Label-free impedimetric glycosensor based on β-galactose-functionalized gold electrode for the determination of cholera toxin

A label-free impedimetric glycosensor has been developed for the direct detection of cholera toxin (CT). The glycosensor has been fabricated by forming the self-assembled monolayers of β-galactose derivatives containing poly-ethyleneglycol (PEG) spacer on gold electrode surfaces. The selective binding of CT to the β-galactose receptors on the fabricated glycosensor has been directly monitored by electrochemical impedance spectroscopy in the presence of 5.0 mM K₃Fe(CN)₆/K₄Fe(CN)₆ (1:1, v/v) redox couple. gmonolayers on gold electrode surface has been determined to be ca. 2.53 × 10¹⁰ M^{− 1}, indicating that the present glycosensor can selectively capture the target CT from sample solutions. Therefore, the present monosaccharide β-galactose derivative can be used as a receptor for CT as an alternative to CT-specific antibodies or pentasaccharide ganglioside GM₁, most widely used in conventional CT assays. The present glycosensor can detect CT in the concentration range from 1.18 × 10^{− 12} M to 1.18 × 10^{− 9} M (r² = 0.963) with a limit of detection (S/N = 3) down to 7.83 × 10^{− 13} M, which is much lower than those obtained with other detection methods. Since the present glycosensor-based CT assay does not require complex and time-consuming signal amplification steps generally employed in sandwich-type immunoassays, it enables the simple and rapid detection of CT.