The self-organization of colloidal particles is a promising approach to create novel structures and materials, with applications spanning from smart materials to optoelectronics to quantum computation. However, designing and producing mesoscale-sized structures remains a major challenge because at length scales of 10–100 μm equilibration times already become prohibitively long. Here, we extend the principle of rapid diffusion-limited cluster aggregation (DLCA) to a multicomponent system of spherical colloidal particles to enable the rational design and production of finite-sized anisotropic structures on the mesoscale. In stark contrast to equilibrium self-assembly techniques, kinetic traps are not avoided but exploited to control and guide mesoscopic structure formation. To this end the affinities, size, and stoichiometry of up to five different types of DNA-coated microspheres are adjusted to kinetically control a higher-order hierarchical aggregation process in time. We show that the aggregation process can be fully rationalized by considering an extended analytical DLCA model, allowing us to produce mesoscopic structures of up to 26 μm in diameter. This scale-free approach can easily be extended to any multicomponent system that allows for multiple orthogonal interactions, thus yielding a high potential of facilitating novel materials with tailored plasmonic excitation bands, scattering, biochemical, or mechanical behavior
F. M. Hecht and A. R. Bausch (2016)
Kinetically guided colloidal structure formation
PNAS 113, 31, 8577-8582.
Dynamic self-organisation far from equilibrium is a key concept towards building autonomously acting materials. Here, we report the coupling of an antagonistic enzymatic reaction of RNA polymerisation and degradation to the aggregation of micron sized DNA coated colloids into fractal structures. A transient colloidal aggregation process is controlled by competing reactions of RNA synthesis of linker strands by a RNA polymerase and their degradation by a ribonuclease. By limiting the energy supply (Ntp) of the enzymatic reactions, colloidal clusters form and subsequently disintegrate without the need of external stimuli. Here, the autonomous colloidal aggregation and disintegration can be modulated in terms of lifetime and cluster size. By restricting the enzyme activity locally, a directed spatial propagation of a colloidal aggregation and disintegration front is realised.
H. Dehne, A. Reitenbach, A. Bausch (2019)
Transient self-organisation of DNA coated colloids directed by enzymatic reactions
Scientific Reports, accepted, 9, 7350.
(A) The DNAcc are dispersed in the unpolymerized polyacrylamide (PAM). (B) The colloidal structure formation is either triggered by ssDNA linker addition, or (C) remains a monodisperse colloidal system. (D and E) The polymerization of PAM is triggered by a light-sensitive catalyst, yielding polymer–colloid hybrid hydrogels with monodisperse or gelated colloids, that exhibit different mechanical responses. Confocal imaging confirms that the colloidal structure formation was completed.
(A) The storage modulus Gmax0 of pure PAM is increased with monomer concentration as a power-law function (0.036 5.13). Frequency sweeps (inset) were used to analyse the elasticity of the gels. G0 was determined at f = 1 Hz (red circle). The blue and green line represent the frequency sweeps for hydrogels with monodispersed and gelated DNAcc. (B) Increasing the concentration of monodisperse DNAcc in the sample at a fixed concentration of PAM (5% w/v) leads to a continuous increase in storage mod
(A) The DNAcc are dispersed in the unpolymerized polyacrylamide (PAM). (B) The colloidal structure formation is either triggered by ssDNA linker addition, or (C) remains a monodisperse colloidal system. (D and E) The polymerization of PAM is triggered by a light-sensitive catalyst, yielding polymer–colloid hybrid hydrogels with monodisperse or gelated colloids, that exhibit different mechanical responses. Confocal imaging confirms that the colloidal structure formation was completed.
The incorporation of monodisperse colloidal particles in hydrogels is a promising approach to create hybrid gels with unique structural, mechanical and functional properties. However, the colloidal structure formation within the hydrogels often remains uncontrolled, leaving behind possible mechanically synergetic effects of the polymeric and the colloidal system. Here we show that colloidal structure formation within the hybrid gels has a significant influence on the elasticity and toughness of the hybrid gels. We combine a polyacrylamide hydrogel with DNA coated colloids (DNAcc), where structure formation can be triggered independently at different points in time. Consequently, we are able to create hybrid gels that are composed of the same components, but do differ in explicit colloidal structure. While monodisperse colloids enhance the storage modulus of the gels, the yield strain is simultaneously drastically reduced. The toughness of these brittle hybrid gels is rescued by colloidal structure formation at higher polyacrylamide concentrations. The toughness is increased at lower polyacrylamide concentrations. We show that the toughness of the hydrogels at 10% (w/v) polyacrylamide and 4% (v/v) DNAcc can be increased by a factor of approx. 35, indicating that control over colloidal structure formation yields access to significant synergetic effects in polymer–colloid hybrid gels.
H. Dehne, F. M. Hecht and A. R. Bausch (2017)
The mechanical properties of polymer-colloid hybrid hydrogels
Soft Matter, 13, 4786
Controlling the structure formation of gold nanoparticle aggregates is a promising approach towards novel applications in many fields, ranging from (bio)sensing to (bio)imaging to medical diagnostics and therapeutics. To steer structure formation, the DNA–DNA interactions of DNA strands that are coated on the surface of the particles have become a valuable tool to achieve precise control over the interparticle potentials. In equilibrium approaches, this technique is commonly used to study particle crystallization and ligand binding. However, regulating the structural growth processes from the nano- to the micro- and mesoscale remains elusive. Here, we show that the non-equilibrium structure formation of gold nanoparticles can be stirred in a binary heterocoagulation process to generate nanoparticle clusters of different sizes. The gold nanoparticles are coated with sticky single stranded DNA and mixed at different stoichiometries and sizes. This not only allows for structural control but also yields access to the optical properties of the nanoparticle suspensions. As a result, we were able to reliably control the kinetic structure formation process to produce cluster sizes between tens of nanometers up to micrometers. Consequently, the intricate optical properties of the gold nanoparticles could be utilized to control the maximum of the nanoparticle suspension extinction spectra between 525 nm and 600 nm.
B.Buchmann, F. M. Hecht, C. Pernpeintner, T. Lohmüller, A. Bausch (2017)
Controlling non-equilibrium structure formation on the nanoscale
ChemPhysChem, accepted, DOI: 10.1002/cphc.201700844
A) Twosets of gold nanoparticles are coated with partially complementary DNA. The DNA strands have sticky ends that favor diffusion-limited binding and thus suppress particle unbinding or rearrangement. B) Particles A and B are mixed at different stoichiometries. C) Different stoichiometries lead to the formation of differently sized clusters.
A-C) Dark field images, (scale bar 20µm). D-F) Cryo-TEM images (scale bar 200nm). The images confirm the hypothesis of cluster size control through mixing ratio.
A) The asymmetry in particle size is reflected in an asymmetric behavior in the extinction spectrum. B) The peak position in dependency of the mixing ratio shows an asymmetric behaviour. C) The binary heterocoagulation of differently sized nanoparticlesdirectly yields access to another set of optical properties.
A) Twosets of gold nanoparticles are coated with partially complementary DNA. The DNA strands have sticky ends that favor diffusion-limited binding and thus suppress particle unbinding or rearrangement. B) Particles A and B are mixed at different stoichiometries. C) Different stoichiometries lead to the formation of differently sized clusters.