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

In this work, novel octahedral Cu 2 O-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 Cu 2 O-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 Cu 2 O nanocrystals , and the Cu 2 O-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 (NH 2 -TBA), and the electroactive toluidine blue (Tb) were immobilized onto the Cu 2 O-Au nanocomposite surfaces through a stable Au-N bond. AuNPs, Cu 2 O and hemin/G-quadruplex co-catalyse the H 2 O 2 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.