Liquid biopsy has emerged as a potential supplement of traditional biopsy for early cancer diagnosis. It consists in monitoring the level of tumour biomarkers present in appropriate bodily fluids. Consequently, the development of non-invasive, easy-to-use and inexpensive methods for the detection of biomarkers is highly demanded for improving diagnosis and minimizing the mortality of cancer. In this context, electrochemical platforms have demonstrated great potential due to their high sensitivity, low cost, fast response as well as compatibility with point-of-care (POC) testing, what contributes to decentralize the analyses and favours the implementation of screening studies. Among them, personal glucose meter (PGM) employed daily in the measurement of blood glucose is the most used analytical method worldwide. Taking advantage of this mature technology, PGM has been recently applied to quantitate a wide range of non-glucose analytes by establishing a relationship between their recognition and glucose generation. This strategy is of particular interest for monitoring tumour biomarkers since PGMs are already approved by international agencies for application to clinical practice, thus paving the way for the launch of the new device to the market.
Thus motivated, we describe the development of a hybridization assay for the detection of prostate cancer antigen-3 or PCA3, a urinary RNA biomarker for prostate cancer diagnosis. Specifically, a sandwich-type genoassay has been implemented onto magnetic microparticles functionalized with streptavidin in combination with a PGM and alkaline phosphatase (ALP) as a glucose-generating enzyme for signal transduction. Moreover, in order to boost the method sensitivity, two fluorescein-tagged reporting probes has been designed for incorporation of two antifluorescein-ALP conjugates per target analyte. This enzyme catalyses the conversion of glucose-1-phosphate into glucose, whose concentration is subsequently determined with a glucometer. The resulting portable approach allows the reliable detection of PCA3 at picomolar levels.