Detection of urine protein by a paper-based analytical device enhanced with ion concentration polarization effect

Charged species can be effectively stacked on paper-based analytical device (PAD) taking advantage of ion concentration polarization (ICP) effect. Protein, as ampholyte species, could also be stacked using this effect to improve its detection sensitivity. In this work, a protein detection method was proposed based on online ICP stacking and successfully used for the detection of total protein from urine samples. We showed that proteins from physiological samples can be directly and repeatedly loaded onto the depletion region of the ICP interface established by a piece of cation exchange membrane on a paper fluidic channel, and the protein content can be cumulatively stacked as a narrow band as visually observed by smartphone camera. Colorimetric detection of model protein (phyco) showed that at least 60-fold preconcentration could be achieved with this method. With post-staining of the stacked albumin from artificial urine, a linear response in the diagnostic meaningful range of 50-350mg/L (R-2=0.994) was achieved. Total protein from clinical urine samples was detected, and the recovery rate was found in the range of 93-108%, and the RSD was less than 11%. Comparative assays showed no significant difference between the results of this and that of the clinical method. This paper demonstrated the feasibility of online stacking and sensitive detection of proteins from physiological samples using PAD-ICP platform.