Abstract: A novel electrochemical aptasensor using magnetic beads, based on the specific binding of aptamer to ampicillin, was developed for the detection of ampicillin in milk. Ampicillin functionalized magnetic beads were prepared and used to compete with ampicillin in samples for binding to its aptamers and horse radish peroxidase. Then a magnetic electrode was used to capture and focus the resulting magnetic beads on its surface. Under the optimal conditions, the net current response was linear with ampicillin concentration in the range of 1.0 × 10-12–1.0 × 10-8 mol/L, with a detection limit of 1.0 × 10-12 mol/L. The method was applied in the determination of ampicillin in milk samples with a satisfactory precision and acceptable recoveries.

Key words: ampicillin, aptamer, magnetic beads, aptasensor