One-step ratiometric fluorescence sensing of ascorbic acid in food samples by carbon dots-referenced lanthanide probe

Electrochemical determination of ascorbic acid using palladium supported on N-doped graphene quantum dot modified electrode

To precise screening concentration of ascorbic acid (AA), a novel electrochemical sensor was prepared using palladium nanoparticles decorated on nitrogen-doped graphene quantum dot modified glassy carbon electrode (PdNPs@N-GQD/GCE). For this purpose, nitrogen doped GQD nanoparticles (N-GQD) were synthesized from a citric acid condensation reaction in the presence of ethylenediamine and subsequently modified by palladium nanoparticles (PdNPs). The electrochemical behavior of AA was investigated, in which the oxidation peak appeared at 0 V related to the AA oxidation. Considering the synergistic effect of Pd nanoparticles as an active electrocatalyst, and N-GQD as an electron transfer accelerator and electrocatalytic activity improving agent, PdNPs@N-GQD hybrid materials showed excellent activity in the direct oxidation of AA. In the optimal conditions, the voltammetric response was linear in the range from 30 to 700 nM and the detection limit was calculated to be 23 nM. The validity and the efficiency of the proposed sensor were successfully tested and confirmed by measuring AA in real samples of chewing tablets, and fruit juice.

Preparation and application of carbon quantum dot fluorescent probes combined with rare earth ions

Globally, antibiotic abuse, organic contamination, and excessive heavy metal ion pollution pose serious threats to human health. In this case, ratiometric fluorescent probes can eliminate the errors caused by environmental factors and provide more accurate detection results than single-emission intensity nanoprobes. Accordingly, based on the excellent biocompatibility and abundant surface functional groups of carbon quantum dots (CQDs) and the properties of large Stokes shifts and narrow emission bands of rare earth ions (RE3+), RE-CQD fluorescent probes have attracted widespread attention. Herein, firstly we review the combination of carbon quantum dots with rare earth ions (rare earth complexes) using various functionalization approaches to improve the defects of rare earth complexes and realize the functionalization of carbon quantum dots and their applications in many fields, such as biology and environmental science. In addition, we classify the methods for the synthesis of RE-CQD hybrids into three groups according to the different binding modes of the RE and CQDs, including doping, covalent grafting, and direct coordination. The excellent properties of these fluorescent probes are also briefly described. Finally, a comprehensive overview of the important applications of RE-CQD fluorescent probes in the fields of public safety sensing, chemical sensing, biomedical sensing, temperature sensing, and pH sensing is presented. In this review, the recent research progress in the field of ratiometric fluorescence sensing based on carbon quantum dots and rare earth ions is summarized and an outlook on the future development of RE-CQD fluorescent probes regarding their construction and potential applications is provided.

The Detection of Anthrax Biomarker DPA by Ratiometric Fluorescence Probe of Carbon Quantum Dots and Europium Hybrid Material Based on Poly(ionic)- Liquid

Bacillus anthracis has gained international attention as a deadly bacterium and a potentially deadly biological warfare agent. Dipicolinic acid (DPA) is the main component of the protective layer of anthracis spores, and is also an anthrax biomarker. Therefore, it is of great significance to explore an efficient and sensitive DPA detection method. Herein, a novel ratio hybrid probe (CQDs-PIL-Eu3+) was prepared by a simple one-step hydrothermal method using carbon quantum dots (CQDs) as an internal reference fluorescence and a covalent bond between CQDs and Eu3+ by using a polyionic liquid (PIL) as a bridge molecule. The ratiometric fluorescence probe was found to have the characteristics of sensitive fluorescence visual sensing in detecting DPA. The structure and the sensing properties of CQDs-PIL-Eu3+ were investigated in detail. In particular, the fluorescence intensity ratio of Eu3+ to CQDs (I616/I440) was linear with the concentration of DPA in the range of 0-50 μM, so the detection limit of the probe was as low as 32 nm, which was far lower than the DPA dose released by the number of anthrax spores in human body (60 μM) and, thus, can achieve sensitive detection. Therefore, the ratiometric fluorescence probe in this work has the characteristics of strong anti-interference, visual sensing, and high sensitivity, which provides a very promising scheme for the realization of anthrax biomarker DPA detection.

A ratiometric luminescence sensing platform based on lanthanide-based silica nanoparticles for selective and sensitive detection of Fe3+ and Cu2+ ions

Detection of Fe(III) and Cu(II) in water is highly desirable because their abnormal levels can cause serious harm to human health and environmental safety. In this work, a ratiometric luminescence sensing platform based on lanthanide-based silica nanoparticles was constructed for the detection of Fe³⁺ and Cu²⁺ ions. The terbium-silica nanoparticles (named SiO₂@Tb) with dual-emission signals were successfully prepared by grafting Tb³⁺ ions onto trimellitic anhydride (TMA) functionalized silica nanospheres. It can serve as a ratiometric fluorescent probe for the detection of Fe³⁺ and Cu²⁺ ions in water with the green emission of Tb³⁺ ions as a response signal and the blue emission of silica nanospheres as the reference signal. Significantly, an easy-to-differentiate color change for visual detection was also realized. SiO₂@Tb shows high sensitivity even in very low concentration regions towards the sensing of Fe³⁺ and Cu²⁺ with low detection limits of 0.75 μM and 0.91 μM, respectively. Moreover, the mechanism for the luminescence quenching of SiO₂@Tb was systematically investigated, and was attributed to the synergetic effect of the absorption competition quenching (ACQ) mechanism and cation exchange. This study demonstrates that SiO₂@Tb can be employed as a promising fluorescent probe for the detection of Fe³⁺ and Cu²⁺ ions, and the combination of lanthanide ions with silica nanoparticles is an effective strategy to construct a ratiometric fluorescent sensing platform for the determination of analytes in environmental detection.

A ratiometric fluorescence sensor for ascorbic acid determination based on an AND-NAND logic pair

An AND-NAND logic pair is reported based on non-purified carbon quantum dots (CDs) for ascorbic acid (AA) detection. In the logic operation, molybdenum oxide nanosheets (MoO3 NSs) and AA are used as two signal inputs. In the presence of AA, MoO3 NSs are reduced to plasmonic molybdenum oxide, which decreases the CD fluorescence intensity because of a static quenching, dynamic quenching, and internal filtration effect. Meanwhile, the AA is oxidized to dehydroascorbic acid and forms fluorescent 3-(dihydroxyethyl) furo [3,4-b] quinoxaline-1-one with o-phenylenediamine from non-purified CDs. On this basis, an AND-NAND logic pair was constructed and used as a ratiometric fluorescence sensor for highly sensitive detection of AA. The method has a wide linear range of 0.05-50 μM, and a detection limit of 34 nM. In addition, it was used to detect AA in fresh fruit. Potential applications include chemical computing, optoelectronic devices, biomedical science, and environmental monitoring. HIGHLIGHTS: 1. A ratiometric fluorescence sensor based on AND-NAND logic pair constructed by CDs and MoO3 NSs was successfully fabricated. 2. The ratiometric fluorescence sensor exhibited satisfactory linear range, high sensitivity, and good selectivity for AA. 3. The ratiometric fluorescence method was able to detect AA in fresh fruit with good results comparable to official fluorescence methods.