Haloalkaliphilic archaea-mediated green synthesis of superparamagnetic Fe₃O₄ nanoparticles for electrochemical detection of ibuprofen in saline environments

Abstract The presence of pharmaceutical residues in aquatic systems poses a growing environmental concern, necessitating the development of sustainable and efficient sensing materials. In this study, haloalkaliphilic archaea were employed as green biocatalysts for the synthesis of magnetite (Fe₃O₄) nanoparticles and their application in the electrochemical detection of ibuprofen under saline conditions. Two archaeal strains produced Fe₃O₄ nanoparticles with well-defined inverse spinel crystal structures, nanoscale dimensions, and superparamagnetic behavior, while exhibiting distinct surface chemistry and magnetic properties. Strain-dependent differences in crystallinity and surface functionalization were found to strongly influence electrochemical performance. RA5-derived nanoparticles exhibited higher crystallinity and enhanced charge-transfer efficiency, achieving a sensitivity of 2.105 µA mg L⁻¹ and a limit of detection of 0.927 mg L⁻¹. In contrast, A6-derived nanoparticles featured a richer organic surface corona that promoted analyte adsorption, resulting in a sensitivity of 2.2186 µA mg L⁻¹ and a detection limit of 1.05 mg L⁻¹. Both modified electrodes enabled reliable ibuprofen detection over a wide linear concentration range of 0–100 mg L⁻¹. These results demonstrate that haloalkaliphilic archaea can function as sustainable nano-factories for producing functional magnetic nanomaterials, offering an eco-friendly strategy for electrochemical monitoring of pharmaceutical contaminants in complex aquatic environments.