Optical characterization of core–shell quantum dots embedded in synthetic saliva: Temporal dynamics
•Characterization of CdSe/ZnS and ultrasmall CdSe/CdS quantum dots (QDs).•Fluorescence spectra of QDs embedded in saliva at different pH values.•Thermo-optical characterization of functionalized and non-functionalized QDs.•High fluorescence quantum efficiency obtained for ultrasmall CdSe/CdS QDs.•The fluorescence temporal dynamics was determined for different pH and QD sizes.
The present work reports the spectroscopic and thermo-optical properties of CdSe/ZnS and CdSe/CdS core–shell quantum dots (QDs) embedded in synthetic saliva. Spectroscopy studies were performed applying nonfunctionalized CdSe/ZnS QDs (3.4, 3.9 and 5.1 nm cores) and hydroxyl group-functionalized ultrasmall CdSe/CdS core–shell quantum dots (1.6 nm core) suspended in artificial saliva at different potential of hydrogen (pH) values. Saliva was chosen because it is important in a variety of functions such as protecting teeth through the buffering capacity of the formed biofilm, hydration, and dental remineralization. Thermo-optical characterizations using the thermal lens (TL) technique were performed in QD-biofluids for different QD sizes and pH values (3.9–8.3) of the synthetic oral fluids. Transient TL measurements were applied to determine the fluorescence quantum efficiency (η) in QD-biomaterial systems. High η value was obtained for ultrasmall CdSe/CdS QDs. Fluorescence spectral measurements of the biomaterials support the TL results. In addition, for nonfunctionalized (3.4 and 5.1 nm) and hydroxyl group-functionalized QDs, the temporal behavior of the fluorescence spectra was accomplished about approximately 1200 h at two different biofluid pH values (3.9 and 8.3). The temporal fluorescence intensity result is dependent on the pH of the saliva in which the QDs were embedded, QD functionalization and QD sizes. The time for an approximately 50% decrease in the peak intensity fluorescence of CdSe/ZnS QDs (3.4 nm core) and ultrasmall CdSe/CdS QDs is respectively 25 h and 312 h at pH 3.9 and 48 h and 360 h at pH 8.3.
Graphical abstractFluorescence and thermo-optical characterizations were performed for (a) CdSe/ZnS core–shell quantum dots (QDs) and (b) ultrasmall CdSe/CdS QDs functionalized with hydroxyl groups and embedded in synthetic saliva and/or aqueous solutions. Fluorescence spectral measurements of the biomaterials support the dependence of the radiative quantum efficiency on biofluid pH, as determined using the transient thermal lens signal. For nonfunctionalized (3.4 and 5.1 nm QD size) and functionalized QDs (1.6 nm) embedded in biofluid, the temporal behavior of the fluorescence signal was obtained at two different saliva pH values.Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 151, October 2015, Pages 208–212