Tunable Assembly of Colloidal Crystal Alloys Using Magnetic Nanoparticle Fluids

We demonstrate a magnetic technique for assembling bidisperse and tridisperse colloidal particle fluids into a variety of complex structures with dimensionality ranging from 0-D (rings) to 1-D (chains) to 2-D (tiles). Compared with prior work on bidisperse particles that are commensurate in size, here we explore the assembly of different sized particles, and we show that due to packing constraints, new particle structures can be realized experimentally. Extending these experiments to a tridisperse system, we demonstrate that at low concentrations the smallest particle does not change the underlying crystal structures of the bidisperse system; however, it can assist in the formation of crystallite structures that were not stable in a bidisperse system. Additionally, we discovered that the smallest particle mimics the role of the ferrofluid, by shifting the locations in phase space where the bidisperse crystal structures can be experimentally obtained. Finally, we demonstrate that 3-particle crystal structures can be tuned by varying the strength of the external field, which is not possible in a 2-particle system

Magnetically Responsive Negative Acoustic Contrast Microparticles for Bioanalytical Applications

Smart colloidal particles are routinely used as carriers for biological molecules, fluorescent reporters, cells, and other analytes for the purposes of sample preparation and detection. However, such particles are typically engineered to respond to a single type of stimulus (e.g., commercial magnetic beads to magnetic fields). Here, we demonstrate a unique class of particles that display both positive magnetic contrast and negative acoustic contrast in water. This dual functionality allows for fine spatiotemporal control, enabling multiple separation modalities and increasing the utility of the particles in various chemical and biological assays