Anisotropic Multitentacle Janus Particles Synthesized by Selective Asymmetric Growth

Anisotropic colloidal particles with asymmetric morphology possess functionally rich heterogeneous structures, thus offering potential for intricate superstructures or nanodevices. However, it is a challenge to achieve controlled asymmetric surface partitioned growth. In this work, an innovative strategy is developed based on the selective adsorption and growth of emulsion droplets onto different regions of object which is controlled by wettability. It is found that the emulsion droplets can selectively adsorb on the hydrophilic surface but not the hydrophobic one, and further form asymmetric tentacle by the interfacial sol-gel process along its trajectory. Janus particles with an anisotropic shape and multitentacle structure are achieved via integration of emulsion droplet (soft) and seed (hard) templates. The size and number of tentacles exhibit tunability mediated by soft and hard templates, respectively. This general strategy can be expanded to a variety of planar substrates or curved particles, further confirming the correlation between tentacle growth and Brownian motion. Most interestingly, it can be employed to selectively modify one region of surface partitioned particles to achieve an ABC three-component Janus structure.

Magnetic matchstick micromotors with switchable motion modes

The ability to in situ tune various motion modes of micromotors is challenging, yet critical for any practical applications of micromotors in complex microenvironments. Here, we designed and synthesized magnetic matchstick micromotors with two motion modes, a persistent rotational motion and a straight-line motion, that can be readily and reversibly switched in situ by an external magnetic field. Such micromotors with switchable motion modes hold considerable promise for local environment sensing and probing at the microscale.

High-Aspect-Ratio Nanostructured Surfaces as Biological Metamaterials

Materials patterned with high-aspect-ratio nanostructures have features on similar length scales to cellular components. These surfaces are an extreme topography on the cellular level and have become useful tools for perturbing and sensing the cellular environment. Motivation comes from the ability of high-aspect-ratio nanostructures to deliver cargoes into cells and tissues, access the intracellular environment, and control cell behavior. These structures directly perturb cells' ability to sense and respond to external forces, influencing cell fate, and enabling new mechanistic studies. Through careful design of their nanoscale structure, these systems act as biological metamaterials, eliciting unusual biological responses. While predominantly used to interface eukaryotic cells, there is growing interest in nonanimal and prokaryotic cell interfacing. Both experimental and theoretical studies have attempted to develop a mechanistic understanding for the observed behaviors, predominantly focusing on the cell-nanostructure interface. This review considers how high-aspect-ratio nanostructured surfaces are used to both stimulate and sense biological systems.

Seeded-Growth of Silica Rods from Silica-Coated Particles

Seeded growth of silica rods from colloidal particles has emerged as a facile method to develop novel complex particle structures with hybrid compositions and asymmetrical shapes. However, this seeded-growth technique has been so far limited to colloidal particles of only a few materials. Here, we first develop a general synthesis for the seeded-growth of silica rods from silica particles. We then demonstrate the growth of silica rods from silica-coated particles with three different cores which highlight the generality of this synthesis: fluorescently labeled organo-silica (fluorescein), metallic (Ag), and organic (PS latex). We also demonstrate the assembly of these particles into supraparticles. This general synthesis method can be extended to the growth of silica rods from any colloidal particle which can be coated with silica.

Precisely Endowing Colloidal Particles with Silica Branches

A method to modify colloidal particles with silica rods in a water/n-pentanol system is reported here. Because of the interfacial tension between aqueous and n-pentanol phase, water which surrounds the colloidal particles de-wets into droplets during the deposition process of silica. As a result of unidirectional deposition, silica rods grow perpendicularly on the surface of the colloidal particles at the site of the smallest curvature where the water droplet has been de-wetted. By controlling the hydrolysis conditions, particles with certain number of branches or rambutan-like particles can be obtained. This approach opens a path towards the higher levels of colloidal complexity.

Frosted Slides Decorated with Silica Nanowires for Detecting Circulating Tumor Cells from Prostate Cancer Patients

Developing low-cost and highly efficient nanobiochips are important for liquid biopsies, real-time monitoring, and precision medicine. By in situ growth of silica nanowires on a commercial frosted slide, we develop a biochip for effective circulating tumor cells (CTCs) detection after modifying epithelial cell adhesion molecule antibody (anti-EpCAM). The biochip shows the specificity and high capture efficiency of 85.4 ± 8.3% for prostate cancer cell line (PC-3). The microsized frosted slides and silica nanowires allow enhanced efficiency in capture EpCAM positive cells by synergistic topographic interactions. And the capture efficiency of biochip increased with the increase of silica nanowires length on frosted slide. The biochip shows that micro/nanocomposite structures improve the capture efficiency of PC-3 more than 70% toward plain slide. Furthermore, the nanobiochip has been successfully applied to identify CTCs from whole blood specimens of prostate cancer patients. Thus, this frosted slide-based biochip may provide a cheap and effective way of clinical monitoring of CTCs.

Regiospecific Nucleation and Growth of Silane Coupling Agent Droplets onto Colloidal Particles

Nucleation-and-growth processes are used extensively in the synthesis of spherical colloids, and more recently regiospecific nucleation-and-growth processes have been exploited to prepare more complex colloids such as patchy particles. We demonstrate that surface geometry alone can be made to play the dominant role in determining the final particle geometry in such syntheses, meaning that intricate chemical surface patternings are not required. We present a synthesis method for "lollipop"-shaped colloidal heterodimers (patchy particles), combining a recently published nucleation-and-growth technique with our recent findings that particle geometry influences the locus of droplet adsorption onto anisotropic template particles. Specifically, 3-methacryloxypropyl trimethoxysilane (MPTMS) is nucleated and grown onto bullet-shaped and nail-shaped colloids. The shape of the template particle can be chosen such that the MPTMS adsorbs regiospecifically onto the flat ends. In particular, we find that particles with a wider base increase the range of droplet volumes for which the minimum in the free energy of adsorption is located at the flat end of the particle compared with bullet-shaped particles of the same aspect ratio. We put forward an extensive analysis of the synthesis mechanism and experimentally determine the physical properties of the heterodimers, supported by theoretical simulations. Here we numerically optimize, for the first time, the shape of finite-sized droplets as a function of their position on the rod-like silica particle surface. We expect that our findings will give an impulse to complex particle creation by regiospecific nucleation and growth.