Selection of high affinity and specific aptamer and its' use in different applications for the detection of the anaphylactic b-conglutin allergen

Lupin és una planta lleguminosa amb un alt valor nutricional utilitzada àmpliament a la regió mediterrània en els àpats diaris, aliments fermentats tradicionals, aliments al forn i salses, sense contenir gluten, podent ser el substitut de la soja. Lupin va ser afegit recentment a la llista d'al·lèrgens que requereixen l'etiquetatge obligatori d'assessorament sobre els productes alimentaris comercialitzats a la Unió Europea, i des de desembre de 2006, tots els productes que continguin fins i tot petites quantitats de tramús han d'estar correctament etiquetats. L'etiquetatge és d'alta importància ja que encara no hi ha un medicament que pugui prevenir les al·lèrgies alimentàries i l'única opció és evitar estrictament l'aliment que causa l'al·lèrgia. Les globulines que es troben en el tramús consisteixen en dos grans subunitats denominades α-conglutina i β-conglutina, i dos menors, γ-conglutina i δ-conglutina. β-conglutina és l'única conglutina actualment inclosa en la llista de la Unió Internacional de Societats d'Immunologia (UISI), designada com l’al·lergen anafilàctic Lup an 1. L'objectiu d'aquest treball és la detecció de l'al·lergen anafilàctic β-conglutina. Han estat descrits aspectes fonamentals com ara la selecció d'un aptàmer (β-CBA II) en contra de β-conglutina i l'avaluació de la seva afinitat i especificitat. Es van utilitzar tres metodologies diferents per a els estudis competitius i es va demostrar que l’aptàmer β-CBA II s’uneix a un lloc diferent de β-conglutina en comparació amb l’aptàmer mencionat anteriorment (β-CBA I). Finalment, el seleccionat aptàmer β-CBA II es va utilitzar per detectar β-conglutina desenvolupant-se una plataforma sensible, ràpida i fàcil d'usar, amb possibilitat d'adaptar-se al punt d'atenció.Lupino es una planta leguminosa con un alto valor nutricional utilizada ampliamente en la región mediterránea en las comidas diarias, alimentos fermentados tradicionales, alimentos horneados y salsas, sin contener gluten, pudiendo ser el sustituto de la soja. Lupino fue añadido recientemente a la lista de alérgenos que requieren el etiquetado obligatorio de asesoramiento sobre los productos alimenticios comercializados en la Unión Europea, y desde diciembre de 2006, todos los productos que contengan incluso pequeñas cantidades de altramuz deben estar correctamente etiquetados. El etiquetado es de alta importancia ya que todavía no existe un medicamento que pueda prevenir las alergias alimentarias y la única opción es evitar estrictamente el alimento que causa la alergia. Las globulinas que se encuentran en el altramuz consisten en dos grandes subunidades denominadas α-conglutina y β-conglutina, y dos menores, γ-conglutina y δ-conglutina. β-conglutina es la única conglutina actualmente incluida en la lista de la Unión Internacional de Sociedades de Inmunología (UISI), designada como el alérgeno anafiláctico Lup an 1. El objetivo de este trabajo es la detección del alérgeno anafiláctico β-conglutina. Han sido descritos aspectos fundamentales tales como la selección de un aptámero (β-CBA II) en contra de β-conglutina y la evaluación de su afinidad y especificidad. Se utilizaron tres metodologías diferentes para los estudios competitivos y se demostró que el aptámero β-CBA II se une en un sitio diferente de β-conglutina en comparación con el aptámero mencionado anteriormente (β-CBA I). Finalmente, el seleccionado aptámero β-CBA II se usó para detectar β-conglutina desarrollándose una plataforma sensible, rápida y fácil de usar, con posibilidad de adaptarse en el punto de atención.Lupin is a leguminous plant with a high nutritional value used widely in the Mediterranean region such as everyday meals, traditional fermented foods, baked foods and sauces with gluten-free properties and a chance for being the soy substitute. Lupin has recently been added to the list of allergens requiring mandatory advisory labelling on foodstuffs sold in the European Union, and since December 2006 all products containing even trace amounts of lupin must be labelled correctly. Labelling is high important since there is not yet a medication that can prevent food allergies and only strict avoidance of the allergy-causing food is the way to prevent a reaction. Lupin globulins consist of two major globulins termed α-conglutin and β-conglutin, and two minor globulins, γ-conglutin and δ-conglutin. β-conglutin is the only conglutin currently included in the list of the International Union of Immunological Societies (IUIS), designated as the anaphylactic Lup an 1 allergen. This work overviews the detection of the anaphylactic β-conglutin allergen. Fundamental aspects such as the selection of a second aptamer (β-CBA II) against β-conglutin and the evaluation of its affinity and specificity have been described. Three different methodologies were used for the competitive studies and it was demonstrated that the β-CBA II aptamer binds to the different aptatope of β-conglutin compared to the aptamer reported previously (β-CBA I). Finally, selected β-CBA II aptamer was used to detect β-conglutin using a sensitive, rapid and user-friendly platform, which can be easily adapted as point-of-care tests

A label-free gold nanoparticles-based optical aptasensor for the detection of retinol binding protein 4

Retinol-binding protein 4 (RBP4) has been implicated in insulin resistance in rodents and humans with obesity and T2DM, making it a potential biomarker for the early diagnosis of T2DM. However, diagnostic tools for low-level detection of RBP4 are still lagging behind. Therefore, there is an urgent need for the development of T2DM diagnostics that are rapid, cost-effective and that can be used at the point-of-care (POC). Recently, nano-enabled biosensors integrating highly selective optical detection techniques and specificity of aptamers have been widely developed for the rapid detection of various targets. This study reports on the development of a rapid gold nanoparticles (AuNPs)-based aptasensor for the detection of RBP4. The retinol-binding protein aptamer (RBP-A) is adsorbed on the surface of the AuNPs through van der Waals and hydrophobic interactions, stabilizing the AuNPs against sodium chloride (NaCl)-induced aggregation. Upon the addition of RBP4, the RBP-A binds to RBP4 and detaches from the surface of the AuNPs, leaving the AuNPs unprotected

Electrochemical Detection of Single-Nucleotide Polymorphism Associated with Rifampicin Resistance in Mycobacterium tuberculosis Using Solid-Phase Primer Elongation with Ferrocene-Linked Redox-Labeled Nucleotides.

Here, we report the electrochemical detection of single-point mutations using solid-phase isothermal primer elongation with redox-labeled oligonucleotides. A single-base mutation associated with resistance to rifampicin, an antibiotic commonly used for the treatment of Mycobacterium tuberculosis, was used as a model system to demonstrate a proof-of-concept of the approach. Four 5'-thiolated primers, designed to be complementary with the same fragment of the target sequence and differing only in the last base, addressing the polymorphic site, were self-assembled via chemisorption on individual gold electrodes of an array. Following hybridization with single-stranded DNA, Klenow (exo-) DNA polymerase-mediated primer extension with ferrocene-labeled 2'-deoxyribonucleoside triphosphates (dNFcTPs) was only observed to proceed at the electrode where there was full complementarity between the surface-tethered probe and the target DNA being interrogated. We tested all four ferrocenylethynyl-linked dNTPs and optimized the ratio of labeled/natural nucleotides to achieve maximum sensitivity. Following a 20 min hybridization step, Klenow (exo-) DNA polymerase-mediated primer elongation at 37 °C for 5 min was optimal for the enzymatic incorporation of a ferrocene-labeled nucleotide, achieving unequivocal electrochemical detection of a single-point mutation in 14 samples of genomic DNA extracted from Mycobacterium tuberculosis strains. The approach is rapid, cost-effective, facile, and can be extended to multiplexed electrochemical single-point mutation genotyping

Exploiting the Nucleic Acid Nature of Aptamers for Signal Amplification

Aptamer-based assays and sensors are garnering increasing interest as alternatives to antibodies, particularly due to their increased flexibility for implementation in alternative assay formats, as they can be employed in assays designed for nucleic acids, such as molecular aptamer beacons or aptamer detection combined with amplification. In this work, we took advantage of the inherent nucleic acid nature of aptamers to enhance sensitivity in a rapid and facile assay format. An aptamer selected against the anaphylactic allergen β-conglutin was used to demonstrate the proof of concept. The aptamer was generated by using biotinylated dUTPs, and the affinity of the modified aptamer as compared to the unmodified aptamer was determined by using surface plasmon resonance to calculate the dissociation constant (KD), and no significant improvement in affinity due to the incorporation of the hydrophobic biotin was observed. The modified aptamer was then applied in a colorimetric competitive enzyme-linked oligonucleotide assay, where β-conglutin was immobilized on the wells of a microtiter plate, competing with β-conglutin free in solution for the binding to the aptamer. The limit of detection achieved was 68 pM, demonstrating an improvement in detection limit of three orders of magnitude as compared with the aptamer simply modified with a terminal biotin label. The concept was then exploited by using electrochemical detection and screen-printed electrodes where detection limits of 326 fM and 7.89 fM were obtained with carbon and gold electrodes, respectively. The assay format is generic in nature and can be applied to all aptamers, facilitating an easy and cost-effective means to achieve lower detection limits

Ultrasensitive determination of β-conglutin food allergen by means an aptamer assay based on inductively coupled plasma mass spectrometry detection

The overall objective of this work is the evaluation of different competitive aptamer assays based on inductively coupled plasma mass spectrometry (ICP-MS) detection for the determination of β-conglutin (food protein allergen from lupin) in flour samples. To this end, two competitive aptamer assay schemes were developed using either thiolated aptamers chemisorbed onto gold nanoparticles (AuNPs) or biotinylated aptamers linked to streptavidin-AuNPs. The influence of ICP-MS detection mode (i.e., conventional vs single particle) on assay performance was explored. In the case of the thiolated aptamer, the limit of detection (LoD) obtained using the single particle mode was improved 2-fold as compared to the LoD provided by the conventional mode. With regards to the biotinylated aptamer, the use of the conventional mode provided a 5-fold improvement of LoD as compared to that obtained for the single particle one. Using the optimized conditions, the best LoD of 2 pM was obtained with the biotinylated aptamer operating with conventional ICP-MS detection. When compared to previous reports using the same aptamer in a competitive assay, the developed method significantly improved the LoD by at least an order of magnitude. Different flour samples containing lupin were successfully analyzed according to European Conformity guidelines for the analysis of food contaminants.The authors would like to thank the Generalitat Valenciana (Project GV/2014/138) and the Vice-Presidency for Research and Knowledge Transfer of the University of Alicante for the financial support of this work (Projects GRE12-19 and VIGROB-050). D. Torregrosa thanks the Spanish Ministerio de Ciencia, Innovación y Universidades for the given fellowship FPU17/02853

A Label-Free Gold Nanoparticles-Based Optical Aptasensor for the Detection of Retinol Binding Protein 4

Retinol-binding protein 4 (RBP4) has been implicated in insulin resistance in rodents and humans with obesity and T2DM, making it a potential biomarker for the early diagnosis of T2DM. However, diagnostic tools for low-level detection of RBP4 are still lagging behind. Therefore, there is an urgent need for the development of T2DM diagnostics that are rapid, cost-effective and that can be used at the point-of-care (POC). Recently, nano-enabled biosensors integrating highly selective optical detection techniques and specificity of aptamers have been widely developed for the rapid detection of various targets. This study reports on the development of a rapid gold nanoparticles (AuNPs)-based aptasensor for the detection of RBP4. The retinol-binding protein aptamer (RBP-A) is adsorbed on the surface of the AuNPs through van der Waals and hydrophobic interactions, stabilizing the AuNPs against sodium chloride (NaCl)-induced aggregation. Upon the addition of RBP4, the RBP-A binds to RBP4 and detaches from the surface of the AuNPs, leaving the AuNPs unprotected. Addition of NaCl causes aggregation of AuNPs, leading to a visible colour change of the AuNPs solution from ruby red to purple/blue. The test result was available within 5 min and the assay had a limit of detection of 90.76 ± 2.81 nM. This study demonstrates the successful development of a simple yet effective, specific, and colorimetric rapid assay for RBP4 detection