Fluorimetric determination of tetracyclines with the europium chelate of 1,10-phenanthroline in micellar solutions of anionic surfactants

Development of Europium-Sensitized Fluorescence-Based Method for Sensitive Detection of Oxytetracycline in Citrus Tissues

Antimicrobial compounds have been successfully used to control many plant and animal diseases. Recently, oxytetracycline (OTC) and streptomycin have been approved for the treatment of Huanglongbing in citrus. Since the application of OTC is under strict regulations, several methods have been developed to determine and monitor its levels in the environment including high-performance liquid chromatography, ELISA, colorimetric, and fluorometric assays. In this study, we developed a fluorometric method for the determination of OTC in plant tissues based on its complexation with europium. Our preliminary trials showed that phenols and flavonoids interfere with the europium assay by reacting with the sensitizing reagent, cetyltrimethylammonium chloride. Consequently, we used the 60 mg hydrophilic–lipophilic balanced (HLB) cartridges to purify the OTC from the plant matrix. The recovery of OTC from spiked leaf samples was 75 ± 7.6%. Using the 500 mg HLB, we were able to detect 0.3 ppm OTC in the final sample extract, which corresponds to 3 µg g⁻¹ fresh weight (FWT). The developed method was successfully used to measure the level of OTC in leaves obtained from trunk-injected trees. The results obtained by the europium method were similar to those obtained using the ELISA assay. We also tested the cross-reactivity of OTC metabolites with the europium method. The 4-epi-OTC showed a high cross-reactivity (50.0 ± 3.6%) with europium assay, whereas α-apo-OTC and β-apo-OTC showed small cross-reactivity. We showed that the europium-sensitized fluorescence-based method can be successfully used to assess OTC in citrus plant tissues after a cleanup step. Our results showed that this method was sensitive, reproducible, and can be used to analyze many samples simultaneously.

Energy transfer in liquid and solid nanoobjects: application in luminescent analysis

Radiationless resonance electronic excitation energy transfer (ET) is a fundamental physical phenomenon in luminescence spectroscopy playing an important role in natural processes, especially in photosynthesis and biochemistry. Besides, it is widely used in photooptics, optoelectronics, and protein chemistry, coordination chemistry of transition metals and lanthanides as well as in luminescent analysis. ET involves the transfer of electronic energy from a donor (D) (molecules or particles) which is initially excited, to an acceptor (A) at the ground state to emit it later. Fluorescence or phosphorescence of the acceptor that occurs during ET is known as sensitized. There do many kinds of ET exist but in all cases along with other factors the rate and efficiency of ET in common solvents depends to a large extent on the distance between the donor and the acceptor. This dependency greatly limits the efficiency of ET and, correspondingly, does not allow the determination of analytes in highly diluted (10–9–10–15 M) solutions. To solve the problem of distance-effect, the effects of concentrating and bring close together the donor and acceptor in surfactant micelles (liquid nanosystems) or sorption on solid nanoparticles are used. Various approaches to promote the efficiency of ET for improvement determination selectivity and sensitivity using liquid and solid nanoobjects is reviewed and analyzed.

Citrate analysis using capillary electrophoresis and complexation with Eu3+-tetracycline

A sensitive assay for citrate was developed. Citrate was incubated with 50 μM Eu³⁺-tetracycline and the complex separated using capillary electrophoresis utilizing post-column laser-induced luminescence detection in a sheath flow cuvette. Signal was linear with citrate concentration from 10 μM to 200 nM. Injection volumes were 320 pL. For the 200 nM sample, this corresponds to the injection of 64 amoles of citrate. Separation time was < 90 s with a total run time of 5 min. As an application the method was used to analyze citrate in agricultural and medicinal products. The method was also used to develop an assay for the enzyme citrate synthase.