Eco-conscious Fe-Cu bimetallic nanozymes as a multimodal colorimetric platform for glucose and hexavalent chromium...

The integration of sustainable nanotechnology with portable analytical systems offers a promising strategy for advancing point-of-care (POC) diagnostic platforms with Green and White Analytical Chemistry. In this work, eco-conscious iron-copper bimetallic nanozymes (Fe-Cu BNPs) were synthesized through a facile aqueous approach and explored as multifunctional peroxidase-mimicking catalysts for biomedical and environmental sensing applications. The synthesized Fe-Cu BNPs functioned as highly active catalytic interfaces converting 3,3',5,5'-tetramethylbenzidine (TMB) into a blue oxidized product through a hydrogen peroxide-dependent reaction, thereby enabling sensitive colorimetric determination. The developed platform exhibited good analytical performance with linear ranges of 10-700 µM for H₂O₂, 10-500 µM for glucose, and 0-500 µM for Cr(vi) (R ² > 0.99). The sensor demonstrated high sensitivity, favorable selectivity, and successful application to human serum samples. Kinetic analysis revealed a low K _m value (0.18 mM) and a V _max of 8.92 × 10^-8 M s^-1 confirming the favorable catalytic efficiency of the Fe-Cu BNP nanozymes. To facilitate portable monitoring, a multimodal sensing platform was developed by integrating spectrophotometric measurements with smartphone-assisted digital image colorimetry and Arduino-enabled data acquisition. The analytical response was monitored by capturing the developed colorimetric signal with a smartphone camera followed by quantitative RGB image analysis allowing convenient point-of-care glucose determination without reliance on laboratory-based instrumentation. The fabricated sensing system displayed effective catalytic performance, an extensive linear working range, high analytical sensitivity, low limits of detection, and good resistance to interference from commonly encountered biomolecules. The practical applicability of the proposed methodology was demonstrated through successful glucose determination in human serum samples while the Fe-Cu BNP platform exhibited promising analytical performance for Cr(vi) detection. Mechanistic studies suggested that the synergistic interaction between iron and copper active centers promotes electron-transfer processes and reactive oxygen species generation resulting in enhanced catalytic activity. Furthermore, sustainability assessment using several assessment tools confirming the environmental compatibility, analytical reliability, and practical utility of the developed platform. Overall, this work presents a sustainable multifunctional Fe-Cu nanozyme system that combines eco-conscious aqueous synthesis, portable digital sensing, and comprehensive sustainability evaluation within a unified analytical framework. The developed strategy provides a promising platform for next-generation point-of-care diagnostics and environmental monitoring.