Calorimetric sensing system for real-time urea and creatinine measurements

A high-sensitivity, calorimetric, point-of-care device for automated bedside urine testing based on a micromachined thermal sensor is presented. Immobilized urease and creatinine iminohydrolase enzymes on thin (25 μm) Kapton^® films are used to measure the catalytic calorimetric output as a function of concentration. The sensor design locates the active Kapton^® film in close proximity to the quartz temperature sensor thereby providing an efficient heat coupling between the two. Measurements of urea concentration at room temperature using the continuous flow set-up and creatinine in open chamber setup at 37 °C are presented. Concentrations of 50 mM for urea and 100 μM for creatinine have been measured. The paper presents the first non-contact, continuous flow thermal sensing measurements. The unique sensor design allows for enzyme immobilized Kapton^® film as an easy to swap disposable cartridge and represents a significant advancement for clinical diagnostic application.