An aptamer based method is described for the electrochemical determination of ampicillin. It is based on the use of DNA aptamer,
DNA functionalized gold nanoparticles (DNA-AuNPs), and single-stranded DNA binding protein (ssDNA-BP). When the
aptamer hybridizes with the target DNA on the AuNPs, the ssDNA-BP is captured on the electrode surface via its specific
interaction with ss-DNA. This results in a decreased electrochemical signal of the redox probe Fe(CN)63− which is measured best
at a voltage of 0.188 mV (vs. reference electrode). In the presence of ampicillin, the formation of aptamer-ampicillin conjugate
blocks the further immobilization of DNA-AuNPs and ssDNA-BP, and this leads to an increased response. The method has a
linear reposne that convers the 1 pM to 5 nM ampicillin concentration range, with a 0.38 pM detection limit (at an S/N ratio of 3).
The assay is selective, stable and reproducible. It was applied to the determination of ampicillin in spiked milk samples where it
gave recoveries ranging from 95.5 to 105.5%.

• Aptamer based voltammetric determination of ampicillin using a single-stranded DNA binding protein and DNA functionalized gold nanoparticles