Optically concentration as new concept for quantitative analysis of nanoparticles

The unique size-dependent properties of Gold Nanoparticles (GNPs) make them superior and indispensable in many areas from biology to electronics. [1]. This strongly motivates development of trapping and manipulation technologies for metallic particles. The single beam optical trapping was introduced by Ashkin et al. [2]. It refers to a particular geometry where a laser beam is focused through a high numerical aperture objective lens to generate a three-dimensional optical trap by exerting a radiation force to small objects. For a high-gradient light field, two optical forces are exerted on small dielectric particles. The first is a momentum transfer due to scattering of the electromagnetic wave from the particle that pushes the particle and may destabilize trapping. The second is the gradient force on the dipole induced in the particle by the laser electric field. The gradient force depends on both the particle polarizability and the electric-field amplitude [3]. For sufficiently high laser intensities, the gradient force is strong enough to overcome the randomizing effect of brownian motion, thus locally enhancing the particle concentration near the focus. As the intensity of the trapping laser is increased, more particles are pulled toward the focus. an optical trap, in which particles can diffuse into and out of the trap, it is the average particle number density that increases with laser intensity [4]. Ou-yang et al. demonstrated for multiple particles in a single trapping consider both energy of trapping per particle and interaction between the particles [5]. optical concentration of substance in solution is a novel concept for enhancement of analytical sensitivity. In this paper, we investigated optical concentration of gold nanoparticle in the focal region of laser beam. We observed that the optical accumulation of nanoparticles in the trap region increases by the raising of laser intensity and number of gold nanoparticle around the focal region. Thus, increase of the molecules or particles in focal region of laser beam could be used for enhancement of analytical sensitivity. Under optimum conditions, linearly calibration curves in the range of 7.2 × 108 to 1. 44 × 1010 particle/ml were obtained for gold nanoparticle at laser power of 400 mW, gold nanoparticle size of 100 nm and 40 s after laser beam illuminated.