Near-Field Optical Immobilization of Antibodies for Novel Fluorescent Bioassays

Abstract

Optical manipulation techniques have enabled the study of single molecules in biophysics. Optical tweezers have allowed force spectroscopic measurements of large biopolymers bond to microspheres. A newer generation of optical traps, based on near field optics, allow trapping of smaller molecules with the hope to manipulate directly the biomolecules rather than through microspheres. We previously developed a photonic crystal trap able to capture small biomolecules, such as Wilson disease molecule, while observing them with fluorescent microscopy. The technique has been shown to be compatible with biophysical experiments as it can be performed in the biological buffer without significant temperature increase. Although these techniques have been developed with the idea of trapping single molecules, in this presentation, we steer away from the single molecule focus. A novel bioassay platform is presented that takes advantage of the optical forces exerted on molecules near the photonic crystal. The aim of this method is to replace the chemical immobilization on a surface by optical immobilization because molecules optically attracted to the optically active surface can freely rotate on it and sample more orientations than molecules bond to a surface. On this platform, using fluorescent microscopy, we observe the aggregation of antibodies in the optical trap and measure their binding rates to antigens at various temperatures. Because of the optical and hydrodynamic forces at play, we expect to observe higher binding rates than in mass-transport limited equivalent systems.