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.

Batch fabrication

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.

Further reading

Carbon nanopipettes for cell probes and intracellular injection (Dec 2007)
Carbon nanopipettes probe individual cells (Aug 2008)
Smallest carbon nanoprobes pierce cells with ease (Jan 2010)