Functionalization-free microfluidic electronic tongue based on a single response
Flavio M. Shimizu,£ Fagner R. Todão,† Angelo L. Gobbi,† Osvaldo N. Oliveira Jr.,£ Carlos D. Garcia,‡ and Renato S. Lima*,†,ϕ
† Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, São Paulo 13083-970, Brasil.
£ Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, São Paulo 13560-970, Brasil.
ϕ Instituto de Química, Universidade Estadual de Campinas, Campinas, São Paulo 13083-970, Brasil.
‡ Department of Chemistry, Clemson University, 219 Hunter Laboratories, Clemson, South Carolina 29634, USA.
ABSTRACT: Electronic tongues (e-tongues) are promising analytical devices for a variety of applications by addressing the challenges of quality control in water monitoring and industries of foods, beverages, and pharmaceuticals. A crucial drawback in the current e-tongues is the need of recalibrating the device when one or more sensing units (usually with modified surface) are replaced. Other downside is the necessity to perform subsequent surface modifications and analyses to each one of the diverse sensing units, undermining the simplicity and velocity of the method. These features have prevented a widespread commercial use of the e-tongues. In this paper, we introduce a microfluidic e-tongue that overcomes all such limitations. The key principle of global selectivity of the e-tongue was achieved by recording only a single response, namely, the equivalent admittance spectrum of an association of resistors in parallel. Such resistors consisted of five non-functionalized stainless steel microwires (sensing units), which were short-circuited and coated with gold, platinum, nickel, iron, and aluminum oxide films. The microwires were inserted in a chip composed of a single piece of polydimethylsiloxane (PDMS). Using impedance spectroscopy, the e-tongue was successfully applied in classification of basic tastes at a concentration below the threshold for human tongue. In addition, our chip allowed the distinction of various chemicals used in oil industry. Finally, our cleanroom-free prototyping allows the mass production of chips with easily replaceable and reproducible sensing units. Hence, one can now envisage the widespread dissemination of e-tongues with fast and reproducible data.
This article was published in ACS Sensors (ACS, DOI: 10.1021/acssensors.7b00302). This project has been conducted in Laboratório de Microfabricação (LMF, LNNano) in collaboration with Universidade de São Paulo and Clemson University.