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Here, we develop an injection molded microfluidic approach for single cell analysis by making use of (1) rapidly curing injectable hydrogels, (2) a high density microfluidic weir trap array, and (3) reversibly bonded PDMS lids that are strong enough to withstand the injection molding process, but which can be peeled off after the hydrogel sets. This approach allows for single cell patterns to be created with densities exceeding 40 cells per mm 2 , is amenable to high speed imaging, and creates microfluidic devices that enable efficient nutrient and gas exchange and the delivery of specific biological and chemical reagents to individual cells. We show that it is possible to organize up to 10 000 single cells in a few minutes on the device, and we developed an image analysis program to automatically analyze the single-cell capture efficiency. The results show single cell trapping rates were better than 80%. We also demonstrate that the genomic DNA of the single cells trapped in the hydrogel can be amplified via localized, multiple displacement amplification in a massively parallel format, which offers a promising strategy for analyzing single cell genomes. Finally, we show the ability to perform selective staining of individual cells with a commercial bioprinter, providing proof of concept of its ability to deliver tailored reagents to specific cells in an array for future downstream analysis. This injection molded microfluidic approach leverages the benefits of both closed and open microfluidics, allows multiday single cell cultures, direct access to the trapped cells for genotypic end point studies.

Advances in electronics and life sciences have generated interest in "lab-on-a-chip" systems utilizing complementary metal oxide semiconductor (CMOS) circuitry for low-power, portable, and cost-effective biosensing platforms. Here, we present a simple and reliable approach for coating "high-κ" metal oxide dielectric materials with "non-fouling" (protein- and cell-resistant) poly(oligo(ethylene glycol) methyl ether methacrylate (POEGMA) polymer brushes as biointerfacial coatings to improve their relevance for biosensing applications utilizing advanced electronic components. By using a surface-initiated "grafting from" strategy, POEGMA films were reliably grown on each material, as confirmed by ellipsometric measurements and X-ray photoelectron spectroscopy (XPS) analysis. The electrical behavior of these POEGMA films was also studied to determine the potential impact on surrounding electronic devices, yielding information on relative permittivity and breakdown field for POEGMA in both dry and hydrated states. We show that the incorporation of POEGMA coatings significantly reduced levels of nonspecific protein adsorption compared to uncoated high-κ dielectric oxide surfaces as shown by protein resistance assays. These attributes, combined with the robust dielectric properties of POEGMA brushes on high-κ surfaces open the way to incorporate this protein and cell resistant polymer interface into CMOS devices for biomolecular detection in a complex liquid milieu.

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.

Ferroelectric surfaces can have very high surface charge densities that can be harnessed for manipulation of charged colloidal particles and soft matter in aqueous environments. Here, we report on the electrical double layer (EDL) formed by polarized ultrasmooth lead zirconium titanate (US-PZT) thin films in dilute electrolyte solutions. Using colloidal probe force microscopy (CPFM) measurements, we show that the ion distribution within the double layer can be changed by reversing the ferroelectric polarization state of US-PZT. The interaction force in dilute 1:1 electrolyte solution between the negatively charged probe and a positive surface charge (upward polarized) US-PZT thin film is attractive, while the interaction force is repulsive for a negative surface charge (downward polarized) film. We modeled these interactions with a constant-potential EDL model between dissimilar surfaces with the inclusion of a Stern layer. We report the surface potentials at the inner and outer-Helmholtz planes both for polarization states and for a range of ionic strength solutions. Effects of free-charge carriers, limitations of the analytical model, and effects of surface roughness are discussed.

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.

A massively parallel magnetic tweezer system has been constructed that utilizes the self-repulsion of colloidal beads from a planar interface via a magnetic dipole image force. Self-repulsion enables the application of a uniform magnetic force to thousands of beads simultaneously, which permits the measurement of unbinding histograms at the lowest loading rates ever tested. The adhesion of 9.8 μm polystyrene beads to a fluorocarbon, PEG, and UV-irradiated PEG surfaces were measured between 10(-3)-10(0) pN/s force loading rates, revealing the presence of both kinetic and quasi-equilibrium unbinding regimes.

This work is motivated by the unexpected experimental observation that field gradients can control the alignment of nonmagnetic nanorods immersed inside magnetic fluids. In the presence of local field gradients, nanorods were observed to align perpendicular to the external field at low field strengths, but parallel to the external field at high field strengths. The switching behavior results from the competition between a preference to align with the external field (orientational potential energy) and preference to move into regions of minimum magnetic field (positional potential energy). A theoretical model is developed to explain this experimental behavior by investigating the statistics of nanorod alignment as a function of both the external uniform magnetic field strength and the local magnetic field variation above a periodic array of micromagnets. Computational phase diagrams are developed which indicate that the relative population of nanorods in parallel and perpendicular states can be adjusted through several control parameters. However, an energy barrier to rotation was discovered to influence the rate kinetics and restrict the utility of this assembly technique to nanorods which are slightly shorter than the micromagnet length. Experimental results concerning the orientation of nanorods inside magnetic fluid are also presented and shown to be in strong agreement with the theoretical work.

A substrate of thin micromagnets covered by a template of microwells is used to direct the assembly of superparamagnetic colloidal beads into two-dimensional arrays. It is confirmed that the magnetization of the micromagnets can direct beads to programmed locations on the substrate with assistance of externally applied magnetic fields. Empirical investigations on this topic were guided by mathematical models with the intent to elucidate the conditions that promote a single bead to be assembled in the desired microwells. To demonstrate that this technique is programmable, heterogeneous arrays of colored beads are produced.