An amperometric l-citrulline biosensor

Plasma l-citrulline is widely recognized as a clinically important biomarker, primarily serving as an indicator of intestinal function; it is used to assess and monitor the severity of intestinal failure and short bowel syndrome, as well as to diagnose congenital citrullinemia associated with urea-cycle disorders. However, its rapid and simple quantification remains challenging. To our knowledge, this is the first report of an amperometric biosensor for l-citrulline. In this work, the biosensor was developed based on mediated electron transfer (MET)-type bioelectrocatalysis of l-citrulline dehydrogenase (CitDH). The enzyme was immobilized on a mesoporous carbon electrode modified with graphene-coated porous silica spheres (G/PSS) and quinoline-5,8-dione (QD). A catalytic current for l-citrulline oxidation was obtained through QD-mediated electron transfer between immobilized CitDH and the electrode. The biosensor exhibited a linear amperometric response to l-citrulline concentrations ranging from 0.040 to 0.787 mM, with a sensitivity of 1.08 ± 0.17 μA cm^-2 mM^-1. Interference from l-arginine was minimal at low concentrations (approximately 0.1 mM), with a 3.7-fold higher sensitivity observed for l-citrulline within the linear response range. The sensor performance covers clinically relevant concentration ranges for hypercitrullinemia, demonstrating the feasibility of amperometric citrulline sensing. This study provides a new electrochemical platform for practical citrulline detection.