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Fluorescence anisotropy metrology of electrostatically and covalently labelled silica nanoparticles

Yip, Philip and Karolin, Jan and Birch, David J. S. (2012) Fluorescence anisotropy metrology of electrostatically and covalently labelled silica nanoparticles. Measurement Science and Technology, 23 (8). -. ISSN 0957-0233

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We compare determining the size of silica nanoparticles using the time-resolved fluorescence anisotropy decay of dye molecules when electrostatically and covalently bound to stable silica nanoparticles. Covalent labelling is shown to offer advantages by simplifying the dye rotational kinetics and the appropriateness of various kinetic models is discussed. Silica nanoparticles produced using Stober synthesis of tetraethylorthosilicate (TEOS) are found to be controllable between similar to 3.1 and 3.8 nm radius by adjusting the relative water: TEOS concentration. Covalent labelling with fluorescein 5(6)-isothiocyanate (FITC) bound to (3-aminopropyl) trimethoxysilane (FITC-APS) predicts a larger particle than electrostatically labelling with rhodamine 6G. The difference is attributed to the presence of an additional depolarization mechanism to Brownian rotation of the nanoparticle and dye wobbling with electrostatic labelling in the form of dye diffusion on the surface of the nanoparticle.