Detecting HER2 on Cancer Cells by TiO<sub>2</sub> Spheres Mie Scattering

This work is the first to describe a bioimaging method that uses highly uniformly sized TiO<sub>2</sub> submicrometer and micrometer spheres based on Mie scattering. Transmembrane proteins (HER2) located on the surface of cancer cells were detected by bonded antibody-linked TiO<sub>2</sub> spheres using optic microscopy and UV−vis spectroscopy. A particular HER2 bond on cancer cells, which has a weaker binding affinity than the biotin/avidin interaction, can be identified between TiO<sub>2</sub> spheres that are linked to anti-HER2 antibodies and those that are linked to nonspecific mouse IgG antibodies by observing the cells under an optical microscope or by measuring absorbance from a UV−vis spectrum. The TiO<sub>2</sub> spheres used in this work was prepared by reacting TTIP with carboxylic acid, as described elsewhere and the uniformity of the TiO<sub>2</sub> sphere was further improved by adjusting the amount of water used. The water content was inversely related to particle size and the size distribution: as more water was used, smaller spheres with a narrower size distribution were obtained. The most uniform sphere obtained had a diameter of about 1 μm with a size variation of 3%.