was used for the cyclic voltammetric and amperometric evaluations. All tests were performed at ambient temperature (approximately 21–23 °C). A 200 µL sample volume of different ALT solution was placed in a 2.0 mL microcentrifuge tube. A testing solution containing 250 mM L-alanine, 2.5 mM α-ketoglutarate and 1,760 UL−1 of PyOx, in addition to the ALT solution of variable concentration 0–544 ng/mL, which corresponds to ALT specific activity 0–80 UL−1. The sensor was inserted into the testing tube to quantify the ALT level. A new fresh sensor was used for each measurement. Each concentration was tested at least three times for the reproducibility. Potential values reported throughout this study were measured versus the screen-printed Ag/AgCl reference electrode on the sensor prototype.