Electrochemical aptasensor for thrombin using co-catalysis of hemin/G-quadruplex DNAzyme and octahedral Cu2O-Au nanocomposites for signal amplification

- An enzyme-free and sensitive electrochemical thrombin aptasensor was designed.
- Cu2O-Au nanocomposites were used as signal amplifying molecules and nanocarriers.
- Hemin/G-quadruplex and Toluidine blue were used to improve the electrochemical signal.

In this work, novel octahedral Cu2O-Au nanocomposites were synthesized and first applied in an electrochemical aptasensor to detect thrombin (TB) with the aid of a DNAzyme for signal amplification. The octahedral Cu2O-Au nanocomposites have not only simultaneously served as signal amplifying molecules but have also been utilized as an ideal loading platform to immobilize a large number of electroactive substances and recognition probes. Gold nanoparticles (AuNPs) were grown directly on the surface of the octahedral Cu2O nanocrystals, and the Cu2O-Au nanocomposites obtained had the advantages of large surface areas and excellent biocompatibilities. The hemin/G-quadruplex, which was formed by intercalating hemin into the amino terminated thrombin binding aptamer (NH2-TBA), and the electroactive toluidine blue (Tb) were immobilized onto the Cu2O-Au nanocomposite surfaces through a stable Au-N bond. AuNPs, Cu2O and hemin/G-quadruplex co-catalyse the H2O2 in the working buffer to promote the electron transfer of Tb as a multiple signal amplification strategy in order to improve the performance of the electrochemical aptasensor. Under optimal conditions, the designed aptasensor exhibited sensitive detection of TB from 100 fM to 20 nM with a lower detection limit of 23fM. This proposed aptasensor exhibited good sensitivity, high specificity and acceptable reproducibility and could be widely applied in bioassay analysis.