Individual Nanotube-Based Needle Nanoprobes for Electrochemical Studies in Picoliter Microenvironments

Abstract

We report the fabrication and characterization of individual nanotube-based, long and straight needle nanoprobes for electrochemistry and the study of their applicability and behavior in microenvironments. The needle nanoprobe, with a nanoscale ring-shaped Au electrode at the tip of the needle serving as the active electrode, was characterized by electrochemical current measurement and cyclic voltammetry and analyzed with electrochemical models. Such a needle nanoprobe, in combination with another metal-coated nanowire as a reference electrode, was further used, for the first time, for local electrochemical sensing inside microdroplets having volumes down to a few picoliters. We explain the acquired voltammetric behaviors of redox-active molecules in confined microscale environments and reveal a unique electrochemical mechanism which allows the regeneration of the redox-active molecules and the establishment of a stable reference potential in the microenvironments.

Three-electrode analytical and preparative electrochemistry in micro-volume hanging droplets

“…The first one, essentially developed in view of the detection of small numbers of molecules released by single cells, consists in the immersion of needle-type micro-electrodes in small chambers, or vials, prepared by micro-fabrication techniques [2,3,13,14]. Alternatively, the second route deals with the immersion of needle-type micro-electrodes within droplets, or meniscus, thus avoiding the preparation of containers [15,16,17]. This approach has been implemented with micro-, nano-, picoand femto-liter droplets deposited either on a substrate or onto the electrode itself.…”

Vertical Carbon Nanotube Devices With Nanoscale Lengths Controlled Without Lithography

“…In fact, the achievable density of nanotubes in the v-SWCNT templates is an order of magnitude greater than the best density reported to date for planar configurations-assuming a channel length of 100 nm and an additional loss of 1 µm 2 for contact metallization in the planar geometry. Other benefits include the ability to use these v-SWCNT templates for fabricating surround-gated vertical CNTFETs [30], [31], creating ordered arrays of v-SWCNTs of adjustable density, or even using the v-SWCNT tips as probes for biological interfacing [32]. A recent modeling study [31] has shown that the presence of a gate underlap (which would be difficult to avoid in a vertical CNTFET geometry) actually suppresses ambipolar conduction and enables I-V characteristics better suited for digital applications.…”

Carbon-based nanoprobes for cell biology

“…Unfortunately, since it was difficult to properly fashion and shield the metal tips for intracellular recording, the use of metal electrodes was initially limited to extracellular recording. However, Yum et al (2007) recently demonstrated electrochemical detection in small aqueous drops (10 lm in diameter) using metal, ring-shaped nanoelectrodes.…”