Angew. Chem. Int. Ed. (2015)

Combining DNA- and enzyme-based logic circuits for the clinical testing of infectious and genetic diseases is advantageous because it increases the diversity of disease markers that can be recognized, and enables the processing of complex biological signals. So far, combined DNA–enzyme systems have involved enzymes that act directly on DNA, such as polymerases and endonucleases, but these enzymes cannot detect certain disease markers. Evgeny Katz, Dmitry Kolpashchikov and colleagues have now reported an interface that can connect output signals from enzymatic circuits with DNA computational systems.

The researchers — who are based at the University of Central Florida and Clarkson University — created the interface using two modified graphite electrodes. The first electrode, which communicates with the enzyme system, has a thin film of polyethyleneimine with pyrroloquinoline quinone (PQQ) covalently attached to it. The second electrode contains a DNA entrapped in an alginate thin film crosslinked by Fe3+. PQQ catalyses the oxidation of nicotinamide adenine dinucleotide (NADH) — an output of the enzyme system — to produce a negative potential, which is sufficient to reduce Fe3+ to Fe2+ on the second electrode. This reduction dissolves the alginate and releases the DNA, which serves as an input for a DNA computing system. Katz and colleagues used two different enzyme systems that produce NADH to create a Boolean AND logic gate, and an OR gate connected to an AND gate. They show that through the electrode interface, the output of these enzyme circuits becomes an input to a DNA AND gate, which could potentially be used to detect cancer markers.