Electrochemical Immunosensor for Point-of-Care Detection of Citrullinated Histone H3 Using Screen-Printed Graphene Electrodes and a Portable Potentiostat.

Citrullinated histone H3 (CitH3) is an emerging biomarker for early sepsis diagnosis. However, its detection based on standard enzyme-linked immunosorbent assay (ELISA) suffers from long analysis time (4-5 h), expensive instruments, and the need for skilled operators, necessitating the development of alternative detection platforms. Herein, a portable electrochemical immunosensor for CitH3 determination was developed using a screen-printed graphene electrode coupled with a custom-designed potentiostat. CitH3 was detected via a sandwich immunoassay employing horseradish peroxidase-conjugated antibody and amperometric measurement in the presence of hydroquinone and hydrogen peroxide. Key fabrication and detection parameters were systematically optimized to achieve high analytical performance. Under optimal conditions, the immunosensor exhibited a linear detection range of 0.1-1000 ng mL-1 with a detection limit of 42.83 pg mL-1 and a quantification limit of 100.89 pg mL-1, enabling the discrimination between sepsis and nonsepsis conditions. Additionally, the developed method provided a lower detection limit and shorter processing time (2 h) compared with ELISA. It also demonstrated high selectivity against common serum interferents, satisfactory accuracy (recovery = 89.49-106.11%), and good repeatability (relative standard deviation < 10%). Analysis of clinical serum samples (n = 50) showed a high correlation coefficient with ELISA (r = 0.9861), and Bland-Altman analysis confirmed their good agreement. Furthermore, the assay diagnostic performance demonstrated 100% specificity with high sensitivity values of 90.01% and 81.25% for sepsis and severe sepsis cases, respectively. These results suggested the potential of the proposed portable electrochemical immunosensor as a practical tool for sepsis diagnosis.