Graphene quantum dots-terbium ions as novel sensitive and selective time-resolved luminescent probes

Luminescent Probe Based on Terbium-Carbon Quantum Dots for the Quantification of Imidacloprid in Caneberries

We propose a modification of terbium-sensitized luminescence (TSL) by means of the introduction of nanoparticles to improve the sensitivity and selectivity of the analytical methods. TSL detection is usually based on the complexation between fluorescent organic compounds (the analytes) and terbium. The organic compound is then excited, and, after an energy transfer towards terbium, the latter emits the luminescence signal. Here, the modification consists of the introduction of nanoparticles (carbon quantum dots, CQDs) into the system. The carboxylic groups of CQDs react with terbium, providing an interesting time-resolved luminescence probe. We applied this system for the determination of the neonicotinoid imidacloprid (IMID). When IMID was introduced in the terbium-CQDs system, the luminescent signal (λexc/λem of 256/545 nm) was quenched, proportionally to IMID concentration in the range of 100-2500 ng·mL-1, obtaining a limit of detection of 30 ng·mL-1. A method detection limit of 0.9 mg·kg-1 was reached in caneberries, thus complying with the maximum residue level of 5 mg·kg-1 established by Codex Alimentarius. We performed recovery experiments in caneberries (blackberries, blueberries, raspberries, and mulberries), obtaining recovery yields close to 100% in all cases. These results show that the use of terbium ions-nanoparticles luminescence probes can be useful for screening purposes in quality control laboratories.

Luminescent determination of propineb fungicide by using a carbon quantum dots-europium ions system

We propose a modification of lanthanide-sensitized luminescence (LSL) to increase the selectivity and sensitivity of analytical methods based on this detection. LSL consists in the formation of complexes of lanthanide ions and organic compounds. Then, an intramolecular energy transfer occurs from the excited state of the ligand (organic analyte) to the emitting level of the lanthanide. The utilization of luminescent nanoparticles (carbon quantum dots, CQDs) in LSL systems can enhance their sensitivity and selectivity. CQDs can react with lanthanide ions through their carboxylic groups. These systems can thus be used as time-resolved luminescent probes. Propineb (PPN), a well-known dithiocarbamate fungicide, has been selected as the target analyte to show the advantages of using CQDs in LSL systems. The method proposed is based on the quenching produced by PPN in europium-CQDs luminescence, obtaining a detection limit of 0.03 μg mL^-1 PPN and a method detection limit of 3 mg kg^-1 in capers (bud and fruit), fulfilling the maximum residue limit in these samples (25 mg kg^-1). The results showed that the use of nanoparticles in LSL systems may provide novel and simple analytical methods for the screening of contaminants in the agri-food sector.

A new fluorescence probe comprising nitrogen-doped graphene quantum dots for the selective and quantitative determination of cerium(iv)

As a novel “turn-off” fluorescent probe for Ce⁴⁺, our N-GQD sensor exhibits a rapid, sensitive, stable and selective response towards Ce⁴⁺.

Selective luminescence determination of cysteine by using terbium-modified silver nanoparticles or terbium-modified graphene quantum dots

Two methods for the luminescence determination of cysteine (Cys) are presented. They make use of either silver nanoparticles (Ag NPs) or graphene quantum dots (GQDs), both doped with terbium(III). The methods are based on the finding that Cys quenches the green luminescence of Tb(III)-Ag NPs and Tb(III)-GQDs. The excitation/emission maxima are at 306/545 and 257/545 nm, for both nanoprobes, respectively. Response is linear in the 0.28-5.0 μg mL^-1 Cys concentration range for the Tb(III)-Ag NP system, and from 0.05-3.0 μg mL^-1 for the Tb(III)-GQD system. The respective limits of detection are 0.09 and 0.015 μg mL^-1. The probes were applied to the time-resolved luminometric determination of Cys in (spiked) food supplements and gave satisfactory results. Graphical abstractSchematic representation of the quenching by cysteine (Cys) of the time-resolved luminescence (TSL) of terbium-graphene quantum dots [Tb(III)-GQD] and of terbium-silver nanoparticles [Tb(III)-Ag NP].