Luminescent, protein-binding and imaging properties of hyper-stable water-soluble silicon quantum dots

Abstract

Silicon quantum dots (SiQDs) bear the advantages of photostability and biocompatibility, but their synthesis and purification are relatively complex, and explorations on their protein-binding behaviors are very limited. Herein, water-soluble amino-terminated SiQDs were firstly synthesized in the absence of any extra reductants or catalysts. The absorption of synthesized SiQDs covered the entire UV band with the maximum absorption wavelength around 290 nm. Both their powder and solution emitted strong blue fluorescence when excited by UV light of 365 nm. The luminescent property of SiQDS aqueous solution was stable under broad regions of acidity (pH 1–12) and temperature (0–80 °C), which was also not affected by proteins. The SiQDs could bind with human serum albumin (HSA) through hydrogen bonds, which made fluorescence resonance energy transfer and quenching occur. The interaction mechanisms were analyzed through fluorescence lifetime decay curves, UV spectra, thermodynamics, and molecular surface modeling. The structural alterations were systematically deciphered by 3D fluorescence and circular dichroism spectra. Meanwhile, the cytotoxicity and cell fluorescence imaging performance were investigated using human cervical carcinoma cell lines (HeLa). The results suggested an exciting prospect of as-synthesized SiQDs in fluorescence imaging and related biomedical applications.