Thread-based colorimetric biosensor for urea determination in serum

Urea is a crucial biomarker in clinical analysis, mainly used to diagnose and monitor kidney condition. However, its reliable determination in serum in point-of-care testing format still remains a vital challenge. Here, we tackled this issue by developing a microfluidic thread-based optical biosensor for serum urea determination. The working principle of the presented device was combining enzymatic urea hydrolysis using urease with the resulting ammonium ions detection using ionophore-chromoionophore chemistry. Urease was immobilized on thread with the aid of synthesized urease-calcium phosphate nanoflowers while components for ammonium ions detection were embedded in PVC-based membrane located on the same thread. In the first step, ammonium ions determination in a thread-based sensor was optimized. Then, urease-calcium posphate nanoflowers (U-CaNFs) were included on the thread to ensure selectivity for urea. U-CaNFs synthesis was optimized and the resulting nanoflowers were characterized using various analytical techniqes (e.g. SEM, EDS, TGA, XRD). The calculated limit of detection for urea was 37 µmol L -1 and the total analysis time was only 8 min. The developed thread-based devices were validated with control sera samples, proving their high accuracy. • Thread-based colorimetric biosensor for urea determination in serum is proposed • Urease enzyme is immobilized on thread as urease-calcium phosphate nanoflowers • Ammonium ion is detected using optode membrane immobilized on thread • Limit of detection of urea is 37 µmol L -1 and total analysis time is 8 min • Thread-based devices were validated with serum samples