RESUMEN
An electrochemiluminescence (ECL) immunosensor for the rapid detection of the Francisella tularensis pathogen using whole antibodies or antibody fragments as capture biomolecule is described. A sandwich immunoassay was used with either lipopolysaccharide (LPS) or the whole inactivated bacterial cell (LVS) as a target, while Ru(bpy)3 (2+)-encapsulated silicate nanoparticles were linked to the secondary antibody and used as ECL labels. The assay was performed in a fluidic chip housed in a custom-built black box incorporating electronics, optics and fluidics. The obtained limit of detection for LPS was 0.4 ng/mL, while for the LVS it was 70 and 45 bacteria/mL when the capturing molecule was the whole antibody and the antibody F(ab) fragment, respectively.
Asunto(s)
Anticuerpos Antibacterianos/química , Anticuerpos Inmovilizados/química , Técnicas Electroquímicas/instrumentación , Francisella tularensis/aislamiento & purificación , Oro/química , Inmunoensayo/instrumentación , Mediciones Luminiscentes/instrumentación , Técnicas Biosensibles/instrumentación , Electrodos , Diseño de Equipo , Humanos , Límite de Detección , Nanopartículas/química , Nanopartículas/ultraestructura , Compuestos Organometálicos/química , Silicatos/química , Tularemia/diagnóstico , Tularemia/microbiologíaRESUMEN
Tularemia, also known as rabbit fever, is a highly infectious zoonotic disease caused by a non-motile and non-spore-forming Gram-negative coccoid rod bacterium, Francisella tularensis. It occurs naturally in lagomorphs (rabbits and hares), but many animals have been reported to be susceptible. Transmission to humans is mostly caused by inhalation of aerosolised bacteria, handling of infected animals, arthropod stings, and ingestion of contaminated foods and water. At present, pathogenic isolation, molecular detection, and serology are the most commonly used methods to confirm the diagnosis of tularemia. In this work, an electrochemical immunosensor for the detection of anti-F. tularensis antibodies was developed, consisting of gold-based self-assembled monolayers of a carboxylic-group-terminated bipodal alkanethiol that is covalently linked to a lipopolysaccharide (LPS) that can be found in the outer membrane of the bacteria F. tularensis. The presence of anti-F. tularensis antibodies was measured using horseradish peroxidase-labelled protein A (HRP-protein A) from Staphylococcus aureus, and the developed immunosensor gave a stable quantitative response to different anti-F. tularensis FB11 antibody concentrations after 30 min with a limit of detection of 15 ng/mL, RSD of 9%, n = 3. The developed immunosensor was tested with serum from animals infected with tularemia and was compared to the results obtained using ELISA showing an excellent degree of correlation.
Asunto(s)
Anticuerpos Antibacterianos/sangre , Zorros/microbiología , Francisella tularensis/aislamiento & purificación , Inmunoensayo/métodos , Proteína Estafilocócica A , Tularemia/sangre , Animales , Técnicas Electroquímicas/veterinaria , HumanosRESUMEN
Tularemia is a highly infectious zoonotic disease caused by a Gram-negative coccoid rod bacterium, Francisella tularensis. Tularemia is considered as a life-threatening potential biological warfare agent due to its high virulence, transmission, mortality and simplicity of cultivation. In the work reported here, different electrochemical immunosensor formats for the detection of whole F. tularensis bacteria were developed and their performance compared. An anti-Francisella antibody (FB11) was used for the detection that recognises the lipopolysaccharide found in the outer membrane of the bacteria. In the first approach, gold-supported self-assembled monolayers of a carboxyl terminated bipodal alkanethiol were used to covalently cross-link with the FB11 antibody. In an alternative second approach F(ab) fragments of the FB11 antibody were generated and directly chemisorbed onto the gold electrode surface. The second approach resulted in an increased capture efficiency and higher sensitivity. Detection limits of 4.5 ng/mL for the lipopolysaccharide antigen and 31 bacteria/mL for the F. tularensis bacteria were achieved. Having demonstrated the functionality of the immunosensor, an electrode array was functionalised with the antibody fragment and integrated with microfluidics and housed in a tester set-up that facilitated complete automation of the assay. The only end-user intervention is sample addition, requiring less than one-minute hands-on time. The use of the automated microfluidic set-up not only required much lower reagent volumes but also the required incubation time was considerably reduced and a notable increase of 3-fold in assay sensitivity was achieved with a total assay time from sample addition to read-out of less than 20 min.