| Nanomaterials have good surface effect,high reactivity and small size effect,and show their excellent properties in catalytic,electrochemical,thermal and optical properties,which have broad application prospects in chemical,life science and environmental protection fields.gold nanoparticles surface plasmon resonance effect can make its morphology change(such as shape and size),inter-particle distance,the refractive index of the surrounding medium and present a tunable color shift.Colloidal gold nanoparticles is generally red or pink in color and becomes violet-blue when aggregated.As an ideal carrier for nanoparticles,graphene oxide can play the role of stabilizing the dispersed nanoparticles.We loaded gold nanoparticles on the surface of graphene oxide to make graphene oxide/gold nanoparticles nanocomposites,and the synergistic effect between the two makes graphene oxide/gold nanoparticles with high simulated enzymatic activity.Using the unique optical properties of nanogold,we established colorimetric analytical detection methods based on positively charged nanogold and negatively charged gold nanoparticles,respectively,and a total of three new methods for the detection of target analytes by colorimetric sensors using the excellent simulated enzymatic properties of graphene oxide/gold nanoparticles.The details of the study are as follows.1.Silver ions,as a common heavy metal contaminant,negatively affect the environment and pose serious risks to human health.Current colorimetric detection methods for target substances based on the principle of aggregation and dispersion of gold nanoparticles usually use sodium chloride as a salt solution to induce aggregation of gold nanoparticles.In this study,it was found that the addition of sodium fluoride is more sensitive than sodium chloride for label-free colorimetric detection of gold nanoparticles particles.Therefore,a biosensor was developed for the colorimetric detection of silver ions by negative electrostatic gold nanoparticles analysis using sodium fluoride as the inducing reagent.Under the optimal experimental conditions,the silver ion concentration was linearly correlated with the absorbance in the range of 5×10-10～5×10-6 M with a detection limit of 3.7×10-11 M.And the detection results were transferred to a paper-based platform and their color grayscale values were obtained using Adobe Photoshop software,and the silver ion concentration was linearly correlated with the color average in the range of 1×10-9～1×10-3 M A good linear relationship was observed between the silver ion concentration in the range of 1×10-9～1×10-3 M and the average color brightness.The colorimetric detection of silver ions based on the negative electrostatic nanogold method is highly selective and does not react with any other metals.The recoveries of the actual environmental samples were 97.4%～104.6%with the relative standard deviations less than 4.1%,which indicated the applicability,wide detection range and high sensitivity of silver ion detection by negative electrostatic gold nanoparticles.2.In this study,a method for colorimetric detection of pesticide residues of acetamiprid based on aptamer with positively charged gold nanoparticles was constructed,which is an improvement of the colorimetric analysis system based on negatively charged gold nanoparticles.This is because the high concentration of salt in the negatively charged gold nanoparticles system affects the affinity between the aptamer and acetamiprid,thus reducing the sensitivity of the analysis.Therefore,positively charged gold nanoparticles particles were used as signal probes.The specific recognition ability of the aptamer makes the positively charged gold nanoparticles colorimetric method highly selective and specific for the detection of the pesticide acetamiprid.The change in conformation of the target substance aminopyralid-induced aptamer is directly translated into the change in color of positively charged gold nanoparticles without the need for high salt concentration to produce aggregation of gold nanoparticles.In this way,a simple and visual colorimetric detection of the target substance acetamiprid was achieved.Under the optimal experimental conditions,the concentration of acetamiprid was in the range of 8.7×10-9 M～9.2×10-7 M,with good linear correlation with the absorbance ratio at the wavelength of A560/A700,and the detection limit was 5.6×10-10 M.This method based on colorimetric analysis of positronium gold nanoparticles for the detection of the pesticide acetamiprid is highly selective.The spiked recovery experiments on real environmental samples showed that the recoveries of the samples ranged from 95.2%to 104.0%with the relative standard deviations less than 4.2%,which indicated the accuracy and reliability of the analysis for the detection of pesticide acetamiprid in real samples.3.Gold nanoparticles is unstable in the environment,prone to aggregation and not easily preserved,so the graphene oxide/gold nanoparticles nanocomposite prepared in this study combines the catalytic interface of graphene oxide with the new properties of gold nanoparticles-mediated electron transfer,which is chemically stable and exhibits strong synergistic catalysis of peroxide-mimetic enzymes.It can effectively catalyze the peroxide oxidase substrate TMB to form the blue TMB oxide.On this basis,a rapid and highly sensitive colorimetric detection of hydrogen peroxide was achieved.The detection limit for the colorimetric detection of hydrogen peroxide is as low as 4.2×10-8 M,which is about 1-2 orders of magnitude lower than that of the analysis using other individual nanoparticles as mimetic enzymes,and it shows high sensitivity.The whole experiment can be completed in a few minutes with a very rapid reaction.This colorimetric analysis also enables rapid and highly sensitive detection of glucose in human serum through the reaction of glucose and glucose oxidase.The effect of DNA on the surface activity of graphene oxide/gold nanoparticles enzymes was also investigated,and the different interactions of single-and double-stranded DNA with nanocomplexes of different dimensional structures were used to change the activity of the nanomimetic enzymes and achieve highly sensitive colorimetric analysis for the detection of DNA hybridization. |
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