All-Optical Detection of Neuronal Membrane Depolarization in Live Cells Using Colloidal Quantum Dots

Area of Science:

• Nanotechnology
• Biophysics
• Materials Science

Background:

• Semiconductor quantum dots (QDs) show promise as voltage probes for cell membranes.
• Assessing QD responses in aqueous, ionic biological environments remains a challenge.
• Limited studies exist on QD voltage sensing in live cells.

Purpose of the Study:

• Develop a platform to monitor QD photoluminescence (PL) responses to AC/DC voltages in aqueous ionic media.
• Evaluate traditional CdSe/CdS and biologically compatible InP/ZnS QDs for voltage sensing.
• Establish QD PL/voltage characteristics across various ion concentrations.

Main Methods:

• Designed an on-chip platform for monitoring QD photoluminescence (PL) under applied voltages.
• Tested CdSe/CdS and InP/ZnS QDs in aqueous solutions with varying ion concentrations.
• Performed wide-field, few-particle PL measurements on neuronal cells.

Main Results:

• Demonstrated QD PL response to AC and DC voltage changes in ionic environments.
• QD imaging showed higher sensitivity (up to 2x) for local voltage changes compared to calcium dyes.
• InP/ZnS QDs exhibited lower cytotoxicity, making them more suitable for live-cell voltage sensing despite lower PL response than CdSe/CdS.

Conclusions:

• The developed platform enables rational development of QD-based voltage sensors.
• QDs offer a sensitive tool for imaging cell membrane voltage, particularly subthreshold events.
• InP/ZnS QDs are a promising candidate for in vivo voltage sensing applications.