Construction And Experiment Of SERS And LSPR Optical Biosensor For Measuring Aflatoxin B1

Aflatoxin B1(AFB1)is a fungal toxin produced by fungal metabolism,which has a high risk of harm.AFB1 can cause pollution of a large number of agricultural products,causing dramatic losses to human life and properties.However,conventional detection methods for AFB1 usually require expensive instruments,complex operations,and long assay times.Therefore,it is highly urgent to develop an efficient,sensitive and simple assay for AFB1 detection.Surface enhanced Raman spectroscopy(SERS)and localized surface plasmon resonance spectroscopy(LSPR)-based optical biosensors have already shown their potential in life sciences,environmental monitoring,agriculture,and food safety due to their rapid,high sensitivity,and strong specificity.In this thesis both SERS and LSPR-based optical biosensors are constructed to quickly detect AFB1.The main research contents are as follows:(1)The Raman characteristic peak of aflatoxin B1(AFB1)was calculated based on the density functional theory(DFT),and the wave number 1586 cm-1 was determined as the AFB1 Raman characteristic peak.According to the molecular frontier orbital theory and electrostatic potential,the minimum extreme point of aflatoxin B1(AFB1)molecule is located between the O(20)and O(25)atoms in the molecule.Therefore,Ag nanoclusters are easily coordinated with AFB1 molecules at this position.The consistency between the SERS experimental results and theoretical calculation results of AgNPs substrate and finally the Raman characteristic peak of AFB1 was confirmed through comparative analysis.(2)A finite difference time domain(FDTD)is applied to do the simulation of Au@Ag to analyse the Au@AgNPs structure.The relationship between the gap and its electric field enhancement is calculated by simulating the electric field intensity under different particle gaps with the excitation of a wavelength532 nm light source.The results indicate that the concentrations of the target sample is related to the structure of Au@AgNPs.The smaller the spacing between NPs particles,the stronger the electric field intensity generated.Then,the electric field distribution of Ag shell structures with different thicknesses was simulated and calculated.Under the excitation of a 532 nm wavelength light source,the electric field distribution of Ag shells with different thicknesses was observed.The results showed that as the thickness of Ag shell increased from 1 nm to 5.2 nm,the electric field intensity of Au@AgNPs significantly increases.However,when the thickness of the Ag shell increases from 5.2 nm to 8.5 nm,the electric field intensity of Au@AgNPs slowly increases because the performance of Au@AgNPs structure is influenced by the pairing effect between Au core and Ag shell,and the thicker Ag shell weakens the electronic pairing effect between Au core and Ag shell.(3)Due to Au@AgNPs having good stability,uniformity,and high SERS enhancement performance,the Au@AgNPs was used to quantitative detection of AFB1.By synthesizing different sizes of Au@AgNPs,and combined with UV visible spectroscopy and FDTD simulation results,a core shell structure of 32 nm Au core and 5.2 nm Ag shell was obtained to do SERS measurement for the detection of aflatoxin B1.The linear correlation coefficient R2=0.9798 with the recovery rate of 95.67%~97.25%,and the detection limit of 0.83 ng·m L-1.(4)Using the optical localized surface plasmon resonance(LSPR)of Au nanoparticles,a Au NPs probe was constructed for making the aflatoxin B1(AFB1)biosensor.The surface of Au NPs is covered with negatively charged citrate ions,and then a negatively charged aflatoxin B1(AFB1)aptamer is present.The aptamer is uniformly dispersed due to electrostatic repulsion after binding to the surface of Au NPs through Au-S bonds;When both Na Cl and different concentrations of AFB1 are present togethe,the ligand specifically binds to AFB1 and detaches from the surface of Au NPs,causing aggregation of Au NPs under the action of Na Cl,resulting in corresponding changes in their LSPR spectra.Thus a method with rapid,highly sensitive,and specific detection of AFB1 was achieved,with a linear correlation coefficient of R2=0.9884,a recovery rate of 92%~97.69%,and a detection limit of 36 ng·m L-1.