Rapid screening for ricin toxin on letter papers using surface enhanced Raman spectroscopy

Ricin has been involved in historic and recent biothreat events. Here we developed a rapid screening method for ricin laced papers using surface enhanced Raman spectroscopy (SRES). Three sample preparation methods and two SERS substrates were evaluated and optimized for their performance on three types of letter papers. The best approach was the use of non-destructive extraction coupled with silver dendrites, which can detect ricin B chain surrogate as low as 0.044 mu g in less than 10 min from paper. The extraction efficiency for the hydrophobic letters was the highest (90%) compared to the other two types of letters. We also demonstrated the great capacity of this method to discriminate ricin B from common beverage residues on letter papers, and the feasibility of using a handheld Raman device for rapid and on-site screening.