Fabrication of Fe-Mn mixed oxide nanosheets via microwave assistance as an advanced probe for ultra-sensitive nepafenac sensing in diverse matrices; paving the way for future applications.

A novel colorimetric sensing platform for the ultra-sensitive detection of nepafenac (NEP) is investigated based on mesoporous Fe-Mn bimetal oxide nanosheets synthesized via a rapid microwave-assisted method. The incorporation of microwave irradiation represents a key innovation, enabling energy-efficient synthesis while enhancing structural uniformity, surface area, and catalytic performance. Comprehensive characterization using transmission electron microscopy (TEM) confirmed the formation of interconnected nanosheets, while X-ray diffraction (XRD) analysis shows a poorly crystalline mixed Fe-Mn oxide, whose nanoscale disorder enhances surface activity and redox cycling, making it highly effective for oxidative applications. Fourier-transform infrared (FTIR) spectroscopy verified metal-oxygen-metal (Fe-O-Mn) framework formation, and energy-dispersive X-ray (EDX) spectroscopy confirmed homogeneous elemental distribution. The fabricated Fe-Mn mixed oxide nanosheets exhibited excellent oxidase-like activity, catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to its blue-coloured oxidized product (oxTMB). In the presence of NEP, a significant decrease in blue colour intensity was observed due to NEP-induced inhibition, enabling accurate quantification. Under optimized conditions, the sensor demonstrated outstanding sensitivity with a detection limit as low as 0.15 ng/mL and a linear range of 0.5-25.0 ng/mL. The method was successfully applied to determine NEP in commercial eye drop formulations and synthetic aqueous humour, with high recovery percentages (99.61% and 99.62%, respectively), confirming its practical applicability. Additionally, the environmental sustainability of the approach was critically assessed using multiple contemporary greenness evaluation tools (ComplexMoGAPI, AGREE, AGSA and BAGI), confirming its alignment with green analytical chemistry principles. This study demonstrates the synergistic benefits of microwave-assisted synthesis and rational nano-catalyst design, offering a promising platform for future applications in pharmaceutical analysis and clinical diagnostics.