Specific discrimination of zinc and manganese ions by label free dual emissive carbon dots by ratio-metric mode

Abstract

Due to the worldwide ecological and environmental issues induced by heavy metal pollution, including zinc and manganese, the ratio-metric discrimination of Zn²⁺ and Mn²⁺ based on CDs is urgently required. In this work, reduced CDs (re-CDs) with the intrinsic dual emissive peaks are obtained, and specific discrimination of Zn²⁺ and Mn²⁺ is realized by re-CDs with ratio-metric mode. With the addition of Zn²⁺, the fluorescent (FL) intensity at 650 nm increases obviously, while that at 680 nm progressively decreases. However, the presence of Mn²⁺ would induce the quenching of FL intensity at 680 nm while that at 650 nm remains constant. Then the Zn²⁺ and Mn²⁺ can be separately determined with the ratio of FL intensity at 650 nm to that at 680 mm (F₆₅₀/F₆₈₀). Under optimal conditions, the limit of detection (LOD) of Zn²⁺ is determined to be 9.09 nmol/L, and that for Mn²⁺ is estimated to be 0.93 nmol/L, which is much lower than previously reported work and standard level of Zn²⁺ and Mn²⁺ permitted in drinking water by WHO. Moreover, the specific recognition of Mn²⁺ and Zn²⁺ can be realized via the addition of different masking agents (ethylenediamine for Zn²⁺ and triethanolamine for Mn²⁺). Furthermore, our results reveal that the structural changes from -NH-CO to -NC-OH induced by Zn²⁺ contribute to the shift of FL peak from 680 to 650 nm while both static and dynamic quenching processes are involved in the detection of Mn²⁺. The ratio-metric probe was successfully applied to Zn²⁺ and Mn²⁺ determination in human serum samples and Sandy Lake water.

Keywords: Carbon dots; Excellent sensitivity; Manganese ions; Ratio-metric sensing; Zinc ions.