Localized Surface Plasmon Resonance (LSPR) Detection of Diphtheria Toxoid Using Gold Nanoparticle-Monoclonal Antibody Conjugates

Detection of diphtheria toxin (DT) which is produced by Corynebacterium diphtheria, a zoonotic pathogen and a leading cause of diphtheria, is the critical step in the clinical laboratory. Traditional methods for DT detection are time consuming with low sensitivity. Herein, a localized surface plasmon resonance (LSPR) nanobioprobe has been developed based on specific immunological interactions between gold nanoparticles (GNPs) conjugated with monoclonal antibody and diphtheria toxoid in order for the rapid detection of DT. For this, plasmonic GNPs were conjugated to monoclonal antibodies covalently. The covalent conjugation has been confirmed by dynamic light scattering (DLS) and electrochemical techniques. Then, structural alterations of the conjugated antibody were monitored by circular dichroism (CD) and fluorescence spectroscopy methods. After that, the sensitivity of the nanobioprobe has been investigated via measuring the LSPR band λmax shifts of GNPs and LSPR sensitivity of nanobioprobe was compared with the ELISA method. Results suggested that this assay is highly selective and sensitive with a lower detection limit of about 10 ng/mL. The LSPR biosensor reduced the DT detection time from 2 or 3 days to less than 1 h compared with traditional methods. In conclusion, the investigation presents a rapid, sensitive, and selective method for the diagnosis of DT in clinical specimens.