Chiral L-histidine-ZIF-8/MWCNTs-based molecularly imprinted electrochemical sensor for L-tryptophan

A molecularly imprinted electrochemical sensor based on chiral L-histidine (L-His)-ZIF-8/multi-walled carbon nanotubes (MWCNTs) was developed for sensitive and selective detection of L-tryptophan (L-Trp). The L-His-ZIF-8/MWCNTs composite combines the chiral recognition environment of L-His-ZIF-8 with the favorable electron-transfer properties of MWCNTs, providing an effective electrode interface for target enrichment and electrochemical sensing. Compared with achiral ZIF-8/MWCNTs, the chiral composite exhibited a markedly higher adsorption capacity toward L-Trp, which is beneficial for increasing target accumulation at the sensing interface before molecularly imprinted polymerization. Molecularly imprinted layers were subsequently constructed by electropolymerization of o-phenylenediamine in the presence of β-cyclodextrin and L-Trp. After removing the template, "imprinted cavities" with specific recognition capabilities were formed, thereby enabling the selective detection of L-Trp. Under optimized conditions, the sensor exhibited a wide linear response from 1 nM to 1 mM with a detection limit of 0.34 nM, together with good selectivity, reproducibility, and stability. The sensor was further applied to L-Trp determination in milk samples with satisfactory recoveries, demonstrating its potential for the analysis of chiral amino acids in complex samples.