Synthesis and optical levitation of ellipsoidal silica particles

In the present work, we present a sol-gel method to synthesize elliptic silica particles using a mixture of CTAB/L-tyrosine as structure-directing agents. Our results demonstrate that L-tyrosine is essential for the formation of ellipsoidal morphology, as reactions carried out under varying CTAB concentration only formed spherical to rod-like particles. With increased concentrations of L-tyrosine, the produced particles go from isotropic spherical particles to anisotropic prolate and oblate ellipsoidal particles with increased dimensions. A typical synthesis of ellipsoidal particles presents an average major axis of 137 nm and an average aspect ratio of 1.6. The small-angle X-ray scattering showed that the distance between centers of adjacent cylinders is on average ∼ 4.6 nm. Optical trapping of single particles was used to perfectly isolate individual ellipsoidal silica particle from their environment while measuring their geometric properties with great precision. We observed an average aspect ratio of 1.5 while measuring the particles in 3D space, which is consistent with the TEM analysis.