The New Detection Methods For Lead And Radon Radiation Dose Based On Nucleic Acid Fluorescence Biosensor

Radon is the only radioactive inert gas,which is known to be an"invisible killer"amongst the indoor air pollutants.The ? and ? radiations generated by radon can enter the human body through the respiratory tract,thereby irradiating various tissues and organs,which may lead to mutagenesis,carcinogenesis or teratogenesis.In addition,the stable daughter lead(²¹⁰Pb)is not only a decay product of radon,but also a common environmental heavy metal pollutant.Lead has the characteristic of being difficult to degrade.Therefore,extremely low doses of lead pollution in the environment can cause serious harm to the human body.Currently,the detection of lead and radon face several hurdles including low sensitivity,difficulty in rapid measurement and human health hazards.Therefore,based on the progress in the detection of lead ions and the decay product of radon using modern biological methods,three sensitive fluorescence sensing methods have been established,that use lead ions to induce a conformational change in the functionalized nucleic acids and their special complexes.In Chapter 2 of this paper,a biosensor was assembled using the lead-induced specific aptamer?HTG?conformational changes and the fluorescence characteristics of the organic dye malachite green?MG?.The Pb²⁺induces a conformational change in the HTG to form an anti-parallel G-quadruplex,while malachite green interacts with the plane of the G-quadruplex,forming a stable rigid structure and producing a strong fluorescence.The detection limits for lead and radon using this method were 6.7 nmol/L and 2.06×10³ Bq·h/m³,respectively.Based on the correlation between radon and its stable decay daughter ²¹⁰Pb,we developed a fluorescence bio-sensing method for the detection of both radon and lead,which was easy to operate,provided a rapid sampling and determination of the analytes and could effectively avoid the radiation harm to the human health.In Chapter 3 of this paper,a sensitive method for the detection of lead based on the GR5-MB DNAzyme and self-assembly signal amplification technology was studied.Enhancement of the fluorescence properties of?-cyclodextrin on interaction with the pyrene molecule through‘the host and guest effect' were investigated.The presence of lead ions(Pb²⁺)can trigger the specific DNAzyme to cleave at the RNA site,and the free target DNA is used as a primer.The primer induces the hybridization of the molecular beacons of the pyrene modified at both ends.Pyrene molecule emits fluorescence in close proximity to each other,and the value of fluorescence is enhanced by?-cyclodextrin.The detection limit of lead using this method was 53 pmol/L.This method was sensitive,accurate,and the detection limit was low.In Chapter 4 of this paper,a new method for the rapid detection of lead ion concentration in the water samples was developed based on the interactions between caffeic acid fluorescent probe and lead ions at different temperature conditions.The lead ions interact with caffeic acid causing the quenching of fluorescence in the system.The method was very simple and fast.The limit of detection for lead using this method was 20.5 nmol/L.On comparing the Stern-Volmer quenching curve and its slope for the caffeic acid fluorescent probe and lead ions at different temperatures,it was proved that the quenching effect of lead ions on caffeic acid fluorescent probe was caused due to the coexistence of various quenching.