May 16, 2014
Carbon nanopipettes for automated injection
The lack of an effective and automated means to inject multiple mammalian cells is the limiting step in many important projects. Carbon nanopipettes (CNPs) combine pulled-glass nanopipettes with a thin carbon layer. They can simultaneously sense cell penetration electrochemically through their carbon lining and controllably inject reagents into cells through their hollow bore. Now, reporting in Nanotechnology, researchers propose to use the measured change in the CNP’s impedance, resulting from cell penetration, to trigger automated injection.
Microinjection is arguably the most controllable method for transfecting and introducing reagents into cells with precise volume and composition. However, the drawbacks of microinjection are the low-throughput, tedious manual operation and the high level of skill required by the operator. Microinjection would benefit greatly from automation.
Carbon nanopipettes are batch-fabricated, hollow, pulled-glass or quartz capillaries that terminate in a carbon nanopipe. A conductive carbon film coats the entire internal surface of the CNPs. Upon cell penetration the impedance of the CNP is altered due to the differences between the intracellular and extracellular environments. By monitoring the CNP’s impedance as it approaches and penetrates the cell, one can sense cell penetration.
Predictable and compatible
The technique has high spatial (sub-micron) and temporal (millisecond) resolution. The measured change in impedance upon cell penetration favourably agrees with predictions of a simple equivalent-circuit model. The magnitude of the impedance change can be used to indicate whether the pipette penetrates into the cytoplasm or nucleus of the cell. The CNPs are compatible with existing pipette fittings, micromanipulators and patch-clamp amplifiers, and are more durable and biocompatible than traditional glass pipettes.
In future work, cell penetration detection will be used to trigger pressure injection into the cell; facilitating automated injection. Additionally, it may also be feasible to use the impedance measurements to indicate the position of the CNP’s tip, whether in the extracellular solution, cytoplasm or nucleus, and the state of the pipette, i.e. broken or clogged.
More information about the research can be found in the journal Nanotechnology 25 245102.
About the author
Sean Anderson is a PhD candidate in mechanical engineering and applied mechanics at the University of Pennsylvania with a broad background in nano- and biotechnology. Sean is working in the Micro and Nanofluidics Lab under the advisement of Haim Bau. Haim H Bau is a professor of mechanical engineering and applied mechanics at the University of Pennsylvania with interests in nanotechnology, micro- and nanofluidics, and biotechnology.