Detection Of Heavy Metal Ions In Foods Based On Polarization Properties Of Anisotropic Nanomaterials

Heavy metal pollution has always been a major threat to food safety.In this paper,taking mercury ion as an example,we utilize the optical properties of anisotropic gold nanomaterials to quantify mercury ion for the first time under polarized light microscopy,which can only image anisotropic materials.Polarized light microscopy mercury ion can be adsorbed on the surface of gold nanorods,gold triangles and dendritic gold nanoparticles after its reduction to mercury,in which alloy was formed and induced their shape transformation to isotropic sphere?disk?nanoparticle.Thus,the polarization ability of nanomaterial gradually disappears and the light intensity gradually weakens under polarized light microscopy.The quantitative study of mercury is realized through the change of light intensity.The imaging method we have developed can quantitatively detect metal ions in micron space scale with trace samples.The research contents are as follow.1)Based on mercury inducing the shape transformation of gold nanorod,we improved the polarized imaging technique and quantified mercury ions by the light intensity.We have confirmed that gold nanorods?length at 72.561 2.17 nm and diameter at 36.05± 0.44 nm?can be regarded as a single dipole.Under polarized light microscopy,the intensity of the gold nanorods under polarized light microscopy is dependent of its orientation relative to of the polarizer,and the light intensity changes with a period of?/2.The merged light intensity value of the gold nanorod and its rotation after ?/4 is stable.Therefore,by rotating the sample or the polarizer,the sum light intensity values of the gold nanorod before and after the rotation are to realize the unbiased imaging of the gold nanorods.The light intensity value is no longer dependent on the angle.Under UV-visible spectrophotometer and transmission electron microscopy?TEM?,it was confirmed that the reduction of mercury ions by NaBH4 into elemental mercury and result induce gold nanorod deformation,accompanied by blue shift of peak position and finally transformation to sphere at high concentration..Under polarized light microscopy,the gold nanorods are red,yellow after adding mercury,and the light intensity gradually decreases.For comparison.Under dark field microscopy,the gold nanorods gradually turned green and the light intensity increased slightly.Under polarized light microscopy,the light intensity of gold nanorods is proportional to the concentration of mercury ions in the range of 0.1-2 pmol/L,and the linear equation is y=2654*CHg²⁺+3832,R2 is 0.997.The ions such as Zn²⁺,Pb²⁺' Cu²⁺ will produce interference.Finally,we detected mercury ions in onion epidermal cells and well water with excellent results.2)The gold nano-triangle can be seen as the three dipoles,and are anisotropic.Mercury element obtained by reducing mercury ion with vitamin C?AA?could be absorbed on the edges,gradually induces the shape-transition of gold nano-triangles and the light intensities of gold nano-triangles are becoming weak.Gold nano-triangles are synthesized by using KI as a reducing agent,which is an equilateral triangle with a side length of 44+1.27 nm.The gold nano-triangles are red and the presence of mercury ion can cause their intensity gradually weakens.Moreover,the intensity change is mercury ion concentration dependent and has a linear relationship to mercury ion concentration of 0.05-1?mol/L.The detection method has good anti-interference to heavy metal ions such as Zn²⁺,Pb²⁺.The assay was applied to the detect mercury ion in animal cells and tap water.3)The anisotropic dendritic gold nanomaterials are composed of central nuclei and branches,which can be used to detect mercury ions with the same principles.They can be regarded as multi-dipoles and exhibit high brightness under polarized light microscopy.Firstly,we synthesized small and larger dendritic gold nanomaterials using 4-?2-hydroxyethyl?-1-piperazine ethyl sulfonic acid?HEPES?and hydroquinone as the reducing agent,respectively.Under UV-visible spectroscopy,it has proved that the dendritic nanomaterials have good response to mercury ions and small dendritic gold nanomaterials can be applied to determine mercury ion sensitively.However,the small dendritic nanomaterials prepared by HEPES is weak under polarized light microscopy.We use larger dendritic gold nanomaterials to quantify mercury ions,where they have an inner diameter of 40±.16 nm and an outer diameter of 70±2.45 nm.They are bright and red under polarized light microscopy.Owing to the specific feature of these nanomaterials,the intensity are impendent on the angle relevant to polarizer.Based on the principle of mercury-inducing transformation of dendritic nanoparticles,we have achieved the detection of mercury,in which the detection range is 0.01-1?mol/L.The sensitivity is better than those of gold nanorods and gold nano-triangles.