Towards One-Step Quantitation of Prostate-Specific Antigen (PSA) in Microfluidic Devices: Feasibility of Optical Detection with Nanoparticle Labels

Rapid and quantitative prostate-specific antigen (PSA) biomarker detection would be beneficial to cancer diagnostics, improving early detection and therefore increasing chances of survival. Nanoparticle-based detection is routinely used in one-step nitrocellulose-based lateral flow (LF) immunoassays; however, it is well established within the scientific diagnostic community that LF technology lacks sensitivity for measuring biomarkers, such as prostate-specific antigen (PSA). A trend in point-of-care (POC) protein biomarker quantitation is the miniaturization of immunoassays in microfluidic devices. This work aimed at testing the feasibility of carbon and gold nanoparticles as immunoassay labels for PSA detection with cost-effective optical detection in a novel microfluidic POC platform called microcapillary film (MCF), consisting of a parallel array of fluoropolymer microcapillaries with 200-μm internal diameter. With neutravidin-coated carbon, nanoparticles were able to quantify an immobilized biotinylated monoclonal antibody (coating solution from 10 to 40 μg/ml) and PSA was successfully quantified in a sandwich assay using silver-enhanced gold nanoparticles and a flatbed scanner; yet, the dynamic range was limited to 10–100 ng/ml. Although direct optical detection of PSA without enzymatic amplification or fluorophores is possible and technically appealing for the simplified fluidics and signal scanning setups involved, ultimately, the binding of a thin layer of nanoparticles onto the wall of transparent microcapillaries is not sufficient to cause a significant drop on the optical colorimetric signal. Future studies will explore the use of fluorescence nanoparticles.