Dark-Field Optical Microscopy Imaging Of Functionalized Gold Nanoparticles

Gold nanoparticles（GNPs）have been widely used in sensing analysis,catalysis,medical diagnosis and treatment due to their unique optical,chemical properties and excellent biocompatibility.This article developed the detection of phosphodiesterase 8A（PDE8A）and malathion based GNPs at the single particle level with the dark-field microscopy imaging.The method improved the sensitivity and obtained good results in the actual samples detection,which provided a reliable method for the sensitive detection of various analytes in the future.In addition,the GNPs coated with cuprous oxide（GNP@Cu₂O NPs）were synthesized,which would apply for optical sensing detection and analysis.The article consists of the following three parts:（1）The level of PDE8A in human body is closely related to many physiological processes.In this chapter,a colorimetric-based single-particle detection（SPD）method was designed by GNPs modified with Mn O₂ nanosheets（GNP@Mn O₂ NPs）to quantify PDE8A.In this system,2-phosphate-L-ascorbic acid trisodium salt（AAP）can be catalyzed by alkaline phosphatase（ALP）to ascorbic acid（AA）,which can be used as a reducing agent to reduce Mn O₂ to Mn²⁺.Due to the local surface plasmon resonance（LSPR）of GNPs,the change of particle color and scattering intensity can be observed under dark field optical microscope（DFM）.However,in the presence of PDE8A,cyclic adenosine monophosphate（c AMP）hydrolysate 5′-monophosphate sodium salt（AMP）can consume ALP,making the generated AA is not enough to etch the Mn O₂ shell.By calculating the scattering intensity of GNP@Mn O₂ NPs,the content of PDE8A can be accurately quantified.The linear range is 12.5-62.5 ng/m L,and the detection limit can be as low as 3.25 ng/m L.This method opens a new way for the quantitative analysis of PDE8A.（2）Malathion is a common pesticide,and its pollution can cause toxic respiratory problems,carcinogenic and neurotoxic effects.In this chapter,GNP@Mn O₂ NPs are used as optical probe to detect malathion with the DFM imaging system and SPD method.ALP hydrolyzes p-aminophenyl phosphate（p-APP）to p-aminophenol（p-AP）,which can reduce Mn O₂ to Mn²⁺.However,the malathion can prevent the formation of p-AP as an inhibitor of ALP and not to etch the Mn O₂ shells.By calculating the change of scattering intensity of GNP@Mn O₂ NPs,the amount of malathion can be accurately quantified.The linear range is0.001-0.1 ng/m L,and the detection limit is 0.82 pg/m L.In addition,the method only requires a small amount of samples,especially suitable for the detection and analysis of trace samples.（3）In this chapter,the GNP@Cu₂O NPs core-shell structures were synthesized.Polyvinylpyrrolidone（PVP）was dissolved in Cu（NO₃）₂solution under constant magnetic agitation.Then the prepared GNPs solution and the N₂H₄·H₂O solution were added to the reaction mixture.After stirring vigorously for five minutes,the GNP@Cu₂O NPs were synthesized.The morphology and optical properties of the particles were characterized by dynamic light scattering（DLS）,transmission electron microscopy（TEM）,dark field microscope（DFM）and UV-visible spectrophotometer（UV-vis）.The results show that the synthesized particles have uniform particle size and good dispersibility.