Quantitation of transgenic Bt event-176 maize using double quantitative competitive polymerase chain reaction and...

In this work, a new procedure useful to quantitatively analyze genetically modified organisms (GMOs) in foods is described and applied to analyze transgenic Bt Event-176 maize. The method developed consists of coamplifications of specific DNA maize sequences with internal standards using quantitative competitive PCR (QC-PCR). The QC-PCR products are quantitatively analyzed using a capillary gel electrophoresis (CGE) with laser-induced fluorescence detection (LIF) method developed at our laboratory that utilizes a physically adsorbed coating. The CGE-LIF procedure allows the use of internal standards differing by only 10 bp from the original target fragments, to our knowledge, the smallest size difference that can be found in the bibliography for QC-PCR of GMOs. A spectrofluorometric procedure using ROX reference dye is proposed to solve calibration problems of input DNA concentration. It is demonstrated that the use of ROX drastically enhances the accuracy of the quantitative analysis by QC-PCR. Reproducibility of analysis times and corrected peak areas (measured as target/competitor PCR products ratio) for the CGE-LIF separations are determined to be better than 0.91 and 1.93% (RSD, n = 15) respectively, for three different days. It is shown that CGE-LIF provides better resolution and a signal/noise ratio improvement of approximately 700-fold compared to slab gel electrophoresis. The good possibilities in terms of quantitative analysis of GMOs provided by this new method are confirmed by determining the Bt Event-176 maize content in certified reference maize powder and food samples of known composition. This procedure opens the possibility for accurate quantitation of multiple GMOs in a single run.