| Localized surface plasmon resonance(LSPR)effect of noble metal nanoparticles has provided new research perspectives and problem solutions in these scientific researches of medicine,chemistry,biology,environment,food and agriculture due to its unique biophotonics properties.In this paper,a dual-channel fiber optic-based LSPR biosensor system was constructed and validated.Both dimethoate in food safety and the melamine in milk are detected and analyzed using this dual-channel fiber optic-based LSPR biosensor system.The main contents of this paper were described as follows:(1)The extinction efficiency of AuNPs and AgNPs related to the properties of LSPR biosensor was simulated based on Mie's scattering theory.The dielectric constant of AuNPs was calculated by following Lorentz-Drude model and the extinction spectra of AuNPs were obtained by software coded by MATLAB.The calculated result showed that the maximum extinction efficiencies of gold nanoparticles(Au nanoparticles,AuNPs)with particle diameter of 13.5 nm,20 nm,25 nm and 30 nm were 1.329,2.0583,2.6741 and 3.3329,respectively.With the change of particle diameter,the extinction wavelength corresponding to the maximum extinction efficiency shifted from 520 nm to 527 nm.What's more,the maximum extinction efficiencies of silver nanoparticles(Ag nanoparticles,AgNPs)with different diameters(13.5 nm,20 nm,25 nm and 30 nm)was 7.5698,10.4621,11.8101 and 12.326,respectively.The maximum extinction wavelength moved from 13.5 nm to 427 nm.The result showed that the maximum extinction efficiency of,AuNPs and AgNPs increases gradually with the increase of nanoparticle diameter in the range from 13.5 nm to 30 nm7 and the maximum extinction wavelength moved to the direction of red light,and the extinction efficiencies of AgNPs were higher than that of AuNPs.(2)The dual-channel fiber optics-based LSPR biosensor signal acquisition system was developed,which consists of a broadband light source,a sample measurement unit,an optical splitting components and a signal acquisition unit.The light source module genetates the light beam in the wavelength range from 360 to 1200 nm.The sample measurement unit includes cuvettes and cuvette holders with 74 UV lens.The signal acquisition module is composed of bifurcated fibers,fiber-optic dual-channel switcher and a fibered spectrometer.The experimental results showed that standard deviations calculated from channel 1 and channel 2 were 0.45%and 0.56%,respectively.Therefore,the consistency calculated from both channels and the stability of the dual-channel LSPR biosensor system were verified.(3)Quantitative detection of dimethoate using this dual-channel LSPR biosensor system was experimented.For rapid detection of dimethoate,the dimethoate was stored at 4? and diluted in different concentrations.First of all,different concentrations of dimethoate with same volume of 80 ?L was mixed with NaOH(35 ?L)and pure water(535 ?L).Subsequently,AuNPs(150 ?L)was added into the mixed solution and the mixed solution was incubated for another 10 min at room temperature before taking the LSPR spectra.The experiment results showed that the linear equation built by the peak absorbance ratio(A520/A640)and dimethoate concentration was expressed as Y=0.062C?0.13(C is the concentration of dimethoate)with the correlation coefficient of 0.96 and the limit of detection(LOD)of 5 nM when the concentration of dimethoate was in the range of 10?100 nM in channel 1.While the linear equation between the peak absorbance ratio(A520/A640)and the dimethoate concentration was obtained as Y=0.051C+0.59 from Channel 2 with the correlation coefficient of 0.98,and the limit of detection(LOD)of 6 nM.Various interfering substances,such as hexachloride benzene,fenvalerate and ethoprophos were applied to verify the selectivity of this dual?channel LSPR biosensing system in order to bring this LSPR biosensor system into the practical detection applications.The experimental results showed that the absorbance ratio(A520/A640)of the mixed solution containing the dimethoate was 3.138,while the absorbance ratio(A520/A640)of the mixed solution containing the other three pesticides was 0.062,1.131 and 0.893,respectively.The absorbance ratio of inference substances was obviously lower than that of dimethoate,indicating that NaOH could only hydrolyze the dimethoate and prevent the aggregation of AuNPs.Furthermore,the recovery rates calculated from channel 1 and channel 2 were 85.9%?105.44%and 92.9%?107.37%respectively.(4)This study also proposed a dual-channel LSPR biosensing system via optical fibers for colorimetric detection of melamine using AuNPs-based aptamer.40 ?L of 1 ?M aptamer was mixed with 100?L of AuNPs solution,diluted with 200 ?L water and incubated for 24 h at room temperature.Afterwards,100 ?L of different concentrations of melamine was added into the AuNPs solution and the solution was again incubated for 30 min.Finally,60?L of NaC;were added into the AuNPs solution by following the measurement principle.There is a linear correlation between melamine concentration and absorbance peak ratio A640/A520(absorbance at 640 nm and 520 nm)when the concentration of melamine is in the range of 0 to 1 ?M.The calibration curve is plotted by using the absorption peak ratio A640/A520 as an ordinate.The linear equation of Y:0.9267C+0.0525(C is the concentration of melamine)was obtained with the square of the correlation coefficient of 0.98.The absorbance was measured from channel 2 when the concentration of melamine in the range of 0 to 1 ?M was added into the aqueous solution.The absorption peak ratio of A640/A520 is also linearly correlated with the concentration of melamine.The linear equation of Y=0.9491C+0.0929(C is the concentration of melamine)was obtained with the square of the correlation coefficient of 0.98.Various interfering substances,such as glucose,fructose,lactose and amneline were applied to verify the selectivity of this LSPR biosensing system in order to put this method into the practical detection of milk samples.Selectivity studies were carried out using interfering substances with the concentration of 10 ?M comparing to measurement results from the concentration of 1 ?M of melamine.The experimental results showed that the absorbance ratio(A640/A520)of solution containing melamine was 0.966,while the absorbance ratios(A640/A520)of the mixed solution containing interferences were 0.29,0.279,0.344 and 0.119,respectively,which were obviously lower than that of melamine mixed solutionon,indicating that only melamine could induce the aggregation of AuNPs and change the color of AuNPs from red to blue,which demonstrated that the aptamer modified AuNPs has good specificity for the detection of melamine.Furthermore,the percent recovery of.channel 1 and channel 2 were 89.23%?114.62%and 89.06%?108.13%,respectively. |
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