Smartphone enabled point of care estimation of urinary protein using a novel sample pad-based Bradford assay

Abstract

Proteinuria, the presence of excess protein in urine, is an early indicator of kidney damage or dysfunction. Its accurate estimation is crucial for the early diagnosis, monitoring, and management of renal and systemic diseases. This study introduces a sample pad-based Bradford reagent (SP@BR) colorimetric sensor integrated with smartphone imaging for rapid, quantitative urinary protein detection. Protein concentration induced color development on the SP@BR device was analyzed by extracting the value (V) component from the hue-saturation-value (HSV) color space. A customized MATLAB-based smartphone algorithm automated the calculation of V%, enabling user-friendly, on-site quantification. The method showed strong linearity with protein concentration (R2 = 0.99 in artificial urine

0.98 in real urine) and closely matched standard spectrophotometric results. The SP@BR sensor displayed high selectivity, long-term stability (300 days), and low detection limits of 67 μg/mL and 96 μg/mL for artificial and real urine, respectively. Clinical validation against commercial dipsticks and spectrophotometric assays confirmed the reliability and accuracy. This work presents the first lyophilized, reagent-retentive sample pad integrated with smartphone-based MATLAB analysis for quantitative urinary protein, detection proving it to below cost, portable, user friendly, and offering a robust alternative to conventional dipsticks. It holds strong potential for early diagnosis and continuous monitoring of kidney health in decentralized and resource-limited healthcare settings. © 2025