The purpose of this research was (1) to synthesize glutathione-capped cadmium telluride quantum dots (QDs), (2) to determine the Cd and Te molar ratios in those QDs, (3) to determine the effect of sonication on QDs in solutions, and (4) to determine the photo-stability and thermal-stability of the GSH-capped CdTe QDs.
Glutathione-capped CdTe QDs were made synthetically using cadmium and tellurium-containing salts in a buffer solution with glutathione as a reducing agent. Freshly prepared QDs, QDs in citrate-borate buffer, and QDs in deionized water solutions were stored in disposable, plastic-capped cuvettes and analyzed using fluorescence spectrometry. QDs exposed to different times of sonication were examined in separate experiments. Cadmium and tellurium elemental compositions were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). Dried QDs, QDs in buffer, and QDs in deionized water were stored at 4oC (under dark and light conditions), at -80oC (under dark conditions), under sunlight, at room temperature (under dark and light), and under 1200 lumens fluorescent light in replicate samples. Fluorescence and absorbance spectrometric data were collected and analyzed periodically for 76 days. Before and after degradation, sulfur contents were determined in QDs in deionized water, supernatant and precipitate using ICP-AES.
Glutathione-capped CdTe QDs were successfully synthesized in powder form and in solutions. QDs degraded under the effects of sonication, and that degradation increased with the sonication time. The Cd:Te molar ratio in QDs is approximately 2:1, but grows slightly with incubation time. Glutathione-capped CdTe QDs undergo thermal and photodegradation. QDs are stable when they are stored in dried powder form, showing no decrease in fluorescence peak emission over 76 days. If QDs are resuspended in deionized water or citrate-borate buffer and stored in low temperatures (-80oC) and in low light intensities (dark conditions), they are more stable than at higher temperatures (25oC) and in higher light intensities (~70% drop in peak fluorescence over 76 days at -80oC). QD photodegradation is associated with the loss of sulfur from GSH-capped QDs.
Keywords: Nanoparticles, Fluorescence Spectrophotometry, Photodegradation, Nanocrystals.