Separation and Analysis of Polydisperse Mixtures of Gold Nanobipyramids via Centrifugation and Digital Photometry

Abstract

One of the notable achievements in the design of plasmon-resonant particles is the synthesis of penta-twinned nanostructures—bipyramids with pentagonal cross-sections, which form through seeded bidirectional growth [1, 2]. However, typical synthesis protocols often yield multimodal polydisperse suspensions containing, in addition to the target bipyramids, nanorods and pseudospherical particles. In such cases, obtaining a monodisperse product necessitates postsynthetic purification, conventionally achieved via depletion flocculation using BDAC [3]. A significant drawback of this approach is the risk of undesirable co-flocculation, which is particularly pronounced for particles larger than 100 nm.
In the present work, we propose an alternative method that is free from the aforementioned limitation and enables the isolation of monodisperse fractions directly from complex multimodal mixtures without the introduction of additional surfactants. The approach is based on a combination of sedimentation separation techniques—namely, differential and zone-velocity centrifugation in a swinging-bucket rotor. Multistage separation employing reversible flocculation ensures the sequential isolation of subpopulations differing in morphometric and optical (plasmon-resonance) characteristics.
An additional advantage of the developed protocol is its compatibility with digital photometry of sedimentation profile images formed in centrifuge tubes. This provides a fundamental capability to reconstruct histograms of particle size and shape distributions without preliminary isolation of individual fractions, thereby substantially reducing analysis time. The proposed approach is distinguished by the accessibility of reagent and instrumentation requirements and can be readily implemented in standard laboratory practice.
The obtained results open up prospects for rapid screening and preparative separation of polydisperse colloidal systems, which is of particular importance for applications in biophotonics, sensing, and nanomedicine.

References
1. T.H. Chow et al., Acc. Chem. Res. 2019, 52, 2136–2146.
2. A. Sánchez-Iglesias and M. Grzelczak, Small 2025, 21, 2407735.
3. J.-H. Lee et al., Nat. Commun. 2015, 6, 7571.

Speaker

Puzanov-Tyurin D.A.
Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences (IBPPM RAS)
Russia

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