Feasibility of using silicon quantum dots to image the tear film

Abstract

Purpose: The tear film has a major role in dry eye disease, however its basic dynamics including spread, replenishment and turnover are not fully understood. This experimental study aimed to investigate the feasibility of using fluroscence of silicon quantum dots (Si-QDs) doped with transition metals such as scandium (Sc-Si-QDs), copper (Cu-Si-QDs) and zinc (Zn-Si-QDs) as a contrast agent to visualise and monitor the tear film. Methods: Sc-Si-QDs, Cu-Si-QDs and Zn-Si-QDs were synthesised in solution phase and characterised using photoluminescence (emission and excitation), absorbance and transient absorption measurements. The size distribution of Si-QDs was measured by TEM images. The fluorescence characteristics of these QDs were investigated when combined with TheraTears (a balanced electrolyte formula for dry eye therapy). An optical imaging system composed of a standard slit lamp biomicroscope combined with a high-resolution Zyla sCOMS camera, SOLIS software, optical mounts and emission filters (460 nm, 510 nm and 530 nm) was used for in vitro imaging of Si-QDs with TheraTears. The stability and intensity of fluorescence of the three different Si-QDs was measured. Cytotoxicity of the Si-QDs was assessed using cultured human corneal epithelial cells by trypan blue staining and MTT assays after 24 hours of exposure. Results: The average size of Si-QDs was 2.65 nm, which is desirable for visible photoluminescence. In vitro imaging of Sc-Si-QDs and Cu-Si-QDs indicated their stable and bright fluorescence with TheraTears. However, Sc-Si-QDs were significantly brighter compared to Cu-Si-QDs and Zn-Si-QDs, and the Zn-Si-QDs tended to clump in TheraTears. The fluorescence of the Si-QDs was detected even at a concentration of 0.01 ug/mL with a total volume of 10 uL. Cu-Si-QDs and Sc-Si-QDs were non-cytotoxic up to 16 ug/mL and Zn-Si-QDs at 8 ug/mL. Conclusions: The fluorescence of Cu-Si-QDs and Sc-Si-QDs was higher than Zn-Si-QDs and these Si-QDs were less toxic. Cu-Si-QDs and Sc-Si-QDs were safe over a wider concentration range than Zn-Si-QDs. Zn-Si-QDs and Cu-Si-QDs showed some aggregation at certain concentrations. Sc-Si-QDs are proposed as a better option for further in vivo imaging of the tear film.