title: Separation of nanorods by density gradient centrifugation.
abstract: The experimental conditions necessary for the synthesis of well-defined nanoparticles are often difficult to control. There is thus a compelling need for post-synthesis separation of nanoparticles polydispersed in size and shape. We demonstrate here both theoretically and experimentally that gold nanorods with diverse aspect ratios can be separated using density gradient centrifugation. By analysing the force balance of a Brownian rod falling in a Stokes flow, we derive a rigorous and predictive model that reveals the quantitative dependency of the nanorod sedimentation rates on their mass and shape. The calculations show that while mass dependency is still the dominating factor during centrifugation, the shape factor is not insignificant. Relatively heavier but long and thin rods could sediment slower than certain size of lighter spheres, and some rods and spheres with different masses and shapes may never be separated. This mass and shape dependency is exploited to separate as-prepared gold nanorod colloids by sucrose gradient centrifugation. Two layers of nanorods with narrow aspect-ratio distributions are obtained.
authors.affiliation: College of Chemistry and Chemical Engineering, State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Xiong
authors.forename: Jing
authors.initials: J
authors.lastname: Cheng
authors.forename: Yanxia
authors.initials: Y
authors.lastname: Qiao
authors.forename: Rui
authors.initials: R
authors.lastname: Zhou
authors.forename: Yan
authors.initials: Y
authors.lastname: He
authors.forename: Edward S
authors.initials: ES
authors.lastname: Yeung
mesh_terms: D002499:Centrifugation, Density Gradient / Q000379:methods*; D006046:Gold / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D043942:Nanotubes / Q000737:chemistry*; D010316:Particle Size
chemical_list: D006046:Gold