Green, Water-Dispersible Photoluminescent On–Off–On Probe for Selective Detection of Fluoride Ions

Abstract

Considering the high toxicity and widespread availability of fluoride ions in different environmental matrices, it is imperative to design a probe for its detection. In view of this, a selective fluorescent on-off-on probe based on carbon quantum dots (CQDs) and Eu has been designed. We have synthesized water-soluble carboxylic acid-functionalized CQDs and monitored their interaction with Eu. Luminescence quenching in the CQD emission was observed (switch-off) on adding Eu ions. We investigate the reason for this luminescence quenching using time-resolved emission and high-resolution transmission electron microscopy (HRTEM) studies and observed that both electron transfer from CQDs to Eu and aggregation of CQDs are responsible for the luminescence quenching. ζ-Potential and X-ray photoelectron spectroscopy studies confirm Eu binding with the COOH groups on CQD surface. Interestingly, luminescence regains after the addition of fluoride ions to the CQDs/Eu system (switch-on). This has been assigned to the removal of Eu from the CQD surface due to the formation of EuF and is confirmed by X-ray diffraction and HRTEM measurements. The sensitivity of the probe was tested by carrying out experiments with other competing ions and was found to be selective for fluoride ions. Experiments with variable concentrations of fluoride ions suggest that the working range of the probe is 1-25 ppm. The probe has been successfully tested for the detection of fluoride ions in a toothpaste sample and the results were compared to those of ion chromatography. To the best of our knowledge, this is the first report based on CQDs and Eu for the detection of fluoride ions, wherein a clear mechanism of the detection has been demonstrated, which, in turn, will help to develop better detection methods. The suggested probe is green, economical, rapid, efficient, and, most importantly, selective and can be used for the detection of fluoride ions in real environmental samples.

Fluorescence detection of fluorine ions in biological fluids based on aggregation-induced emission

“…The relative standard deviation (RSD) of uorescence intensities without F À and those containing mM F À , which were detected in parallel for 11 consecutive times, was 3.1%. The detection limit of this method was lower than that of uorescence method, 25,52,53 approximating to that of absorbance method 54 ( Table 1). In comparison with general uorescence methods for organic small molecules based on "Turning on" pattern, 52,53 this detection system can not only realize uorescence analysis and detection of uorine ions under "Turning on-off" pattern, but also improve the selectivity of uorescence detection of AIE-based organic molecules.…”

“…[12][13][14][15][16][17][18][19][20][21] In recent years, aggregation-induced emission (AIE) materials have attracted high attention from researchers. 13,15,19,[22][23][24][25][26][27][28][29] No matter AIE materials emit weak uorescence or don't emit uorescent under dissolved state, the uorescence will be obviously enhanced under aggregation state. 16,23,24,28,30 AIE phenomenon has been applied to various elds, e.g.…”

EDTA-bonded multi-connected carbon-dots and their Eu3+ complex: preparation and optical properties

“…31 The detection of rare earth elements with C-dots has been relatively less reported. Singhal et al used Eu-coordinated Cdots to detect F À ions, 33 and indicated that the Eu 3+ ions interacted relatively loosely with the carboxylic acid moiety on the C-dots. Kailasa et al recently reported that Eu 3+ hybrid Cdots could be used as a uorescent nanosensor to detect Hg 2+ ions, 34 but in their sensor the Eu 3+ ions did not directly coordinate with the C-dots.…”

A π‐Conjugated Chromophore Dye and Its Functional Paper Strips for Visually On‐Site Sensing F− and Its Reaction Mechanism

“…For fluoride ion (F − ), the smallest size and highest charge density, any chronic deficiency of F − will lead to gastric and kidney disorder or osteoporosis, while excess F − would induce dental and skeletal fluorosis and other serious diseases including collagen breakdown, bone disorders and immune system disruption . Great efforts have been devoted for F − detection, such as chromatography, electrochemistry, photoluminescence, mass spectrometry,, fluorescent spectrophotometry and colorimetric spectrophotometry . For example, Bhosale, et al .…”