A Novel Immunochromatographic Test Strip Using Lanthanide-Labeled Fluorescent Nanoparticles for the Serological Detection of Toxoplasma gondii in Dogs and Cats

<i>Toxoplasma gondii</i> (<i>T. gondii</i>) is an important zoonotic pathogen which induces both acute and chronic toxoplasmosis. Timely diagnosis of <i>T. gondii</i> is crucial for effective disease management. Here, we present a pioneering approach using europium (III)-chelated nanoparticles (EuNPs) in a rapid lateral flow immunochromatographic test strip (ICTS) for detecting <i>T. gondii</i> antibodies in serum samples. By conjugating EuNPs with Staphylococcus aureus protein A, we efficiently captured <i>T. gondii</i>-specific antibodies, which bound to <i>T. gondii</i> antigens on the test line (T-line), generating a distinct fluorescent signal. Employing this novel method, we conducted an extensive epidemiological investigation of <i>T. gondii</i> infections among dogs and cats in Shanghai, China. This innovative ICTS allows for rapid results within 25 min, which include a qualitative result through naked-eye observation under an ultraviolet lamp and a quantitative one derived using a strip reader. With a detection limit of 1:6400 for dog positive serum and no cross-reactivity with other canine and feline pathogens, the EuNPs-ICTS demonstrated excellent consistency with standard enzyme-linked immunosorbent assay results for dogs (κ = 0.91) and cats (κ = 0.92). In addition, 20.38% of 996 dog serum samples and 14.18% of 416 cat serum samples revealed <i>T. gondii</i> antibodies, highlighting the efficacy of this approach. Our study presents a rapid, sensitive, specific, and reproducible EuNPs-ICTS, serving as a promising tool for on-the-spot diagnosis of <i>T. gondii</i> infections in dogs and cats.