Polymer-Enhanced Capillary Transient Isotachophoresis with Boronic Acid-Functionalized Squarylium Dyes for the Fluorescent Determination of Digoxin and Digoxigenin

Evaluation of digoxin-boronate ester formation through in-capillary derivatisation-large volume sample stacking-capillary zone electrophoresis

Determination of digoxin through in-capillary derivatisation based on the formation of o-tolyl- and 2-naphthyl-anionic boronate esters in combination with large volume sample stacking-capillary electrophoresis is proposed. The derivatisation reaction was performed at basic pH values to obtain compounds with a charge and chromophore group during the stacking process. After stacking, the species were separated and detected at 225 nm using p-nitrophenol as an internal standard. Stacking and derivatisation parameters such as pre-concentration time, preconcentration voltage and injection time (relation between the analyte and the derivatisation agent) were evaluated using a Box-Behnken design. Under optimal conditions, the proposed method exhibits a linear range of 1.08-50.00 μM with a limit of detection of 0.36 μM; additionally, adequate repeatability and reproducibility was obtained (%RSD ≤ 5.0%). The methodology was validated by comparing it to an HPLC-UV established methodology and was successfully applied for the determination of digoxin in pharmaceutical tablets and blood serum samples, showing a positive performance for these matrices.

Designing and construction of genetically encoded FRET-based nanosensor for qualitative analysis of digoxin

Nanobiotechnological improvements defined on the utilization of biological materials and principles have enormously partaken to revolutionize physical, chemical, and biological sciences. However, the exploration of plant nanobiotechnology is still in its outset. The search for novel tools to monitor plant biomolecules is an emerging issue for the nanobiotechnologists. Given this, a genetically encoded FRET-based nanobiosensor has been developed to monitor the popular plant cardiac glycoside - digoxin, which is used as the most common prescription drug for heart-related illnesses across the world. Digoxin is sourced from the leaves of the foxglove plant (Digitalis purpurea L.) and has a significant demand in the medical sector. Moreover, with the rising popularity of the herbal formulations in the global market, attention towards the authentication and quality control of the herbal drugs is important. Furthermore, digoxin has a very narrow therapeutic range, i.e., 0.6 nM - 2.6 nM. Therefore, strict monitoring of blood digoxin levels is necessary. Besides, previously used techniques for drug authentication and quantification of small-molecule drugs in blood samples are not the best choice available. The nanobiosensor is based on the FRET (Fluorescence Resonance Energy Transfer) mechanism, and it is constructed in such a way that it gives a changed FRET output in the presence of digoxin. Two fluorophores, enhanced cyan fluorescent protein (ECFP) and Venus, were attached on either end of the sensory domain - human nuclear receptor ROR-gamma (RORγt). The developed nanobiosensor was named as fluorescent indicator protein for digoxin, (FLIP-digoxin). The ligand binding affinity of FLIP-digoxin was calculated as 425 μM. Affinity mutants of the FLIP-digoxin were also generated to measure digoxin in wide concentration ranges. This sensor offers high-throughput qualitative analysis of digoxin in Digitalis preparations procured from local drug stores. It confirms the authenticity of the preparations through the detection of digoxin. The FLIP-1n was also able to monitor digoxin concentration in serum samples in lesser than 5 min. The nanobiosensor was found pH stable, digoxin-specific, non- interfered by the biological serum species and can perform high throughput screening of the Digitalis powder, infusion and tincture preparations.