Nanoparticle metrology in sol-gels using multiphoton excited fluorescence

The authors have developed a method of measuring the growth of nanoparticles during sol - gel glass formation based on labelling the particle with a fluorescent dye and determining the multiphoton excited decay of fluorescence anisotropy due to Brownian rotation. Multiphoton excitation is shown to give a higher dynamic range of measurement than 1-photon excitation. Illustrates the subnanometre resolution and stability of the approach by detecting a 0.8-1.1 nm silica particle hydrodynamic mean radius increase in a tetramethylorthosilicate sol at pH 2.3 labelled with rhodamine 6G and observed over 4 weeks; and also with a stable silica colloid of radius 6 nm, pH 8.9, labelled with a 6-methoxyquinoline-type dye. (Original abstract)