Fluorimetric and ratiometric colorimetric dual-mode detection of organophosphorus pesticides based on carbon dots/DTNB

In this work, a fluorimetric and ratiometric colorimetric dual-mode detection method was developed for the detection of organophosphorus pesticides (OPs) based on carbon dots (CDs)/5,5-dithiobis-(2-nitrobenzoic acid) (DTNB). Its main mechanism is that OPs inhibit the catalysis of acetylcholinesterase (AChE) in the hydrolysis of acetylthiocholine (ATCh) to form thiocholine (TCh). It specifically reacts with DTNB which has a characteristic absorption band at 325 nm to produce 5-thio-2-nitrobenzoic acid (TNB) with an absorption peak at 410 nm overlapped with the excitation spectrum of the CDs. Thus, TNB can exert an inner filter effect (IFE) on the CDs. Upon the addition of chlorpyrifos (CPF, a representative of OPs), the activity of AChE is gradually inhibited, resulting in an increase in absorbance at 325 nm and a decrease in absorbance at 410 nm, as well as a weakening of the IFE on the CDs. Therefore, a good linear relationship between the fluorescence intensity of the CDs and the logarithm of the concentration of CPF was established in a broad range from 0.3 to 200 ng mL(-1) with a limit of detection (LOD) of 0.081 ng mL(-1). Furthermore, an excellent linear relationship was fitted between the ratio of absorbance at 410 nm to that at 325 nm (R-410/325) and the logarithm of the concentration of CPF in the range of 0.3-200 ng mL(-1) with a LOD of 0.054 ng mL(-1). The proposed dual-mode method could recover CPF from the tap water and pork samples in the range from 93.3% to 108.8%. Therefore, it can be potentially developed as a reliable detection method for OPs with high selectivity, sensitivity and accuracy.