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.