Rapid, sensitive and real-time multiplexing platform for the analysis of protein and nucleic-acid biomarkers.

We describe a multiplexing technology, named Evalution, based on novel digitally encoded microparticles in microfluidic channels. Quantitative multiplexing is becoming increasingly important for research and routine clinical diagnostics, but fast, easy-to-use, flexible and highly reproducible technologies are needed to leverage the advantages of multiplexing. The presented technology has been tailored to ensure (i) short assay times and high reproducibility thanks to reaction-limited binding regime, (ii) dynamic control of assay conditions and real-time binding monitoring allowing optimization of multiple parameters within a single assay run, (iii) compatibility with various immunoassay formats such as coflowing the samples and detection antibodies simultaneously and hence simplifying workflows, (iv) analyte quantification based on initial binding rates leading to increased system dynamic range and (v) high sensitivity via enhanced fluorescence collection. These key features are demonstrated with assays for proteins and nucleic acids showing the versatility of this technology.

Separation of platelets from other blood cells in continuous-flow by dielectrophoresis field-flow-fractionation.

We present a microfluidic device capable of separating platelets from other blood cells in continuous flow using dielectrophoresis field-flow-fractionation. The use of hydrodynamic focusing in combination with the application of a dielectrophoretic force allows the separation of platelets from red blood cells due to their size difference. The theoretical cell trajectory has been calculated by numerical simulations of the electrical field and flow speed, and is in agreement with the experimental results. The proposed device uses the so-called "liquid electrodes" design and can be used with low applied voltages, as low as 10 V(pp). The obtained separation is very efficient, the device being able to achieve a very high purity of platelets of 98.8% with less than 2% cell loss. Its low-voltage operation makes it particularly suitable for point-of-care applications. It could further be used for the separation of other cell types based on their size difference, as well as in combination with other sorting techniques to separate multiple cell populations from each other.

Wide channel dielectrophoresis-based particle exchanger with electrophoretic diffusion compensation.

We present here a microfluidic device for the chemical modification of particles. In order to alleviate diffusive mixing issues beads are pushed from a starting buffer to a reagent over a wide channel by an array of shifted electrodes. We also show that the effect of reagent diffusion can be compensated by electrophoretic forces.

Dielectrophoresis-based particle exchanger for the manipulation and surface functionalization of particles.

We present a microfluidic device where micro- and nanoparticles can be continuously functionalized in flow. This device relies on an element called "particle exchanger", which allows for particles to be taken from one medium and exposed to some reagent while minimizing mixing of the two liquids. In the exchanger, two liquids are brought in contact and particles are pushed from one to the other by the application of a dielectrophoretic force. We determined the maximum flow velocity at which all the particles are exchanged for a range of particle sizes. We also present a simple theory that accounts for the behaviour of the device when the particle size is scaled. Diffusion mixing in the exchanger is also evaluated. Finally, we demonstrate particle functionalization within the microfluidic device by coupling a fluorescent tag to avidin-modified 880 nm particles. The concept presented in this paper has been developed for synthesis of modified particles but is also applicable to on-chip bead-based chemistry or cellular biology.

A virtual valve for smooth contamination-free flow switching.

We present a channel geometry that allows for clean switching between different inlets of a microchip without any contamination of the inlets or the downstream flow. We drive this virtual valve with a pneumatic pressure setup that minimizes disturbance of the downstream flow during the switching procedure by simultaneous variation of the pressures applied to the different inlets. We assess the efficiency of the setup by spectroscopic measurement of downstream dye concentrations, and demonstrate its practical utility by sequentially constructing multiple layers of alginate hydrogel. The method is potentially useful for a whole series of further applications, such as changing perfusion liquids for cell culture and cell analysis, metering, chemical-reaction initiation and multi-sample chromatography, to name a few.