Small diameter carbon nanopipettes

Abstract

Nanoscale multifunctional carbon probes facilitate cellular studies due to their small size, which makes it possible to interrogate organelles within living cells in a minimally invasive fashion. However, connecting nanotubes to macroscopic devices and constructing an integrated system for the purpose of fluid and electrical signal transfer is challenging, as is often the case with nanoscale components. We describe a non-catalytic chemical vapor deposition based method for batch fabrication of integrated multifunctional carbon nanopipettes (CNPs) with tip diameters much smaller (10-30 nm) than previously reported (200 nm and above) and approaching those observed for multiwalled carbon nanotubes. This eliminates the need for complicated attachment/assembly of nanotubes into nanofluidic devices. Variable tip geometries and structures were obtained by controlled deposition of carbon inside and outside quartz pipettes. We have shown that the capillary length and gas flow rate have a marked effect on the carbon deposition. This gives us a flexible protocol, useful for growing carbon layers of different thicknesses at selective locations on a glass pipette to yield a large variety of cellular probes in bulk quantities. The CNPs possess an open channel for fluid transfer with the carbon deposited inside at 875 degrees C behaving like an amorphous semiconductor. Vacuum annealing of the CNP tips at temperatures up to 2000 degrees C yields graphitic carbon structures with an increase in conductivity of two orders of magnitude. Penetration of the integrated carbon nanoprobes into cells was shown to produce minimal Ca(2+) signals, fast recovery of basal Ca(2+) levels and no adverse activation of the cellular metabolism during interrogation times as long as 0.5-1 h.

Resistive-pulse and rectification sensing with glass and carbon nanopipettes

“…875°C) to avoid softening the nanometre-sized tip [24,26,44]. In most cases, methane was used as a carbon source and argon-as a protector.…”

“…On the other hand, if the gate electrode is exposed to the solution, it can serve as a working electrode to enable the quantitation of the electroactive analytes in addition to ion current-based resistive-pulse or rectification sensing. A CNP produced by coating the inside of the pulled quartz capillary with a nanometre-thick carbon layer can be employed for a wide range of electrochemical and sensing applications [24][25][26]40]. The extent of ICR in a CNP depends on the potential applied to carbon, which determines the surface charge and electrical double-layer at the pipette wall ( figure 9).…”

“…Functionalization of the interior surface of the nanochannels by depositing conductive materials (e.g. carbon) [24][25][26] or embedding electrodes [27] has also been performed to control and manipulate the ion transport processes. Thus, the electrostatic interactions can be directly controlled by biasing the inner pipette surface, and at the same time they can provide additional means for optical [28], conductometric [29] and electrochemical measurements of the transport processes.…”

One-Dimensional Nanoprobes for Single-Cell Studies

“…The authors successfully recorded the electrical signal of mouse hippocampal cells (line HT-22) with limited membrane damage ( Figure 4A & B). Further improvements were demonstrated by Singhal et al through decreasing the tip diameter and using a carbon nanotube assembled at the tip of a glass pipette with conductive epoxy [21,52]. The carbon nanotubetipped probe was later confirmed to be minimally invasive through statistical analysis of the actin network stability and cytosolic calcium ion release.…”

Carbon nanoelectrodes for single-cell probing

“…(6, 7, 23–27, 32, 37) CNPs hold much promise for the above listed applications due to their small size, high spatial resolution, tunable dimensions, easy fabrication, and amenability to interfacing with standard electrophysiology and cell injection equipment. (3–5, 28, 29, 31) …”