from Theron et al. in Nanotechnology in Water Treatment Applications

In addition to QDs, luminescent dye-doped silica nanoparticles (FloDots), which consist of luminescent organic or inorganic dye molecules dispersed inside a silica matrix, have also been developed for ultra-sensitive bioanalysis and diagnostics. Owing to the silica matrix shielding effect, the doped dye molecules are protected from environmental oxygen, enabling the fluorescence to be constant and thus providing an accurate measurement for bioanalysis. Moreover, the silica matrix provides a versatile substrate for surface immobilization and various biorecognition molecules, including oligonucleotides and antibodies, have been conjugated to FloDots.

FloDots have been used successfully for the detection of DNA hybridization and in immunoassays. Using FloDots functionalized with oligonucleotides as labels for chip-based sandwich DNA assays, Zhao et al. reported a detection limit of 1 fM target DNA. The high sensitivity of the assay can be ascribed to the fact that each FloDot has the fluorescence intensity of thousands of dye molecules; therefore, each gene hybridization is reported by thousands of fluorophores. FloDot-immunoassays, using FloDots conjugated with monoclonal antibodies specific for the O-antigen of E. coli O157:H7, have also been developed to achieve rapid E. coli O157:H7 detection at the single-cell level. The fluorescence intensity emitted by one E. coli O157:H7 cell was sufficient to be detected using a normal spectrofluorometer in a conventional plate-based immunological assay, or to be accurately enumerated using a flow cytometer within 1 min of sample preparation. Although the use of FloDots represents an improvement over conventional fluorophore-based assays, they remain somewhat limited by the fundamental drawbacks of conventional fluorophores, including broad adsorption and emission profiles, which ultimately limit multiplexing capabilities.

Tags: Bioanalysis | Microbial Detection | Pathogen Detection | Biodiagnostics | Biodetection Assays | Biomolecular Detection