Patterned fluorescent particles as nanoprobes for the investigation of molecular interactions

Fluorescent colloidal particles, fabricated by depositing a thin gold film on one side of the particle, show intensity fluctuation (blinking) under an optical microscope because of their rotational Brownian motion. Interactions between molecules immobilized on the surfaces of the particle and the solid substrate restrict the rotation of the particle, thus modulating the intensity fluctuations. Because we can obtain the time-dependent rotational angle from the fluorescent intensity, we can use the intensity signals to investigate the weak interactions between unlabeled molecules by analyzing the angular distribution of the particle. To the best of our knowledge, this is the first demonstration of an optical measurement of the rotations of nanoparticles and the first attempt at using such a technique to study molecular interactions.