Urea Biosensor Based on a Field‐Effect Capacitor Modified With a Stacked Weak Polyelectrolyte/Enzyme Bilayer

ABSTRACT Urea is formed from the metabolism of proteins and used as a biomarker for diagnosing and monitoring various medical conditions. In this work, a urea biosensor based on an electrolyte‐insulator‐semiconductor capacitor (EISCAP) modified with a stacked polyelectrolyte polyallylamine hydrochloride (PAH)/urease bilayer prepared by the layer‐by‐layer (LbL) technique is presented for the first time. The LbL formation of the PAH/urease bilayer was monitored with an underlying charge‐sensitive Al/p‐Si/SiO 2 /Ta 2 O 5 EISCAP using convenient capacitive‐voltage and constant‐capacitance mode measurements. Urea‐sensitive EISCAP biosensors were electrochemically characterised in buffer solutions and artificial urine (AU) samples spiked with various concentrations of urea between 0.1 mM and 50 mM. The biosensors exhibited urea sensitivities of ca. 35.4 mV/dec and 32.1 mV/dec in buffer and AU solutions, respectively. Finally, local surface pH changes as a function of urea concentration have been evaluated. The obtained findings demonstrate the potential of PAH/urease‐modified EISCAPs for non‐invasive urea biomarker detection in urine samples at homecare or in‐field settings.