Constructing combinational and sequential logic devices through an intelligent electrocatalytic interface with immobilized MoS₂ quantum dots and enzymes

Stable molybdenum disulfide quantum dots (MoS₂ QDs) were synthesized using a simple method and embedded into chitosan (Chit) films with glucose oxidase (GOD) on the surface of a polyaniline (PANI) pre-electrodeposited ITO electrode, designated as Chit-MoS₂-GOD/PANI. At the prepared film electrode, the fluorescence property of MoS₂ QDs as well as the catalytic properties of MoS₂ QDs and GOD were well maintained and could be reversibly regulated by external stimuli, such as pH, potential, and the concentrations of glucose and ascorbic acid (AA) in the solution. By controlling the redox state of PANI with an externally applied voltage, the color of the film electrode switched between violet blue and nearly transparent, simultaneously quenching/dequenching the fluorescence signals from MoS₂ QDs through Fӧster resonance energy transfer (FRET). The electrocatalytic signals toward hydrogen peroxide (H₂O₂), a product formed by biocatalysis between glucose and GOD, could be tuned through the catalytic capacity of MoS₂ QDs in the films. Thus, an intelligent platform was built based on the film electrode with pH, potential, glucose and AA as inputs and UV-vis extinction (E), photoluminescent intensity (PL), and amperometric current (I) as outputs. Combinational logic operations such as a 4-input/5-output logic network and sequential logic operations such as a keypad lock and a reprogrammable delay/data (D) flip flop was first simulated in a biocomputing system with the film-modified electrode. This work demonstrated the construction of a multiple stimulus-responsive system with dual-functional nanomaterials and provided a new approach for sequential logic operations for further applications in the information storage.