Loofah-Inspired CuS/Fe3O4@BC nanozyme: A multifunctional platform for mercury(II) detection, visual biosensing, and dye degradation

The accumulation of toxic heavy metal ions and organic pollutants in biological systems presents critical challenges for clinical diagnostics and therapeutic safety, demanding innovative solutions for sensitive detection and targeted remediation. Here, a nanozyme referred to as CuS/Fe 3 O 4 @BC has been developed by integrating copper sulfide (CuS) and iron oxide (Fe 3 O 4 ) onto a biochar (BC) matrix. This material exhibits biomimetic hierarchical porosity and enhanced peroxidase-like activity, making it specifically tailored for biomedical analysis applications. This multifunctional platform achieves ultrasensitive mercury(II) detection in biological fluids through structural optimization of mass transfer kinetics combined with a 29.3-fold enhancement in catalytic activity compared to conventional CuS nanozymes. To bridge laboratory diagnostics with point-of-care applications, the nanozyme is integrated into smartphone-coupled hydrogel spheres, enabling portable colorimetric quantification of Hg 2 + with a detection limit of 0.28 μM. Additionally, the system demonstrates efficient enzyme-mimetic clearance of dyes such as methylene blue and Congo red under flow conditions, achieving 99 % degradation efficiency within 20 min. By synergizing biosensing, catalytic remediation, and mobile health technologies, this nanozyme platform establishes a transformative approach for integrated diagnostic-therapeutic strategies, addressing unmet needs in toxicology monitoring, medical wastewater management, and therapeutic dye detoxification.