| Ampicillin?AMP?that can be employed to treat sensitive bacterial infections is a?-lactam semi-synthetic antibiotic.AMP is widely used in dairy farming because of its characteristics,such as inhibiting bacterial growth and reproduction,improving the animal growth environment.The abuse of AMP in the animal husbandry may have significant impacts on consumers.For example,frequent consumption of dairy products with AMP residue may result in allergic reactions,drug resistance or even liver and kidney damage.Therefore,the strict norms for the detection of AMP residues in dairy products have been established in many countries and regions.At present,several commonly used antibiotic detecting methods mainly include:physical and chemical method,microbial method and immunoassay method.However,their further application and popularization were subject to some special requirements because these methods involve different detecting fields and targets,and demand solid professional knowledge,long detecting period,complicated operation,and high cost.Therefore,it is necessary to develop an easy-to-use,high-sensitivity,low-cost method for analyzing AMP residue in milk.In this study,the methods based on electrochemical aptasensor were developed for the detection of AMP residue in milk with AMP as the research object.The magnetic beads were selected as the carriers to connect with AMP.The formed magnetic beads were subsequently used to compete aptamer with free AMP in solution.With the help of its own magnetism,the magnetic beads were confined on its detecting surface of magnetic electrode for further electrochemical detection.The high-efficiency detection of AMP residues in milk can be achieved by measuring the electrochemical signal change before and after the competitive reactions.The results are as follows:1.Magnetic beads-electrochemical aptasensor for the detection of ampicillin in milk.Based on the magnetic beads as the carrier and the specific bind between the aptamer and AMP,an AMP electrochemical aptasensor was constructed.Magnetic beads modified with AMP were prepared by carbodiimide cross-linking method,and used to compete with AMP in samples for the binding to its aptamers and horse radish peroxidase.Then the magnetic electrode was used to capture and focus the resulting magnetic beads on its detecting surface.Optimize parameters that affect sensor performance,determine the optimal competitive reaction time was 30 min,the reaction pH was 8.0,the magnetic signal probe was 50?g,and both of the concentrations of H2O2 and HQ in the test solution were 0.5 mmol/L.Under the optimal conditions,the sensor response current and AMP concentration showed a good linear relationship in the concentration range of 1.0×10-121.0×10-8 mol/L,and the detection limit was1.0×10-12 mol/L.This method was used to determine AMP in milk samples with satisfactory precision and recovery.2.Carboxylated multi-walled carbon nanotubes doped magnetic beads-electrochemical aptasensor for the detection of ampicillin in milk.In order to improve the electron transfer in the electrochemical detection,based on the above aptasensor,carboxylated multi-walled carbon nanotubes?CMWCNTs?were added after the competitive reaction to construct a novel electrochemical aptasensor for the detection of AMP residue.A series of parameters were optimized in the study to determine the optimal coupling time was 90 min,the amount of CMWCNTs used was 1.5?g,and the concentration of HQ and H2O2 in the test solution were both 1.0 mmol/L.Under the optimal conditions,the aptasensor has a good linear relationship between the response current and the AMP concentration in the concentration range of 1.0×10-131.0×10-8mol/L,and the detection limit was 1.0×10-13 mol/L.Because of the addition of CMWCNTs,the sensitivity of this method was enhanced.Furthermore,this method was successfully applied to analyze AMP in commercially available milk samples with satisfied results. |
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