Paper-based multiplex colorimetric vertical flow assay with smartphone readout for point-of-care detection of acute kidney injury biomarkers

Acute kidney injury (AKI) is a serious renal emergency that is often underdiagnosed and associated with high mortality rates. Early diagnosis of AKI is crucial to improve patient prognosis and reduce healthcare costs. In this study, a paper-based colloidal gold multiplex vertical flow assay was developed for rapid detection of three AKI biomarkers, namely, NGAL, CysC, and RBP4, in a single test kit. In this system, specific capture antibodies were pre-immobilized on the sensing membrane at four spatially isolated immunoreactive sites. Gold nanoparticles were conjugated with detection antibodies as the colorimetrical labels. The resultant images could be read out qualitatively by the naked eyes or quantitatively by a smartphone-based readout device. Three AKI biomarkers could be simultaneously detected in 10–15 min. The detection sensitivity and specificity for clinical serum samples collected from 25 patients with AKI and 25 healthy individuals were determined as 92% and 88%. This vertical flow assay platform is easy to use, rapid, and low cost. It is a promising diagnostic tool for multiplex detection of disease biomarkers at point of care.