Smartphone-Interfaced Serum Calcium-Level Quantification on a Simple Paper Strip Assay for Diagnostics at Extreme Point of Care

Due to its pivotal role in many physiological processes and calcium-depleting diseases like osteoporosis, accurate quantification of the concentration of calcium in blood serum is imperative in monitoring multifarious facets of human health and disease. Established laboratory-based protocols for serum calcium-level detection are expensive, resource-intensive, and functionally dependent on skilled technicians. Circumventing these constraints, here we innovate a novel adaptation of Bradford’s assay as a decisive preprocessing step of a highly specific diagnostic test for serum calcium-level detection. This ensures the binding of protein molecules to Coomassie dye under acidic conditions with a resulting alteration in its color to quench out the possibilities of unwarranted side reactions with excess proteins abundantly present in patient samples. This specific adaptation renders the test to be implemented on a simple paper strip without deploying a controlled laboratory-based procedure, obviating any adverse interference in the subsequent reaction of calcium in the serum with Arsenazo III, a metallochromic dye used for the final colorimetric detection step. The method is affordable, user-friendly, and can be deployed by minimally trained personnel at the point of use in extremely harsh environments. By mapping the resulting colorimetric information quantitatively with the serum concentration level from a panel of training datasets prestandardized via established laboratory-based gold standard examination, a simple smartphone-based readout system may be developed, bearing the potential of replacing the currently existing expensive, time-consuming, and environmentally restrictive diagnostic solutions.