Plasmonic Sensor for Detection of β-Lactam Antibiotics based on the Conjugated Antibody with Gold Nanoparticles

This study aims to detect β-lactam antibiotics using a conjugated antibody with gold nanoparticles (GNPs). For this purpose, the gold nanoparticles synthesized from Chinese lettuce leaf extract (as reductant) were used for the colorimetric detection of β-lactam antibiotics (such as ampicillin, amoxicillin, penicillin G, oxacillin, and carbenicillin). XRD, FTIR spectroscopy, TEM, and dynamic light scattering were utilized to detect the crystallinity, to identify functional groups involved in the synthesis of GNPs, and to measure the size of the GNPs; pH 8 and a concentration of 8.4 μg of antibody at 1 mL GNPs solution were selected as the best pH and concentration of antibody for the conjugation of antibody with GNPs. The maximum wavelengths of the colloidal GNPs, conjugation of antibody with GNPs, and detection of antibiotics (from 1 nM to 1 mM) with GNPs–PAb were recorded using a micro-volume spectrophotometer system. The results indicated that the localized surface plasmon resonance spectrometer absorption wavelength of GNPs red-shifted with increasing concentration of β-lactam antibiotics. With increasing concentration of ampicillin, penicillin G, and carbenicillin, the wavelength of maximum changed, and after saturation of antibiotics concentration, the curve reaches a plateau. This indicated that the antibody showed similar behavior in the detection of these antibiotics. But regarding amoxicillin, the saturation concentration is much higher, indicating that the antibody was more specific for its detection. In contrast, for oxacillin, saturation occurred very soon, which demonstrated that the antibody had an extremely low detection capability for this antibiotic. Finally, the results showed that the antibody was sensitive to 1 nM of the five β-lactam antibiotics studied.