From Buffers to Food Matrices: tKeima-Based Fluorescent Biosensing of Metal Ions in Beverages

Metal ions such as iron and copper can affect the quality and stability of beverages, necessitating biosensor development. In this study, we evaluated the applicability of the fluorescent protein tKeima as a fluorescence-quenching platform for screening Fe2+, Fe3+, and Cu2+ in beverage matrices. tKeima showed concentration-dependent fluorescence quenching toward all three metal ions in soft drinks, ion drinks, vegetable juices, matcha, and milk. Analysis of the matrix effects of these beverages revealed that tKeima retained approximately 72–82% of the quenching response observed under buffer conditions, indicating that metal-responsive fluorescence was largely retained. Spike recovery analysis demonstrated that added Fe2+, Fe3+, and Cu2+ could be detected in the beverage matrices, with recovery values generally ranging from approximately 70 to 84% at higher spike concentrations. Overall, these findings suggest that tKeima retains measurable metal-responsive fluorescence quenching in complex beverage matrices and provide a basis for its use as a simple fluorescence-based platform for first-line screening of iron and copper ions in beverage samples. This study provides a first proof-of-concept evaluation of fluorescent protein-based metal-responsive sensing of real food matrices using pretreated commercial beverages.