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Electronic tongue identifies heavy metals in water
The device was trained using petroleum residues and identified mercury, silver, and iron ions in contaminated samples
The sensor demonstrated the ability to distinguish with high precision various types of metals present in water simultaneously, even at low concentrations – Photo: EPA Victoria/Wikimedia Commons/CC BY 4.0
Sulfur resulting from petroleum refining, currently underutilized, served as the basis for Brazilian researchers to develop a new model of electronic tongue. The residue was transformed into polysulfides, polymers used in the device’s sensors, capable of detecting heavy metals such as iron and mercury. The equipment may be used to monitor the quality and contamination of various types of water. Its operation is described in the article Polysulfides From Inverse Vulcanization Used in Electronic Tongues for Heavy Metal Sensing, published in the journal Journal of Applied Polymer Science.
“An electronic tongue consists of a set of sensors whose electrical responses make it possible to obtain a unique pattern for each liquid, as if it were a ‘fingerprint’”, said Osvaldo Novais de Oliveira Junior, a professor at USP’s São Carlos Institute of Physics (IFSC) and a member of the research group that developed the device. “The sensors, usually numbering from three to six in an electronic tongue, are not selective for any particular substance. The detection of a metal, for example, occurs through the identification of its specific electrical response pattern”.
“The main objective of the study was to explore the properties of polysulfides – polymers known to interact with heavy metals – as materials with potential application in their sensing”, Oliveira Junior noted. “Different polysulfides were used, which is important to generate varied electrical responses to the liquids analyzed. These responses form specific patterns that are identified using statistical or computational techniques”.
Osvaldo Novais de Oliveira Junior - Photo: IFSC
The polymers contain a high sulfur content and are obtained through inverse vulcanization, a sustainable solvent-free process. “It uses the excess sulfur resulting from petroleum refining and transforms it into polysulfides, thus representing an interesting alternative for adding value to this residue”, the professor emphasized. “The interaction with metals enabled high performance for the electronic tongue”,
The device identified mercury, silver, and iron metal ions. “The detection is carried out using an impedance analyzer, which essentially measures the electrical response – that is, the current as a function of an applied voltage at different frequencies – for aqueous solutions”, said the professor from the São Carlos Institute of Physics (IFSC). “Measurements were conducted in solutions containing each metal separately, at different concentrations, as well as in real tap water samples artificially contaminated and containing possible interferents – metal ions commonly found in waters contaminated by the metals of interest, such as lead and chromium”.
The device is based on polysulfides — polymers that interact with heavy metals and are applied in sensing — obtained through inverse vulcanization using residual sulfur from petroleum refining - Photo: IFSC
“Statistical and computational methods are used to identify the response pattern of each sample. In this study, high performance was achieved in metal detection by employing machine learning algorithms to process the electrical impedance data”, said Oliveira Junior.
“The results confirmed that polysulfides can be used as active materials for heavy metal detection in an electronic tongue, with the ability to distinguish with high precision not only a broad range of metals but also different concentrations simultaneously, even at very low levels”, the researcher stated.
According to the professor from USP’s São Carlos Institute of Physics (IFSC), several steps must be completed before the prototype can become a market-ready device. “First, the development of methods capable of producing the sensors on a large scale and at low cost”, he said, “followed by exhaustive testing with hundreds of devices to ensure reproducibility and repeatability”.
“Unfortunately, these two stages are very costly in terms of time and financial resources, and they only make sense if there are companies interested in commercializing the electronic tongue”, Oliveira Junior noted. “For this reason, it is not possible to predict how long it would take to reach the market. If there is corporate interest and investment, two years would likely be sufficient”.
The operation of the electronic tongue is described in the scientific article Polysulfides From Inverse Vulcanization Used in Electronic Tongues for Heavy Metal Sensing, published in the journal Journal of Applied Polymer Science. At the São Carlos Institute of Physics (IFSC) of USP, the research team included Stella Valle, currently at the Lorena School of Engineering (EEL) of USP, Andrey Coatrini Soares, and Osvaldo Novais de Oliveira Junior. Also participating in the study were Mario Popolin Neto, from the Federal Institute of São Paulo (IFSP), Araraquara campus; and Cauê Ribeiro and Luiz Henrique Capparelli Mattoso, from Embrapa Instrumentation, in São Carlos.
More information: chu@ifsc.usp.br, with Osvaldo Novais de Oliveira Junior
English version: Nexus Traduções, edited by Denis Pacheco
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A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.