Silver Microdisc Array Electrode Chip for Urea Detection in Saliva Samples from Patients with Chronic Nephritis

Urea is an important biomarker for diagnosing various kidney and liver disorders. However, many existing methods rely on invasive blood sampling, which can potentially harm patients. Saliva has been recently recognized as a noninvasive and easily collectible alternative to blood for urea quantification. Electrochemical urea detection in saliva remains limited, with catalytic materials typically applied to the electrode surface via drop casting. This results in a random distribution of materials and potential aggregation on the electrode, which inevitably hinders the efficient mass transport of analytes, reducing both detection sensitivity and the utilization of catalytic materials. In this work, a silver nanoparticle (AgNP)-integrated microdisc array electrode chip was fabricated through the in situ growth of AgNPs on polydopamine (PDA) arrays, which were patterned using the microcontact printing (μCP) technique on an indium tin oxide (ITO) glassy substrate. The resulting AgNP microdisc array chip sensor exhibited much higher sensitivity toward urea sensing and greater material utilization as compared to traditional drop-cast electrodes, due to the enhanced mass transfer. Furthermore, the chip sensors demonstrated superior selectivity when challenged with potential interferences. More importantly, reliable urea quantification was achieved in clinical saliva samples from nephritis patients. These results indicate that the current sensor presents great opportunities for developing a noninvasive and sensitive liquid biopsy platform for urea determination in clinical diagnosis applications.