Carbon Pipette-Based Electrochemical Nanosampler Yun Yu, Jean-Marc Noë l, ⊥ and Michael V. Mirkin* Department of Chemistry and Biochemistry, Queens College−CUNY, Flushing, New York 11367, United States Yang Gao, †,§ Olha Mashtalir, ‡,§ Gary Friedman, †,§ and Yury Gogotsi* ,‡,§ † Department of Electrical and Computer Engineering, ‡ Department of Materials Science and Engineering, and § A.J. Drexel Nanotechnology Institute, Drexel University, 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, Unites States * S Supporting Information ABSTRACT: Sampling ultrasmall volumes of liquids for analysis is essential in a number of fields from cell biology to microfluidics to nanotechnology and electrochemical energy storage. In this article, we demonstrate the possibility of using nanometer-sized quartz pipettes with a layer of carbon deposited on the inner wall for sampling attoliter-to-picoliter volumes of fluids and determining redox species by voltammetry and coulometry. Very fast mass-transport inside the carbon-coated nanocavity allows for rapid exhaustive electrolysis of the sampled material. By using a carbon pipette as the tip in the scanning electrochemical microscope (SECM), it can be precisely positioned at the sampling location. The developed device is potentially useful for solution sampling from biological cells, micropores, and other microscopic objects. A dvances in nanoelectrochemistry made over the last two decades 1,2 provided new tools for electrochemical experi- ments in ultrasmall (pico- to zeptoliter) volumes. 3−6 In addition to fundamentally interesting physicochemical measure- ments at the level of single molecules, 7−9 such experiments can offer important advantages for cell biology, 10−12 microfluidics, 13 and nanotechnology. 14 The two alternative strategies for these experiments are either to take measurements in situ (e.g., inside a biological cell 3,6 or a vesicle 5 ) or to sample solution for subsequent analysis (e.g., in a picoliter vial 15 ). The former approach may be more straightforward, but not always feasible, whereas the latter requires a suitable tool for solution sampling and transfer. The sampling devices are often plagued by the common problem, a relatively large tip size. Additionally, the sampled solution must not be significantly diluted or contaminated before the analysis. For example, the contamination and alteration of a sample was a potential issue with the “attosyringe”, a nanopipette-based device, which we previously employed for solution sampling and intracellular injections: organic solvent contained inside the pipette could damage the sampled biomolecules. 16 The electrochemical nanosampler discussed in this paper is free from both problems. It is produced by chemical vapor deposition (CVD) of a thin carbon layer on the inner surface of a quartz pipette whose tip radius can be as small as a few nanometers. 17 The resulting geometry is shown schematically in Figure 1. When a nanosampler is placed in either aqueous or organic solution, a small volume of liquid gets driven into the carbon-coated nanopipette (CNP) by capillary forces. The redox species contained in solution (e.g., the reduced form, R, pictured in Figure 1A) can be oxidized or reduced at the carbon nanoring exposed to external solution and at the carbon surface inside the pipette. The voltammetric response of such an electrode should include a steady-state component produced by the convergent diffusion and a transient component due to the oxidation/reduction of Received: November 2, 2013 Accepted: March 11, 2014 Published: March 21, 2014 Figure 1. Schematic representation of an electrochemical nano- sampler. (A) Oxidation of redox active species (R) occurs on the carbon-coated inner pipette wall and on the carbon nanoring exposed to solution. (B) Nanosampler behavior depends on the depth of its cavity: (i) shallow, (ii) relatively deep, and (iii) very deep (open CNP). Article pubs.acs.org/ac © 2014 American Chemical Society 3365 dx.doi.org/10.1021/ac403547b | Anal. Chem. 2014, 86, 3365−3372