Diatoms are single-celled photosynthetic algae that make silica shells or "frustules" with intricate features patterned at
the nano and microscales. In this study, antibody-functionalized diatom biosilica frustules serve as a biosensor platform
for selective and label free antibody-antigen immunocomplex formation by enhanced photoluminescence. Biosilica
frustules of 10 micron diameter were isolated from cells of the centric marine diatom Cyclotella sp. They were then
mounted on glass and covalently functionalized with the model antibody Rabbit Immunoglobulin G (IgG) to yield a
uniform nanostructured surface that selectively binds to its complimentary antigen, Goat anti-Rabbit IgG. Diatom
frustules possess an intrinsic capacity to emit blue light when excited with a UV laser light source, a property called
photoluminescence. Binding the antibody-functionalized diatom frustule with its complimentary antigen selectively
enhanced the intrinsic photoluminescence intensity of the diatom frustule by a factor of three, whereas challenging the
antibody-functionalized diatom frustule with a non-complimentary antigen, Goat anti-human IgG did not change the
intrinsic photoluminescence intensity. The nucleophilic immunocomplex increases the photoluminescence by donating
electrons to non-radiative sites on the photoluminescent diatom biosilica, thereby decreasing non-radiative electron
decay and increasing radiative emission. The intensified photoluminescence intensity is correlated to the antigen, goat
anti-rabbit IgG concentration, with a binding constant of 2.8 ± 0.7x10-7 M.
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