A dual-mode portable colorimetric platform for smartphone and Arduino-based point-of-care glucose detection with whiteness-based sustainability assessment.

Rapid and decentralized glucose monitoring requires analytical platforms that combine sensitivity, portability, affordability, and environmental sustainability. In this work, iron- and nitrogen-co-doped carbon dots (Fe,N-CDs) were synthesized through a simple one-step thermal approach and employed as nanozymes exhibiting intrinsic peroxidase-like activity for colorimetric sensing. Structural and morphological characterization confirmed the successful formation of Fe,N-CDs with favorable catalytic properties. The synthesized nanozymes efficiently catalyzed the oxidation of o-phenylenediamine in the presence of hydrogen peroxide producing a concentration-dependent colorimetric response with a linear range of 50-600 µM and a detection limit of 20 µM. By coupling the nanozyme system with glucose oxidase, a cascade sensing strategy was established for indirect glucose determination over a linear range of 100-600 µM. To enable portable and point-of-care analysis, the sensing platform was integrated with smartphone-assisted image analysis and an Arduino-based RGB detection module providing dual-mode digital colorimetric readout. Both portable approaches showed excellent agreement with conventional spectrophotometric measurements confirming the reliability of the proposed analytical platform. The developed assay demonstrated high selectivity toward glucose over common interfering species, excellent reproducibility (RSD < 1.5%), and successful application to serum glucose analysis. Furthermore, sustainability assessment using the whiteness score, BAGI (Blue Applicability Grade Index), RAPI (Red Analytical Performance Index), and VIGI (Violet Innovation Grade Index) tools confirmed favorable environmental compatibility, analytical performance, applicability, and innovation. Overall, the proposed platform combines low-cost nanozyme synthesis, dual-mode portable detection, reliable analytical performance, and sustainability offering a promising strategy for point-of-care glucose monitoring and decentralized biosensing applications.