Exo I was added to motivate the autocatalytic target cycling which remarkably increased the current change of electrochemical signal over 2 times. Therefore, the promising strategy gave rise to an optional dual-signal current readout in both the signal-on of Fc and the signal-off of Tn. In this work, the prepared biosensor exhibited high sensitivity to malathion via the combination of dual-signal design and autocatalytic target cycling amplification. Under the optimized conditions, the proposed sensor showed a wide linear range from 0.5 to 600 ng/L malathion. It also exhibited excellent specificity, acceptable repeatability and good stability. The application of real samples obtained satisfactory recovery results, demonstrating a promising potential in food safety analysis.