Hydrogel-filled micropipette contact systems for solid state electrochemical measurements

Abstract

This paper reports on the use of a novel microcapillary system for solid contact electrochemical measurements. The probe is made of moveable micropipettes, with orifice of 1-30-μm radii, filled with a conducting hydrogel, which forms a thin-gelled meniscus at the pipette end. The hydrogel is made of 2 % (w/v) agarose and water solutions, containing KCl or KNO 3 as supporting electrolytes. The micropipette can be brought in contact with a conducting substrate to form a microcell, which allows performing voltammetric measurements confined within limited contact regions. The suitability of the proposed probe for local electrochemical measurements are tested using two electroactive species, dissolved in the hydrogel, namely [Fe (CN 6)] 4and Ag + ions. Mass transport characteristics of the two species, in bulk hydrogel and at micropipette meniscuses of different radii, are examined in detail in the frame of existing theory. For comparison, voltammetric measurements are also performed with micropipettes filled with the corresponding aqueous solutions. It is shown that the gel-filled micropipette, at variance with the aqueous one, prevents the spreading and leakage of solution on the sample surface. The microprobe developed here can be useful to perform electrochemical measurements on surfaces, which suffer from direct contact with liquid electrolytes. A proof-of-concept hydrogelcapillary measurement is performed to distinguish the presence of metallic silver deposited on a graphite-on-paper-based material, realized through simple pencil strokes.

Electrochemical devices based on conducting surfaces modified with smart hydrogels: Outlook and perspective

“…Donnici and Daniele showed for the first time a hydrogel based device that utilized the principle of the microcapillary based technique. [ 62 ] The authors presented hydrogel‐integrated electrochemical microprobe as an alternative device for contact electrochemistry. The pipet was filled with natural gel agarose that contained supporting electrolyte and a redox probe.…”