Exploring the Feasibility of Paper-Based Substrates for User-Friendly Electrochemiluminescent Sensors

Electrochemiluminescence (ECL) is a light-emitting process in which electrochemically generated excited states relax to the ground state and emit photons; in many systems, this excitation is produced through reactions involving a coreactant. ECL has been successfully employed in devising analytical methodologies requiring exceptional sensitivity and ultralow background, critical for precise measurements. Its seamless integration with paper-based platforms further enhances easiness of use, portability and cost-efficiency, expanding its applicability across biomedical, environmental, and point-of-care fields. This novel study aims at integrating the sensitivity offered by ECL and the experimental convenience of paper-based substrates, thus bridging a gap in the science of measurements and providing a new analytical tool with relevant features. Office paper and filter paper were evaluated and compared to conventional and widely used polyester-based screen-printed electrodes. The main goal was to assess their electrochemical behavior, analytical performance and reliability for long-term reagent storage. In fact, the use of paper might lead to a key innovation in the field: tripropylamine, the sacrificial coreactant successfully employed in combination with the luminophore tris(2,2'-bipiridine)ruthenium(II), namely Ru(bpy)₃²⁺, in a model ECL system, was dried by taking advantage of the paper's porosity. This allowed eliminating manual reagent addition/mixing during analysis, with the result of simplifying the experimental procedure at the end-user and enhancing storage stability. As promising results, the electrochemical characterization revealed that office paper exhibited superior sensor's performance due to its lower porosity, while the highly porous filter paper caused signal loss and reduced analytical performance. Features such as sensitivity, stability, repeatability and storage ability were assessed. Overall, this study demonstrates the potential of paper-based substrates, especially commercial office paper, as sustainable and cost-effective platforms for ECL sensing.