A reliable upconversion nanoparticle-based immunochromatographic assay for the highly sensitive determination of olaquindox in fish muscle and water samples

Olaquindox residues in food from its illegal use has received great attention. Here, an immunoassay strategy integrating an upconversion nanoparticle (UCNP)-based immunochromatographic strip with a fluorescence reader was proposed for the highly selective and sensitive detection of olaquindox. Polyacrylic acid-functionalized UCNPs were synthesized using a simple ligand exchange process and combined with an olaquindox polyclonal antibody to form a fluorescent probe. This approach achieved a sensitive response and specific recognition of olaquindox. A convenient upconversion fluorescence reader was introduced to implement accurate and sensitive quantitative analysis of olaquindox based on the fluorescence intensity of control and test lines on a strip. Under optimal conditions, the method demonstrated a favorable linear range (0–50 ng/mL) and sensitive detection (1.42 ng/mL, S/N = 3). This method was applied successfully to determine olaquindox in fish muscle and water samples, and results were consistent with an HPLC approach, and considered a promising strategy for monitoring olaquindox residuals.