Manganese-engineered carbon nanomodulators with predominant epidermal localization: Nanobiointerface interactions and tyrosinase modulation

Understanding how nanomaterials interact with biological interfaces is essential for the development of spatially controlled bioactive systems. Here, we report protein-derived manganese-engineered carbon quantum dots (Mn:CQDs) designed to investigate nanobiointerface interactions and tyrosinase modulation. The Mn:CQDs exhibited homogeneous morphology, with an average size of approximately 12 nm, a strongly positive surface charge ( ζ = +38.2 mV), intrinsic fluorescence, and concentration-dependent cytotoxicity. Spectroscopic analyses indicated strong interaction between Mn:CQDs and the melanogenic model enzyme (K A ≈ 10 6 M − 1 ), while thermodynamic analysis supported a spontaneous association process. Kinetic analysis revealed a mixed inhibition profile, with preferential interaction with the free enzyme and inhibition in the nanomolar range. Molecular docking further supported favorable interactions with the tyrosinase catalytic region. The Mn:CQDs exhibited an IC 50 of 49.76 ± 3.78 nM for tyrosinase modulation, whereas significant cytotoxic effects were observed at 500 μ g/mL and became more pronounced at higher concentrations. The ex vivo fluorescence study of the porcine skin under the conditions tested demonstrated a prominent localization in the superficial epidermal compartments and a significantly weaker fluorescence signal in the deeper tissue sections. Together, these findings demonstrate how engineered carbon nanostructures can integrate surface properties, biomolecular interactions, enzymatic modulation, and preferential tissue localization, providing a platform for studying spatially controlled nanobiointerfaces.