Detection of Ricin in Water Samples using DisposableScreen-printed Electrodes

Abstract

Ricin is a highly toxic plant toxin, which is extracted from the beans of the castor plant,Ricinus communis. Ricin is thousand times more poisonous than cyanide and thirty times morepotent than nerve gases. The toxin (ricin) could be used to contaminate food or water, causingpanic. Attempts were made for the detection of ricin in water samples by utilising amperometricimmunosensors. Single-use screen-printed electrodes were made using polystyrene and graphite.These electrodes were tested  for  their ability  to detect 1-naphthol which is the product of thereaction between 1-naphthyl phosphate and the enzyme alkaline phosphatase conjugate. Anindirect enzyme-linked immunosorbent assay (ELISA) system was used to detect ricin. First,ricin antigen was incubated on the screen-printed electrode. This was followed by blocking withBSA and incubation with antibody raised against ricin in rabbit. The last step wass the incubationwith anti-antibody of rabbit conjugated to enzyme alkaline phosphatase. This electrode is insertedin an electrochemical cell containing diethanolamine buffer and a potential of 0.4 V wrt referenceelectrode (Ag/AgCl) was applied  using a potentiostat.  Various experiments were carried out  foroptimising the conditions like substrate concentration, amount of antibody raised against ricin,anti-antibody alkaline phosphatase conjugate, and blocking agents. It was found that the responseof amperometric sensor is proportional to the logarithmic of ricin concentration from 100 ng/mlto 3200 ng/ml.  Using traditional methods, it is possible to detect ricin concentration up to 300ng/ml in 18 h, while with amperometric immunosensor, one can detect ricin as low as 40 ng/mlwithin 90 min. The details of making the screen-printed electrodes, characterisation, optimisationof various conditions for the highest sensitivity have been discussed.