Electrochemical sensing properties of cobalt-based coordination polymers for trace L-tryptophan in milk

Two Co(II)-based coordination polymers (CPs), {[Co₃(L)₂(H₂O)₈]·6H₂O} (1) and [Co(L)(H₂O)(4,4'-dipy)_0.5] (2) (H₃L = 2-(4-carboxyphenyl)-1H-imidazole-4,5-dicarboxylic acid and 4,4'-dipy = 4,4'-bipyridine), were synthesized via a hydrothermal method and characterized using single crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD), and electrochemical methods. We obtained sensors 1@GCE and 2@GCE by modifying a glassy carbon electrode (GCE), and their electrochemical sensing behavior for L-tryptophan (L-Try) was investigated. The linear range for L-Try sensing was 1-10 μmol, and the limit of detection (LOD) was 0.039 μmol and 0.4 μmol, for 1 and 2, respectively. It was verified by theoretical calculation that their superior electrochemical sensing performance for L-Try was due to the influence of the structure of the CPs. The CP with more active sites and larger void area could interact with L-Try better, and thus, 1 exhibited an excellent sensing effect. In addition, as 1 and 2 successfully detected L-Try in the analysis of milk samples, these materials are expected to serve as high-performance electrochemical sensors for the detection of L-Try.