Voltammetric enantiomeric differentiation of tryptophan by using multiwalled carbon nanotubes functionalized with ferrocene and β-cyclodextrin

Two types of ferrocene-functionalized multiwalled carbon nanotubes (MWCNTs) are described. The first was obtained by adsorption of ferrocene (Fc) on MWCNTs via π-π stacking and is referred to as Fc/MWCNTs. The second was prepared via a conjugation reaction between ferrocenecarboxylic acid and aminated MWCNTs to result on covalently modified MWCNTs referred to as MWCNT-Fc. MWCNT/Fc has a better conductivity than MWCNT-Fc. But electrochemical recognition results clearly showed the MWCNTs-Fc/β-CD/GCE can exhibit better chiral recognition ability to tryptophan enantiomers than β-CD/Fc/MWCNTs/GCE. By combining the merits of β-cyclodextrin (β-CD) and MWCNTs-Fc, an electrochemical sensor for l -tryptophan was obtained. Its characterizations by SEM, TEM , TGA , Raman spectroscopy and XPS showed that the Fc/MWCNTs and MWCNTs-Fc have successfully been synthesized. Enantioselective recognition was accomplished by differential pulse voltammetry . Tryptophan enantiomers can be differentiated with an enantioselectivity coefficient (I D-Trp /I L-Trp ) of 5.78. Moreover, the chiral recognition mechanism of β-CD recognition tryptophan enantiomers was proposed.