5′-Hydroxymethyl fluorescein: A colorimetric chemosensor for naked-eye sensing of cyanide ion in a biological fluid

A two-step synthetic method to prepare a highly sensitive and selective chemosensor 5'-hydroxymethyl fluorescein (5'-HMF) is described herein. This sensor was explored as a colorimetric sensor for naked-eye detection of cyanide ion in the biological fluid as well as in organic and aqueous media. The addition of cyanide ion to 5'-HMF resulted in a rapid change in color in aqueous medium from light green to dark fluorescent green, and in acetonitrile from light pink to purple. A significant bathochromic shift in the absorption spectra enables cyanide ion to be detected by naked eyes in water and acetonitrile without any interference of the competing anions such as, AcO-, F- and SCN- in aqueous solution. Using the (HNMR)-H-1 titration experiments and Job's plot from absorbance spectroscopy, the interaction of CN- ion with 5'-HMF has been investigated and binding stoichiometry was found to be 1:2 (5'-HMF to CN-). The limit of detection (LOD) of the sensor for CN- was 3.68 mu M in water with a linearity (R-2 = 0.9923) in the range of 0.50 to 30.0 mu M concentration assuming 1:2 (5'-HMF to CN-) binding stoichiometry. In addition, the sensor 5'-HMF sensed the CN- ion in human saliva with the LOD as 7.0 mu M in aq. medium. (C) 2020 Elsevier B.V. All rights reserved.