Copper Coordinated Congo-Red as a Solvent Assisted Selective Fluorometric and Colorimetric Chemosensor for Determination and Naked-Eye Detection of Multiple Analytes in Nanomolar Scale: A Reversible Fluorescent CN−/CO32− Switch that Works as Keypad Lock

Abstract

<span style="font-family: Times New Roman;"><span style="line-height: 90%; font-size: 9pt; mso-bidi-font-family: 'Times New Roman';">A new diazo based, Congo-Red-Cu , was developed to act as an ‘Off–On' reversible fluorescent probe for CN⁻detection. The changes in solvent composition has been shown greatly effective on selectivity of anion sensing through eliminate of sulfite interference. Increasing the amount of ethanol up to 5% (v/v) cause a dramatic development in selectivity of CN⁻</span><span style="line-height: 90%; font-size: 9pt; mso-bidi-font-family: 'Times New Roman';">via inhibitory effect on sulfite interferent. The chemosensing behavior of the CR-Cu has been demonstrated through fluorescence, absorption, visual color changes and FT-IR studies. This chemosensor (CR-Cu) has been shown a significant visible color change and displays a remarkable fluorescent switch on in the presence of CN⁻ ions. The ‘in situ' prepared CN⁻ complexes of CR-Cu shows high “Turn-Off" selectivity toward CO₃²⁻over the other anions. The detection limits for CN⁻ were 90 and 20 nM for colorimetric and fluorometric methods respectively, that is far lower than the WHO guideline of 1.9 µM. The complex of CN⁻ with CR-Cu also displayed ability to detect up to 15 nM CO₃²⁻ among other competing anions through a fast response time of less than 30 s which is much lower than most recently reported chemosensor probes. It has been possible to build an INHIBIT logic gate for two binary inputs viz., CN⁻ and CO₃²⁻ by monitoring the fluorescence emission band at 446 nm as output. The development of fluorometric an ‘‘Off–On'' reversible switch for three chemical inputs Cu²⁺, CN⁻ and CO₃²⁻ ions and mimics a molecular level keypad lock.</span></span>