Cell Imaging Using Two-Photon Excited CdS Fluorescent Quantum Dots Working within the Biological Window

Area of Science:

• Nanotechnology
• Biomedical Engineering
• Materials Science

Background:

• Semiconductor quantum dots (QDs) are investigated for optical bioimaging due to their long excitation wavelength, enabling deeper penetration and higher resolution.
• Two-photon excitation (TPE) with QDs offers advantages in bioimaging by utilizing longer excitation wavelengths.

Purpose of the Study:

• To synthesize water-soluble Cadmium Sulfide (CdS) quantum dots (QDs) using a hydrothermal method.
• To evaluate the potential of these CdS QDs for cellular imaging of human liver hepatocellular carcinoma (HepG2) cells.
• To investigate the optical properties and biocompatibility of the synthesized CdS QDs.

Main Methods:

• Hydrothermal synthesis of water-soluble CdS QDs.
• First-principles calculations to understand the electronic structure and band gap.
• In vitro studies using HepG2 cells for uptake and cell viability assays.
• Two-photon excited scanning microscopy for imaging.

Main Results:

• Synthesized CdS QDs exhibit red-shifted fluorescence attributed to S-rich defect states and deep defect states emission.
• Large Stokes shifts (>200 nm) minimize crosstalk between excitation and emission light.
• CdS QDs demonstrate good biocompatibility and low toxicity in HepG2 cells.
• Two-photon microscopy revealed bright red upconversion fluorescence in HepG2 cells, 38.2 times brighter than the control.

Conclusions:

• CdS QDs possess favorable optical properties, including large Stokes shifts and red fluorescence emission, suitable for bioimaging.
• The synthesized CdS QDs exhibit excellent biocompatibility and low toxicity, making them safe for cellular applications.
• These findings support the application of CdS QDs as effective fluorescent probes for cellular imaging, particularly in HepG2 cells.