Bt11 event detection by real-time PCR: single-laboratory validation, comparison of DNA extraction and quantification techniques and application

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C.S.W. Miaw
E.N. Vasconcelos
N.C.C. Guimarães
S.V.C. Souza


qualitative method validation, genetically modified organisms, Bt11 maize, real-time PCR, DNA extraction, DNA quantification


The detection of genetically modified organisms (GMO) by real-time polymerase chain reaction (PCR) is recommended due to its effectiveness in GMO analysis. A complete in-house validation method was applied to the detection of Bt11 events by real-time PCR. A full factorial design was used to compare DNA extraction (cetyltrimethyl ammonium bromide; CTAB, and NucleoSpin® Plant II Kit) and DNA quantification techniques (conventional GENESYS™ 10S UV-Vis spectrophotometer and confined drop-based NANOVUE™ Plus spectrophotometer). In the validation, various levels (0.0007 to 0.0315%) of Bt11 maize were formulated with blank maize and certified Bt11 reference material. A false-positive rate of 0% was obtained for blank samples, which corresponded to selectivity and reliability rates of 100%. The false-negative rate varied from 0 to 83.3%, consistent with sensitivity and reliability rates ranging from 16.7 to 100%. The Bt11 level that presented 100% positive results was 0.0315%, which indicated the sensitivity of the method. Non-linear models were used to estimate the region of unreliability and to calculate the detection limit of 0.014%. Accordance and concordance values of 1.0 were obtained for the 0.0315% level, which indicated method standardisation. Selectivity in the presence of interference was confirmed by the detection of Bt11 maize in the presence of other events. The method was considered robust for different DNA extraction and DNA quantification techniques. Higher DNA concentration values were obtained using CTAB. The absorbance ratio of A260/A230 was negatively influenced by quantification using a conventional spectrophotometer. Both DNA extraction techniques gave values of A260/A280 higher than 1.7, which indicated DNA of great purity. This validated method was applied to routine samples.

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