Nanopipettes

Since the mass-transfer coefficient at a micropipette is inversely proportional to its radius, the smaller the pipette the faster heterogeneous rate constants can be measured. Micrometer-sized pipettes are too large to probe rapid CT reactions at the ITIES. Such measurements require smaller (nm-sized) pipettes. Nanopipettes are also potentially useful as SECM tips (see Section IV.D) because they can greatly improve spatial resolution of that technique. The fabrication of nanopipettes was made possible by the use of a micro-processor-controlled laser pipette puller capable of puling quartz capillaries [26]. Using this technique, Wei et al. produced nanopipettes as small as 20 nm tip radius and employed them in amperometric experiments [9]. 

Even smaller pipettes, down to 3nm radius, were used to measure facilitated IT kinetics [8a]. Unlike micrometer-sized pipettes, the size and shape of a nanometer-radius ITIES cannot be evaluated by optical microscopy. Thus, a thorough electrochemical characterization of nanopipettes is required. Another problem is a higher internal resistance, which increases with decreasing radius and can become as high as 100 [8a]. A... 

Zhou, Y. and Shimizu, T. (2008) Lipid nanotubes a unique template to create diverse one-dimensional nanostructures. Chemistry of Materials, 20 (3), 625-633. Nogawa, K., Tagawa, Y., Nakajima, M., Arai, F., Shimizu, T., Kamiya, S. and Fukuda, T. (2007) Development of novel nanopipette with a lipid nanotube as nanochannel. Journal of Robotics and Mechatronics, 19 (5), 528-534. 

Fig. 4 (a) SEM image of a cantilevered nanopipette used for nanofountain pen (NFP). Inset a zoom on aperture created at cantilever s tip for deposition. Reprinted with permission from [61]. Copyright (2005] American Chemical Society. 

Figure 1. CNTs and other nano-sized carbon particles (a) scrolling a graphene sheet (b) closed and opened single-walled CNT (c) double-walled CNT (d) CNT sites doped with boron and nitrogen (e) nanopipettes (f) nanocones and (g) nanorings.

To summarize, although rate constants (or, perhaps, apparent rate constants) for IT across the ITIES have been reported for more than 20 years, there is still controversy about the interpretation of this phenomenon, not least because the reported rate constants have increased over the years as experimental measurements became more and more sophisticated [127]. As noted above, a general problem has been that the characteristic timescales of the (apparent) kinetic process are often not markedly lower than the timescales of the experimental technique, a fact that has been remarked upon in the literature [128]. For example, in some of the recent data [94, 96] the time constants of the technique are frequently of the same order of magnitude as the timescales of the process they are purporting to measure. The question therefore becomes whether the rate constants reported for IT using nanopipettes [104, 107, 108] will increase in the future or whether these represent true values. Clearly at this point it is reasonable to ask whether theory predicts that a barrier to interfacial IT should exist and, if so, what the physical origin of such a barrier might be. 

Kaihanek, M, Kemp, J. T., et al. Single DNA Molecule Detection Using Nanopipettes andNanoparticles. Nano Letters,5(2), 403 07 (2005). 

Enzyme Nanolithography, Fig. 2 (a) SEM image of a nanopipette, (b) Nano-channels etched in BSA by trypsin deposited with NEP... 

AFM tips (diameter <50nm metalized with silver) on transparent samples were illuminated by a focused laser beam from below through the support and the sample to reach a 30 times increase of the scattered Raman light. This apertureless scatter SERS SNOM succeeded also with an etched gold wire in shear-force distance with 40-fold increase of the Raman signal, but this shifted the Raman lines with respect to those in the bulk Raman spectra. Nanopipette probes for apertureless SERS SNOM with gold or silver particles held in the aperture are also available. However, none of these elaborate techniques approaches the capabilities and versatility of the easiest apertureless SNOM with sharp pulled tips and enhanced internal reflection (Figure lb). 

Kranz C (2014) Recent advancements in nanoelectrodes and nanopipettes used in combined scaiming electrochemical microscopy techniques. Analyst 139(2) 336—352... 

Fixed volume pipettes of 100 nL and 200 nL are available in the form of platinum-iridium capillaries melted in a glass holder. Repeatability of the volume dispensed by such a nanopipette is very good (< 1 %), but the absolute volume accuracy is only about 5%. This means that for quantitative analysis, all samples and calibration standards on one plate must be applied with the same nanopipette unless calibration is by internal standard. 

Figure 2 Nanomat. The fixed volume pipette (nanopipette or glass capillary in holder) is held by a magnet. The applicator head is moved to the desired position in the precision notch system, then the head is pushed down manually. Contact pressure is determined solely by the friction of rest against the magnet.

CNT electrode ensembles consisting of a dense array of CNTs (15-80 nm diameter, 30-100 pm long, with a 100-200 nm nanotube separation) were produced from an ion-sputtered Fe catalyst film on an Al-coated Si wafer. As depicted in Figure 7.3d, the CNTs and the conducting substrate act as the electrode and increase the electroactive surface area. Nanoelectrodes were made from carbon nanopipettes (CNPs) (10-15 nm tip diameter, several micrometers long) on Pt substrates" and low-density arrays of vertically aligned CNTs (50-80 nm diameter, 10-12 pm long, with a nanotube separation of more than 5 pm) from electrodeposited Ni nanoparticles on a Cr-coated Si substrate." 5 To limit the electroactive area to the tips of the CNTs or CNFs, these arrays can be coated with an epoxy to insulate the conductive substrate to expose needle-like tips or surface-polished tips so as to expose only the ends of the nanotubes. 

FIGURE 7.5 Probes tipped with carbon nanostructures, (a) CNT-tipped AFM probe. (Adapted from Hafner, J.H. et al., J Phys Chem B, 105, 743-746, 2001. With permission.) (b) CNT-tipped electrode. (Adapted from Kaempgen, M. and Roth S., Synthetic Met, 152, 353-356, 2005. With permission.) (c) Carbon nanopipette. (Adapted from Schrlau, M.G. et al.. Nanotechnology, 19, 015101 (4pp), 2008. With permission.)... 

FIGURE 1.8 (a) Scheme of an SECM line scan with a nanopipette-supported ITIES tip... 

Noticeably, the advantages of a pair of the steady-state voltammograms based on forward and reverse processes of a nearly reversible reaction were originally demonstrated by voltammetry of ion transfer at nanopipette-supported ITIES [100,110],... 

Quasi-steady state conditions were unknowingly used for the study of an IT reaction at the macroscopic DCE/water interface by using nanopipette-supported ITIES tips [111-112], In these studies, a nanopipette was filled with an aqueous K+ solution and immersed in the DCE solution of dibenzo-18-crown-6 (DB18C6) to drive the interfadal complexation reaction at the nanoscale ITIES as given by... 

A nanometer-scale ITIES can be supported by a nanopipette to serve as a versatile SECM tip to probe both electron-transfer and ion-transfer reactions [120]. 

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