Use of quantum nanodot crystals as imaging probes for cereal proteins

Quantum dots (QDs) also known as fluorescent semiconductor nanocrystals have unique optical and chemical properties. Their properties make them excellent fluorescent probes for biological applications which enable long term high quality imaging with the ability to conjugate to multiple biological targets. There are many applications of QDs in the biomedical field; however no applications exist in imaging of food structures. In this paper a detailed protocol for the use of QDs in imaging of gluten network in flat bread and zein in corn extrudates by combining covalent bioconjugation principles to the rules of immunohistochemistry is presented. In this study water soluble CdSe/ZnS core/shell quantum dots containing carboxyl terminated groups were used. The quantum dots had a wavelength of emission of 620 nm. Confocal laser scanning microscopy was used to observe the structure of cereal proteins tagged by QDs to visualize their location within the food matrix. Optical sections were collected within a sample size of 20 μm and processed with Zen 2009 image analysis software (Carl Zeiss MicroImaging GmbH) to obtain three dimensional images. Results showed that QDs can be covalently conjugated to both gluten and zein. They provide long term bright stable imaging capability for wheat gluten with very little quenching after multiple laser excitations overtime.