Bis(2,4,6-trichlorophenyl)oxalate-based chemically initiated electron exchange chromogenic reaction system for colorimetric detection of fentanyl and norfentanyl

Bioenzymes or nanoenzymes-involved aqueous chromogenic systems play a central role in colorimetric analysis. A lack of high and general chromogenic reactions that work in a hydrophobic medium has hampered the development of colorimetric methods for the detection of many hydrophobic analytes. To address this challenge, a series of chemically initiated electron exchange chromogenic (CIEEC) reaction systems are presented that functions in an ethanol-water mixture solvent. The resulting CIEEC systems are based on the oxidation capacity of biradical intermediate produced by the reaction between bis(2,4,6-trichlorophenyl)oxalate (TCPO) and H2O2, and it oxidizes various chromogenic substrates such as 3, 3′, 5, 5′-tetramethylbenzidine (TMB), o-phenylenediamine, diazoaminobenzene, and 2,2ʹ-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) to create colored products. Taking advantage of the catalytic effect of fentanyl (FTN) and norfentanyl (NFTN), we fabricate a visual colorimetric assay based on the TCPO-H2O2-TMB CIEEC reaction system, and the resulting sensitivity is comparable to that of the reported colorimetric assays for FTN. Moreover, the present assay is capable of detecting both FTN and NFTN in human urine samples.