| Photochemical sensor draws wide concern due to its simple operation, low cost, highefficiency and fast response, which has been widely used in environmental monitoring, foodsafety analysis, heavy metal ions detection, biological analysis and other fields. It bases on thechange of the color of the solution and ultraviolet absorption peak, fluorescence emissionpeak. In this study, three photochemical sensors were constructed to detect cysteine, E. coliO157:H7, cyromazine. The main contents could be outlined as follows:(1) A sensitive and selective colorimetric detection method for Cysteine (Cys) wasestablished in this paper. The detection mechanism is based on the oxidation of Cys by H2O2,which prevents the catalysis of the2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid(ABTS)-H2O2reaction by G-quadruplex halves. With the addition of Cys, the amount of theblue-green-colored free-radical cation (ABTS·+) was reduced. The absorbance of ABTS·+at421nm weakened as the color of the solution changed from blue-green to colorless. Theconcentration of Cys can be determined by monitoring this competitive reaction with thenaked eye or using a UV-vis spectrometer. The calibration curve showed that the netabsorption value at421nm linearly increased over the Cys concentration range from0.005to100μmol/L with a detection limit of5nmol/L. Furthermore, amino acids other than Cyscannot mediate the color change under the identical conditions because of the absence of thiolgroups, thereby suggesting the selectivity towards Cys of the proposed method.(2) The presence of Escherichia coli in food and drinking water is a chronic worldwideproblem. Food protection against bacterial contamination and rapid diagnosis of infectionrequire simple and rapid assays for detection of bacterial pathogens, including E. coliO157:H7. Here we report a rapid and novel colorimetric method for detecting E. coliO157:H7. This colorimetric method is based on the catalytic oxidation of the peroxidatesubstrate3,3,5,5-tetramethylbenzidine by hydrogen peroxide using4-mercaptophenylboronicacid-functioned Au@Pt nanoparticles adsorbed on the surface of E. coli O157:H7. The assayshowed excellent sensitivity both with the naked eye and based on absorbance measurements.The absorbance at652nm was proportional to the concentration of E. coli O157:H7rangingfrom7to6×106cfu/mL with a limit of detection of7cfu/mL.(3) This paper describes a novel fluorescence gold nanoparticles probe for detectingcyromazine. Gold nanoparticles (GNPs) were synthesized in one step at ambient temperatureusing gallic acid (GA) as reducer and stabilizer. Typically the-prepared gold nanoparticles with the average diameter of37nm can emit stable fluorescence at318nm when theexcitation wavelength was selected as296nm. Upon the addition of cyromazine, the reducerGA can interact with cyromazine through strong hydrogen-bonding interaction, which caninterrupt the formation of gold nanoparticles. Consequently, the color change from purple toyellow-green with increasing cyromazine concentration was observed, coupling with thesolution fluorescence intensity weaken at the same time. Because of the unconspicuous colorchange, we focus on detecting the change of the fluorescence intensity. Under the optimumconditions, the weakening of the fluorescence intensity exhibited a linear dependence oncyromazine concentration in range of0.07to5.90mol/L. The selectivity of cyromazine overother metal ions and pesticides in aqueous solution is remarkably high with a low detectionlimit of0.07mol/L. In the analysis of practical spiked milk and pet food samples, the newmethod yielded satisfactory results. |
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