Prostate cancer (PCa) is the most common cancer among men diagnosed worldwide. The conventional non-invasive test for detection and staging of prostate cancer include prostate specific antigen (PSA) test which often can give false positives and is unable to distinguish between aggressive and indolent stages of PCa. This results in doing unnecessary invasive tests like digital rectal examination (DRE), biopsy etc., which only gives further anxiety to patients. Here we describe a rapid and oxygen-insensitive microfluidic immunoassay for on-line capture and precise detection of potential prostate cancer protein biomarkers. Measurement of a panel of biomarkers will help in not only diagnosing the PCa precisely but may also help in staging the cancer.

The microfluidic system includes protein capture from serum using a sandwich ELISA arrangement and signal-transducing poly-horseradish peroxidase (poly-HRP) enzyme labels on an 8-electrode screen-printed carbon array. A major challenge in using these screen-printed electrode arrays is the estimation of the electrochemical surface area (ECSA) of electrodes because the current signal is proportional to ECSA and variability in the electrode surface areas generate variability in the corresponding currents. We show that normalization of electrode responses having different surface areas can be achieved using in-situ experimental methods and that the normalization methods can improve the precision of the immunoassay. Another challenge in electrochemical immunoassay systems is the interference of oxygen using the mediator hydroquinone¹. A range of osmium polypyridyl complexes were studied to find the best mediator that is not affected by oxygen.

Using an optimized mediator and a simple method to estimate carbon electrode surface area, immunoassays can be designed with improved detection characteristics.

(1) Dhanapala, L.; Jones, A. L.; Czarnecki, P.; Rusling, J. F. Sub-Zeptomole Detection of Biomarker Proteins Using a Microfluidic Immunoarray with Nanostructured Sensors. Anal. Chem. 2020, 92 (12), 8021–8025. ttps://doi.org/10.1021/acs.analchem.0c01507.