Lanthanide-labeled immunochromatographic strips for the rapid detection of Pantoea stewartii subsp. stewartii

• We made simplifications in the preparation of lanthanide-labeled nanoparticles.
• The fluorescent nanoparticles can easily bind antibodies with dextran as a linker.
• A novel fluorescence strip reader was based on lanthanide labeling and an immunoreaction.
• It was developed to detect Pantoea stewartii subsp. stewartii (Pss) in maize.
• The fluorescence strip may provide a universal platform for quantifying bacteria.

The lateral flow immunoassay is used in commercial pregnancy detection, and is an accepted point-of-care testing technique. The most widely used format for lateral flow immunochromatographic strips uses gold nanoparticles for colorimetric detection. However, this method often suffers from poor quantitative discrimination and low analytical sensitivity. To address these limitations, lanthanide chelate-loaded silica nanoparticles have been used as fluorescent labels. The fluorescent nanoparticles can easily bind to antibodies, with dextran as a linker. The strip reader described here was based on a sandwich immunoreaction performed on a strip, using lanthanide-labeled antibodies that served as signal vehicles for the fluorescent readout. The strip reader was used as a quantitative test system. In this work, Pantoea stewartii subsp. stewartii (Pss) was used as a model analyte to demonstrate the use of the strip reader. Under optimal conditions, the detection limit was determined as 103 cfu/mL. The quantification limit was calculated to be 104 cfu/mL. The detection limit for Pss was 100 times lower than those displayed by colloidal gold-labeled strips or ELISAs. No cross-reactions were observed with the other nine strains, indicating the good specificity of the Pss strip. This strip showed good stability in repeated tests. The tests using the fluorescence immunochromatographic strip were easy to perform, rapid, and sensitive. Methods using fluorescence strips and a strip reader have the potential to be a powerful tool for the quantification of bacteria.