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

Abstract

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.