Surface-Enhanced Raman Spectroscopy Detection of Ricin B Chain in Human Blood

Over the past few years, ricin has been discussed frequently because of letters sent to high-ranking government officials containing the easily extracted protein native to castor beans. Ricin B chain, commercially available and not dangerous when separated from the A chain, enables development of ricin sensors while minimizing the hazards of working with a bioterror agent that does not have a known antidote. Recent events have increased the risk of ricin exposure for civilians, and there is a need for rapid, real-time detection of ricin. To this end, aptamers have been used recently as an affinity agent to enable the detection of ricin in food products via surface-enhanced Raman spectroscopy (SERS) on colloidal substrates. One goal of this work is to extend ricin sensing into human whole blood; this goal requires application of a commonly used plasmonic surface, the silver film-over-nanosphere (AgFON) substrate, which offers stable SERS enhancement factors of 10⁶ in human whole blood. Herein, this aptamer-conjugated AgFON platform enabled ricin B chain detection even after the aptamer-modified substrate had dwelled for up to 10 days in human whole blood. Principle component analysis (PCA) of the SERS data clearly identifies the presence or absence of ricin B chain in blood.