Application Of Nanomaterial-based Signal Cyclic Amplification Aptamer Probes In The Field Of Heavy Metal Ion Detection

Nowadays,heavy metal ions bring on serious public health problems in the environmental and living systems.Owing to the progress of technology and the rapid development of industry,the content of heavy metals in the earth's biosphere has increased dramatically,far beyond the normal level,which directly leads to the deterioration of living environment and endangers the health of human beings and other organisms.In addition,some bioactive small molecules which can cause many diseases in human body have also attracted wide attention.Therefore,it is of great significance to establish an efficient,sensitive and simple detection method for bioactive small molecules and heavy metal ions in the field of disease prevention,diagnosis and environmental detection.Aptamers are selected in vitro by exponential ligand-enriched phylogenetic evolution(SELEX)technology.Nanomaterials have the advantages of good biocompatibility,special optical and physical properties,which can protect the aptamers from being degraded by enzymes,and provide an excellent biochemical application platform for them.The coupling of aptamers with nanomaterials offers many opportunities for the development of highly sensitive and selective sensing systems.In this paper,two biosensors and one chemical sensor were constructed on the basis of fluorescein-labeled aptamers and nanomaterials.Different types of nanomaterials and their advantages and disadvantages were studied.Finally,the development prospect of aptamer assembled nanomaterials is prospected.We believe that the signal enhancement biosensor induced by this molecular design will promote the further development of heavy metal ion detection.(1)MoS2 nanosheets/Ag+/Aptasensors was constructed based on the conformational transformation of multifunctional adaptor probe induced by silver ions.First,we synthesized layered MoS2 nanosheets by hydrothermal method.Through the study,MoS2 has obvious fluorescence quenching effect on ssDNA.When the dye labeled ssDNA was adsorbed on the surface of MoS2 nanosheets,the modified fluorescein labeled ssDNA was fluorescently quenched.In the presence of Ag+,the aptamer probe was fold into a hairpin structure owing to C-Ag+-C coordination.As a result,ROX-ssDNA was separated from the surface of MoS2 nanosheets and thus retained the dye fluorescence.Then,adding the DNase I into the solution,the hairpin structure will be destroyed.The released Ag+binds other dyes-labeled ssDNA on the MoS2 nanosheets surface,meanwhile,the dye-labeled ssDNA was released from the surface of MoS2 nanosheets.Thus,the recycling reflection is generated.Under the optimized conditions,the assay shows a good linear range from 10 nM to 100 nM and the limit of detection(LOD)is 3.8 nM.Furthermore,we utilized the lake water as an analysis of the actual sample and the ideal recovery rate is obtained.This is a novel method for the determination of Ag+and it can be applied in real samples.(2)Gold nanoparticles(AuNPs)/Hg2+/Aptasensors was constructed based on conformational transformation of multifunctional aptamer probe induced by Hg2+.In this work,AuNPs are used for the first time as a sensitive and effective fluorescence sensing platform for Hg2+detection.The platform is based on AuNPs and dye labeled single non-covalently assembled single strand DNA(ssDNA).To further improve the sensitivity,DNase I amplification strategy was introduced.Nucleases can cleaves the fluorescent labeled ssDNA,thus releasing the fluorophore and eventually the target.The released Hg2+then binds to another fluorescently labeled ssDNA,and the cycle is restarted,leading to significant amplification of the signal.The detection limit of the fluorescence sensor platform is as low as 2.11 nM,and the detection range is 10 to 300 nM(R2=0.9637).It is much lower than the traditional non-amplification homogeneous analysis and has excellent selectivity.The constructed probe was also applied to the analysis of lake water samples,and the desired effect was obtained.(3)Based on the fact that Mn(?)can induce aggregation of silicon nanoparticles(SiNPs)and the REDOX reaction between Mn(VII)and ascorbic acid(AA)can regulate the fluorescence intensity of SiNPs,a chemical sensor capable of detecting both divalent Mn(VII)and AA was constructed.Firstly,yellow-green fluorescence SiNPs were synthesized by a pot of hydrothermal method.In the presence of Mn2+,SiNPs exhibit obvious aggregation,and the fluorescence of SiNPs can be significantly quenched by Mn2+ ions.By introducing AA,MnO4-1 can be reduced to Mn2+,which leads to quenching of the fluorescence signal of SiNPs.The degree of quenching of the fluorescence intensity of SiNPs was proportional to the concentration of AA.Therefore,a SiNPs "off" fluorescent sensor for AA and Mn2+modulation was constructed.This strategy shows high selectivity against AA and Mn2+.The feasibility of the proposed sensor system in practical sample determination is also studied and satisfactory results are obtained.