Photoluminescent CdTe Quantum Dot-Polynitroxylated Albumin Composites for Glutathione Detection

We have linked a new type of stable nitroxyl radical, polynitroxylated albumin (PNA), to cadmium telluride (CdTe) quantum dots (QDs) to form CdTe-PNA nanocomposites, in which PNA can effectively quench QDs' photoluminescence (PL). We have demonstrated that CdTe-PNA can be used for glutathione detection by measuring the PL recovery. Utilizing the albumin as a linker between QDs and the radicals, the water-soluble CdTe-PNA probe exhibits good biocompatibility and luminescent properties. Using static PL, lifetime, and electron paramagnetic resonance spectroscopy measurements, we have proposed a CdTe PL quenching mechanism based on quencher PNA. The results indicate that QDs reduce nitroxides on PNA to hydroxylamines, and dynamic quenching is the predominant process. The optimized formula has a 2200:1 molar ratio of nitroxide to QDs, which gives a lower limit of glutathione detection of 20 nM and a linearity range of 5-60 μM (R²= 0.99). In addition, cytotoxicity testing shows that introducing albumin can effectively reduce the cytotoxicity from both CdTe QDs and nitroxide radicals. Because PNA has 30 nitroxides per albumin, the detection advantages of CdTe-PNA can be attributed to the high local concentration of nitroxides and a redox cycling process of electron transfer between QDs and polynitroxides. The new CdTe-PNA PL nanocomposite has broadened application perspectives of QDs in the diagnosis of cancers or other diseases when using glutathione as a biomarker.