Electrochemical biosensor for detection of ampicillin in milk based on Au₅Pt and DNA cycle dual-signal amplification strategy

A biosensor is reported for electrochemical detection of ampicillin based on Au₅Pt and DNA cycle dual-signal amplification strategy. Firstly, Au₅Pt is prepared by reduction of chloroauric acid and chloroplatinic acid with serine-functionalized graphene quantum dot (SGQD). The resulting Au₅Pt shows an excellent catalytic activity because of the synergy of Au and Pt. Then, Au₅Pt is covalently combined with hairpin DNA and thionine molecule to form a redox probe. The probe was used for construction of the ampicillin biosensor coupling with DNA cycling. In the presence of ampicillin, the DNA cycle was triggered and leads to many redox probes being carried to the biosensor. This produces a significant signal amplification by oxidation and reduction of thionine molecules in these probes. The combination of Au₅Pt catalysis with DNA cycle achieve ultrahigh sensitivity, selectivity, and stability for the electrochemical detection of ampicillin. Differential pulse voltammetry current linearly increases with the increase of ampicillin concentration in the range 1 × 10⁻¹⁸–1 × 10⁻¹² M with a detection limit of 3.2 × 10⁻¹⁹ M (S/N = 3). The proposed analytical method has been satisfactorily used for electrochemical detection of ampicillin in milk.