Electrochemical Boron Detection with Ferrocene and Catechol-Functionalized Cyclodextrin Inclusion Complex

We demonstrate a rapid and sensitive boron detection method through current amplification mediated by supramolecular interaction. Oxidation peak currents obtained by cyclic voltammetry (CV) measurements of a ferrocene/catechol-functionalized <i>β</i>-cyclodextrin inclusion complex were amplified through an EC' reaction (where EC' denotes an electrochemical step followed by a catalytic chemical step). However, the amplified current was decreased by boric acid (the primary form of boron in water) addition at pH 8.6 owing to interactions of boron with the <i>cis</i>-diol structure of dihydroxybenzoic acid-<i>β</i>-cyclodextrin and ferrocene for ester formation. We determined the optimum CyD functionalization sites and measurement conditions and obtained a limit of detection of 0.16 mg B L^-1 for ferrocene/3,4-dihydroxybenzoic acid-<i>β</i>-cyclodextrin (Fc/3,4-DHBA-<i>β</i>-CyD). The binding constant (assuming a 1:1 binding model) for the interaction between Fc/3,4-DHBA-<i>β</i>-CyD and boric acid was estimated to be approximately 1500 M^-1. Boron concentrations in spiked real samples showed good recoveries and linear calibration curves. The electrochemical response of this system was not significantly affected by the presence of other anions or cations. We also found that an aqueous solution of 3,4-DHBA-<i>β</i>-CyD remained stable for at least 112 days.