Researchers from North Carolina State University have constructed self-assembling protein-based circuits that can execute basic logic functions in a proof-of-concept study.
One of the difficulties in developing molecular circuits is that as the circuit size shrinks, the circuits become less trustworthy. At the quantum scale, the electrons required to generate current act like waves, not particles. For example, in a circuit with two wires separated by one nanometer, an electron can “tunnel” through them and be in both places at the same time, making it difficult to control the current direction. Molecular circuits can help solve these issues, however single-molecule junctions are short-lived or low-yielding due to the difficulties of producing electrodes on such a small scale.
“Our goal was to try and create a molecular circuit that uses tunneling to our advantage, rather than fighting against it,” says Ryan Chiechi, Associate Professor of Chemistry at North Carolina State University and co-corresponding author of a paper describing the work. They started by installing two distinct types of fullerene cages on patterned gold surfaces to create the circuits. The structure was then immersed in a solution of photosystem one (PSI), a typical chlorophyll protein complex.
“Where we wanted resistors we patterned one type of fullerene on the electrodes upon which PSI self-assembles, and where we wanted diodes we patterned another type,” Chiechi says. “Oriented PSI rectifies current – meaning it only allows electrons to flow in one direction. By controlling the net orientation in ensembles of PSI, we can dictate how charge flows through them.”
“These proteins scatter the electron wave function, mediating tunneling in ways that are still not completely understood,” explains Chiechi. “The result is that despite being 10 nanometers thick, this circuit functions at the quantum level, operating in a tunneling regime. And because we are using a group of molecules, rather than single molecules, the structure is stable. We can actually print electrodes on top of these circuits and build devices.”
These circuits were used to make simple diode-based AND/OR logic gates, which were then incorporated into pulse modulators. You can read the entire study here.