Optical Biosensor for Sensitive and Fast Detection of Ampicillin Residues in Milk Samples

The use of a surface Plasmon resonance immunosensor for the analysis of ampicillin is described. An immunoassay was developed with a miniature surface plasmon resonance (SPR) biosensor to quantify the ampicillin residues in milk samples. It was a competitive inhibition assay with ampicillin covalently immobilized on the sensor surface. A fixed amount of monoclonal anti-ampicillin antibody was mixed with the sample and then the amount of free antibody was determined using biospecific interaction analysis by injection of the mixture over the ampicillin immobilized sensor surface. The limit of detection of the ampicillin is 2.5 ng mL^-1, which is below the maximum residue limits (4 ng mL^-1). The measurement period for one is 10 min. Repeatability of the assay is very good, and the coefficient of variation at 2.5 ng mL^-1 is 5.4% in different days.