Method for quantification of a prostate cancer biomarker in urine without sample preparation

We describe a macrocantilever-based method for detecting a prostate cancer biomarker (alpha-methylacyl-CoA racemase; AMACR) directly in patient urine without a sample preparation step and without the use of labeled reagents. Clean catch voided urine specimens were prospectively collected from five confirmed prostate cancer patients 3 weeks postbiopsy. The presence of AMACR was measured in a blinded manner by exposing 3 mL of urine to the anti-AMACR-immobilized piezoelectric-excited millimeter-sized (PEMC) sensor. The resonance frequency of PEMC decreases as AMACR from sample binds to the antibody on the sensor. The resonance frequency changes for the five patients tested were 4,314 +/- 35 (n = 2), 269 +/- 17 (n = 2), 977 +/- 64 (n = 3), 600 +/- 31 (n = 2), and 801 +/- 81 (n = 2) Hz, respectively. Positive detection was observed within approximately 15 min. The responses to positive, negative, and buffer controls were -9 +/- 13, -34 +/- 18, and -6 +/- 18 Hz, respectively. Positive verification of AMACR attachment was confirmed by low-pH buffer release. The sensor response was quantitatively related to AMACR concentration in control urine, and the relationship was used in developing an in situ calibration method for quantifying AMACR in patient urine. Estimated concentrations of 42, 2, and 3 fg/mL AMACR were calculated for the three patients' urine, while absence of AMACR was confirmed in control urine (n = 13). Because of simplicity of measurement combined with high sensitivity and specificity, the method may be a useful adjunct in a point-of-care setting to identify men at increased risk for prostate cancer.