Paper sensor of curcumin by fluorescence resonance energy transfer on nitrogen-doped carbon quantum dot

Fluorescent Molybdenum Disulfide Quantum Dots for Sensitive Detecting Curcumin in Food Samples through FRET Mechanism

A selective and sensitive fluorometric assay was developed for specific determination of curcumin (Cur) based on fluorescence resonance energy transfer (FRET) between molybdenum disulfide quantum dots (MoS2 QDs) and Cur. The MoS2 QDs were prepared via a one-step hydrothermal protocol using sodium molybdate dihydrate, L-cysteine (Cys) as precursors, and sodium cholate (SC) as a modification agent. The as-prepared MoS2 QDs possessed maximum fluorescence emission at 460 nm with a 20% of fluorescence quantum yield (FQY). It was found that the fluorescence of MoS2 QDs could be quantitatively quenched by Cur through FRET mechanism. Therefore, Cur could be detected in the range of 0.1-20 µg mL- 1 with a detection limit of 5 ng mL- 1. Additionally, the developed MoS2 QDs based fluorescent assay has been successfully applied for real food sample analysis with satisfactory results.

Detection of tetracycline antibiotics using fluorescent "Turn-off" sensor based on S, N-doped carbon quantum dots

In recent years, antibiotic residues in food have been of great concern to regulators and consumers. In this study, a novel fluorescent sensor based on S, N-doped carbon quantum dots (S, N-CQDs) was established for rapid detection of tetracycline antibiotics (TCs). Through the internal filter effect (IFE), QDs fluorescence can be effectively quenched by TCs, endowing it an "off" condition. Under the optimal conditions, the TC concentration in the range of 1.88-60 μmol/L had a good linear relationship with the change of QDs fluorescence intensity, and the limit of detection (LOD) was calculated as 0.56 μmol/L (S/N = 3). Furthermore, the proposed "Turn-off" sensor could be employed to quickly and accurately quantify TCs residues even in milk, honey and tap water. The recovery rate was as high as between 93.61% and 102.31%. The established sensor has great application value in the fields of food safety and drug analysis, and provides broad prospects for the future food industry.

Preparation of yellow emissive nitrogen-doped carbon dots from o-phenylenediamine and their application in curcumin sensing

In this work, o-phenylenediamine (o-PD) and ethanol are used as raw materials, and a simple solvothermal method is used to prepare yellow emissive nitrogen-doped CDs (YNCDs) (with yellow emission λex/λem = 410/555 nm).

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.