Development of a selective fluorescence derivatization strategy for thyroid hormones based on the Sonogashira coupling reaction

Dual-color and specific luminescence detection of Pd2+ ions using iridium(III) complex-based probes in food samples

The toxicity of palladium (Pd) is highly associated with its oxidative states, thus it is important to develop specific detection methods for Pd2+ ions in food and environmental systems. However, the reliable and selective detection of Pd2+ ions remains challenging. Here, we report two iridium(III) complexes with dual colors (717 nm and 637 nm) for the specific detection of Pd2+ ions, with the 3,3'-diamino group being used as a specific recognition unit for Pd2+ ions for the first time. The dual-color probes showed a luminescence quenching response to Pd2+ ions in aqueous solution within 1 min, along with an obvious color change under UV irradiation. Moreover, complexes 1-2 allow sensitive and selective detection of Pd2+ ions with a limit of detection (LOD) of 0.69 μM and 0.26 μM, respectively, showing a good linear response for Pd2+ ions in the range of 1-13 μM (R2 = 0.985) and 1-9 μM (R2 = 0.996). Finally, the probes were successfully applied for the detection of Pd2+ ions in food and environmental samples with good recoveries ranging from 85.4 to 118.7 %, providing a robust analytical tool for Pd2+ ions quantification for onsite setting.

Determination of Thyroid Hormones and 11 Metabolites in the Human Serum Using a Simple Derivatization Strategy and Analysis by Isotope-Dilution Liquid Chromatography Tandem Mass Spectrometry

Many analytical methods for thyroid hormone (TH) determination lack sensitivity and/or specificity. The thyroid hormone metabolites (THMs) are usually not measured at all. This study describes the development of sensitive high-throughput analytical methods for determining the total concentration and free fraction of TH and THM in the human serum. For the analysis of the TOTAL fraction, we employed protein precipitation and anionic exchanger solid-phase extraction. For the FREE fraction, ultrafiltration and salt-out liquid partitioning were used. Derivatization using dansyl chloride was employed to enhance the sensitivity of HPLC-ESI-MS/MS analysis. Both protocols were validated according to the European Analytical Guidelines (2002/657/EC). We obtained very good recoveries (73-115%) and precision. Interday coefficients of variation (CVs) for most of the analytes ranged from 1.2 to 16.4%. The sensitivity was excellent with detection limits in the sub ppt range for the majority of TH and THM. A significant enhancement in sensitivity (>10 fold) was achieved through derivatization. The applicability was proved on a set of samples from pregnant women enrolled in the CELSPAC cohort (n = 120). Our TH reference ranges are in good agreement with those reported in the literature. The methods also allowed us to quantify the levels of 11 THM, including some previously undetected THM in total and free fractions, and proved to be suitable for high-throughput routine TH and THM analyses. Our approach offers an important advancement in thyroid hormone analysis. To the best of our knowledge, it is for the first time that data for T1A and T2A as well as for free THM levels in the human serum are published in the literature. Moreover, our study also brings the first information about the levels of most of the THM in pregnant women.

Establishment of a Quenchbody-based L-thyroxine detection method and its comparison with ELISA systems

The quantification of L-thyroxine (T4) is crucial for regulating metabolism, diagnosing diseases, and monitoring the efficacy of T4 replacement therapy. However, because T4 is a hapten biomarker with a molecular weight of 777 g/mol, conventional immunoassay approaches, including Western blotting and some types of ELISA, have limited accuracy in the quantification of small molecules, including T4. Furthermore, these methods are time-consuming and involve multiple incubation and reaction steps. Therefore, a novel immunoassay method is required for simple and rapid on-site detection of T4. In this study, we expressed a recombinant anti-T4 single-chain variable fragment (scFv) in soluble form using Escherichia coli. The scFv exhibited high T4-binding efficiency, and T4 concentration-dependent titration curves indicated that the sandwich ELISA could detect T4 in the nanogram range. We labeled the scFv using a fluorescent dye for a Quenchbody (Q-body)-based one-pot immunoassay, which yielded a T4 concentration-dependent fluorescent response in 3 min. A comparison of the Q-body-based T4 detection system with ELISA-based methods demonstrated that the ELISA system was more sensitive but the Q-body assay was more rapid. Therefore, both ELISA and Q-body systems can be used depending on the experimental purpose, with the newly developed anti-T4 Q-body system being applicable for convenient in situ immunoassay of T4.

Unique biomedical application of fluorescence derivatization based on palladium-catalyzed coupling reactions for HPLC analysis of pharmaceuticals and biomolecules

Palladium-catalyzed coupling reactions are versatile and powerful tools for the construction of carbon-carbon bonds in organic synthesis. Although these reactions have favorable features that proceed selectively in mild reaction conditions using aqueous organic solvents, no attention has been given to their application in the field of biomedical analysis. Therefore, we focused on these reactions and evaluated the scope and limitations of their analytical performance. In this review, we describe the pros and cons and future trends of fluorescence derivatization of pharmaceuticals and biomolecules based on palladium-catalyzed coupling reactions such as Suzuki-Miyaura coupling, Mizoroki-Heck coupling, and Sonogashira coupling reactions for HPLC analysis.

Microwave prepared nitrogen and sulfur co-doped carbon quantum dots for rapid determination of ascorbic acid through a turn off-on strategy

A simple and eco-friendly microwave method was applied for the preparation of highly fluorescent nitrogen and sulfur co-doped carbon quantum dots (NS-CQDs) and used for the determination of ascorbic acid (ASC) in pharmaceutical dosage forms. The prepared NS-CQDs had bright blue fluorescence at a maximum emission wavelength of 440 nm, after excitation with 350 nm, with a quantum yield of 62.5 %. The developed NS-CQDs were prepared from citric acid and l-cysteine in one minute. The native fluorescence of NS-CQDs was quenched by ferric ions due to the formation of non-fluorescent CQDs/ Fe³⁺ complex. The quenched fluorescence could be restored by the addition of ASC due to the reducing properties of ASC which converts Fe³⁺ to Fe²⁺. The method was found linear over the concentration range of 2.0-100 μg/mL, with a limit of detection was 0.6 μg/mL and a coefficient of determination of 0.9965. The proposed method was cross-validated and statistically compared with a reported HPLC method. The results indicated that the developed method was greener, according to the analytical eco-scale and the green analytical procedure index (GAPI). The prepared NS-CQDs were used for spectrofluorometric determination of ASC in pharmaceutical dosage forms, with percentage recoveries ranging between 98 and 102 %, and relative standard deviations less than 2 %. The method was easy, rapid, reliable, and sensitive and did not require expensive reagents or sophisticated equipment.