A novel biosensor for on-line dialysis monitoring

Monitoring of urea in dialysate is critical to determine if patients with renal insufficiency receive adequate dialysis. Currently, dialysate is monitored through conductance measurements, yet questions exist if conductance can specifically monitor urea. A novel optical sensing method was developed that utilizes layer-by-layer self-assembled ultrathin films of polyions, an absorbing pH-sensitive dye, and urease which may be directly applied to dialysis tubing. Changes in pH caused by conversion of urea to ammonia cause the dye to change color which can be tracked through a photodetection system. A prototype sensor was suspended in solutions of different pH levels to test the sensitivity, and measurements of spectral absorbance changes in the sensor were collected with a UV-Vis spectrometer. Discrete wavelengths were also monitored with a compact, custom photodetection circuit. Experiments with urease were also conducted to determine the changes in pH due to typical urea concentrations in dialysate. Through measurements of absorbance, the sensor was found to be sensitive to pH changes with a nearly linear relationship between pH and absorbance. These findings suggest that the application of the layer-by-layer technique for sensor chemistry immobilization and basic absorbance detection circuitry to produce a device for clinical environments may increase dialysis efficiency.