Intelligent monitoring of the available lead (Pb) and cadmium (Cd) in soil samples based on half adder and half subtractor molecular logic gates.

The available heavy metals in soil samples can cause the direct toxicity on ecosystems, plants, and human health. Traditional chemical extraction and recombinant bacterial methods for the available heavy metals assay often suffer from inaccuracy and poor specificity. In this work, we construct half adder and half subtractor molecular logic gates with molecular-level biocomputation capabilities for the intelligent sensing of the available lead (Pb) and cadmium (Cd). The available Pb and Cd can cleave DNAzyme sequences to release the trigger DNA, which can activate the hairpin probe assembly in the logic system. This multifunctional logic system can not only achieve the intelligent recognition of the available Pb and Cd according to the truth tables, but also can realize the simultaneous quantification with high sensitivity, with the detection limits of 2.8 pM and 25.6 pM, respectively. The logic biosensor is robust and has been applied to determination of the available Pb and Cd in soil samples with good accuracy and reliability. The relative error (Re) between the logic biosensor and the DTPA + ICP-MS method was from -8.1 % to 7.9 %. With the advantages of programmability, scalability, and multicomputing capacity, the molecular logic system can provide a simple, rapid, and smart method for intelligent monitoring of the available Pb and Cd in environmental samples.