title: Optimization of size, morphology and colloidal stability of fluorescein dye-doped silica NPs for application in immunoassays.
abstract: Fluorescent nanoparticle (NP) labels are of great interest for point-of-care medical diagnostics where high fluorescence signals combined with low limits of detection are required. In this work, hydrophilic and hydrophobic fluorescein dye derivatives were covalently doped into silica NPs. The NPs were prepared in a range of sizes from 16 to 80 nm using both ternary and quaternary microemulsion methods where the diameter varied linearly with changes in the water to surfactant ratio. The morphology and colloidal stability of the NPs were characterised using transmission electron microscopy and photon correlation spectroscopy; NPs doped with hydrophobic fluorescein dye were significantly smaller and more polydispersed. Optical properties including absorption, fluorescence and quantum efficiency were also determined. Representative NPs from each microemulsion method (ternary, Ø = 25 nm and quaternary, Ø = 80 nm) were tested as labels in a fluorescence based immunoassay for the detection of human IgG and human chorionic gonadotropin. Both sets of nanoparticle assays showed lower limits of detection and better coefficients of variance than a free dye label with good day to day reproducibility. The optimal surface coverage of detection antibody was also found to depend on the size of the nanoparticle.
authors.affiliation: Biomedical Diagnostic Institute, National Centre for Sensor Research, School of Physical Sciences, Dublin City University, Collins Avenue, Glasnevin, Dublin 9, Ireland.
authors.forename: Robert I
authors.initials: RI
authors.lastname: Nooney
authors.forename: Eoin
authors.initials: E
authors.lastname: McCormack
authors.forename: Colette
authors.initials: C
authors.lastname: McDonagh
mesh_terms: D006063:Chorionic Gonadotropin / Q000032:analysis*; D003102:Colloids / Q000737:chemistry; D019793:Fluorescein / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007074:Immunoglobulin G / Q000032:analysis*; D057230:Limit of Detection; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D006063:Chorionic Gonadotropin; D003102:Colloids; D005456:Fluorescent Dyes; D007074:Immunoglobulin G; D012822:Silicon Dioxide; D019793:Fluorescein