Detection of β-Lactam Antibiotics Based on Conjugated Antibody with Gold Nanorods by Localized Surface Plasmon Resonance Spectrometer

This study aimed to determine the β-lactam antibiotics (ampicillin, amoxicillin, penicillin G, oxacillin, and carbenicillin) using conjugated antibody along with gold nanorods (AuNRs). For this purpose, XRD, ATR-FTIR spectroscopy, transmission electron microscopy, and dynamic light scattering were utilized to detect the crystallinity, to identify functional groups involved in the synthesis of AuNRs, and to measure the size of the AuNRs, respectively. In this regard, pH of 9 and a concentration of 9.6 μg of antibody at 1 mL poly(4-styrenesulfonic acid (PSS))-modified AuNRs solution were selected as the best levels of pH and concentration of antibody for the conjugation of antibody with PSS-modified AuNRs. Thereafter, the maximum wavelength rates of the PSS-modified AuNRs, conjugation of antibody with PSS-modified AuNRs, and detection of antibiotics (from 1 nM to 1 mM) with PSS-modified AuNRs–PAb were recorded using a microvolume spectrophotometer system. The results indicate that the LSPR absorption wavelength of PSS-modified AuNRs is red-shifted by increasing the concentration of β-lactam antibiotics. By increasing the concentrations of ampicillin, penicillin G, and carbenicillin, the maximum wavelength changed, and after the saturation of the antibiotic concentration, the curve reached a plateau. Correspondingly, this indicated that the antibody had a similar behavior in the detection of these antibiotics. However, regarding amoxicillin, the saturation concentration is much higher, which indicate that the antibody is more specific for its detection. In contrast, for oxacillin, saturation occurred immediately, demonstrating that the antibody had an extremely low detection capability for this antibiotic. Finally, the findings showed that the antibody was sensitive to 1 nM of five studied β-lactam antibiotics.