Single 5-nm quantum dot detection via microtoroid optical resonator photothermal microscopy

Area of Science:

• Physics
• Chemistry
• Materials Science
• Nanotechnology

Background:

• Label-free detection is crucial for analyzing single particles and molecules in various scientific fields.
• Fluorescence microscopy, while useful, faces limitations due to probes and photobleaching.
• Photothermal microscopy offers a sensitive, label-free alternative for detecting nanoabsorbers.

Purpose of the Study:

• To develop and demonstrate an ultra-sensitive photothermal microscopy platform for label-free detection of single nanoparticles.
• To detect 5nm quantum dots (QDs) with high signal-to-noise ratio using microtoroid resonators.
• To establish a new benchmark for heat dissipation detection sensitivity in nanoscale imaging.

Main Methods:

• Integration of microtoroid optical resonators with photothermal microscopy.
• Point-by-point scanning with a low-amplitude modulated pump laser.
• Utilizing proportional-integral-derivative controller output for signal processing to enhance stability and reduce noise.

Main Results:

• Successful spatial detection of single 5nm quantum dots with a signal-to-noise ratio exceeding 10^4.
• Demonstrated capability to detect a minimum heat dissipation of 0.75 picowatts.
• Confirmed detection of 5nm QDs through theoretical comparison and 18nm QDs via fluorescence imaging.

Conclusions:

• Microtoroid-based photothermal microscopy provides ultra-sensitive, label-free detection of nanoscale materials.
• The technique surpasses the sensitivity of single dye molecule detection.
• This advancement holds significant potential for applications in biological sciences, nanotechnology, materials science, chemistry, and medicine.