Device and methods of using device for detection of aminoacidopathies

A biosensor comprising:

• at least one electrically conductive support, the at least one electrically conductive support attached to a hydrogel, the hydrogel comprising at least one electron mediator, at least one reduction agent, and at least one metabolic enzyme from a thermophilic bacterial cell or functional fragment thereof, wherein the hydrogel comprises alginate;
• and
• an amperometer and/or voltmeter operably connected to the at least one electrically conductive support;
• wherein the at least one electrically conductive support comprises a phenylalanine dehydrogenase or functional fragments thereof;
• and
• wherein the phenylalanine dehydrogenase or functional fragment thereof comprises at least about 70% sequence identity to SEQ ID NO:1 or SEQ ID NO:2.