An ancillary-ligand strategy for the improvement of electrochemical sensing towards S-containing amines with ultralow detection limits

Abstract

Two new Zn(II) metal–organic frameworks (MOFs), namely [Zn₂(bptc)(DMF)₂(H₂O)]·4H₂O (1) and [Zn₂(bptc)(azpy)(H₂O)₂]·2H₂O (2) (H₄bptc = 3,3′,5,5′-biphenyltetracarboxylic acid, azpy = 4,4′-azopyridine), were synthesized through a solvothermal reaction. The incorporation of the redox-active ancillary ligand azpy endows 2 with electrochemical activity, which enables sensing of S-containing amines (including L-methionine and L-penicillamine) compared to that of 1. The sensor demonstrates exceptional selectivity towards L-methionine due to specific host–guest interactions resulting from hydrogen bonding and size-selective discrimination, leading to an ultralow detection limit of 6.4 × 10⁻³ nM. Furthermore, the detection of L-penicillamine becomes viable due to the structural and size resemblance with L-methionine. This deduction is substantiated through both computational analysis and empirical investigations, which supplies a new way for the construction and modification of electroactive MOF sensors with superior selectivity and sensitivity.