Particle separation under the co-action of Brownian motion and optical force in near-field speckle patterns

Continuous separation of nano-sized molecules has great importance in biomedical applications. This paper represents a near-field optical approach to separate nanoparticles using speckle patterns. Near-field random light patterns (speckle pattern) are generated by the repeated coupling and interference of light in nano-waveguide arrays. The movements of 2-μm and 0.5-μm particles are studied under the co-action of Brownian motion and the exerted optical force. The experimental results show that the 2-μm particle has an average lateral displacement of 10 μm, which is considerably larger than that of the 0.5-μm particle. This method avoids the stringent optical systems and broadens the perspectives of optical manipulation in real-life applications.