Figure 2.

(A) The EAB sensor response to increasing concentrations of phenylalanine produces the expected Langmuir binding curve. As is common for sensors in this class, the device’s response is signal on at higher square wave frequencies and signal-off at lower frequencies. The physiologically relevant range of plasma phenylalanine levels in healthy individuals and individuals suffering from PKU is shown in blue.^24–26 (B) To show that the sensor achieves clinically relevant specificity we challenged it with tryptophan (trp), tyrosine (tyr), a mixture of the amino acids glutamine, histidine, proline, arginine, and alanine (AA mix), and the phenylalanine metabolites phenylpyruvate (Pyr) and phenylacetate (Ace). Using the same frequencies as in (A), the sensor does not measurably respond to any of these at concentrations below 300 μM, a level far above those seen physiologically. (C) Finally, the sensor is rapid, responding in just a few seconds to the addition of physiologically relevant target concentrations.