Researchers from the Gogotsi group at Drexel University, US, have successfully fabricated carbon nanopipettes with tip diameters as small as 15 nm, similar to those observed for multiwalled carbon nanotubes. The fabrication method involved non-catalytic chemical vapour deposition of methane on the inner walls of quartz templates, which were nanopipettes themselves. After carbon deposition, quartz from the tip was etched to reveal a carbon tip (figure a). The researchers further showed that the structure of carbon, and therefore the electrical conductivity of the resulting carbon pipettes, could be tuned from that of amorphous carbon to graphite by annealing the probes at suitable temperatures under vacuum.

To test the viability of the design for cell probing, cells were pierced using the group's nanopipettes. The cellular response in the form of released calcium was measured and compared with data for glass pipettes of similar dimensions.

It was found that carbon nanopipettes could pierce cells with ease and reside inside them for as long as an hour without inducing significant stimulus response. A quick recovery to optimal intracellular calcium level was observed within a few seconds of probing (figure b). Minimally intrusive interrogation with carbon nanopipettes is a highly desirable feature enabling cell measurements that require a prolonged presence of a pipette inside the cell.

Moreover, the fabrication process involved controlled feedstock flow and the researchers showed that it was possible to control the carbon deposition both inside and outside the quartz template, just by changing the gas flow parameters. In this way, numerous pipettes with different carbon configurations, useful for a variety of applications, could be generated.

The researchers presented their work in the journal Nanotechnology.