Food Chemistry: Smartphone-Based Analytical Platform for Real-Time and Reversible Detection of Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ Ions

The rapid and portable detection of transition metal ions such as cobalt (Co²⁺), nickel (Ni²⁺), copper (Cu²⁺), and zinc (Zn²⁺) is essential for environmental, industrial, and biological monitoring. Conventional laboratory-based analytical methods, though sensitive, are time consuming, expensive, and unsuitable for on-site analysis. In this study, we propose the development of a smartphone-based analytical platform capable of real-time, reversible detection of Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions using a colorimetric/ fluorometric sensing film integrated with a smartphone camera and data-processing application. Reversibility is achieved through regeneration of the sensing film using mild chelating agents (e.g., EDTA or citrate buffer), allowing multiple detection cycles without significant loss of sensitivity. The proposed platform offers a detection limit in the micromolar range, response time under two minutes, and reusability across several cycles, enabling low cost, real-time, and portable quantification of these metal ions in environmental and biological samples. This work provides a sustainable alternative to traditional analytical instruments, demonstrating the integration of smartphone optics, reversible sensing chemistry, and digital analytics into a single user-friendly platform for field-deployable heavy metal ion monitoring.