Optics and Photonics Society of Iran

Abstract- Thanks to their biocompatibility property, metallic nanoparticles have found many applications in biophysics and they are a good candidate for cancer therapy. Trapping such particles by optical tweezers have led to a wide range of research in different areas from biophysics to biotechnology. The main issue is that the particles smaller than 200 nm are smaller than diffraction limit and cannot be observed by bright field microscope. However, novel metallic nanoparticles such as gold or silver are good scatterers of light in the visible range, because of their plasmonic properties. In this paper, we added an extra laser beam with power of a few tens of microwatts to the optical tweezers setup to study its ability for detection of an optically trapped particle. Our results show that gold nanospheres down to 24 nm can be detected by the backscattered light from the particle. The experimental results of trapping stiffness also show that the secondary laser beam’s effect on the optical force is negligible.