Fluorescent chemosensors for toxic organophosphorus pesticides: a review

Abstract

Many organophosphorus (OP) based compounds are highly toxic and powerful inhibitors of cholinesterases that generate serious environmental and human health concerns. Organothiophosphates with a thiophosphoryl (P=S) functional group constitute a broad class of these widely used pesticides. They are related to the more reactive phosphoryl (P=O) organophosphates, which include very lethal nerve agents and chemical warfare agents, such as, VX, Soman and Sarin. Unfortunately, widespread and frequent commercial use of OP-based compounds in agricultural lands has resulted in their presence as residues in crops, livestock, and poultry products and also led to their migration into aquifers. Thus, the design of new sensors with improved analyte selectivity and sensitivity is of paramount importance in this area. Herein, we review recent advances in the development of fluorescent chemosensors for toxic OP pesticides and related compounds. We also discuss challenges and progress towards the design of future chemosensors with dual modes for signal transduction.

Keywords: dual modes of signal transduction; fluorescent chemosensors; organophosphorus compounds; pollutants.

Figure 1.

General chemical structure of oxon and thion OP compounds.

Figure 2.

Schematic representation of the possible routes of environmental exposure of OP pesticides to humans and wildlife. Adopted from Reference [12].

Figure 3.

(a) Structure of fluorescein isothiocyanate (FITC) at different pH, (b) its relative fluorescence intensity at selected pH values. Reproduced with permission from reference [44], published by Elsevier, 2004.

Figure 4.

Mechanism for the hydrolysis of OP compounds by OPH.

Figure 5.

Mechanism of the chemically reactive sensor developed by Van Houten et al. Reproduced with permission from Reference [29], published by American Chemical Society, 1998.

Figure 6.

Schematic representation of the chemosensor developed by Zhang and Swager [49]. Reproduced with permission from reference [49], published by American Chemical Society, 2003.

Figure 7.

The chemically reactive sensor reported by Rebek’s group. Taken with Reproduced with permission from Reference [50], published by American Chemical Society, 2006.

Figure 8.

Coumarin 1, fluorescent compound and inhibitor reported by Simonian’s group. Reproduced with permission from reference [51], published by Elsevier, 2007.

Figure 9.

Inclusion phenomena of a guest in CDs molecules. Reproduced with permission from Reference [52], published by Bentham Science, 2009.

Figure 10.

Schematic representation of the formation of the indole-based SAM sensor. Reproduced with permission from Reference [53], published by Elsevier, 2008.

Figure 11.

Schematic representation of uncomplexed (left) and complexed (right) azastilbene [55]. (EDG = electron donating group).

Figure 12.

Chemical structures of ethion, malathion, parathion, and fenthion pesticides.

Figure 13.

Changes in UV-visible absorbance of DQA upon binding to OP pesticides: (a) titration with ethion; (b) titration with malathion; (c) titration with parathion; and (d) titration with fenthion. In each case the direction of the arrow indicates concentration of 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 μM.

Figure 14.

Changes in DQA fluorescence emission spectra upon binding to OPs. (a) titration with ethion, from top to bottom concentration of ethion = 0, 2, 4, 6 μM; (b) titration with malathion, from top to bottom concentration of malathion = 0, 2, 4, 8 μM; (c) titration with parathion, from top to bottom concentration of ethion = 0, 2, 4, 6, 8, 10, 12 μM; and (d) titration with fenthion, with up to 24 μM of fenthion being added with no change observed. The arrow indicates the direction in which the fluorescence intensity change takes place.

Figure 15.

Cyclic voltammograms of DQA before and after addition of (a) ethion, (b) malathion, (c) parathion, and (d) fenthion.

Scheme 1.

Schematic representation for the synthesis of DQA.