Directed Self-Assembly of Nanoparticles (original) (raw)

Structure and dynamics of optically directed self-assembly of nanoparticles

Scientific Reports, 2016

Self-assembly of nanoparticles leading to the formation of colloidal clusters often serves as the representative analogue for understanding molecular assembly. Unravelling the in situ structure and dynamics of such clusters in liquid suspensions is highly challenging. Presently colloidal clusters are first isolated from their generating environment and then their structures are probed by light scattering methods. In order to measure the in situ structure and dynamics of colloidal clusters, we have generated them using the high-repetition-rate femtosecond laser pulse optical tweezer. Since the constituent of our dimer, trimer or tetramer clusters are 250 nm radius two-photon resonant fluorophore coated nanospheres under the optical trap, they inherently produce Two-Photon Fluorescence, which undergo intra-nanosphere Fluorescence Energy Transfer. This unique energy transfer signature, in turn, enables us to visualize structures and orientations of these colloidal clusters during the process of their formation and subsequent dynamics in a liquid suspension. We also show that due to shape-birefringence, orientation and structural control of these colloidal clusters are possible as the polarization of the trapping laser is changed from linear to circular. We thus report important progress in sampling the smallest possible aggregates of nanoparticles, dimers, trimers or tetramers, formed early in the self-assembly process. Colloidal structures result from coagulation or self-assembly of nanoparticles. Study of colloidal clusters play an important role in understanding macromolecular assembly leading to protein aggregation and clustering 1,2. Yet the in situ formation dynamics of colloidal cluster remains to be unraveled. Studies performed under isolated conditions, i.e., when the colloids are extracted from their generating environment, show that the most stable conformers for aggregated colloids have body-centered and face-centered cubic packing 3. Here we present a direct approach to measure the in situ formation dynamics of colloidal cluster by using the optical gradient force-field directed assembly of fluorophore coated colloidal nanospheres into clusters that exhibit a ubiquitous type of energy transfer. This energy transfer signature, in turn, enables us to determine the structure of colloidal clusters. Since these colloidal clusters exhibit shape birefringence, we propose that colloidal cluster shapes can be dictated by the polarization of incident laser beam. Trapping of multiple particles can occur in case of optical trapping in dense environment such as dense colloidal suspensions 4 , or inside cells 5 due to the optical gradient forces generated from the tightly focused laser beam. As the optical gradient forces pull all the trapped objects towards the trap center, formation of close-packed optically bound clusters happen (shown schematically in Fig. 1). We specifically demonstrate sampling of smallest possible aggregates of nanoparticles, dimers, trimers or tetramers, formed early in the self-assembly process. We generate colloidal clusters consisting up to four dye-coated polystyrene nanospheres, each of radius 250 nm, under optical tweezers, which provide the necessary optical gradient force-field 6,7. Structures of colloidal clusters are typically studied using light scattering methods 8-11. By the same token, we also use backscatter signal from the optical trap. However, while all the other light scattering approaches are used for characterizing isolated clusters, our backscatter signal measurement specifically probes the in situ self-assembly process. Furthermore, in our particular approach, since we have fluorophore coated nanospheres, we have the additional advantage of comparing the light scattering results with their two-photon fluorescence (TPF) signal 12. In fact, we show that there is an inherent decay present in the TPF signal that enables us to determine the in situ structures and dynamics of our colloidal clusters more accurately. When the sizes of the trapped clusters become larger than the focal spot size, partial illumination of our fluorophore coated nanospheres occur (Fig. 1). This

Theory and experiment for one-dimensional directed self-assembly of nanoparticles

Journal of Applied Physics, 2005

A promising method of particle self-assembly using patterned surfaces is described. A set of long ͑order of millimeters͒, nanoscale-width grooves is etched into a substrate, and an aqueous solution containing particles of ϳ50or 80-nm diameter is deposited on the surface. Upon the evaporation of the solution, the particles are dragged into the grooves by the receding contact line. A partial differential equation, incorporating screening, is constructed to investigate the final distribution of particles in the grooves. A complete analysis of the stationary states for the density equation in one and two dimensions is performed. Additionally, the nonlinear evolution of the density is studied numerically and the results compare well with both the analytic results and the experiments.

Rich complex behaviour of self-assembled nanoparticles far from equilibrium

Nature communications, 2017

A profoundly fundamental question at the interface between physics and biology remains open: what are the minimum requirements for emergence of complex behaviour from nonliving systems? Here, we address this question and report complex behaviour of tens to thousands of colloidal nanoparticles in a system designed to be as plain as possible: the system is driven far from equilibrium by ultrafast laser pulses that create spatiotemporal temperature gradients, inducing Marangoni flow that drags particles towards aggregation; strong Brownian motion, used as source of fluctuations, opposes aggregation. Nonlinear feedback mechanisms naturally arise between flow, aggregate and Brownian motion, allowing fast external control with minimal intervention. Consequently, complex behaviour, analogous to those seen in living organisms, emerges, whereby aggregates can self-sustain, self-regulate, self-replicate, self-heal and can be transferred from one location to another, all within seconds. Aggreg...

Nonisotropic Self-Assembly of Nanoparticles: From Compact Packing to Functional Aggregates

Advanced materials (Deerfield Beach, Fla.), 2018

Quantum strongly correlated systems that exhibit interesting features in condensed matter physics often need an unachievable temperature or pressure range in classical materials. One solution is to introduce a scaling factor, namely, the lattice parameter. Synthetic heterostructures named superlattices or supracrystals are synthesized by the assembling of colloidal atoms. These include semiconductors, metals, and insulators for the exploitation of their unique properties. Most of them are currently limited to dense packing. However, some of desired properties need to adjust the colloidal atoms neighboring number. Here, the current state of research in nondense packing is summarized, discussing the benefits, outlining possible scenarios and methodologies, describing examples reported in the literature, briefly discussing the challenges, and offering preliminary conclusions. Penetrating such new and intriguing research fields demands a multidisciplinary approach accounting for the cou...

Higher-Order Organization by Mesoscale Self-Assembly and Transformation of Hybrid Nanostructures

Angewandte Chemie International Edition, 2003

The organization of nanostructures across extended length scales is a key challenge in the design of integrated materials with advanced functions. Current approaches tend to be based on physical methods, such as patterning, rather than the spontaneous chemical assembly and transformation of building blocks across multiple length scales. It should be possible to develop a chemistry of organized matter based on emergent processes in which time-and scale-dependent coupling of interactive components generate higher-order architectures with embedded structure. Herein we highlight how the interplay between aggregation and crystallization can give rise to mesoscale selfassembly and cooperative transformation and reorganization of hybrid inorganic-organic building blocks to produce single-crystal mosaics, nanoparticle arrays, and emergent nanostructures with complex form and hierarchy. We propose that similar mesoscale processes are also relevant to models of matrix-mediated nucleation in biomineralization. From the Contents 1. Introduction 2351 2. Kinetic Control of Nucleation and Growth 2352 3. Aggregation-Mediated Pathways of Crystal Growth 2353 4. Mesoscale Self-Assembly of Nanoparticle Arrays 2356 5. Mesoscale Transformations and Emergent Nanostructures 2357 6. Mesoscale Transformations and Matrix-Mediated Nucleation in Biomineralization 2361