McKelvey, Kim M. (Kim Martin), Kinnear, Sophie L., Perry, David, Momotenko, Dmitry and Unwin, Patrick R. (2014) Surface charge mapping with a nanopipette. Journal of the American Chemical Society, Volume 136 (Number 39). pp. 13735-13744. doi:10.1021/ja506139u ISSN 0002-7863.

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Abstract

Nanopipettes are emerging as simple but powerful tools for probing chemistry at the nanoscale. In this contribution the use of nanopipettes for simultaneous surface charge mapping and topographical imaging is demonstrated, using a scanning ion conductance microscopy (SICM) format. When a nanopipette is positioned close to a surface in electrolyte solution, the direct ion current (DC), driven by an applied bias between a quasi-reference counter electrode (QRCE) in the nanopipette and a second QRCE in the bulk solution, is sensitive to surface charge. The charge sensitivity arises because the diffuse double layers at the nanopipette and the surface interact, creating a perm-selective region which becomes increasingly significant at low ionic strengths (10 mM 1:1 aqueous electrolyte herein). This leads to a polarity-dependent ion current and surface-induced rectification as the bias is varied. Using distance-modulated SICM, which induces an alternating ion current component (AC) by periodically modulating the distance between the nanopipette and the surface, the effect of surface charge on the DC and AC is explored and rationalized. The impact of surface charge on the AC phase (with respect to the driving sinusoidal signal) is highlighted in particular; this quantity shows a shift that is highly sensitive to interfacial charge and provides the basis for visualizing charge simultaneously with topography. The studies herein highlight the use of nanopipettes for functional imaging with applications from cell biology to materials characterization where understanding surface charge is of key importance. They also provide a framework for the design of SICM experiments, which may be convoluted by topographical and surface charge effects, especially for small nanopipettes.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics
Divisions:	Faculty of Science, Engineering and Medicine > Science > Chemistry
Library of Congress Subject Headings (LCSH):	Microprobe analysis, Nanostructured materials, Scanning probe microscopy
Journal or Publication Title:	Journal of the American Chemical Society
Publisher:	American Chemical Society
ISSN:	0002-7863
Official Date:	1 October 2014
Dates:	Date Event 1 October 2014 Published 19 September 2014 Available 2 September 2014 Accepted 18 June 2014 Submitted
Volume:	Volume 136
Number:	Number 39
Number of Pages:	10
Page Range:	pp. 13735-13744
DOI:	10.1021/ja506139u
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Date of first compliant deposit:	28 December 2015
Date of first compliant Open Access:	28 December 2015
Funder:	European Research Council (ERC), Engineering and Physical Sciences Research Council (EPSRC)
Grant number:	ERC-2009-AdG247143-QUANTIF

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