Circular Dichroism Measurement of Single Metal Nanoparticles Using Photothermal Imaging.

Area of Science:

• Optical Spectroscopy
• Nanotechnology
• Chiroptical Techniques

Background:

• Circular dichroism (CD) spectroscopy is vital for analyzing chiral molecules and materials.
• Conventional CD signals are weak, limiting studies to large molecular ensembles.
• Protein secondary structure and conformational states are routinely assessed using CD.

Purpose of the Study:

• To develop a highly sensitive technique for detecting chiral nano-objects.
• To overcome the signal-to-noise limitations of traditional circular dichroism spectroscopy.
• To enable the study of individual chiral nanostructures.

Main Methods:

• Experimental realization of photothermal circular dichroism (CD).
• Integration of CD's enantioselective signal with photothermal microscopy's sensitivity.
• Study of single plasmonic nanostructures in the visible spectrum.

Main Results:

• Achieved a signal-to-noise ratio exceeding 40 for chiral nanostructures with 30 ms integration time.
• Quantified CD signals for individual nanoparticles.
• Distinguished relative absorption differences as low as g_min = 4 × 10^-3 for polarized light.

Conclusions:

• Photothermal CD significantly enhances sensitivity for detecting chiral nano-objects.
• The technique allows for the study of single nanostructures, a breakthrough for CD spectroscopy.
• Opens new avenues for chiroptical studies with significantly lower molecule counts.