Paper-based electrochemical device for the determination of H₂S in murine lysates for liquid biopsy application

Background: Hydrogen Sulfide (H₂S) is a biologically active endogenous gas, produced in mammalian tissues, which plays a critical role in several pathophysiological processes, including oncogenesis. This gas-transmitter can exert diametrically opposite effects on neoplastic cell proliferation, depending on the duration and concentration of H₂S exposure. Due to this dual role, antineoplastic drugs, aimed at modulating H₂S levels, are attracting considerable interest in both research and clinical settings. On this basis, H₂S could serve as a diagnostic biomarker, potentially indicating the presence and stage of a tumor in body fluids that can be analyzed by liquid biopsy. Results: In this work, an electrochemical sensor, screen-printed on filter paper, and then modified with a dispersion of Prussian blue, synthesized directly on the paper, was developed in order to detect H₂S in tissue lysates. After the optimization of several experimental parameters, the sensor was analytically characterized in standard solution, achieving a good repeatability and a detection limit of 3 μM, and the repeatability of the entire platform appeared to be lower than 10 %. The sensor was then applied to determine H₂S in biological samples, including a murine skin lysate, two pharmacologically treated neoplastic murine lysates, and an untreated neoplastic murine lysate, obtaining results in agreement with those observed with the standard methylene blue-based assay for H₂S determination, demonstrating the applicability of the developed electroanalytical method for liquid biopsy. Significance and novelty: It might represent a significant revolution in cancer diagnosis, and the use of point of care (PoC) platforms is a promising strategy to speed up and simplify operations, providing rapid and on-site analysis. In particular, the possibility of using portable miniaturized sensors allowed to reduce the amount of sample to analyzed: it usually represents an issue of traditional approaches.