Label-free fluorescent enzymatic assay of citrate synthase by CoA–Au(I) co-ordination polymer and its application in a multi-enzyme logic gate cascade

Abstract

Citrate synthase (CS) is one of the key metabolic enzymes in the Krebs tricarboxylic acid (TCA) cycle. It regulates energy generation in mitochondrial respiration by catalysing the reaction between oxaloacetic acid (OAA) and acetyl coenzyme A (Ac-CoA) to generate citrate and coenzyme A (CoA). CS has been shown to be a biomarker of neurological diseases and various kinds of cancers. Here, a label-free fluorescent assay has been developed for homogeneously detecting CS and its inhibitor based on the in situ generation of CoA–Au(I) co-ordination polymer (CP) and the fluorescence signal-on by SYBR Green II-stained CoA–Au(I) CP. Because of the unique property of the CoA–Au(I) CP, this CS activity assay method could achieve excellent selectivity and sensitivity, with a linear range from 0.0033 U/μL to 0.264 U/μL and a limit of detection to be 0.00165 U/μL. Meanwhile, this assay method has advantages of being facile and cost effective with quick detection. Moreover, based on this method, a biomimetic logic system was established by rationally exploiting the cascade enzymatic interactions in TCA cycle for chemical information processing. In the TCA cycle-derived logic system, an AND–AND–AND-cascaded gate was rigorously operated step by step in one pot, and is outputted by a label-free fluorescent signal with visualized readout.