Efficient Portable Urea Biosensor Based on Urease Immobilized Membrane for Monitoring of Physiological Fluids

Numerous studies have addressed the utilization of glutaraldehyde (GA) as a homobifunctional cross-linker. However, its applicability has been impeded due to several issues, including the tendency of GA molecules to undergo polymerization. Herein, a portable urea biosensor was developed for the real-time monitoring of the flow of physiological fluids; this was achieved by using disuccinimidyl cross-linker-based urease immobilization. Urease was immobilized on a porous polytetrafluoroethylene (PTFE) solid support using different disuccinimidyl cross-linkers, namely disuccinimidyl glutarate (DSG), disuccinimidyl suberate (DSS) and bis-N-succinimidyl-(pentaethylene glycol) ester (BS(PEG)₅). A urease activity test revealed that DSS exhibited the highest urease immobilizing efficiency, whereas FT-IR analysis confirmed that urease was immobilized on the PTFE membrane via DSS cross-linking. The membrane was inserted in a polydimethylsiloxane (PDMS) fluidic chamber that generated an electrochemical signal in the presence of a flowing fluid containing urea. Urea samples were allowed to flow into the urea biosensor (1.0 mL/min) and the signal was measured using chronoamperometry. The sensitivity of the DSS urea biosensor was the highest of all the trialed biosensors and was found to be superior to the more commonly used GA cross-linker. To simulate real-time monitoring in a human patient, flowing urea-spiked human serum was measured and the effective urease immobilization of the DSS urea biosensor was confirmed. The repeatability and interference of the urea biosensor were suitable for monitoring urea concentrations typically found in human patients.

Parylene-Coated Polytetrafluoroethylene-Membrane-Based Portable Urea Sensor for Real-Time Monitoring of Urea in Peritoneal Dialysate

A portable urea sensor for use in fast flow conditions was fabricated using porous polytetrafluoroethylene (PTFE) membranes coated with amine-functionalized parylene, parylene-A, by vapor deposition. The urea-hydrolyzing enzyme urease was immobilized on the parylene-A-coated PTFE membranes using glutaraldehyde. The urease-immobilized membranes were assembled in a polydimethylsiloxane (PDMS) fluidic chamber, and a screen-printed carbon three-electrode system was used for electrochemical measurements. The success of urease immobilization was confirmed using scanning electron microscopy, and fourier-transform infrared spectroscopy. The optimum concentration of urease for immobilization on the parylene-A-coated PTFE membranes was determined to be 48 mg/mL, and the optimum number of membranes in the PDMS chamber was found to be eight. Using these optimized conditions, we fabricated the urea biosensor and monitored urea samples under various flow rates ranging from 0.5 to 10 mL/min in the flow condition using chronoamperometry. To test the applicability of the sensor for physiological samples, we used it for monitoring urea concentration in the waste peritoneal dialysate of a patient with chronic renal failure, at a flow rate of 0.5 mL/min. This developed urea biosensor is considered applicable for (portable) applications, such as artificial kidney systems and portable dialysis systems.