Determination of Fe3+ upon Special "Upconversion Luminescence" of Dopamine

Tunable fluorescent amino-functionalized Ti3C2Tx MXene quantum dots for ultrasensitive Fe3+ ion sensing

The development of sensors with high sensitivity, good selectivity and reproducibility are of great importance for the detection of Fe³⁺ in contaminated water for environmental monitoring. In this work, a reflux approach has been adopted to synthesize Ti₃C₂T_x quantum dots (QDs) based on the cutting effect of tetramethylammonium hydroxide (TMAOH) on Ti₃C₂T_x at high temperature. The surface-functionalized Ti₃C₂T_x QDs contained abundant amino groups and exhibited tunable pH-dependent emission, which was attributed to the protonation and deprotonation of the surface terminations. The linearity of the radiometric fluorescence intensity versus pH indicates its great potential as a dual-emission ratiometric pH sensor. Additionally, the Ti₃C₂T_x QDs exhibited tunable excitation-dependent emission behavior, which was related to the degree of passivation by the amino groups on the surface. Furthermore, the fluorescence intensity of the Ti₃C₂T_x QDs shows a linear response toward Fe³⁺ in the nanomolar to micromolar range with a low detection limit of 2 nM, originating from the oxidation and reduction between Fe³⁺ and Ti₃C₂T_x. This ultra-sensitive and selective detection capability demonstrated the environmental application potential for Ti₃C₂T_x QDs as a nanoprobe to monitor Fe³⁺.

Highly fluorescent nitrogen and boron doped carbon quantum dots for selective and sensitive detection of Fe3

Due to the essential role of Fe3+ in physiological and pathological processes, the detection of Fe3+ has drawn increasing attention in the field of disease diagnosis and environmental protection. However, most existing methods require either cumbersome sample pretreatment or sophisticated and expensive test equipment. Recently, carbon quantum dots have found a wide range of applications such as nanoprobes for Fe3+ determination, albeit with limited sensitivity and selectivity. Herein, we report core-shell carbon quantum dots B1N2CQDs via a two-step hydrothermal approach using citric acid, boric acid and ethylenediamine as precursors. The obtained B1N2CQDs exhibit excellent water solubility and remarkable stability as well as a high fluorescence quantum yield of 15.4%. In addition, the fluorescence of B1N2CQDs is quenched exclusively by Fe3+ with minimal interference from other metal ions. A linear relationship with R2 = 0.998 was observed between the fluorescence quenching capacity and the Fe3+ concentration in the range of 2-160 μM, with the limit of detection calculated to be 80 nM. Finally, the as-prepared B1N2CQDs were successfully applied as a highly efficient fluorescent probe for Fe3+ detection in river water samples and intracellular Fe3+ imaging in biological systems.

Luminescence of Eu (III) complex under near-infrared light excitation for curcumin detection

An intrinsic Eu(III) luminescence phenomenon of Eu(III) complex was found under near-infrared light (NIRL) excitation of xenon lamp, and the maximum excitation wavelength is about twice the excitation wavelength of its Stokes fluorescence. The NIRL excitation fluorescence was mainly originated from second order diffracted light (SODL) excitation. The Eu(III) complex was consist of Eu(III), Gd(III), 2-trifluoroacetylacetone (TTA) and cetyltrimethylammonium bromide (CTAB). Curcumin (Cur) could notably quench the luminescence intensity of the Eu(III) complex. Based on this, a sensitive method for Cur detection was developed. Under optimum conditions, the decrease extent in the fluorescence intensity at 611 nm exhibited a good linear relationship with the Cur concentration in the range of 2.0 × 10^-9 mol/L - 6.0 × 10^-8 mol/L under 746 nm excitation, the limit of detection (LOD, S/N = 3) was 5.2 × 10^-10 mol/L. While, the linear relationship and the LOD of Stokes fluorescence method (λ_ex/λ_em = 360/611 nm) were found to be 1.0 × 10^-8 mol/L - 6.0 × 10^-8 mol/L and 2.6 × 10^-9 mol/L, respectively. The former method is superior to the latter one in Cur detection. Both two methods were successfully applied to determine Cur in real samples. The luminescence mechanism of Eu(III) complex under the NIRL excitation and the quenching mechanism of Cur on the Eu(III) fluorescence was also investigated.