Charge-regulated and enthalpy-driven supramolecular assembly of boron-doped carbon dots enables robust ferric ion (Fe3+) sensing in food matrices.

Background

The sensitive quantification of trace metal ions, particularly Fe3+, in complex environmental and food matrices remains a formidable challenge due to severe matrix-induced interference. While fluorescent carbon dots (CDs) are widely employed, their quenching mechanisms are frequently oversimplified as isolated single-particle events, neglecting the critical role of colloidal behavior and interparticle dynamics. Consequently, conventional CD probes often suffer from poor signal stability in real-world applications. Therefore, there is a pressing need to establish rigorous physical chemistry frameworks to rationally design CD sensors that utilize controlled collective behaviors to achieve robust, matrix-resistant target recognition.

Results

Herein, we demonstrate that boron-doped carbon dots (BCDs) enable highly selective Fe3+ quantification via a distinct, charge-regulated supramolecular assembly mechanism rather than conventional molecular-scale quenching. Spectroscopic analyses reveal that specific Fe3+ coordination with oxygen-containing surface ligands initiates ligand-to-metal charge transfer (LMCT). This interaction progressively neutralizes the surface charge of BCDs, triggering spontaneous and enthalpy-driven interparticle bridging (ΔH = -24.54 kJ mol-1). Both DLS measurements and molecular dynamics simulations confirm that optimal fluorescence attenuation occurs exclusively when these BCD-Fe3+ complexes reach a near-neutral charge state, forcing them into compact, structurally constrained assemblies. Unlike generic aggregation, this specific assembly is highly resistant to abundant salts and biomacromolecules. Exploiting this locked-in signal readout, the BCD sensor accurately quantified Fe3+ in highly complex, real-world matrices-including milk, orange juice, and lake water-achieving high recoveries (95.2-104.1%) that perfectly matched conventional ICP-MS analysis.

Significance

AND NOVELTY This work reframes carbon-dot-based sensing from an empirical observation of isolated nanoparticle quenching to a rationally designed, charge-regulated collective assembly phenomenon. By deciphering the thermodynamic and electrostatic principles driving this cooperative interfacial interaction, we provide a robust conceptual framework for designing next-generation fluorescent nanoprobes whose signal stability and selectivity in complex matrices are intrinsically governed by controlled supramolecular organization.