Instant and low-cost detection of urinary microalbumin using smartphone technology and a paper-based platform with a...

Early detection of microalbuminuria is essential for preventing the progression of nephropathy and improving patient management. The present research proposes a simple, low-cost dye-binding method based on a standard addition principle for determining urinary albumin at clinically significant levels. The assay principle of the proposed paper-based analytical device is based on utilizing a specific and sensitive dye, bis(3',3″-diiodo-4',4″-dihydroxy-5',5″-dinitrophenyl) -3,4,5,6-tetrabromosulfonphthalein (DIDNTB), which binds to urinary albumin under extreme low pH conditions. The strategy was based on testing with three different albumin concentrations in the urine samples to obtain different color intensity ratios denoted as R1, R2, and R3, and further used to calculate a semi-quantitative amount of albumin. Under the optimized conditions, the linear range from 10 to 200 mg/L albumin and the detection limit 8.2 mg/L (R² = 0.99) was obtained. Interference studies revealed that glucose, ascorbic acid, uric acid, L-histidine, and globulin were in the acceptable recovery range (89-109%). Reproducibility assessments showed that the coefficients of variation (CV) for this method ranged between 3.7% and 7.7%. Additionally, receiver operating characteristic (ROC) plots were generated to establish the cut-off value for instant semi-quantitative interpretation of the results. Results from real sample analysis revealed that the proposed method is comparable to a widely used quantitative immunoturbidity method (r = 0.94, n = 50).