Majority and minority gates realized in enzyme-biocatalyzed systems integrated with logic networks and interfaced with bioelectronic systems.

Abstract

Biocatalytic reactions operating in parallel and resulting in reduction of NAD(+) or oxidation of NADH were used to mimic 3-input majority and minority logic gates, respectively. The substrates corresponding to the enzyme reactions were used as the input signals. When the input signals were applied at their high concentrations, defined as logic 1 input values, the corresponding biocatalytic reactions were activated, resulting in changes of the NADH concentration defined as the output signal. The NADH concentration changes were dependent on the number of parallel reactions activated by the input signals. The absence of the substrates, meaning their logic 0 input values, kept the reactions mute with no changes in the NADH concentration. In the system mimicking the majority function, the enzyme-biocatalyzed reactions resulted in a higher production of NADH when more than one input signal was applied at the logic 1 value. Another system mimicking the minority function consumed more NADH, thus leaving a smaller residual output signal, when more than one input signal was applied at the logic 1 value. The performance of the majority gate was improved by processing the output signal through a filter system in which another biocatalytic reaction consumed a fraction of the output signal, thus reducing its physical value to zero when the logic 0 value was obtained. The majority gate was integrated with a preceding AND logic gate to illustrate the possibility of complex networks. The output signal, NADH, was also used to activate a process mimicking drug release, thus illustrating the use of the majority gate in decision-making biomedical systems. The 3-input majority gate was also used as a switchable AND/OR gate when one of the input signals was reserved as a command signal, switching the logic operation for processing of the other two inputs. Overall, the designed majority and minority logic gates demonstrate novel functions of biomolecular information processing systems.