Total urinary protein sensor based on a piezoelectric quartz crystal

A protein sensing system using a piezoelectric sensor with an AT-cut quartz crystal of a basic resonant frequency of 9 MHz has been developed and applied to the determination of total protein in urine. The measurement method is based on the sedimentation of proteins by a turbidimetric procedure. The amount of precipitate formed was determined as the resonant frequency change of the quartz crystal because of the mass change on the surface of the piezoelectric sensor due to the precipitation. A satisfactory correlation was observed between the protein concentration and the frequency change at the range from 50 to 1000 mg/l, and a coefficient of variation (C.V.) of 5.3% (n = 10) was given for 300 mg/l albumin when sulfosalicylic acid was used as the precipitation reagent. When trichloroacetic acid was used as the precipitator, the C.V. was 3.2% (n = 12), and the difference in results for the same concentration of albumin and globulin was much less than that when using sulfosalicylic acid. Treatment with a protease after the measurement was effective for cleaning the electrode surface, allowing the device to be repeatedly used over 300 times.