Improving the fluorescence intensity of lanthanide-doped microspheres via incorporation of lauryl methacrylate: Synthesis and their application in C-reactive protein detection

Lanthanide-doped microspheres, especially europium complexes, are widely utilized as fluorescent reporters in lateral flow immunoassays. High fluorescence signal output, which is closely associated with the synthesis of microsphere, is critical for this procedure. Here, the interior structure of microspheres was attempted to be adjusted by introducing plasticizer lauryl methacrylate (LMA) into the polymerization of styrene monomer to improve the amount of europium complexes encapsulated in microspheres. The scanning electron microscope (SEM) results showed that the microspheres containing LMA were spherical and uniform in size (the average size 291 nm). A maximal fluorescence signal was reached when the microspheres were prepared by adding 10 wt% LMA relatively to styrene, which is almost three times that of microspheres without LMA. Such elevation in fluorescence signal can be attributed to the increment in content of encapsulated europium complexes (about 47.10 mg/g, which is far higher than other reported methods (3.72 or 1.023 mg/g)) induced by reducing the regularity of the polymer chain and increasing its flexibility as well as distensibility inside microspheres with LMA. Thanks to such superior fluorescence property, lateral flow immunoassay was successfully founded to detect C-reactive protein (CRP) with a linear response in concentration range of 1.3–210.7 μg/L. Therefore, the fundamental advance in this work is to provide the way to adjust the environment inside microspheres for encapsulation of europium complexes, which lays a good foundation for preparing microsphere with high fluorescence intensity.