Versatile Sensing Platform for Cd2+ Detection in Rice Samples and Its Applications in Logic Gate Computation

A versatile sensing platform was designed for Cd2+ detection utilizing Mg2+-dependent DNAzyme as the biocatalyst and toehold-mediated strand replacement as the reaction mechanism. The Cd2+–aptamer interaction brings the split subunits of the Mg2+-dependent DNAzyme into close-enough proximity, which generates an active DNAzyme that can catalyze the cleavage reaction toward the hairpin substrate strand (H1). The trigger DNA fragment in H1 can open another hairpin probe (H2) to activate the cyclic signal amplification process. The generated numerous G-quadruplex DNAzyme structures will produce a high fluorescence response after incubation with the fluorescence dye N-methyl mesoporphyrin IX (NMM). This detection platform is ultrasensitive and the detection limit (LOD) is 2.5 pM (S/N = 3). The sensing system is robust and can work effectively even in a complex sample matrix, enabling the quantitative analysis of Cd2+ content in rice samples with good reliability. Showing the unique features of simple operation, label-free and enzyme-free format, high sensitivity and selectivity, and universal signal amplification mode, our proposed sensing protocol holds great promise for becoming a competitive alternative for the routine monitoring of Cd2+ pollution. Importantly, this flexible and versatile sensing platform was used to construct some exquisite logic gates, including AND, OR, INHIBIT, IMPLICATION, NOR, and NAND.