Development of quantum dot based fluorescence sensor for metabolite detection

Most of the diseases occurring in the body can be detected by changes in the amount of metabolites. Metabolite amounts that differ between healthy and patient individuals play an important role in diagnosing diseases, determining their stage and planning treatment. Although many different methods are used to detect metabolites, the advantages of fluorescence-based detection method include less sample consumption, no need for preliminary preparation, and faster response when compared to other methods. In addition, the well-known structures of quantum dots (QDs) that emit fluorescence, their high luminescence, adjustable size and high absorption cross-section ratio make QDs stand out in metabolite detection studies. In this study, a fluorescent sensor system has been developed that can detect vitamin C (VitC), folic acid (FA) and glucose quickly, sensitively, selectively and reliably for the first-time by using aqueously synthesized cadmium (Cd)-based QDs with mercaptopropionic acid (MPA). First of all, the synthesized QDs (CdSe, CdSeTe, CdTeSe, CdTe/ZnS and CdSe/ZnS) were characterized by UV-Vis, XRD, FT-IR and HR-TEM. It was observed that the synthesized QDs were of high quality and suitable for metabolite detection studies. In the system where QD concentration, pH and incubation times were optimized, the fluorescence responses obtained from QDs against the addition of increasing amounts of CVit, FA and glucose were examined. With the addition of metabolites, quenching of the fluorescence responses of QDs was observed based on the FRET mechanism. In this study, the dynamic range for the QDs tested in the sensor system has been determined 0.3-8000 µg/mL for CVit, 3.5E-4-3.5E+4 ng/mL for FA and 0.175-90 mM for glucose. These specified dynamic ranges are wider than the studies in the literature. In addition, selectivity studies were carried out to observe that QDs respond specifically to metabolites, and as a result, it was determined that QDs have selective responses to metabolites. This presented method has also been used to quantify metabolites in real blood samples. In blood serum samples, metabolite amounts were determined with over 95% accuracy in linear ranges of 10-20 µg/mL for CVit, 7.5-20 ng/mL for FA and 0.25-1.5 mg/mL for glucose. This result is compatible with the results found for different QDs and metabolites in the literature, but is superior in terms of the selected dynamic range and the obtained linear range. As a result, with this thesis, an alternative fluorescence-based sensor system to existing QDs that has a fast response time, sensitive, selective, reliable, low cost and can be used in real samples for the detection of CVit, FA and glucose has been introduced to the literature.