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

Abstract

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.