Impedimetric detection of galactose based on a galactose-binding lectin, Ricinus communis agglutinin I (RCA₁₂₀)

A highly sensitive lectin-based impedimetric detection method has been developed for the determination of galactose in human serum samples. The present method is based on the selective interaction between a target galactose and a galactose-binding lectin, Ricinus communis agglutinin I (RCA₁₂₀). The quantitative detection of galactose in human serum samples relies on the competition reaction of the target galactose of interest with β-galactose derivative immobilized on a gold electrode surface for a limited amount of RCA₁₂₀. At equilibrium, the amount of bound RCA₁₂₀-β-galactose complex on gold electrode surface is inversely proportional to the amount of the target galactose in sample solution. The binding of RCA₁₂₀ onto the β-galactose-immobilized gold electrode was monitored through electron transfer resistance, which was directly measured by electrochemical impedance spectroscopy. The present method can detect galactose from 8.33 × 10⁻⁹ M to 1.25 × 10⁻⁶ M (r² = 0.992) with a limit of detection of 5.87 × 10⁻⁹ M (S/N = 3), which is much lower than those obtained with enzyme-based amperometric and colorimetric detection methods. The present method was successfully applied to the determination of galactose in human serum samples.