The Research Of Two-Dimensional Photonic Crystal Enzyme Sensors For The Detection Of Agricultural Pollutants

The agricultural pollution has become a prominent problem with the rapid development of China's agricultural economy due to the continuous advancement of agricultural modernization,meanwhile,the unreasonable use of chemical fertilizers and pesticides has made this problem more serious.A variety of analytical methods have been reported for the detection of agricultural pollutants based on fluorescence,electrochemistry,surface-enhanced Raman spectroscopy,high-performance liquid chromatography,etc.Although various methods have achieved good results,they often need expensive equipment and complicated operation processes,which limit their application in a certain degree.Thus,it is of great significance to develop miniaturized,simple,label-free and economical sensors for the monitor of agricultural pollutants.In recent years,photonic crystals have been favored by many researchers because of the unique optical properties,and responsive photonic crystal hydrogel which is constructed by incorporating the responsive polymer into the regular structure of the photonic crystals has attracted increasing attention in the fields of chemical and biochemical sensing on account of the sensitivity to external stimuli and the perceptible optical signals.Compared with the maturely developed sensors based on three-dimensional photonic crystals,there are more potential for two-dimensional(2D)photonic crystals.In this paper,we developed a simple and convenient sensing platform based on 2D photonic crystal hydrogel for the visual detection of agricultural pollutants.The details are as follows:(1)A label-free urease coupled photonic crystal hydrogel biosensor for the visual monitor of urea and urease inhibitor was developed by embedding a regular 2D polystyrene array in the surface of the urease functionalized hydrogel.In the presence of urea,ammonium and bicarbonate ions are produced owing to the enzymatic reaction.These ions reduce the electrostatic repulsion between the carboxylates of hydrogel backbone,which shrinks the 2D photonic crystal hydrogel volume and leads to an evident blue-shift in the diffraction wavelength.The hydrolysis of urea can be hindered when the urease inhibitor is introduced in the solution along with urea,and a decrease in the blue-shift of the diffraction wavelength occurs.The monitors of urea and urease inhibitor are also realized by measuring the diameter of Debye diffraction ring,and the detection limits for urea and PPD(a urease inhibitor)are 1 mM and 5.8 nM,respectively.In addition,the proposed 2D photonic crystal hydrogel biosensor is demonstrated to be of good selectivity and reproducibility for urea owing to the biological compatibility and structural stability of the responsive hydrogel film.(2)In order to broaden the range of applications of 2D photonic crystal hydrogel,a 2D hydrogel biosensor modified with acetylcholinesterase was constructed for the rapid and sensitive detection of paraoxon pesticides.Paraoxon can affect the microenvironment of the hydrogel by inhibiting the catalytic reaction of acetylcholinesterase,and then trigger the change of Debye diffraction ring of 2D photonic crystals.According to this response principle,we can realize the detection of paraoxon without any signal label,and the detection limit was as low as 1 ng mL-1.In addition,this biosensor also holds well anti-interference ability,and shows desirable performance for paraoxon analysis in real samples.