Fabrication Of High Sensitive Nano-biosensiors For Environmental Monitoring

As environmental problems increasing,more sensitive and reliable detection methods for environmental monitoring and environmental control are of great importance.In this paper,high sensitive analytical methods for environmental pollutions,environmental microorganisms,and glucose were developed with lower background signal or enhanced detection signals.The detailed contains are as follows:?1?A sensitive method for Pb²⁺was developed based on graphene oxide?GO?and hybridization chain reaction.The author designed two molecular beacons in this detection system.H1 was G-rich designed,and partly complementary with H2.There is a single base mismatch in the stem of H1.H1 and H2 are absorbed on the surface of GO due to the strong binding force between ssDNA and GO.In the presence of Pb²⁺,the formation of G-rich sequence inspired the hybridization chain reaction.More and more molecular beacons open and form long double strains.The long double strains easily detach from the GO,due to the weak binding force between long dsDNA and GO,and lead to the amplified fluorescence emission.A detection limit as low as 0.61nM was obtained.The detection method is sensitive,selective,simple,and performed well in Pb²⁺determination in real water samples.?chapter 2??2?A new fluorescence method for the detection of mercury???was introduced using magnetic Fe₃O₄ and hybridization chain reaction.The detection system comprise three probes:capture probe H1,report probe H2 and report probe H3.H1and part of H2 are T-rich sequences,and H2 and H3 are partly complementary to each other.In the presence of Hg²⁺,the T-rich capture probes and report probes hybrid into double strains with the aid of T-Hg²⁺-T coordination chemistry.Trigged by this reaction,more molecular beacons open and form a super tandem structure.Fluorescence signal was amplified in hybridization chain reaction,guaranteed the sensitivity of this method.The detection limit of this method is 0.36 nmol/L,with is much lower than the WHO's?the international World Health Organization?regulation on Hg²⁺in drink water.Fe₃O₄ was used as a reaction platform and separator here.Separating the target and captured report-probes from reaction solution reduced the background and interference from other metal ions.This method was sensitive,selective,and performed well in the determination of mercury???in environmental samples.?chapter 3??3?A method for Hg²⁺fishing,enriching and detection was developed based on magnetic GO.The detection system comprises two probes:the capture probe H1 and releasing probe H2.H1 was designed to have a dual function.One part of the H1molecule is able to specifically capture the target Hg²⁺.The other part is used as an anchor to keep the whole probe on the surface of magnetic GO.After fishing,magnetic separation and enrichment,H2 was added to form a complete double strain.The double stains easily detach from the magnetic GO with enhanced fluorescence emission.With the optimum experimental conditions,a detection limit as low as 1.54nM was obtained.This simple method has a broad linear range from 5⁴0 nM.It is sensitive,selective,and performed well in environmental samples.?chapter4??4?A high sensitive colorimetric method for Hg²⁺was developed based on gold nanparticles?Au NPs?and hybridization chain reaction.In the absence of Hg²⁺,the single strain parts of H1 and H2 attach on the surface of Au NPs and protect Au NPs from agglomeration in high ions solution.In the presence of Hg²⁺,hybridization chain reaction inspired and form long double strains,leading to the agglomeration of naked Au NPs.The solution changed from red to blue in this process.This method is simple,sensitive,and selective.In addition,it performed well in the applicable experiments in real water samples.?chapter 5??5?Based on the fluorescence resonance energy transfer?FRET?between Au NPs and fluorescein,a sensitive and selective detection approach for hydrochloric acid was developed.As the maximum absorption wavelength of AuNPs?13 nm?and the emission wavelength of fluorescein are both 520 nm,the emission fluorescence of fluorescein could be absorbed by AuNPs intensively.Without hydrochloric acid in the AuNPs-fluorescein detection system,the fluorescence of fluorescein is quenched by the AuNPs.When there is hydrochloric acid in the mixed solution,the shape and size of AuNPs changed,leading to the release of fluorescence.With this strategy,as low as 0.6?mol L^-1 of hydrochloric acid can be recognized within 30 min.The proposed method also has good selectivity over several common inorganic acid and salts.In addition,satisfactory results were obtained when it was applied in the practical samples.?chapter 6??6?The author introduced an innovative method based on time-resolved fluorescence to quantify ammonia oxidizing bacteria as a representative of the major functional microorganisms in sewage water treatment.A bifunctional europium complex with the characteristics of long lifetime and intense luminescence was used as labels in the experiments.The time-gated mode reduced the fluorescence background and increased the sensitivity of this method.Tow specific DNA probes for ammonia oxidizing bacteria were designed.They are partly complimentary sequences of the target probes.The capture probe was modified on the surface of glass slides,and the report probe was modified with a europium complex.In the detection,the capture probe and dye-labeled reporter probe could form a two-probe tandem with the target sequence,and the determination of target DNA was done by monitoring the time-resolved fluorescence signals of europium complex-labeled reporter probe left on the glass slide surface.This method is sensitive and presents satisfactory specificity to common bacteria such as Nitrobacter winogradskyi,Escherichia coli and Paenibacillus polymyxa.This detection system enables us to rapidly and sensitively analyze the microbial population variety in sewage water treatment.?chapter 7??7?A sensitive label-free method for glucose was developed based on Mn-doped CdS/ZnS QDs and glucose oxidase?GOD?.As the fluorescence intensity of quantum dots?QDs?can be quenched by H₂O₂ produced in oxidization of glucose,glucose can be determined by measuring the fluorescence change in this reaction process.However,H₂O₂ is not intensive quencher,resulting that the sensitivity of these methods are not very satisfactory.By introducing p-phenylenediamine to the hybrid system of Mn-doped CdS/ZnS QDs and GOD,a sensitive label-free method was proposed for direct detection of glucose.With glucose and p-phenylenediamine as substrates,an efficient fluorescence quencher can be produced by the catalysis of GOD and improve the sensitivity of the method.Mn-doped QDs with long lifetime fluorescence was used as indicator in the present method to eliminate the autofluorescence of biological samples.The proposed method provided improved sensitivity and satisfactory selectivity.In addition,this method has simple experimental procedures without enzymatic labeling and favored biological applications in real human serum samples without any complicated sample pretreatments.?chapter 8?...