Review Article Electroanalytical sensing of dyes and colorants Q11 Q10 Guilherme G. Bessegato 1 , Michelle F. Brugnera 2 and Maria Valnice Boldrin Zanoni 3 Abstract Color is an important element of the final product of many in- dustries, including the textile, leather, food, cosmetic, phar- maceutical, plastic, and fuel-marking industries. Dyes are complex organic substances with chromophore and auxo- chromic groups, which can be electrochemically oxidized and/ or reduced; this constitutes the basis of their electroanalytical determination. Despite some controversies, dyes pose risks to living organisms, especially after biotransformation, as the metabolites can be more toxic, mutagenic, or carcinogenic than the original dyes. The present work provides a brief overview of the recent progress in electrochemical sensors used for dye detection in diversified matrices. Sensors devel- oped over the recent years are characterized by high sensi- tivity and selectivity, besides being economically advantageous once they allow the use of little or no clean-up samples in portable and miniaturized systems. Q2 Addresses 1 Universidade Estadual do Oeste do Paraná (UNIOESTE), Rua da Faculdade, 645, 85903-000, Toledo, PR, Brazil 2 Universidade Federal de Mato Grosso (UFMT), Departamento de Química, Av. Fernando Correa da Costa, 2367, 78070-090, Cuiabá, MT, Brazil 3 Universidade Estadual Paulista (Unesp), Instituto de Química, Araraquara. Av. Prof. Francisco Degni, 55, 14800-060, Araraquara, SP, Brazil Corresponding author: Zanoni, Maria Valnice Boldrin (boldrinv@iq. unesp.br) Current Opinion in Electrochemistry xxxx, xxx:xxx This review comes from a themed issue on Sensors and Biosensors Edited by Paolo Ugo For a complete overview see the Issue and the Editorial Available online xxx https://doi.org/10.1016/j.coelec.2019.05.008 2451-9103/© 2019 Elsevier B.V. All rights reserved. Introduction Synthetic dyes are chemical compounds used in various industries, including the textile, cosmetic, food, leather, drug, and fuel-marking industries. The color is derived from complex organic structures with chromophore groups (including azo, anthraquinone, polymethine, nitro, nitroso, aryl methyl, xanthine, and coumarin) and auxochromic groups (such aseOH, eNH 2 , eSO 3 H, etc.), which increase solubility, enhance affinity to the substrate and are electrochemically oxidizable/reducible [1,2]. Azo dyes are, undoubtedly, the main class of dyes in industrial applications. There are over 3000 azo dyes in use worldwide, and they account for 65% of the com- mercial dye market [3]. They are characterized by the presence of azo groups (eN=Ne) and offer a wide spectrum of colors depending on their structures. However, under anaerobic conditions, azo dyes can be readily reduced to form aromatic amines (AAs) [3], which are carcinogenic. In fact, since 2002, legal re- strictions have been imposed regarding the use of azo dyes in the European Union, based on the amendment of the Council Directive 76/769/EEC [3]. In addition, European Union Regulation (EC) 1907/2006 prohibits the use of certain azo dyes that release AAs [4]. More recently, studies have shown that azo dyes in textile clothing undergo biotransformation through the action of various skin bacteria, leading to the potential release of AAs, which might be dermally absorbed. Among the products released in the biotransformation process include 40 different AAs derived from approximately 180 azo dyes and which are found to be mutagenic [5]. The azo group is a chromophore present in dyes used in textile production, hair dyeing, leather dyeing, food dyeing, and petrol markers, among others. It is esti- mated that at least 20% of the dyes produced are discarded in effluents because of losses occurring during manufacturing or dyeing processes. From the environmental viewpoint, dye removal from industrial waste is one of the major problems in the textile industry. This is so because dyes do not belong to the same class of chemical compounds but are rather composed of several compounds with different func- tional groups characterized by significant differences in reactivity, solubility, volatility, stability, etc. The pres- ence of diverse compounds in dyes means that specific methods are required for the identification, quantifica- tion, and degradation of these compounds. Owing to the risks posed by dyes to living organisms, the relevance of developing analytical methods capable of detecting dyes in surface water, commercial formula- tions, industrial effluents, food, hair dye, and other Available online at www.sciencedirect.com ScienceDirect Current Opinion in Electrochemistry www.sciencedirect.com Current Opinion in Electrochemistry xxxx, xxx:xxx 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 COELEC427_proof ■ 8 June 2019 ■ 1/9