Detection of Ricin Contamination in Liquid Egg by Electrochemiluminescence Immunosorbent Assay

A sensitive and low background fluorescent sensing strategy based on g-C3N4-MnO2 sandwich nanocomposite and liposome amplification for ricin detection

Ricin is an extremely potent ribosome-inactivating protein and serves as a likely food biocontaminant or biological weapon. Thus, simple, sensitive and accurate analytical assays capable of detecting ricin are urgently needed to be established. Herein, we present a novel method for ricin B-chain (RTB) detection by using two materials: (a) a highly efficient hybrid probe that was formed by linking a glucose oxidase (GOD)-encapsulated liposome (GOD-L) to magnetic beads (MBs) through hybridization between an aptamer and a blocker and (b) a new low-background g-C3N4-MnO2 sandwich nanocomposite that exhibits fluorescence resonance energy transfer (FRET) between the g-C3N4 nanosheet and MnO2. In the presence of RTB, the strong binding between RTB and the aptamer can release the blocker-linked liposome from the surface of the MBs. After magnetic separation, the decomposed liposome can release GOD to catalyze the oxidation of glucose, generating a certain amount of H2O2. Then, H2O2 can reduce MnO2 of the g-C3N4-MnO2 nanocomposite to Mn2+, which leads to the elimination of FRET. Thus, the fluorescence of the g-C3N4 nanosheet will be turned on. Because of the excellent signal amplification ability of liposome and the characteristic highly sensitive response of the g-C3N4-MnO2 nanocomposite toward H2O2, RTB could be detected sensitively based on the significantly enhanced fluorescent intensity. The linear range of detection was from 0.25 μg mL-1 to 50 μg mL-1 and the limit of detection (LOD) was 190 ng mL-1. Moreover, the proposed assay was successfully applied in the detection of the entire ricin toxin content in a castor seed.

Milk matrix effects on antibody binding analyzed by enzyme-linked immunosorbent assay and biolayer interferometry

Biolayer interferometry (BLI) was employed to study the impact of the milk matrix on the binding of ricin to asialofetuin (ASF) and to antibodies. This optical sensing platform used ligands immobilized covalently or via biotin-streptavidin linkage, and the results were compared to those obtained by enzyme-linked immunosorbent assay (ELISA). In sandwich ELISA, the binding of ricin to ASF was dramatically decreased when galactose was present during the analyte or detection antibody binding step. Low concentrations of milk (1%, v/v) produced a similar reduction in ricin binding to ASF but not to a high-affinity monoclonal antibody (mAb), increasing the dissociation rate of ASF-ricin complexes up to 100-fold. The effect of milk on the binding of ricin to ASF was ascribable to dialyzable factors, and milk sugar can account for these effects. The use of high-affinity mAbs in ELISA effectively limits the milk matrix effect on ricin analysis.