Imaging intracellular quantum dots: fluorescence microscopy and transmission electron microscopy.

Area of Science:

• Nanotechnology
• Cell Biology
• Biophysics

Background:

• Intracellular delivery and targeting of quantum dots (QDs) are crucial for applications but remain inefficient.
• Extracellular QDs bound to the plasma membrane create background fluorescence, obscuring intracellular signals.
• Existing methods struggle to differentiate between membrane-bound and internalized QDs.

Purpose of the Study:

• To present novel methods for reducing and discriminating signal from plasma membrane-bound QDs.
• To improve the accuracy of intracellular QD imaging and applications.
• To overcome limitations in current QD delivery and detection techniques.

Main Methods:

• Photophysical approach using extracellular quenchers (QSY-21, trypan blue) to reduce extracellular QD fluorescence.
• Transmission electron microscopy (TEM) on thin cell sections to distinguish membrane-bound from intracellular QDs.
• Silver enhancement method to improve QD contrast in TEM images.

Main Results:

• Extracellular quenchers significantly reduced background fluorescence from membrane-bound QDs.
• TEM imaging of sectioned cells allowed clear discrimination between extracellular and intracellular QDs.
• Silver enhancement enhanced QD visibility in TEM, aiding in their localization.

Conclusions:

• Two effective methods, photophysical quenching and enhanced TEM imaging, can significantly improve intracellular QD signal detection.
• These methods address the challenge of background noise from extracellular QDs, enhancing imaging specificity.
• The developed techniques offer broader applicability for various fluorophores and cellular imaging studies.