This critical review is focused on examples reported in the year 2009 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions (264 references).

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Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010-2011.

Highly blue fluorescent graphitic carbon nitride quantum dots (g-CNQDs) were synthesized by a simple microwave mediated method from formamide (HCONH2). The fluorescence emission of g-CNQDs is found to be strongly dependent on solvent, pH as well as on excitation wavelengths; the life time of the emission decreases with increasing polarity of the solvent. These quantum dots are highly sensitive and selective florescent probes for mercuric ions in aqueous media due to the “superquenching” of fluorescence. The complex formation of Hg2+ ions with the CNx sheet involving π delocalized electron moieties of the latter, in fact, is responsible for the quenching of fluorescence. The addition of iodide ions abstracts the bound Hg2+ forming HgI2 and gives back the fluorescence characteristic of g-CNQDs. Thus, g-CNQDs can play a dual role for selective and sensitive detection of mercuric ions as well as iodide ions in aqueous media via “ON–OFF–ON” fluorescence response.

Facile bulk production of highly blue fluorescent graphitic carbon nitride quantum dots and their application as highly selective and sensitive sensors for the detection of mercuric and iodide ions in aqueous media

We report on a simple method for the determination of iodide in aqueous solution by exploiting the fluorescence enhancement that is observed if the complex formed between carbon dots and mercury ion is exposed to iodide. Fluorescent carbon dots (C-dots) were treated with Hg(II) ion which causes quenching of the emission of the C-dots. On addition of iodide, the Hg(II) ions are removed from the complex due to the strong interaction between Hg(II) and iodide. This causes the fluorescence to be restored and enables iodide to be determined in the 0.5 to 20 μM concentration range and with a detection limit of ~430 nM. The test is highly selective for iodide (over common other anions) and was used for the determination of iodide in urine.

Carbon dots-based fluorescent probes for sensitive and selective detection of iodide

Iodide plays a vital role in many biological processes, including neurological activity and thyroid function. Due to its physiological relevance, a method for the rapid, sensitive, and selective detection of iodide in food, pharmaceutical products, and biological samples such as urine is of great importance. Herein, we demonstrate a novel and facile strategy for constructing a fluorescence turn-on sensor for iodide based on a T-Hg(II)-T complex (T=thymine). A fluorescent anthracene-thymine dyad (An-T) was synthesized, the binding of which to a mercury(II) ion lead to the formation of a An-T-Hg(II)-T-An complex, thereby quenching the fluorescent emission of this dyad. In this respect, the dyad An-T constituted a fluorescence turn-off sensor for mercury(II) ions in aqueous media. More importantly, it was found that upon addition of iodide, the mercury(II) ion was extracted from the complex due to the even stronger binding between mercury(II) ions and iodide, leading to the release of the free dyad and restoration of the fluorescence. By virtue of this fluorescence quenching and recovery process, the An-T-Hg(II)-T-An complex constitutes a fluorescence turn-on sensor for iodide with a detection limit of 126 nM. Moreover, this sensor is highly selective for iodide over other common anions, and can be used in the determination of iodide in drinking water and biological samples such as urine. This strategy may provide a new approach for sensing some other anions.

Doo Ok Jang

Papers

Chromogenic and Fluorescent Recognition of Iodide with a Benzimidazole-Based Tripodal Receptor