Towards low-cost bioanalytical tools for sarcosine assays for cancer diagnostics
Sarcosine is an amino acid that has been listed as a new indicator for prostate cancer. We present here two low-cost tools with the potential to detect this biomarker excreted in urine. The first one is a paper-based microfluidic device manufactured by wax printing technology in which an enzymatic assay is performed. The enzymatic assay comprises two coupled enzymatic reactions between sarcosine oxidase and horseradish peroxidase, with the ABTS redox indicator oxidized when sarcosine is present in the sample. This enzymatic assay on paper could be used as a preliminary screening method and presents a linear range up to 1 mmol L−1, with a sensitivity of 21.2 A.U. (mmol L−1)−1; LOD = 0.21 mmol L−1; LOQ = 0.61 mmol L−1 and r2 = 0.8898. The second bioanalytical approach consists of a capillary electrophoresis method with capacitively coupled contactless conductivity detection (CE-C4D). This method proved to be useful to separate sarcosine from 12 amino acids typically found in normal human urine using 10 mmol L−1 of triethylamine (TEA) as the background electrolyte. This method could be used as a follow-up method after the initial screening and presented a stable baseline, LOD = 0.034 mmol L−1 and LOQ = 0.069 mmol L−1. Migration time reproducibility (RSD) for intraday and inter-day assays was smaller than 0.6% and 4.4%, respectively. Both tools were able to analyze this potential tumor marker for prostate cancer, with capabilities of miniaturization and low-cost, essential characteristics for point-of-care testing (POCT) technology. Paper-based devices are inexpensive and simple, making them ideal for screening tests and telemedicine, while separation by CE-C4D presents high sensitivity and throughput, useful characteristics for exploratory studies.