On-chip light sheet illumination enables diagnostic size and concentration measurements of membrane vesicles in biofluids.

Cell-derived membrane vesicles that are released in biofluids, like blood or saliva, are emerging as potential non-invasive biomarkers for diseases, such as cancer. Techniques capable of measuring the size and concentration of membrane vesicles directly in biofluids are urgently needed. Fluorescence single particle tracking microscopy has the potential of doing exactly that by labelling the membrane vesicles with a fluorescent label and analysing their Brownian motion in the biofluid. However, an unbound dye in the biofluid can cause high background intensity that strongly biases the fluorescence single particle tracking size and concentration measurements. While such background intensity can be avoided with light sheet illumination, current set-ups require specialty sample holders that are not compatible with high-throughput diagnostics. Here, a microfluidic chip with integrated light sheet illumination is reported, and accurate fluorescence single particle tracking size and concentration measurements of membrane vesicles in cell culture medium and in interstitial fluid collected from primary human breast tumours are demonstrated.

Characterization of a novel impedance cytometer design and its integration with lateral focusing by dielectrophoresis.

This paper reports a novel impedance cytometer design, easily integrable with dielectrophoretic focusing using a simple fabrication process with a single metal layer. Patterning of electrodes recessed in lateral channels - so-called "liquid electrodes" - allows the use of large electrodes while keeping a good spatial resolution. This larger area allows measurements at low frequencies, down to 1 kHz. It also decreases the current density, leading to electrodes more robust against electrochemical degradation. The relative change in impedance is simulated and compared to values reported in the literature for traditional designs, showing a smaller sensitivity for the proposed design due to the larger measurement volume. The device is evaluated with specific target applications, such as viability measurement and high-speed cell counting. Numerical simulations indicate that the proposed design reduces the dependence of the measurement on the vertical position of the particle compared to conventional designs, with a variation of only 5%, but is still dependent on its lateral position. This dependence is studied using focusing by dielectrophoresis (DEP) at different lateral positions across the microchannel, showing a larger sensitivity when the particles are close to the measurement electrodes, as confirmed by the numerical simulations. The integration of lateral dielectrophoresis to focus particles in the middle of the channel reduces the variation of the measurements to very small values, with a coefficient of variation of 5.6%, and allows precise particle sizing. Such a design can be very powerful to simplify the fabrication process of impedance cytometers and enables the production of cost-effective, possibly disposable devices.

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.

Continuous-flow electrical lysis device with integrated control by dielectrophoretic cell sorting.

We present a device capable of electrical cell lysis and evaluation of lysis efficiency in continuous flow using dielectrophoretic cell sorting. We use a combination of AC electrical fields and so-called liquid electrodes to avoid bubble creation at the electrode surface. The electrical field distribution is calculated in different electrode configurations by numerical simulations. Cell sorting shows high lysis efficiency, 99% of yeast cells sorted after lysis featuring dielectric properties similar to dead cells. A study of the potential device throughput is performed.

On-chip chemical stimulation of neurons by local and controlled release of neurotransmitter.

This paper describes the fabrication and in vitro testing of a device capable of chemically stimulating individual neurons. Electrophoretic actuation is used to locally induce the release of the neurotransmitter L-glutamate in a network of hippocampal neurons cultured on top of the device. Cell activation by the neurotransmitter is visualized using calcium imaging. Single-cell stimulation is demonstrated close to the release site after application of a voltage of 500 mV. Such a device could provide a useful tool in both basic and clinical neuroscience. In a broader context, this device can be used to locally release small amounts of chemical compounds in Lab-on-Chip and drug delivery applications.