Study Of The Optical Fiber LSPR Signal Acquisition And Its Application In The Detection Of Residual Amount Of Melamine

The optical localized surface plasmon resonance(LSPR)is a coherent,collective spatial oscillation of the conduction electrons in a metallic nanoparticle,which can be directly excited by near-visible light.The optical LSPR is related to the combination of the electronic properties of the nanoparticles,the nanoparticle size and shape,the nanoparticle temperature,the dielectric environment in close proximity of the nanoparticles.Optical LSPR biosensing technology is rapid,sensitive and can meet the demand of practical work in a wide detection range of sample concentration with high detection efficiency.Compared to traditional detection methods,LSPR has emerged as a leader among label-free biosensing techniques in that it offers sensitive,robust,compact and facile detection.It has been applied in the field of label-free biosensors,optical switch and optical waveguide,nanoparticle enhanced Raman spectroscopy,lithography and sub-wavelength image.More attention has been paid to the field of agricultural biochemistry and it has a broad application prospect in agriculture.The main research content of this thesis is listed as follows.(1)The mechanism of optical LSPR biosensor and the method of photoelectric signal acquisition are analyzed and understood,mainly including the principle of the optical SPR and the optical LSPR biosensing technology.It lays the foundation for the construction of the optical LSPR biosensor by understanding the existing optical LSPR signal acquisition method.(2)The optical LSPR spectra from the melamine solution were obtained by using the multi-channel UV-Vis spectrophotometer.The calibration curve established by the absorption peak ratio(A640 /A520)was linear in the concentration range of 0~1?M of melamine in aqueous solutions with the correlation coefficient(R2)of 0.986 and the limit of detection(LOD)of 22 n M,whereas,the correlation coefficient(R2)of 0.998 and the LOD of 14.9 n M were achieved at the concentration of melamine below 0.5 ?M in milk samples.The optimized performance of this colorimetric assay of melamine using aptamer-functionalized Au NPs was obtained with 100 ?L of 13.5 nm Au NPs solution,60?L of 1 ?M(100 dilutions)aptamers,500 m M of Na Cl and the pre-reaction time of 25 min.(3)A single-channel and dual-channel optical fiber LSPR biosensor including thedevice for obtaining the LSPR signal are constructed,respectively.The experimental verification and improvement are performed by using both experimental platforms.A linear equationA(28)0.14?Cwas obtained from the single channel optical fiber LSPR platform to quantitatively determine the concentration of melamine.The standard deviation of 0.26%from channel 1 and 0.59% from channel 2 in absorbance are calculated from the dual-channel platform.The experimental results show that the dual-channel optical fiber LSPR platform provides a on-line biosensing system with high stability and good consistency.(4)The feasibility of quantitative detection of melamine using unmodified Au NPs was experimented by the single channel optical fiber LSPR platform.The linear equation Y(28)0.026?C(10)0.01 was established by the delta absorption peak in the concentration range of 0~1?M of melamine in aqueous solutions with the correlation coefficient(R2)of 0.99 and the limit of detection(LOD)of 33 n M.From the recovery rate,it shows that the recovery rate was 98.9%~101%.In addition,in order to better determine melamine in milk samples,this thesis studied the interference of the compounds,such as fructose,lactose,glucose,and ammeline in raw milk.The experiment results showed that melamine exhibited the highest absorption peak ratio(A640/A520)and the interference absorption peak ratio of others was roughly an order of magnitude low even if others concentration was 10 times higher than melamine.This may conclude that there is only weak affinity between them with aptamers by few or no hydrogen bond forming.These results proved the efficient selectivity and sensitivity of this optical LSPR method and the possibility of detecting melamine in the raw milk samples.