Stability of ‘quantum dot human epidermal growth factor’ bioconjugates prepared using quantum dots synthesised in aqueous solution

As advantaged nanoscale fluorescent bioprobes, quantum dot (QD) bioconjugates have been widely used in biomedical research. However, the stability of these bioconjugates stored over a period of time has been rarely reported. Here, we synthesised water-soluble QDs by conjugating the human epidermal growth factor (EGF) to these low-cost QDs using 1-ethyl-3(3-dimethylamino propyl)-carbodiimide (EDC) as a cross-linking reagent. These bioconjugates nanomaterials were then used to label cancer cells (MDA-MB-435S and SMMC-7721) and normal cells (HL-7702) whose surfaces expressed high-level (for the cancer cells) and low-level (for the normal cells) EGF receptors (EGFR). We found that although the fluorescence intensity of these bioconjugates decreased with prolonged storage time at 4°C for more than 4 months, their aqueous solution retained a transparent appearance, good particle dispersion and very bright fluorescence. Furthermore, the bioconjugates could still well recognise cancer cells. As a control, the normal cells were labelled with a small amount of the fresh and stored bioconjugates. The results presented in this work indicated that QD bioconjugates prepared with QDs synthesised in aqueous solution may be used as a low-cost biomedical test kit for biomedical imaging and diagnosis, where the QD bioconjugates could be stored for long periods of time.