Ratiometric electrochemical detection of tryptophan based on ferrocene and carboxylated-pillar[6]arene hybrid metal-organic layers

Abstract

Metal-organic layers (MOLs), which have an ultrathin structure, are a novel class of two dimensional coordination polymers. In comparison with three dimensional metal-organic frameworks, MOLs have more accessible active sites on the surfaces and better electron transfer efficiency. These advantages endow MOLs with great potential for the construction of multifunctional nano-platforms, especially electrochemical sensing platforms. In this study, a ratiometric electrochemical sensing platform based on functionalized Zr-MOL was designed and constructed. Ferrocenecarboxylic acid (Fc) was modified on the surface of Zr-MOL on the basis of the solvent-assisted ligand incorporation method, thus obtaining Fc-MOL. Then, carboxylated-pillar[6]arene (WP6) was assembled on the surface of Fc-MOL on the basis of the coordination interaction between bare metal joints and carboxyl groups. The as-prepared hybrid materials WP6@Fc-MOL were characterized by powder X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy mapping, and inductively coupled plasma-optical emission spectroscopy. With the use of the host-guest interaction between WP6 and tryptophan (Trp), WP6@Fc-MOL exhibited high selectivity for Trp sensing. In addition, Fc, as the interior label, can not only reduce the interference of other factors but also increase the electron transfer efficiency during sensing. Results demonstrate that the R2 of linear fitting of the single-signal method and the ratiometric method was 0.9777 and 0.9958, respectively. Benefiting from the advantages of the ratiometric detection method, WP6@Fc-MOL showed improved stability and accuracy for Trp sensing.