Aptamer-mediated Carbon-based Nanoprobe And Its Catalytic Amplification-gold Nanosol SERS/RRS Detection Of Trace Lead And Potassium Ions

Harmful heavy metals in the environment can contaminate food and drinking water through a variety of ways,thereby pose a threat to human health and ecological balance.Rapid detection and screening of these pollutants are important means to reduce or avoid environmental pollution hazards.Relative to detection methods that required large-scale instruments,fluorescence and Raman scattering molecular spectral methods are economical and convenient.However,most of these metal ions have the shortcomings of lack of Raman activity and fluorescence signal,or small scattering cross section and weak signal,which limit the applications of some molecular spectral methods such as surface enhanced Raman scattering(SERS),fluorescence(FL),resonance Rayleigh scattering(RRS).In this paper,we intend to take the detection of lead ions(Pb²⁺),potassium ions(K⁺),and arsenite(As O₂^-)as examples to amplify the SERS signal by constructing a carbon-based nanoenzyme-catalyzed nanoreaction system.The two nanoenzymes of carbon dots and nitrogen carbide were chosen as the research objects,and their synthesis,the catalytic performance of the nanoindicator reaction to form nanosols as SERS substrate,and the application in molecular spectroscopy are studied.At the same time,the specific binding of aptamers and target molecules was utilized to regulate the enzyme catalytic activity,and a new strategy for the quantitative detection of trace metal ions with highly selective and sensitive label-free SERS were proposed.Using triammonium citrate(CA)and ethylenediaminetetraacetic acid(EDTA)as precursors,by adjusting the molar ratio of the precursors,using microwave heating method to prepare fluorescent adjustable nitrogen-doped carbon quantum dots(CD_N),and using transmission electron microscopy(TEM),infrared(IR),absorption(Abs),three-dimensional fluorescence(3D-FL)and other methods were characterized.Experiments have found that the prepared CD_N has a strong fluorescence peak at 443 nm,and its quantum yield is 0.42.When an aptamer(Apt)such as lead is added to the analysis system,Apt can be adsorbed on the surface of the CD_N and inhibit its fluorescence intensity.When there is an analyte in the system,the analyte can specifically bind to the corresponding Apt and release the CD_N,the FL signal recovery and enhanced.Synchronous fluorescence method(SFL)was used for detection.When the Pb²⁺concentration was in the range of 10-100 nmol/L,the linear equation was?I_368nm=19.1 C+109.2(R²=0.9899),with a detection limit of 4.31 nmol/L.In addition,the aptamer fluorescence analysis platform is also suitable for quick and easy analysis of arsenite.The As O₂^-concentration is in the range of 10-100 nmol/L,and the linear equation is?I_368nm=7.7 C+47.3(R²=0.9797),and the detection limit is 5.52 nmol/L.This method is simple,sensitive,and highly selective.It is used for the determination of Pb²⁺in actual samples.The relative standard deviation is 0.77%-2.78%,and the recovery rate is 96.22%-103.00%,respectively.The mechanism of high-efficiency synthesis of nitrogen-doped carbon dots by hydrothermal method was discussed.As a nanoparticle,CD_N can catalyze the reaction of reducing sugars such as glucose and fructose(GLc,FLc)and HAu Cl₄ to produce gold nanoparticles(Au NP).Using malachite green(MG)as a probe,the SERS intensity of the analytical system at 1617 cm^-1 increased linearly with the increase of CD_N;the RRS intensity at 375 nm increased linearly with the increase of CD_N.In the system,Apt can be adsorbed on the surface of the CD_N as a catalyst,thereby affect the catalytic ability of the CD_N.Apt and the analyte are in an adsorption competition relationship,but when there is a target molecule that binds more closely to Apt in the system,Apt will desorb with it,and the catalytic ability of CD_N will be enhanced.Based on this,an aptamer-mediated nanocatalytic amplification SERS/RRS quantitative detection platform for metal ions was constructed.For Pb²⁺:In the SERS detection method,the Pb²⁺concentration is in the range of 0.5-120 nmol/L,and the linear equation with the SERS intensity?I_1617cm-1 is?_I1617cm-1=461.5 C+699.3(R²=0.9983),and the detection limit is 0.11 nmol/L.In the RRS detection method,the Pb²⁺concentration is in the range of 50-400 nmol/L,and the linear equation of the RRS intensity?I_375nm is?I_375nm=11.4 C+24.7,(R²=0.9829),and the detection limit is 15.32 nmol/L.For As O₂^-:In the SERS detection method,the As O₂^-concentration is in the range of 1-80 nmol/L,the linear equation with the SERS intensity?I_1617cm-1 is?I_1617cm-1=206.4 C+793.7(R²=0.9849),the detection limit is 0.34 nmol/L.In the RRS detection method,the As O₂^-concentration is in the range of 50-350 nmol/L,the linear equation with the RRS intensity?I_375nm is?I_375nm=4.1 C+103.9(R²=0.9791),and the detection limit is 20.24 nmol/L.This analysis platform uses CD_N to catalyze the formation of SERS substrates,overcomes the shortcomings of Pb²⁺and As O₂^-without Raman activity,and makes it possible for SERS and RRS to detect metal ions;the combination of Apt and CDs and target molecules does not affect SERS substrates and probes.This will not reduce the SERS detection sensitivity.For the determination of Pb²⁺in actual samples,the relative standard deviation is0.94%-2.71%,and the recovery rate is 99.00%-103.70%.Our method is simple and fast,has high sensitivity,good reproducibility,and has good practical value.In addition,CD_N nanozymes heterogeneously catalyzed the reaction of gold nanoparticles were discussed from the perspective of mechanism.Using citric acid(CA)and thiourea(TU)as precursors,silver nitrate as dopant,silver-doped nitrogen carbide quantum dots(Ag CNs)were prepared by microwave,and TEM,IR,SERS,RRS,FL,Abs,etc.The method characterizes the quantum dots.The experiment found that Ag CNs strongly catalyze the reduction of HAu Cl₄ by glucose(GLc)to produce Au NP,and Au NP has strong SERS activity and RRS effect.With Victoria Blue B(VBB)as the molecular probe,its SERS intensity at 1616 cm^-1 increased linearly with the increase of Ag CNs concentration;the RRS intensity at 370nm increased linearly with the increase of Ag CNs concentration.When K⁺aptamer(Apt)is added,Apt is adsorbed on the surface of Ag CNs,inhibiting its catalytic activity,and the intensity of SERS and RRS is reduced.When K⁺is present,it can combine with Apt to form a stable G-quadruplex,and release Ag CNs catalyst,and its SERS and RRS signal recovery will be enhanced.Coupling the two scattering spectroscopy techniques of inelastic SERS and elastic RRS,developed an ultra-trace K⁺label-free dual-mode quantitative analysis method for aptamers,with a linear range of 5-150 nmol/L and a detection limit 0.92 nmol/L K⁺.In addition,molecular spectroscopy technology was used to study in detail the nano-gold reaction catalyzed by nitrogen carbide,and a reasonable mechanism of Ag CNs-enhanced catalytic reaction was proposed.In this thesis,environmentally friendly green carbon-based nanomaterials such as nitrogen carbide quantum dots and carbon quantum dots are used as catalysts to catalyze the formation of SERS substrates Au NPs,and the aptamer-regulated nanocatalytic molecular spectral analytical system was established.At the same time,the high fluorescence characteristics of carbon quantum dots are used to develop a series of fast and easy new methods for detecting trace metal ions.Using molecular spectral analysis results of SERS/RRS/FL,a reasonable nanocatalytic mechanism is proposed,which provides a reference for improving the selectivity and sensitivity of molecular spectral analysis methods.The establishment of aptamer-mediated nanocatalytic amplification and SERS quantitative analysis platform has expanded the application range of SERS for the detection of trace metal ions,which has certain practical significance.