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Reliable detection of decreasing amounts of gluten in food is the only way of ensuring the safety of all coeliac patients. Results obtained with the method of choice, immunochemical assays, are not entirely comparable and many of them are sandwich assays that cannot recognize hydrolyzed proteins. In this work, we propose a competitive electrochemical sensor based on a recently described aptamer targeting the gliadin immunodominant peptide 33-mer that triggers the coeliac disease. The sensing layer is built on the surface of a screen-printed carbon electrode (SPCE) by adsorption of streptavidin and subsequent peptide immobilization. A competition between the peptide and gluten proteins from samples for a defined concentration of biotinylated Gli 4 aptamer is established. The aptamer bound to the peptide on the surface is finally measured after enzyme labelling and chronoamperometric detection of an enzymatically obtained electrochemically active product. This method is able to detect as low as 0.113 μg L −1 of gliadin, which corresponds to 380 μg kg −1 of gluten in food, taking all dilutions and conversion factors into consideration, with a reproducibility lower than 11%. The aptasensor was applied to food samples with gluten contents above and below the legislated threshold for gluten-free labelling in the EU, obtaining good agreement with the official R5 immunochemical method. [ABSTRACT FROM AUTHOR]

Aptamers are starting to increase the reagents tool box to develop more sensitive and reliable methods for food allergens. In most of these assays, aptamers have to be modified for detection and/or immobilization purposes. To take full advantage of their affinity, which decisively influence the detectability, these modifications must be faced rationally. In this work, a recently developed aptamer for an immunotoxic peptide of gliadin associated to celiac disease is used in different configurations and modified with various markers and anchored groups to evaluate the influence of such modifications on the real affinity. The interaction in solution with the peptide is strong for a relatively small molecule ( K d = 45 ± 10 nM, 17 °C) and slightly stronger than that for the immobilized intact protein due to a cooperative binding effect. Comparatively, while only minor differences were found when the peptide or the aptamer were immobilized, labeling with a biotin resulted preferable over fluorescein ( K d = 102 ± 11 vs 208 ± 54 nM, 25 °C). These findings are of prime importance for the design of an aptamer-based analytical method for gluten quantification. [ABSTRACT FROM AUTHOR]

Enzyme-linked immunosorbent assays are currently the most popular methods to quantify gluten in foods. Unfortunately, the antibodies used as specific receptors in such methods are not compatible with the usual solvents for the extraction of gluten proteins. In consequence, commercial tests require a high dilution of the sample after the extraction, increasing the limit of quantification and decreasing convenience. In this work, we have rationally truncated an aptamer capable of recognizing gliadin in a deep eutectic solvent (DES). The truncated aptamer is a 19-nucleotides-long DNA that minimizes self-hybridization, allowing the development of an electrochemical sandwich-based sensor for the quantification of gluten in the DES ethaline. The sensor incorporates two identical biotin-labeled truncated aptamers, one of which is immobilized on a carbon screen-printed electrode and the other reports the binding of gliadin after incubation in streptavidin-peroxidase. This sensor can detect gliadin in DES, with a dynamic range between 1 and 100 μg/L and an intra-assay coefficient of variation of 11%. This analytical performance allows the quantification of 20 μg of gluten/kg of food when 1 g of food is extracted with 10 mL of ethaline. We demonstrate the ability of this method to achieve the measurement of gluten in food samples, after the extraction with pure ethaline. The assay is useful for the analysis of residual gluten levels in foods, thus facilitating the evaluation of any potential health risk associated with the consumption of such food by people with celiac disease or other gluten-related disorders. Image 1 • First aptamer-based sensor directly deployed in a deep-eutectic solvent. • A truncated aptamer is designed to be applied in a sandwich format. • Electrochemical sensor exhibits a limit of quantification of 20 μg gluten/kg sample. • Detection of residual gluten levels in food for highly-sensitive celiac patients. [ABSTRACT FROM AUTHOR]