ABSTRACT Accurate measurement of serum calcium is vital for evaluating calcium balance in the body and identifying conditions such as osteoporosis and disorders of the parathyroid gland. However, conventional laboratory‐based methods, although reliable, are often limited by high cost, dependence on sophisticated instrumentation, and the need for trained personnel, restricting their accessibility in resource‐limited settings. This work presents a low‐cost, paper‐based testing device for rapid serum calcium measurement using only 5 µL of sample. The system employs a chromogenic reaction in which arsenazo III is immobilized onto a defined region of a paper strip. Upon application of the serum sample, calcium ions interact with the dye, producing a visible color change. This change is captured using a smartphone camera and analyzed through a mobile application to determine calcium concentration. The assay is completed within 2 min without requiring laboratory instrumentation or specialized training. The device demonstrates high accuracy (99%) with a coefficient of variation below 3%, and the reagents remain stable under ambient conditions. Overall, this approach provides a portable and easy‐to‐use diagnostic tool suitable for community clinics and decentralized healthcare settings, with strong potential for future integration into digital health platforms and large‐scale point‐of‐care applications.
Sudip Chattopadhyay (Mon,) studied this question.