Research Of Surface Enhanced Raman Spectroscopy In Detection Of Main Harmful Pollutant In Milk

With the increase of milk consumption,the harmful pollutant in milk has been paid more and more attention.The existing detection methods either time-consuming,have complex preprocessing steps or need bulky and expensive instruments,which are not suitable for rapid and real-time detection.Surface-enhanced Raman spectroscopy(SERS)technique has the merits of simple preprocessing,fast detection,high sensitivity,informative and easy operation.Therefore,the main harmful pollutant in milk including foodborne pathogens,antibiotic and heavy metal are selected as the detection objects,we attempted to combine this technique with the existing methods to realize the rapid and sensitive detection of harmful pollutant in milk,and the details are listed as follows:1.Detection of foodborne pathogens in milk based on SERS technology.A new competitive immune SERS method based on particle distance regulation has been proposed,Salmonella typhimurium was used as the object of research;firstly,GNRs with moderate aspect ratio and obvious Raman enhancement effect were fabricated and used as the SERS substrate.Then aptamers adsorbed to the surface of p-Aminothiophenol(PATP)conjugated GNRs by electrostatic adsorption,aptamers can stable GNRs in salty solution to monodisperse state;and PATP can report signal.In the presence of Salmonella typhimurium and c DNA simultaneously,the target and c DNA would competitively combine with the aptamers,inducing the aptamers no longer stabilizes the GNRs in salt solution,particle spacing of GNRs reduction,and SERS signal enhancement,thus realizing detection.The experimental results showthat the SERS intensity was observed to increase linearly with Salmonella typhimurium concentration from 56-56×107 cfu/m L,with a LOD of 9 cfu/m L;additionally,the ability of the proposed method to detect Salmonella typhimurium was also confirmed in adulterated milk samples,the recovery was 98%-126%.The research shows that it is feasible to detect the foodborne pathogens in milk by competitive immune SERS method based on particle distance regulation.2.Detection of antibiotic residues in milk based on SERS technology.A new competitive immunomagnetic SERS method has been proposed,tetracycline was used as the object of research;firstly,magnetic nanospheres possessed high saturation magnetization and uniform particle size was fabricated.Then conjugated with the aptamers as recognition probes for capturing tetracycline.PATP modified Au@Si O2 core shell material conjugated with c DNA as signal probes.In the presence of tetracycline,tetracycline bound successfully to the aptamer upon its addition with the subsequent release of some c DNA-APS into the bulk solution.By measuring the Raman spectrum of the released signal probe,we obtained the Raman intensity based on the location of the PATP characteristic peak,and established the standard curve of its relationship with tetracycline concentration,thus realizing detection.The experimental results show that the SERS intensity was observed to increase linearly with tetracycline concentration from 0.001-100 ng/m L,with a LOD of 0.001 ng/m L;additionally,the ability of the proposed method to detect tetracycline was also confirmed in adulterated milk samples,the recovery was 97%-120%.The research shows that it is feasible to detect the antibiotic residues in milk by the competitiveimmunomagnetic SERS method.3.Detection of heavy metal ions in milk based on SERS technology.A new SERS method based on spirolactam ring-opening process of rhodamine derivatives R has been proposed to detect heavy metal ions in milk.Hg2+ was used as the object of research;firstly,Au NS@Ag core-shell nanocube(CSN)with uniform particle size and obvious Raman enhancement effect was fabricated as the SERS substrate.Then CSN was conjugated with the rhodamine derivatives R(Rh D)as recognition probes for capturing Hg2+.In the presence of Hg2+,Hg2+ binds to Rh D,resulting the spirolactam ring-opening process of Rh D;by measuring the Raman spectrum of the above mixture,establishing the standard curve of its relationship with Hg2+ concentration,thus realizing detection.The experimental results show that the SERS intensity was observed to increase linearly with Hg2+ concentration from 0.01-100 ppm,with a LOD of 5.16 ppb.Additionally,the ability of the proposed method to detect Hg2+ was also confirmed in adulterated milk samples,the recovery was 98.83%-110%.The research shows that it is feasible to detect the heavy metal ions in milk by SERS method based on spirolactam ring-opening process of Rh D.4.Detection of harmful pollutants in milk based on SERS and chemometrics method.Based on the first three chapters,we further explore a more rapid and convenient detection method to meet the needs of rapid and real-time detection.Hg2+was still used as the object of research;firstly,Au@Si O2 was preferred as SERS substrate,and mixing with different concentration of Hg2+,measuring the Raman spectra of mixture.Then the SG-FD method was applied to pretreat spectra,eliminating the influence of baseline offset,drift,and noise interference;Subsequently,GA and ACO are used to extract the characteristic variables,and two linear(MLR and PLS)and nonlinear(BPANN and BP-Adaboost)pattern recognition methods were employed comparatively for modeling.Experimental results showed that the results of nonlinear methods were better than those of linear methods,especially for ACO optimized BP-Adaboost model,R = 0.997 and RMSEP = 0.092 in the prediction set;additionally,the ability of the proposed method to detect Hg2+ was also confirmed in adulterated milk samples,the recovery was 98.3%-115%.The research shows that it is feasible to detect the heavy metal ions in milk based on the SERS and chemometrics method.5.Detection of harmful pollutants in milk based on SERS/Fluorescence dual-modal method.Based on the first four chapters,this study further explores the dual-modal method by combining SERS with fluorescence spectroscopy to improve the broad-spectrum applicability of the method.Hg2+ was still used as the object of research,firstly,magnetic nanospheres was fabricated and conjugated with the aptamers as recognition probes for capturing Hg2+.Au@Ag/Graphene-UCNPs prepared by optimization was conjugated with c DNA as dual-modal signal probes.In the presence of Hg2+,Hg2+ bound successfully to the aptamer upon its addition with the subsequent release of some Au@Ag/Graphene-UCNPs into the bulk solution,establishing the standard curve of its relationship with Hg2+ concentration,thus realizing detection.The experimental results show that the linear detection range of Hg2+ with SERS was 0.001-800 ppm,with a LOD of 0.32 ppb.The linear detectionrange of Hg2+ with Fluorescence was 0.001-100 ppm,with a LOD of 0.001 ppm;additionally,the ability of the proposed method to detect Hg2+ was also confirmed in adulterated milk samples,and the recovery was 99.23%-110% and 96.98%-109%,respectively.The research shows that it is feasible to dual-modal detect the heavy metal ions in milk based on the SERS and Fluorescence method.