Fluorescent cellulose nanocrystals for the detection of lead ions in complete aqueous solution

A fluorescent probe for the detection of lead ions in complete aqueous solution was synthesized by covalently combining a fluorescent 1,8-naphthalimide dye with cellulose nanocrystals (CNCs). The dye-labelled CNCs have lots of carboxyl and hydroxyl groups on the surface, which make them disperse well in water. There is little fluorescence discrimination for 1,8-naphthalimide dye in the presence of different metal ions, while the fluorescent CNCs exhibit selective and sensitive response to Pb(II) with remarkably enhanced emission intensity. The limit of detection of the fluorescent CNCs is as low as 1.5 × 10⁻⁷ mol/L, and there is good linear relationship between the fluorescence maxima and the Pb(II) concentration in a wide range of 2.5 × 10⁻⁷–5.0 × 10⁻⁵ mol/L. The sensing ability of the dye-labeled CNCs to Pb(II) is ascribed to the synergistic complexation of Pb(II) with both the grafted dye groups and the adjacent carboxyl groups on the surface of the CNCs. The combination ratio of Pb(II) to the fluorophore on CNCs is determined to be 1.2:1 via Job’s plot experiment, which is basically consistent with the theoretical value of 1:1. The offered fluorescent CNCs can be employed as a nanosensor for the detection of metal ions and can be further promoted for many applications in chemical, environmental, and biological systems.

Water-dispersible fluorescent probe via covalent immobilization of 1,8-naphthalimide on cellulose nanocrystals (CNCs) exhibits selective and sensitive detection of lead ions in complete aqueous solution. The inhibited intramolecular charge transfer process (ICT) of the fluorophores loaded on CNCs contributes to the remarkably enhanced fluorescence emission in the presence of lead ions.