Visualizing Dose-Dependent Spike Protein Uptake with Quantum Dot Conjugates

Begin with a multi-well plate containing a culture of adherent mammalian cells.

These cells are engineered to express the human angiotensin-converting enzyme 2 receptor, tagged with green fluorescent protein (ACE2-GFP).

Remove the culture medium.

Wash the cells with an imaging medium to eliminate residual culture medium.

Prepare serial dilutions of quantum dot-spike (QD-Spike), in the imaging medium supplemented with a blocking agent to minimize nonspecific binding.

QD-Spike mimics a pseudovirus composed of fluorescent quantum dots conjugated to coronavirus spike proteins.

Add each dilution to a separate well and incubate.

The spike proteins bind specifically to the ACE2-GFP receptors on the host cell membrane.

This interaction triggers receptor-mediated endocytosis, leading to QD-Spike internalization.

After incubation, use confocal imaging to capture intracellular fluorescence signals.

Higher concentrations of QD-Spike produce stronger intracellular fluorescence, confirming concentration-dependent spike binding.

Further, co-localization of QD-Spike with ACE2-GFP confirms receptor-mediated uptake.

To prepare 0.1% BSA, add 130 microliters of 7.5% BSA to 10 milliliters of imaging media in mix. For a 6.1 to three serial dilution and triplicate add 14.26 microliters of QD Spike to 285.74 microliters of the 0.1% BSA to make the highest concentration of 20 nanomolar.

Then add 100 microliters of 20 nanomolar or QD Spike to 200 microliters of 0.1% BSA to make the second delusion of 6.67 nanomolar QD Spike. Remove all spent media from each well with a multi-channel aspirator, wash once with a multi-channel pipette with 100 microliters of imaging media per well, then aspirate 100 microliters of the imaging media. Add back 50 microliters of QD Spike solution per well and incubate the plate for three hours in a humidified incubator at 37 degree Celsius with 5% carbon dioxide.