Single molecules observed by near-field scanning optical microscopy.

Area of Science:

• Optics and Photonics
• Molecular Imaging
• Nanotechnology

Background:

• Sub-monolayer molecular imaging presents challenges in sensitivity and spatial resolution.
• Understanding near-field optical phenomena requires precise molecular localization and orientation determination.

Purpose of the Study:

• To demonstrate the capability of near-field scanning optical microscopy (NSOM) for imaging individual dye molecules.
• To determine the spatial localization, sensitivity, and dipole orientation of imaged molecules.
• To utilize molecular imaging for mapping electric field distributions in NSOM apertures.

Main Methods:

• Utilized near-field scanning optical microscopy (NSOM) to image carbocyanine dye molecules in a sub-monolayer.
• Achieved high spatial localization of approximately lambda/50 (where lambda is the wavelength of light).
• Quantified detection sensitivity at a minimum of 0.005 molecules/(Hz)(1/2) and determined molecular dipole orientation.

Main Results:

• Successfully imaged individual carbocyanine dye molecules repeatedly.
• Demonstrated high-precision spatial localization and sensitive molecule detection.
• Determined the orientation of each molecular dipole within the imaged area.
• Mapped the electric field distribution in the near-field aperture with molecular spatial resolution.

Conclusions:

• NSOM enables high-resolution imaging and characterization of individual dye molecules.
• Molecular dipole orientation and localization provide insights into near-field optical properties.
• This technique offers a pathway for detailed mapping of electric fields at the nanoscale.