RESUMEN
One of the most important reasons for an increased mortality rate of cancer is late diagnosis. Point-of-care (POC) diagnostic sensors can provide rapid and cost-effective diagnosis and monitoring of cancer biomarkers. Portable, disposable, and sensitive sarcosine solid-contact ion-selective potentiometric sensors (SC-ISEs) were fabricated as POC analyzers for the rapid determination of the prostate cancer biomarker sarcosine. Tungsten trioxide nanoparticles (WO3 NPs), polyaniline nanoparticles (PANI NPs), and PANI-WO3 nanocomposite were used as ion-to-electron transducers on screen-printed sensors. WO3 NPs and PANI-WO3 nanocomposite have not been investigated before as ion-to-electron transducer layers in potentiometric SC sensors. The designated sensors were characterized using SEM, XRD, FTIR, UV-VIS spectroscopy, and EIS. The inclusion of WO3 and PANI in SC sensors enhanced the transduction at the interface between the screen-printed SC and the ion-selective membrane, offering lower potential drift, a longer lifetime, shorter response time, and better sensitivity. The proposed sarcosine sensors exhibited Nernstian slopes over linear response ranges 10-3-10-7 M, 10-3-10-8 M, 10-5-10-9 M, and 10-7-10-12 M for control, WO3 NPs, PANI NPs, and PANI-WO3 nanocomposite-based sensors, respectively. From a comparative point of view between the four sensors, PANI-WO3 nanocomposite inclusion offered the lowest potential drift (0.5 mV h-1), the longest lifetime (4 months), and the best LOD (9.95 × 10-13 M). The proposed sensors were successfully applied to determine sarcosine as a potential prostate cancer biomarker in urine without prior sample treatment steps. The WHO ASSURED criteria for point-of-care diagnostics are met by the proposed sensors.