| Gold nanoparticles(GNPs)is a noble metal nanoparticle that has a certain size and can keep a stable colloidal state.The color of GNPs is very obvious and widely used as a color developer in detection field.GNPs has high molar extinction coefficient and adjustable visible light absorption peak,so it can be used as quencher in the detection field.Aflatoxin M1(AFM1)is a hydroxylated metabolite of Aflatoxin B1(AFB1).In humid conditions,AFB1 can appear in feeds through contamination of cereals.Dairy cows which were fed AFB1-contaminated feeds may produce the milk contained AFM1,so AFM1 is known as“milk toxin”.Escherichia coli O157:H7(E.coli O157:H7)is a serious threat to human health;thus,a rapid and sensitive method for detecting them is necessary.E.coli O157:H7 or AFM1 will be detected in this paper based on the functions of color and quenching of GNPs.Mycotoxin or pathogens may exist in a food sample.It is necessary to detect them simultaneously within a short time.A rapid and convenient lateral flow immunoassay(LFI)integrated with competitive and sandwich models based on the color function of GNPs was developed to detect micromolecular(AFM1)and macromolecular(E.coli O157:H7)substances.Results showed that the limit of detection(LOD)for detecting AFM1 was 50 pg/mL with a linear range from 100pg/mL to 1000 pg/mL.The LOD of E.coli O157:H7 was 1.58×10~4 CFU/mL with a linear range from 1.65×10~4 CFU/mL to 3.3×10~6 CFU/mL.The recoveries of GNP-LFI ranging from 78.0%to 111.6%with CV in the range of 3.9%to 8.5%for the detection of AFM1.For the detection of E.coli O157:H7,the range of recoveries was from 70.1%to 89.6%with CV ranging from 4.9%to 13.0%.In this work,the location of two test lines in the LFI test strip were evaluated to detect AFM1 and E.coli O157:H7 by competitive and sandwich models.Results showed that if the competitive and sandwich models coexist in the LFI,the test line of sandwich model should be close to the sample pad to increase the signal of the positive sample,whereas the test line of the competitive model should be kept away from the sample pad to increase the inhibition rate.A single-stranded DNA that contained an appended block and an anchoring block was designed.The appended block acted as a scaffold to prepare fluorescent Ag nanoclusters(AgNCs).The anchoring block contained Poly A,which bound with the surface of CG to quench the fluorescence of AgNCs.An interesting ELISA approach for detecting E.coli O157:H7 was established via fluorescent quenching of DNA-stabilized AgNCs by using a sandwich complex.The changes in fluorescence intensity of AgNCs were used to quantitatively detect E.coli O157:H7.The sensitivity for detecting E.coli O157:H7 reached 1.905×10~3 CFU/mL with a good linear range.Compared with conventional ELISA,the sensitivity of this technique increased by 30-fold.The recovery experiment for detecting E.coli O157:H7 based on the conventional ELISA was from 91.2%to 104.9%with CV in the range of 7.5%to 10.1%in the PBS.The recovery rate for detecting E.coli O157:H7 based on this work was from 90.1%to 96.2%with CV in the range of 8.1%to 13.0%in the PBS,from 89.8%to 100.6%with CV in the range of 7.3%to 8.5%in the low-fat milk,and from 87.6%to 95.0%with CV in the range of 8.8%to 10.2%in the whole milk. |
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