Universal Noble Metal Nanoparticle Seeds Realized Through Iterative Reductive Growth and Oxidative Dissolution Reactions

Abstract

Control over nanoparticle shape and size is commonly achieved via a seed-mediated approach, where nanoparticle precursors, or seeds, are hypothesized to act as templates for the heterogeneous nucleation of anisotropic products. Despite the wide variety of shapes that have been produced via this approach, high yield and uniformity have been more difficult to achieve. These shortcomings are attributed to limited structural control and characterization of the initial distribution of seeds. Herein, we report how iterative reductive growth and oxidative dissolution reactions can be used to systematically control seed structural uniformity. Using these reactions, we verify that seed structure dictates anisotropic nanoparticle uniformity and show that iterative seed refinement leads to unprecedented noble metal nanoparticle uniformities and purities for eight different shapes produced from a single seed source. Because of this uniformity, the first nanoparticle optical extinction coefficients for these eight shapes were analytically determined.

Nonadditivity of nanoparticle interactions

“…The crystallinity of a NP core, on the other hand, leads to a great expansion of the palette of particle shapes: rods, dumbbells, cubes, hexagons, tetrahedrons, octahedrons, concave rhombic dodecahedra, tetrahexahedra, and others ( Fig. 1, B to G) (20). Even NPs that are considered to be spherical are often actually prolate in shape, with an aspect ratio of 1.1 to 1.2 (21), and are also often faceted (20).…”

Exploring the zone of anisotropy and broken symmetries in DNA-mediated nanoparticle crystallization

“…1A), and can be synthesized via a seed-mediated method that yields >95% of the desired shape with <5% variation in size (Fig. 1A) (21). Particle uniformity was rigorously analyzed with a recently reported and freely available program that algorithmically analyzes transmission electron microscopy (TEM) images to analytically determine nanoparticle structure (22).…”

The nature and implications of uniformity in the hierarchical organization of nanomaterials

“…Similar effects occur in polytypic semiconductors (i.e., materials capable of adopting two different crystalline structures), where the energy difference between polytypes can fall within the temperature fluctuations of the system (15,16,22). These problems can be circumvented with larger seeds whose fate can be monitored and directly correlated with product structure (28). Indeed, if literaturereported seed-mediated syntheses optimized for a particular shape are repeated with larger, more uniform seeds, yields can be improved to >95% with CV <5% for at least eight different nonspherical shapes with widely tunable sizes (28).…”

“…In particular, the automated, algorithmic analysis of electron microscopy (EM) images holds tremendous potential to improve the rigor of nanomaterial characterization. This powerful tool can be used to minimize sampling bias, to improve throughput, and to quantitatively measure structure with single-nanoparticle resolution (28,29). The largest limitation associated with this approach pertains to the informational loss in the conversion of 2D projections from EM images to 3D shapes (30,31).…”

“…These problems can be circumvented with larger seeds whose fate can be monitored and directly correlated with product structure (28). Indeed, if literaturereported seed-mediated syntheses optimized for a particular shape are repeated with larger, more uniform seeds, yields can be improved to >95% with CV <5% for at least eight different nonspherical shapes with widely tunable sizes (28). This represents a particularly powerful advance that emphasizes the importance of seed stability and uniformity in the synthesis of homogeneous products.…”