A Microfluidic Paper-Based Electrochemical Immunosensor for Point-of-Care Testing of Kidney Injury Molecule-1

Acute kidney injury (AKI) is a global health problem due to its high rates of morbidity and mortality. Kidney injury molecule-1 (KIM-1) is considered as a potential biomarker for the diagnosis of AKI. In this study, we proposed an oriented antibody immobilization strategy for reliable detection of KIM-1 by utilizing single-stranded DNA with a methylene blue tag (MB-ssDNA) to achieve directional immobilization of antibodies onto poly methylene blue (PMB) on the electrode surfaces through cyclic voltammetry (CV). PMB not only enhanced electron transfer rate but also provided a platform for the oriented immobilization of antibody. The proposed immunosensor demonstrated a limit of detection (LOD) of 5.8 pg/mL with a linear range from 1 to 100 pg/mL. The immunosensor exhibited good repeatability and reusability as well as excellent operational stability. Furthermore, we successfully developed a low-cost and portable paper-based microfluidic electrochemical device to measure KIM-1 concentrations in artificial urine. Integrated flexible electrochemical immunosensors based on antibody orientation immobilization and electrochemical signal amplification have great application potential in personalized point-of-care (POC) clinical diagnosis.