Online sample clean-up and enrichment of proteins from salty media with dynamic double gradients on a paper fluidic channel.

Paper-based analytical device (PAD) has received more and more attention in the field of point-of-care test (POCT) due to its low cost, portability and simple operation. Sensitivity and selectivity are two important aspects in clinical diagnostic analysis. However, low sensitivity of a PAD limits its wider application for POCT. Here we introduced a PAD that can clean and enrich the protein content from salty media with both electric field (E) and pH gradient (double E/pH gradients), with which 100-fold enrichment effect could be achieved within 70 s as demonstrated by fluorescein isothiocyanate labeled bovine serum albumin (FITC-BSA) from artificial urine media. With post staining of the protein stacking band with bromophenol blue (BPB), selective colorimetric detection of human serum albumin (HSA) was achieved simply with smartphone camera in the clinically significant range of 10–300 mg‧L−1 (R2 = 0.99) with a limit of detection (LOD) of 4.9 mg‧L−1. Detection of microalbuminuria (MAU) of diabetic patients was demonstrated with this method without difference (ɑ = 0.01) to that by the clinical method (immunoturbidimetry). This work demonstrated the potential of this PAD method in online sample pretreatment and detection of target component from complex physiological samples. Image 1 • Both electric field and pH gradient (E/pH double gradients) can be established and sustained on a paper fluidic channel. • Ampholytic content from salty sample media can be stacked/separated from other types of species. • Proteins from urine can be cumulatively stacked on the double gradient interface without intensive pre-treatment. • Sensitive and selective colorimetric detection of microalbuminuria (MAU) from clinical samples was successfully demonstrated. [ABSTRACT FROM AUTHOR]