Highly sensitive impedimetric glycosensor for the determination of a ricin surrogate, Ricinus communis agglutinin I (RCA₁₂₀)

A highly sensitive impedimetric glycosensor has been developed for the label-free detection of Ricinus communis Agglutinin I (RCA₁₂₀) - a surrogate of potential security threat toxin ricin. In order to accomplish strong binding of RCA₁₂₀ onto the glycosensor surface, the coverage of self-assembled monolayers of thiolated β-galactose derivative on gold electrode was optimized with varying ratios of thiolated ethylene glycol derivative. The association constant between the RCA₁₂₀ and the β-galactose derivative with 10% coverage on gold electrode surface has been determined to be ca. 1.54 × 10⁹ M^{− 1}, implying that the β-galactose derivative can be used as an effective recognition element for RCA₁₂₀. The increase in electron transfer resistance through the selective binding of RCA₁₂₀ onto the glycosensor measured by electron impedance spectroscopy was directly dependent upon the amount of RCA₁₂₀ in sample solution. The present glycosensor can detect RCA₁₂₀ from 8.33 × 10^{− 11} M to 4.17 × 10^{− 6} M with a limit of detection (S/N = 3) of 1.23 × 10^{− 11} M, which is much lower than those of the previous reports. Since the proposed glycosensor does not need time-consuming labeling or signal amplification steps commonly carried out in sandwich-type RCA₁₂₀ immunoassays, it provides the potential for a simple and rapid detection of a security threat toxin ricin.