David W. Inglis

Deterministic hydrodynamics : Taking blood apart

We show the fractionation of whole blood components and isolation of blood plasma with no dilution by using a continuous-flow deterministic array that separates blood components by their hydrodynamic size, independent of their mass. We use the technology we developed of deterministic arrays which separate white blood cells, red blood cells, and platelets from blood plasma at flow velocities of 1,000 μm/sec and volume rates up to 1 μl/min. We verified by flow cytometry that an array using focused injection removed 100% of the lymphocytes and monocytes from the main red blood cell and platelet stream. Using a second design, we demonstrated the separation of blood plasma from the blood cells (white, red, and platelets) with virtually no dilution of the plasma and no cellular contamination of the plasma.

Continuous microfluidic immunomagnetic cell separation

We present a continuous-flow microfluidic device that enables cell by cell separation of cells selectively tagged with magnetic nanoparticles. The cells flow over an array of microfabricated magnetic stripes, which create a series of high magnetic field gradients that trap the magnetically labeled cells and alter their flow direction. The process was observed in real time using a low power microscope. The device has been demonstrated by the separation of leukocytes from whole human blood.

Five-nanometer diamond with luminescent nitrogen-vacancy defect centers

A study was conducted to investigate the properties of weakly bound clusters of single-digit nanodiamonds (SND) using spectrally and temporally resolved luminescence detection, electron paramagnetic resonance (EPR) spectroscopy, and transmission electron microscopy (SEM). Nitrogen-vacancy (NV) centers were created in diamonds by high-energy proton irradiation followed by thermal annealing. Samples containing equal weights of 55-nm HTHP diamonds and SNDs were uniformly distributed on quartz substrates for luminescence measurements. It was observed that the SNDs exhibited significant luminescence in the red spectral region before irradiation. The emission was blue-shifted and the absence of the zero-phonon lines at 637 and 575 nm indicated that the luminescence did not originate from NV centers as compared with the NV spectrum.

Microfluidic high gradient magnetic cell separation

Separation of blood cells by native susceptibility and by the selective attachment of magnetic beads has recently been demonstrated on microfluidic devices. We discuss the basic principles of how forces are generated via the magnetic susceptibility of an object and how microfluidics can be combined with micron-scale magnetic field gradients to greatly enhance in principle the fractionating power of magnetic fields. We discuss our efforts and those of others to build practical microfluidic devices for the magnetic separation of blood cells. We also discuss our attempts to integrate magnetic separation with other microfluidic features for developing handheld medical diagnostic tools.

Hydrodynamic metamaterials: Microfabricated arrays to steer, refract, and focus streams of biomaterials

We show that it is possible to direct particles entrained in a fluid along trajectories much like rays of light in classical optics. A microstructured, asymmetric post array forms the core hydrodynamic element and is used as a building block to construct microfluidic metamaterials and to demonstrate refractive, focusing, and dispersive pathways for flowing beads and cells. The core element is based on the concept of deterministic lateral displacement where particles choose different paths through the asymmetric array based on their size: Particles larger than a critical size are displaced laterally at each row by a post and move along the asymmetric axis at an angle to the flow, while smaller particles move along streamline paths. We create compound elements with complex particle handling modes by tiling this core element using multiple transformation operations; we show that particle trajectories can be bent at an interface between two elements and that particles can be focused into hydrodynamic jets by using a single inlet port. Although particles propagate through these elements in a way that strongly resembles light rays propagating through optical elements, there are unique differences in the paths of our particles as compared with photons. The unusual aspects of these modular, microfluidic metamaterials form a rich design toolkit for mixing, separating, and analyzing cells and functional beads on-chip.

Scaling deterministic lateral displacement arrays for high throughput and dilution-free enrichment of leukocytes

A disposable device for fractionation of blood into its components that is simple to operate and provides throughput of greater than 1 mL min−1 is highly sought after in medical diagnostics and therapies. This paper describes a device with parallel deterministic lateral displacement devices for enrichment of leukocytes from blood. We show capture of 98% and approximately ten-fold enrichment of leukocytes in whole blood. We demonstrate scaling up through the integration of six parallel devices to achieve a flow rate of 115 µL of undiluted blood per minute per atmosphere of applied pressure.

Efficient microfluidic particle separation arrays

Microfluidic particle separation arrays are capable of passive sorting of microparticles or cells by size while avoiding blockage. Despite the usefulness of boundaries for concentration and parallel integration of arrays, separation efficiency is severely degraded in the areas adjacent to the boundaries due to the aberrant fluid flow found there. This letter shows how to eliminate this problem by modifying the boundary interface. At each row the boundary is moved by a specific amount to ensure a linear change in flux from row to row, which leads to uniform flow patterns and improved separation characteristics throughout the array.

Simultaneous Concentration and Separation of Proteins in a Nanochannel

Molecular separation technologies such as gel electrophoresis and liquid chromatography coupled with mass spectrometry detection have been the foundations of biomarker discovery. This is because medically significant biomarkers, for example in blood, can be as much as 10 fold less common than the most abundant protein, albumin and detecting these low abundance molecules requires high sensitivity and selective depletion of the dominant species. Conventional approaches including antibody depletion remove selected molecules by less than 3 orders of magnitude only. This prevents the isolation, characterization and discovery of millions of new proteins where key disease markers could be identified. Overcoming this barrier requires new approaches to analytical detection that minimize sample pre-processing steps while achieving high throughput with very high levels of sensitivity. Here we describe a new device that demonstrates simultaneous concentration and separation of proteins by conductivity gradient focusing without membranes, external pumps, temperature gradients or ampholytes. Concentration and separation take place in an electric field driven, 120-nm deep nanochannel, supporting a stable salt and conductivity gradient. Conductivity gradient focusing is one of many techniques that use opposing convective flow and electrophoretic forces to focus molecules to an equilibrium position. These methods include a step change in chromatographic packings, electrochromatorgraphy, varying the molecular charge (as in isoelectric focusing), temperature gradient focusing, varying the cross section through which the electric current flows, and varying the buffer conductivity. In contrast to all of these approaches, the device presented here does not require ampholytes, matrices or gels, membranes, temperature gradients, or an external pump. Electrokinetic phenomena at the nanoscale have recently been shown to produce rapid and high preconcentration of proteins and peptides in physiological buffers. In these reports nanochannels in microfluidic devices create gradients in the electric field by their charge selective transport characteristics. By combining this with a transport mechanism, often electro-osmosis, charged molecules can be trapped and accumulated owing to a balance in the viscous drag force and the electrophoretic force. The interaction of surface charges, mobile charges, and water molecules with each other and the electric field is complex but our understanding has been advanced by a number of excellent fundamental studies. Concentration polarization, as it is sometimes known, at the entrance to a nanochannel, gives rise to a gradient in the concentration of salt ions, which, in turn, perturbs the electric field creating a trap. Typically these traps cause sample stacking on the microchannel side of the microto nanochannel junction. In such cases the electric field gradient is very abrupt, causing all molecules to accumulate in a tightly confined region with limited scope for separation.

Highly accurate deterministic lateral displacement device and its application to purification of fungal spores

We have designed, built, and evaluated a microfluidic device that uses deterministic lateral displacement for size-based separation. The device achieves almost 100% purity and recovery in continuously sorting two, four, and six micrometer microspheres. We have applied this highly efficient device to the purification of fungal (Aspergillus) spores that are spherical ( approximately 4 mum diameter) with a narrow size distribution. Such separation directly from culture using unfiltered A. niger suspensions is difficult due to a high level of debris. The device produces a two to three increase in the ratio of spores to debris as measured by light scatter in a flow cytometer. The procedure is feasible at densities up to 4.4x10(6) sporesml. This is one of the first studies to apply microfluidic techniques to spore separations and has demonstrated that a passive separation system could significantly reduce the amount of debris in a suspension of fungal spores with virtually no loss of spore material.

A method for reducing pressure-induced deformation in silicone microfluidics

Poly(dimethylsiloxane) or PDMS is an excellent material for replica molding, widely used in microfluidics research. Its low elastic modulus, or high deformability, assists its release from challenging molds, such as those with high feature density, high aspect ratios, and even negative sidewalls. However, owing to the same properties, PDMS-based microfluidic devices stretch and change shape when fluid is pushed or pulled through them. This paper shows how severe this change can be and gives a simple method for limiting this change that sacrifices few of the desirable characteristics of PDMS. A thin layer of PDMS between two rigid glass substrates is shown to drastically reduce pressure-induced shape changes while preserving deformability during mold separation and gas permeability.