Enzyme logic gates based on enzyme-coated carbon nanotubes

Enzyme-based Boolean logic gates were developed by using highly stable enzyme precipitate coatings (EPCs) on carbon nanotubes (CNTs). EPCs of three enzymes, glucose oxidase (GOx), horseradish peroxidase (HRP), and invertase (INV), were prepared in a three-step process that consists of covalent enzyme attachment, enzyme precipitation, and enzyme crosslinking. The AND logic gate was formulated based on an ON output signal in response to the combined inputs of glucose and dye. The OR logic gate was based on the ON output signal of glucose oxidation in the presence of EPC-GOx and EPC-INV with one of the two inputs, either glucose or sucrose. The use of EPCs will provide an effective tool for the development of sensitive and repeatedly-usable Boolean logic gates with a long lifetime, which can be employed in various biosignaling systems.