The Importance of Salt-Enhanced Electrostatic Repulsion in Colloidal Crystal Engineering with DNA

Abstract

Realizing functional colloidal single crystals requires precise control over nanoparticles in three dimensions across multiple size regimes. In this regard, colloidal crystallization with programmable atom equivalents (PAEs) composed of DNA-modified nanoparticles allows one to program in a sequence-specific manner crystal symmetry, lattice parameter, and, in certain cases, crystal habit. Here, we explore how salt and the electrostatic properties of DNA regulate the attachment kinetics between PAEs. Counterintuitively, simulations and theory show that at high salt concentrations (1 M NaCl), the energy barrier for crystal growth increases by over an order of magnitude compared to low concentration (0.3 M), resulting in a transition from interface-limited to diffusion-limited crystal growth at larger crystal sizes. Remarkably, at elevated salt concentrations, well-formed rhombic dodecahedron-shaped microcrystals up to 21 μm in size grow, whereas at low salt concentration, the crystal size typically does not exceed 2 μm. Simulations show an increased barrier to hybridization between complementary PAEs at elevated salt concentrations. Therefore, although one might intuitively conclude that higher salt concentration would lead to less electrostatic repulsion and faster PAE-to-PAE hybridization kinetics, the opposite is the case, especially at larger inter-PAE distances. These observations provide important insight into how solution ionic strength can be used to control the attachment kinetics of nanoparticles coated with charged polymeric materials in general and DNA in particular.

Single-crystal Winterbottom constructions of nanoparticle superlattices

“…This unexpected trend contrasts prior solution phase work, which showed that crystal size decreases with increasing concentration of PAEs. 19 In principle, the nucleation rate should increase with increasing PAE concentration, resulting in an increased number of crystals and overall lower crystal size. The observed lack of increase in nucleation rate for substrate-bound crystals is hypothesized to arise because the concentration of PAEs in solution vastly exceeds the concentration that has been demonstrated to saturate the substrate 20,21 ; this result was also corroborated using a twodimensional Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach (see Supplementary Note 1 for calculations).…”

DNA‐ and Field‐Mediated Assembly of Magnetic Nanoparticles into High‐Aspect Ratio Crystals

“…[4,[12][13][14] Indeed, hundreds of crystals have been generated, spanning over 50 different crystal symmetries. [11,[15][16][17][18] Chemical parameters (e.g., core identity, [12,19,20] shell identity, [21,22] solvent, [18] pH, [23] salt concentration [24] ) have been widely used to control particle assembly; however, the influence of physical parameters on the crystallization process has not been fully explored, with temperature and irradiation wavelength and time (in the case of photo-sensitive PAEs) being primarily utilized to affect crystal growth. [25,26] In the case of magnetic particles, magnetism is a powerful tool that can be used to influence crystal growth.…”

Imaging how thermal capillary waves and anisotropic interfacial stiffness shape nanoparticle supracrystals

“…Our capability to measure facet-dependent interfacial stiffness and our demonstration on their role in shaping the supracrystals can advance crystal design at the nanoscale. For example, one can control the interfacial stiffness and crystal habit by utilizing the toolkits of both intrinsic parameters of NP shape and surface chemistry 41 , 54 – 56 as well as extrinsic parameters, such as temperature, pH, and ionic strength 57 – 59 . Previously reports have shown that changing the length of DNA ligands on the same gold NPs has led to tunability in the lattice symmetry of the interior structure and exposed facets of the supracrystal 17 , 55 , 60 .…”