A stable two-fold interpenetrated 3D Zn(ii) MOF for fluorescence sensing of uric acid and tryptophan†

Abstract

Uric acid (UA) is a vital indicator of various metabolic diseases, and tryptophan (Trp) is one of the eight essential amino acids in the human body. UA and Trp play important roles in maintaining human health. Herein, a fluorescent Zn(II) metal–organic framework (MOF), {[Zn₂(bptc)(1,2-mbix)₂]₂·EtOH}_n (1) (H₄bptc = 3,3′,4,4′-biphenyltetracarboxylic acid, 1,2-mbix = 1,2-bis(2-methyl-imidazol-1-ylmethyl)benzene), was obtained and explored for sensing UA and Trp. MOF 1 is a 3D framework with an interesting two-fold interpenetrated bbf topology. It exhibits excellent fluorescence performance for turn-off sensing of UA and turn-on sensing of Trp in water. The limits of detection (LODs) for UA and Trp are 1.26 and 0.30 μM, respectively. Experimental results and theoretical calculations indicate that the turn-off sensing of UA should be attributed to the competitive absorption between 1 and UA and that the turn-on sensing of Trp should be attributed to the photoinduced electron transfer (PET) from Trp to the ligands of 1. Moreover, the practicality of 1 was verified by detecting UA in serum and Trp in milk.