Wax-printed paper-based device for direct electrochemical detection of 3-nitrotyrosine

An overview of the last trends in lab-on-chip technology highlights the continuous development of biosensing approaches in terms of simplicity, low-cost, and quick response, with a higher sensitivity and selectivity. In this context, electrochemical sensors arrived to overcome the need to develop small, accurate, portable and compact sensing devices, compatible with routine use in loco analysis, especially in point-of-care (POC) assessment. Herein, we have presented the first paper-based electrochemical sensor towards the detection of 3-nitrotyrosine (3-NT), a relevant oxidative stress biomarker. This innovative sensor was designed by, first, modifying paper to become a hydrophobic support and, second applying carbon and silver conductive inks to generate a three electrode-system on a small spot. An intensive voltammetric investigation of the paper-based screen-printed electrodes (SPEs), including the study of different redox-probes, scan-rate values, probe concentrations and supporting electrolyte solutions, confirmed their suitable and reliable electrochemical performance. Square wave voltammetry (SWV) was employed to assess the sensitivity of the proposed sensor at various concentrations of 3-NT, ranging from 500 nM to 1 mM, enabling a low detection limit (LOD) of 49.2 nM. The interference of co-existing species was also tested and good selectivity against 3-NT was accomplished. Overall, this flexible paper-based platform constitutes a promising sensor material towards a quick, sensitive, cost-effective, sustainable and reproducible detection of 3-NT biomarker.