No abstract

Tacrolimus (FK506) is an immunosuppressant drug (ISD) used to prevent organ rejection after transplantation that exhibits a narrow therapeutic window and is subject to wide interand intra-individual pharmacokinetic fluctuations requiring careful monitoring. The immunosuppressive capacity of FK506 arises from the formation of a complex with immunophilin FKBP1A. This paper describes the use of FKBP1A as an alternative to common antibodies for biosensing purposes. Bioassays use recombinant FKBP1A fused to the emerald green fluorescent protein (FKBP1A−EmGFP). Samples containing the immunosuppressant are incubated with the recombinant protein, and free FKBP1A− EmGFP is captured by magnetic beads functionalized with FK506 to generate a fluorescence signal. Recombinant receptor−drug interaction is evaluated by using a quartz crystal microbalance and nuclear magnetic resonance. The limit of detection (3 ng mL −1 ) and dynamic range thus obtained (5−70 ng mL −1 ) fulfill therapeutic requirements. The assay is selective for other ISD usually coadministered with FK506 and allows the drug to be determined in human whole blood samples from organ transplant patients with results comparing favorably with those of an external laboratory.

No abstract

Mycotoxins are low molecular weight toxic compounds, which can cause severe health problems in animals and humans. Immunoassays allow rapid, simple and cost-effective screening of mycotoxins. Sandwich assays with a direct readout provide great improvement in terms of selectivity and sensitivity, compared to the widely used competitive assay formats, for the analysis of low molecular weight molecules. In this work, we report a non-competitive fluorescence anti-immune complex (IC) immunoassay, based on the specific recognition of HT-2 toxin with a pair of recombinant antibody fragments, namely antigen-binding fragment (Fab) (anti-HT-2 (10) Fab) and single-chain variable fragment (scFv) (anti-IC HT-2 (10) scFv). The SpyTag and SpyCatcher glue proteins were applied for the first time as a bioconjugation tool for the analysis of mycotoxins. To this aim, a SpyTag-mScarlet-I (fluorescent protein) and scFv-SpyCatcher fusion proteins were constructed, produced and fused in situ during the assay by spontaneous Tag-Catcher binding. The assay showed an excellent sensitivity with an EC50 of 4.8 ± 0.4 ng mL−1 and a dynamic range from 1.7 ± 0.3 to 13 ± 2 ng mL−1, an inter-day reproducibility of 8.5% and a high selectivity towards HT-2 toxin without cross-reactivity with other Fusarium toxins. The bioassay was applied to the analysis of the toxin in an oat reference material and in oat samples, with a LOD of 0.6 µg kg−1, and the results were validated by analysing a certificate reference material and by HPLC–MS/MS. Graphical abstract

No abstract