Biophysical Interactions of Silicon Quantum Dots With Human Tears and Dry Eye Drops: A Langmuir Trough Study

Silicon quantum dots (Si-QDs) have emerged for nanoscale bioimaging of the tear film. However, their biophysical impact on the tear film is unknown. This study investigates the interfacial interactions of Si-QDs with human tears and dry eye drops.

Surface pressure-area isotherms of Si-QDs, human tears, dry eye drops, and their combinations were recorded using a Langmuir Blodgett trough over a 15-75 cm² area. Samples (10 or 40 µL) were applied to the air-water interface and subjected to five compression-expansion cycles at 10 mm/min. Surface pressure was measured with a Wilhelmy plate and analyzed using the Kruskal-Wallis test with Dunn-Bonferroni correction (P < 0.05).

Amphiphilic Si-QDs exhibited higher surface pressure (30 mN/m) than hydrophilic Si-QDs (20 mN/m). Combined with tears or drops, amphiphilic Si-QDs showed enhanced interfacial retention at 10 µL, particularly with lipid-rich formulations. The highest surface pressure (50 mN/m) was observed with amphiphilic Si-QDs and Systane. Both Si-QDs demonstrated strong interfacial stability with Cationorm, whereas minimal interaction with TheraTears was observed, likely because of QD partitioning into the phosphate-buffered saline solution (PBS) subphase. At 40 µL, surface pressure decreased across all combinations.

Si-QDs are surface-active at the air-PBS interface. Amphiphilic Si-QDs interact with lipids and mimic the behavior of surfactants, whereas hydrophilic Si-QDs remain compatible with an aqueous phase.

This study highlights the potential of Si-QDs in real-time layer-specific imaging of the tear film and targeted drug delivery for dry eye disease.