Engineering an aptamer-based recognition sensor for electrochemical opium alkaloid biosensing

Here we propose an electrochemical aptamer-based sensing strategy for sensitive detection of the codeine (COD). Platform construction was started by decoration NH 2 -functionalized Fe 3 O 4 with gold nanoparticles (Fe 3 O 4 /AuNPs). Carbon nanotubes were then placed on a glassy carbon electrode and decorated with the Fe 3 O 4 /AuNPs to serve as a signal amplifier (Fe 3 O 4 /AuNPs/CNTs/GC). The proposed nanoaptasensor integrated the merits of the deposition of Fe 3 O 4 /AuNPs and CNTs and the covalent attachment of the detection probe at the surface of platform. In this concept, COD was captured at the surface of sensing interface due to the specific binding of aptamer and COD, which led to COD detection. The long tunnels on modified electrode surface were formed owning to the attachment of COD-aptamer at the surface of sensor, while aptamer acted as gate of the tunnels. The change in conformation of aptamer upon target binding caused the closure of aptamer gate. Coupling the “Off–On” electrochemical switching properties of the aptamer modified electrode with inherent capabilities of nanocomposite led to high sensitivity, simplicity, stability and reproducibility of aptasensor. The assay has a 3.2 pM detection limit, and the response is linear up to 900 nM concentration of COD.