β Scribed by Nikolai G. Khlebtsov; Vladimir A. Bogatyrev; Lev A. Dykman; Andrei G. Melnikov
No coin nor oath required. For personal study only.
nature of aggregated colloids (6). Recently, the fractal na-We have prepared gold sols with mean particle diameters d m in ture of clusters of metal particles has been shown theoretithe range 4 to 50 nm and measured their extinction spectra and cally (7) and experimentally (8) to give rise to unique optisize dependences of the extinction peak position l max and value cal properties. For instance, the optical fields acting on a E max . The measured increasing function l max (d m ) displays a pro-single particle in a cluster may far exceed the mean field, nounced bend near the particle diameter d m Γ 10 nm, where the which leads to gigantic nonlinear effects and even to irrevalue of l max sharply decreases with reduction in the particle size.
To explain these findings, the extinction spectra of sols with the careful quantitative study of the spectral properties of both particle size and axial ratio polydispersity are calculated using Mie's theory, the T-matrix method, and various experimental sets the sols themselves and their conjugates with biomacromoof the bulk gold optical constants modified with regard to sizelecules seems to be of interest. limiting effects. It is shown that the measured l max (d m ) and Absorption and scattering of light by diluted metal sols have E max (d m ) dependences are inconsistent with calculations based on been sufficiently well described in terms of Lorenz-Drude's Mie's theory and the bulk gold optical constants. The most generalfree-electron theory and the optical theories of Rayleigh and ized model including the size dependence of the imaginary part Mie (2, 3, 9-15). However, an exact quantitative description of the dielectric permeability and the size and shape polydispersity of the absorption spectra of gold sols calls for a careful considgives good agreement with experimental extinction spectra for eration of the geometrical and optical parameters of particles 5-, 10-, 24-, and 40-nm sols, as well as with the measured functions such as: (i) size and shape polydispersity; (ii) size-dependent l max (d m ) and E max (d m ). Based on electron-microscopic and speccontribution to the bulk dielectric permeability; and (iii) strong tral data, calibration curves are obtained for efficient spectrophotometric control over the particle size and for estimation of the dependence of the theoretical position of the extinction peak amount of restorer essential for the preparation of particles of a on the input experimental wavelength-dependent set of optical given size. A simplest two-layer spherical model is employed to constants. Work (3) serves as an excellent example of such elucidate the basic changes in sol spectra after conjugation with investigations for gold particles deposited onto a glass substrate. specific biomacromolecules and to draw some conclusions about Similar research on the absorption spectra of silver particles in the conjugate shell structure.
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