Hydrolytic Enzymes as (Bio)-Logic for Wireless and Chipless Biosensors

The switchable activity of allosteric, hydrolytic enzymes was used as a single-input, “buffer” logic gate (performing YES and NOT) in a screen-printable biosensor. The enzyme substrate functioned as an “AND” logic gate with the enzyme and cofactor as inputs. These (bio)-logic materials transduced a signal by the cofactor activating the enzyme which then degraded the substrate that formed the dielectric of a tuning capacitor in an inductor-capacitor (LC) circuit. The degradation of the substrate was engineered to shift the capacitance and thus the resonant frequency of the device. The resonant frequency was monitored wirelessly with a low-power vector network analyzer observing the S21 parameter. Proof of concept was shown with subtilisin as the enzyme, activated by calcium (100 μg/mL and 5 mM, respectively) degrading a collagen substrate with a demonstrated wireless read range of up to 4 cm. Selectivity over other divalent cations (magnesium, copper II, and manganese II) and the effect of receiver motion were also shown on the wireless measurement.