Urease quantification with a newly designed microfluidic device

Chronic Kidney Disease (CKD) is a condition characterized by the malfunction of the kidneys and the consequent accumulation of metabolic toxins in biological fluids (blood and saliva). To remove these toxins, CKD patients need frequent sessions of dialysis or alternatively a kidney transplant (Thepchuay et al., 2020). One of the main toxins to accumulate is urea, a nitrogenous product of the protein metabolism by the urea cycle primarily excreted in the urine. The increase of urea concentration in the body, including in saliva, results in the proliferation of urease-producing microorganisms (Costa et al., 2021; Thepchuay et al., 2020), and therefore both urea and urease become valuable biomarkers of kidney health. Although there are some commercially available kits to measure urease activity, they require specialized technicians and specific lab equipment (Chang, et al., 2022). In this context, μPADs (Microfluidic Paper-based Analytical Devices) can be an effective alternative as on-hand, point-of-care biosensors since they can perform the analytical determinations in a simpler, user-friendly procedure. In this work, a newly developed μPAD for the determination of urease in saliva samples is described. The determination was based on the conversion of urea to ammonium by urease, followed by the ammonium determination, after its conversion to ammonia and diffusion through a hydrophobic membrane, by the colour change of bromothymol blue indicator (BTB).