Dual-Emission Fluorescent Probe for the Simultaneous Detection of Nitrite and Mercury(II) in Environmental Water Samples Based on the Tb3+-Modified Carbon Quantum Dot/3-Aminophenylboronic Acid Hybrid

Nitrite (NO₂^-) and mercury (Hg²⁺) ions are recognized as two typical inorganic contaminations that can cause severe damage to the environment and humans. In this paper, the energy transfer from carbon quantum dots (CQDs) to Tb³⁺ by the antenna effect was found, which can promote the f-f transition of Tb³⁺ and emit strong characteristic fluorescence of Tb³⁺. Based on CQD-Tb³⁺ and 3-aminophenylboronic acid (APBA), which have respectively sensitive and specific fluorescent response to NO₂^- and Hg²⁺ with different fluorescent signals, a dual-emission fluorescent probe of the CQD-Tb³⁺/APBA hybrid was thus fabricated for the simultaneous detection of NO₂^- and Hg²⁺ in environmental water samples. They emit dual-emission fluorescence peaks centered at 373 and 545 nm, respectively. A good linearity between the quenching efficiency of (F₀ - F)/F₀ and the concentrations of NO₂^- and Hg²⁺ was in the range of 5.0-1200.0 nM for NO₂^- and 0.1-6.0 μM for Hg²⁺. The limit of detection (LOD, 3σ/K) is ultrasensitive for NO₂^- (2.0 nM), and the LOD for Hg²⁺ is 38.1 nM. The dual-emission fluorescent probe was successfully applied for the determination of NO₂^- and Hg²⁺ in various environmental water samples. The possible luminescence and fluorescence quenching mechanisms of the probe are also discussed in detail. This study provides a new approach for fabricating a multifunctional fluorescent probe or sensor and a prospective application in environmental monitoring.