A highly sensitive fluorescence sensor based on lucigenin/chitosan/SiO2 composite nanoparticles for microRNA detection using magnetic separation

In this paper, a convenient reverse-phase microemulsion method for the synthesis of SiO 2 nanoparticles (NPs) by simply introducing the chitosan and fluorescent dye of lucigenin during the formation reaction of SiO 2 NPs was proposed. Addition of chitosan can make the SiO 2 NPs porous, and increases lucigenin molecule incorporation into chitosan/SiO 2 NPs nanopores based on electrostatic interaction and supermolecular forces. Therefore, fluorescence quantum yield of the lucigenin/chitosan/SiO 2 composite nanoparticles was increased by introduction of chitosan and compared with lucigenin/SiO 2 NPs without chitosan. Because the number of negative charges carried when using single-stranded DNA (ssDNA) was different from that of double-stranded DNA (dsDNA), the numbers of lucigenin/chitosan/SiO 2 composite nanoparticles with positive charge adsorbed using ssDNA or dsDNA were different. Consequently, fluorescence intensity caused using ssDNA or dsDNA/miRNA was clearly discriminative. With increase in target DNA/miRNA concentration, the difference in fluorescence intensity also increased, resulting in a good linear relationship between fluorescence intensity sensitizing value and target miRNA concentrations. Therefore, a new fluorescence analysis method for direct detection of let-7a in human gastric cancer cell samples without enzyme, label free and no immobilization was established using lucigenin/chitosan/SiO 2 composite nanoparticles as a DNA hybrid indicator. The proposed method had high sensitivity and selectivity, low cost and the detection limit was 10 fM (S/ N = 3).