Versatile Triple-Output Molecular Logic Gate for Cysteine and Silver (I) in Foods and the Environment Based on I-Motif DNA Modulation.

DNA-based molecular logic gates have been developed rapidly but most of them have a single output mode. This study is to develop a triple-output label-free fluorescent DNA-based multifunctional molecular logic gate with berberine as a fluorescent signal and a Ag-aptamer as a recognition matrix. The Ag-aptamer has been identified to switch from a random coil to an i-motif structure of C-Ag-C from a Ag-induced responsive conformational change. As a fluorescent probe, berberine is ultrasensitive to the changes of microenvironments, and the binding to i-motif DNA's more rigid structure causes a significant increase in fluorescence, anisotropy, and lifetime. The addition of cysteine to the berberine/C-Ag-C system disintegrates the i-motif DNA structure because of the strong coordination between Ag and cysteine, and then the triple-output signals are almost retrieved. Given this, a highly sensitive triple-output molecular logic gate for the analyses of Ag and cysteine is constructed with high specificity. Moreover, this simple and cost-effective molecular logic gate has been applied for the detection of cysteine and Ag in various real environmental samples including river water, PM, soil, and food samples with satisfactory recoveries from 89.83 to 106.04%.