Sorting nanoparticles by their optical absorption

This work demonstrates the continuous-flow separation of ≈50 nm metal nanoparticles by their optical properties using counter-propagating laser beams. Metal nanoparticles are widely used, particularly in biotechnology, where their optical properties depend on size, shape, and chemistry. Heterogeneous mixtures are common, and greater homogeneity improves product performance and expands applications. We characterize the motion of gold and silver nanoparticles in solution under intense blue and green laser irradiation, imaging them via light scattering. When mixed and illuminated, 58 nm silver nanoparticles are primarily pushed by the blue laser, while 47 nm gold nanoparticles respond to the green laser. Continuous flow mitigates bulk temperature rise. This approach offers a potentially practical and efficient method for separating nanoparticles with desirable optical properties from less valuable byproducts, addressing a key challenge in nanoparticle synthesis.