A fluorescent nanoprobe based on cellulose nanocrystals with porphyrin pendants for selective quantitative trace detection of Hg2+

Abstract

A well-dispersed chemosensor based on cellulose nanocrystals (CNCs) with porphyrin pendants (CNC-SA-COOC₆TPP) was facilely synthesized by the combination of carboxylation, extended esterification and dicyclohexylcarbodiimide (DCC) reaction. The CNC-SA-COOC₆TPP nanomaterials promoted the solubility of porphyrin groups in water and the nanomaterials could be easily separated from water by filtering. The structure of CNC-SA-COOC₆TPP nanomaterials could be verified by FT-IR, ¹H NMR and XPS characterization. The TEM images showed that CNC-SA-COOC₆TPP nanomaterials presented needle-like morphologies. The unique properties of high sensitivity and selectivity for Hg²⁺ of porphyrin-modified CNCs were investigated separately via fluorescence emission spectroscopy under characteristic excitation wavelengths of porphyrin moieties. Further investigation revealed that CNC-SA-COOC₆TPP nanomaterials (0.01 wt% in H₂O) could specifically detect Hg²⁺ with a detection limit for Hg²⁺ of ca. 5.0 × 10⁻⁸ mol L⁻¹ (50 nM). In addition, Hg²⁺ was specifically detected with interference from other metal ions, which was attributed to the specific formation of the Hg²⁺–porphyrin complex with an interaction stoichiometry of one Hg²⁺ per porphyrin moiety. The concentration of all other metal ions could be qualitatively detected based on the relationship between fluorescence intensity and concentration. As a result, the good dispersion of cellulose nanocrystals and the high selectively and sensitivity of porphyrin pendants resulted in the highly efficient detection of Hg²⁺ in water, which makes CNC-SA-COOC₆TPP a promising fluorescence chemosensor.