Nanozyme-enhanced lateral flow immunochromatographic tests for the sensitive detection of Francisella tularensis cells in water samples

Abstract

Francisella tularensis is a bacterial pathogen that can contaminate drinking water and food products, causing tularemia – a severe zoonotic disease that affects both humans and animals. This infection is dangerous to human health and may be fatal without diagnosis and treatment. Therefore, rapid, sensitive, and selective detection of this microorganism is in high demand for clinical diagnostics, environmental monitoring, and ensuring food safety. This study presents the development of immunochromatographic (lateral flow) tests for revealing F. tularensis cells in natural and drinking water samples. A special feature of the test system is catalytically active Au@Pt nanoparticles (a peroxidase-like nanozyme) used as a label for specific antibodies. Au@Pt nanozyme can catalyze the oxidation of the peroxidase substrate, followed by the formation of a colored product, which amplifies the colorimetric signal on the test strip and significantly improves detection sensitivity. The tests allow for the detection of F. tularensis cells in concentrations down to 102–103 cells/mL, depending on the strain, with visual result assessment. The application of Au@Pt nanozyme decreased the detection limits by 321–9600 times compared to gold nanoparticles commonly used in immunochromatography. The assay duration is 14 min, including the catalytic enhancement step. Monoclonal antibodies against bacterial lipopolysaccharide provide selective detection of virulent strains, excluding cross-reactions with non-pathogenic strains of F. tularensis and other microorganisms that also may contaminate water sources. The effective testing of natural and tap water samples analyzed with no preliminary sample preparation has proven the relevance of the developed approach.