| Over the past few decades, organophosphorus pesticides (OPs) have been widely used in the field of agriculture, animal husbandry and medicine. However, the OPs residual in soil, vegetable, and drinking water has put severe threat to human health due to accumulation in human body and dysfunction to AChE, an important enzyme in nerves system. To control the abuse of pesticide, the development of rapid, sensitive, and portable analytical methods for OPs detection is of great significance. To this end, two paper-based colorimetric methods are developed in this thesis, based on the excellent light absorbance ability of gold nanoparticles and MnO2 nanosheets. Detailed work is described as follows:I. AuNPs based paper assay for sensitively colorimetric detection of OPsA colorimetric method was developed for the sensitive detection of OPs by taking advantage of the excellent surface plasmon resonance property of AuNPs, the high redox activity of AuNPs and the enzymatic activity of AChE. In the absence of OPs, the concentration of thiolcholine (TCh, enzymatically hydrolysis product) is high, which could comsume all the Au3+in the system, protecting the AuNPs paper from dissolution and remaining the red color of AuNPs modified paper. However, in the presence of OPs, the activity of the AChE would be inhibited and only less amount of TCh could be produced. In this case, the Au3+can not be consumed completely, so the residual Au3+ would dissolve AuNPs to form colorless Au+, thus leading to color change of the AuNPs modified paper from red to colorless or light pink. Based on the color change, the concentration of OPs could be semiquantitatively evaluated. The enzymatic hydrolysis and dissolution progress were monitored by UV-vis absorbance spectra and TEM pictures. Under the optimal conditions, the AuNPs modified paper could be used for highly sensitive detection of OPs, with the limit of detection of 7 ppb for parathion,0.03 ppm for DDVP, and 0.07 ppm for fenitrothion, respectively. Due to the advantages of high sensitivity, low cost, and easy operation, this AuNPs based paper assay showed great potential for point-of-care OPs detections.II. Colorimetric detection of OPs based on MnO2 nanosheetA colorimetric method for OPs detection was developed by combining the redox activity and strong visible light absorbance ability of Mnd nanosheets, and the enzymatically catalytic activity of AChE. MnO2 nanosheet with brown color was synthesized by a sol-gel method, and characterized by UV-vis spectrum and TEM images. Interestingly, the brown nanosheet could be reduced by the enzymatic hydrolysis product of TCh to form colorless Mn2+. Therefore, it could be used as a readout for the colorimetric detection of OPs. In the absence of OPs, the MnO2 nanosheet could be completely reduced to corlorless Mn2+ due to the high activity of AChE which could produce a large amount of TCh. However, in the presence of OPs, the activity of AChE was inhibited which could only generate less amount of TCh that could not consume all the MnO2 nanosheet, thus keeping the brown color of MnO2 nanosheet. Therefore, based on the color change, the OPs could be detected. Under the optimal conditions, OPs with concentration as low as ppb level could be detected by this method. |
