For the amplification step, we first selected Glucose Oxidase (GOx) as enzyme to be conjugated to the DNA output strand. We chose GOx because of its stability, high turnover rate and its wide use in electrochemical biosensor technology. For conjugation, we used a 30-nt DNA strand modified with dibenzocyclooctin (DBCO), which can be covalently conjugated to GOx via a crosslinker with a primary amine-reactive NHS group (Figure ). After the conjugation reaction, the enzyme-DNA hybrid was purified by ion exchange chromatography (Figure , Figure ). We then characterized the enzymatic amplification reaction by electrochemical measurements. For this purpose, we added increasing concentrations (from 10 -15 to 10 -6 M) of the GOx-DNA hybrid conjugate to a gold screen-printed disposable electrode modified with a complementary capture strand (Figure ). After an incubation step, we added glucose (200 mM) and measured the H2O2 produced using chronoamperometry (Figure ). We observed a concentration-dependent increase in the measured current with a K1/2 (defined here as the GOx-DNA hybrid concentration at which the observed signal change is half of the maximum change) of 1.2 ± 0.3 x 10 -12 M (Figure ). Control experiments, using electrodes modified with a non-specific capture strand or with mercaptohexanol alone produced a signal indistinguishable from the background signal even at saturating concentrations of the GOx-DNA hybrid strand (10 -7 M) (see red and green dots respectively in Figure ). Next, we proceeded to characterize the antibody-responsive reaction (step 1 in Figure ). In this case, the reaction is based on the antibody-induced hybridization between two antigen-conjugated DNA strands.