Many transfection techniques can deliver biomolecules into cells, but the dose cannot be controlled precisely. Delivering well-defined amounts of materials into cells is important for various biological studies and therapeutic applications. Here, we show that nanochannel electroporation can deliver precise amounts of a variety of transfection agents into living cells. The device consists of two microchannels connected by a nanochannel. The cell to be transfected is positioned in one microchannel using optical tweezers, and the transfection agent is located in the second microchannel. Delivering a voltage pulse between the microchannels produces an intense electric field over a very small area on the cell membrane, allowing a precise amount of transfection agent to be electrophoretically driven through the nanochannel, the cell membrane and into the cell cytoplasm, without affecting cell viability. Dose control is achieved by adjusting the duration and number of pulses. The nanochannel electroporation device is expected to have high-throughput delivery applications.
This work obtains the first molecular imaging of wall slip in entangled solutions. Using a combination of confocal fluorescence microscopy and rheometry, molecular images were captured in the nonlinear response regime of entangled DNA solutions. Conformations of DNA molecules were imaged during shear to correlate with the magnitude of wall slip. Interfacial chain disentanglement results in wall slip beyond the stress overshoot. Sufficient disentanglement can produce tumbling of individual DNA in the entangled solutions.
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