Synthesis and Study of pH Independent L-Cysteine Capped Zirconium Oxide Quantum Dots as a Potential Bio-Imaging Probe Using HeLa Cells.

Here we propose an eco-friendly hydrothermal approach to synthesise fluorescent L-cysteine capped zirconium oxide quantum dots (L-Cys-ZrO₂ QDs). The UV-Vis absorption, PL-emission, pH independence, size, functional group attached over surface QDs, binding energy, and stability of QDs in aqueous solvent were systematically studied. The TEM results revealed the mean particle size ∼5.7 nm of QDs. The synthesised QDs have UV-Vis absorption peaks at 320 nm, 265 nm, and 245 nm with PL emission from 360 nm to 500 nm and have a quantum yield ∼3.6%. The functional groups attached over surface of QDs such as -CO, -NH₂, SO₄^-- etc. were confirmed by FT-IR spectrum which were supported by XPS spectrum analysis. An in-vitro optical bio-imaging method was employed, focusing on cancer cell line such as HeLa Cells as a model cell. Cytotoxicity is analysed using MTT assay showing that QDs are biocompatible in nature. The photoluminescence properties of the synthesized L-Cys-ZrO₂ QDs were examined on the HeLa cells under green laser. The quantum dots proved to be effective labels for bioimaging as evidenced by strong emission when observed under a confocal fluorescence microscope by green laser.