Rapid detection of whole active ricin using a surface‐enhanced Raman scattering‐based sandwich immunoassay

Ricin is one of the most toxic proteins known, which has been listed as both chemical and biological warfare agent due to its unique properties. Rapid and sensitive method capable of detecting and distinguishing activity of the whole ricin has very important realistic significance in view of national security and defense. This study reports a reliable surface‐enhanced Raman scattering (SERS)‐based sandwich immunoassay for the detection and differentiation of active ricin from other homologous toxins. In the immunoassay design, magnetic bead conjugated with a monoclonal antibody (mAb) MIL50 that can recognize the ricin in its holotoxin form was used as a capture probe to separate ricin from complex matrix, whereas both Raman reporter molecule Nile blue A (NBA) and ricin‐specific mAb 14C12 were modified on gold nanoparticles (AuNPs) to form SERS nanoprobes. In the presence of ricin, SERS nanoprobes bound to the antigen‐captured magnetic beads and formed a sandwich immunocomplex to produce specific hot spots and then generated highly sensitive signals. As a result, the whole ricin could be detected as low as 1 and 5 ng/ml in phosphate‐buffered saline (PBS) and in plasma, respectively. Not only active and inactive ricin can be discriminated distinctly but also ricin from other type II ribosome‐inactivating proteins and their agglutinins. Furthermore, the proposed method made an application to practical samples from the Organization for the Prohibition of Chemical Weapons (OPCW) biotoxin exercise test, proving this SERS‐based sandwich immunoassay a promising assay for timely response of ricin‐related risk assessment in terrorist event and human intoxication. Ricin is one of the most poisonous protein toxins known to humankind. Here, a reliable surface‐enhanced Raman scattering (SERS)‐based sandwich immunoassay was developed to detect whole active ricin. The LODs of the established method were 1 and 5 ng/ml in PBS and plasma, respectively. Based on the formed sandwich immunocomplex “magnetic beads‐ricin‐SERS nanoprobes,” whole ricin can be detected. In addition, active ricin can be differentiated from other homologous toxins.