Study On The Biosensing Of Heavy Metal Ions Based On Functional Nucleic Acids And Protamine Sulfate-gold Nanoclusters

Heavy metal ions are distributed widely in the environment,which have received great attention due to their high toxicity to humans.Mercury ion can lead to damage of brain,kidneys,the central nervous system,the immune system and the endocrine system.Lead ion is a potential neurotoxin that can cause memory loss,anemia,muscle paralysis,and mental retardation.Uranyl ion represents the most stable form for uranium in aerobic environments,and is radioactive and chemically toxic.Thus,it is still of continued attention and great importance to explore simple and efficient detecting approaches for heavy metal ions.In the chapter 1,the significance and development on the assay of heavy metal ions are reviewed.The reafter,the concepts and usage of gold nanoclusters material and wireless magnetoelastic sensor?WMS?technology are also outlined.Furthermore,the main topics of this article are introduced.In the chapter 2,a novel sensitive strategy for the determination of Hg²⁺was established by combining biotin-streptavidin-gold nanoparticles dual signal amplification strategy and wireless magnetoelastic sensor technology.Graphene oxide?GO?is used as an adsorbent for single-strand DNA.The introduction of Hg²⁺results in the conformation change of aptamer probe.The released CDNA-biotin can be adsorbed to the surface of GO that was immobilized on the WMS,along with a change of the resonance frequency of the sensor.High affinity between streptavidin and biotin was used to amplify the detection signal of the system.Meanwhile,the second signal amplification was realized by the introduction of gold nanotechnology.The sensitivity of detection system was improved based on the biotin-streptavidin?SA?-gold nanoparticles?AuNPs?system designed in this work,with a detection limit of 0.885nM.The mechanism for structure switching and signal amplification was also studied by transmission electron microscopy,UV-vis spectra and resonance spectroscopy.This WMS has additional advantages of being less time-consuming,low cost,real-time and in situ detection of Hg²⁺,and can be expected to expand to other areas of material analysis.In the chapter 3,a novel reagent of PS-AuNCs was prepared for the first time.The properties of PS-AuNCs were characterized by X-ray photoelectron spectroscopy,transmission electron microscopy and UV-vis spectra.We found that the PS-AuNCs described in this work possess horseradish peroxidase-like activity and oxidase-like properties.It can be used for the colorimetric detection of heavy metal ions;and also employed as fluorescent reagent for heavy metal pollutants detection,replacing the current organic fluorescent dyes.The PS-AuNCs were supposed to have a broad application prospect,expecting to expand the application for analyzing the disease markers and related substances in environmental and biomedical fields.Inspired by this discovery,a colorimetric sensing method for detecting mercury ions has been developed based on the enhancement of mercury ions on the catalytic activity of PS-AuNCs.Meanwhile,the interaction mechanism between Hg²⁺and PS-Au NCs was studied using XPS and ultraviolet spectrum.The method can be employed for visual inspection by naked eye,with a detection limit of 1.16×10^–9 mol·L^-1.It is able to be used for on site,real-time monitoring of mercury ions.In the chapter 4,the simple,reliable and sensitive fluorescence methods for the determination of Pb²⁺and UO₂²⁺were established in the different experimental conditions,respectively.They were based on the quenching effect of Pb²⁺and UO₂²⁺on the intrinsic fluorescence of PS-AuNCs.The reaction mechanisms were studied by XPS,infrared spectroscopy and fluorescence spectrum.The fluorescence detections of lead and uranyl ions using protamine-gold nanoclusters were sensitive,reliable and inexpensive without the need of costly instruments.The detection limits of the proposed methods are 6.1×10^–9 mol·L^-1(UO₂²⁺)and2.4×10^–8 mol·L^-1(Pb²⁺),respectively.This strategy is expected to develop into a universal platform for low cost,sensitive and simple detection of heavy metals,providing new ideas and new methods for clinical diagnosis,environmental analysis and biomedical research.