Auxiliary electrode oxidation for naked-eye electrochemical determinations in microfluidics: Towards on-the-spot applications

Author(s)

Martucci, Diego H. ^[1] ; Todao, Fagner R. ^[1] ; Shimizu, Flavio M. ^{[2, 1]} ; Fukudome, Tiago M. ^[1] ; Schwarz, Stephane de F. ^[1] ; Carrilho, Emanuel ^[3] ; Gobbi, Angelo L. ^[1] ; Oliveira, Jr., Osvaldo N. ^[2] ; Lima, Renato S. ^{[1, 4]}

Affiliation

^[1] CNPEM, Lab Nacl Nanotecnol LNNano, BR-13083970 Campinas, SP - Brazil

^[2] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil

^[3] Univ Sao Paulo, Inst Quim Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil

^[4] Univ Estadual Campinas UNICAMP, Inst Quim, BR-13083970 Sao Carlos, SP - Brazil

• Document type: Journal article
• Source: Electrochimica Acta; v. 292, p. 125-135, DEC 1 2018.
• Web of Science Citations: 2

Abstract

In this paper, we describe a new microfluidic cell to perform naked-eye electrochemical detection (NEED) through the oxidation of Ag-based auxiliary electrodes (AEs) in the presence of a cathodic current on the working electrode (WE). The chips were fabricated in polydimethylsiloxane by a simple, cost-effective, and cleanroom-free prototyping that allows reuse of each AE up to 60 times. Stainless steel microwires coated with Ag film and in electric contact to each other acted as AEs, whereas single microwires coated with Au and Ag films operated as WE and quasi-reference electrode, respectively. All the electrodes were reversibly introduced into the devices. The high contrast among nonoxidized and oxidized (black Ag2O nanostructures of up to 400 nm) Ag ensures the naked-eye monitoring of the AE oxidation extent. The number of oxidized AEs was taken as the analytical signal for semi-quantitative assays of p-benzoquinone as proof-of-concept. In addition to the low cost, a key advantage within the point-of-use testing philosophy, further contributions from our work include: i) simultaneous semi-quantitative naked-eye tests for the same analyte from a single WE to speed up electroanalytical assays and ii) the use of the time needed to oxidize one AE as the signal, which led to quantitative assays with enhanced sensitivity for hydrogen peroxide. To attain a fully portable and user-friendly NEED method, the sensor was integrated into a handheld platform that consisted of a homemade potentiostat and gravity-assisted pumping, with which on-site tests can be performed by nontrained personnel anywhere. The portable potentiostat has the lowest cost (US\$7.72) reported in the literature compared with setups to measure electric current. (C) 2018 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 13/14262-7 - Nanostructured films from biologically-relevant materials
• Grantee: Osvaldo Novais de Oliveira Junior
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 13/03487-8 - Center of characterization of new mineral species: Raman spectroscopy, electron microprobe and X-ray and neutron diffraction
• Grantee: Marcelo Barbosa de Andrade
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 14/24126-6 - Microemulsification in Analytical Chemistry for the development of point-of-care platforms: study of intervening parameters and automation in microfluidics
• Grantee: Renato Sousa Lima
• Support Opportunities: Regular Research Grants