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Optical characteristics of atomic force microscopy tips for single-molecule fluorescence applications
Alexander Gaiduk1, Ralf Kühnemuth, Matthew Antonik
1Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, Universitätsstrasse 1, Geb 26.32, 40225 Düsseldorf, Germany.
Summary
Optical properties of atomic force microscopy (AFM) tips were analyzed. Si3N4, silicon, and high-density carbon tips showed varying scatter and fluorescence, with signal intensity dependent on tip geometry.
Area of Science:
- Materials Science
- Optical Physics
- Nanotechnology
Background:
- Combining optical spectroscopy with atomic force microscopy (AFM) requires understanding AFM tip optical properties.
- Characterizing tip luminescence is crucial for spectroscopic applications.
Purpose of the Study:
- To characterize the optical and luminescence properties of commercial AFM tips.
- To evaluate the suitability of different AFM tip materials for combined optical and force spectroscopy.
Main Methods:
- Utilized multiparameter fluorescence detection (MFD) and scanning confocal microscopy.
- Analyzed time-decay histograms to quantify scatter, background, and fluorescence.
- Generated intensity and anisotropy images at diffraction-limited resolution.
Main Results:
- Si3N4 tips exhibited optical signals 0.7-1.9 times single Rhodamine 110 molecule rates, primarily scatter (>85%) with minor fluorescence (1-3 ns lifetime).
- Signal intensity decreased with distance from the apex, falling below single-molecule levels by 300 nm.
- Silicon tips showed low signal and minimal fluorescence; HDC tips had low signal with short fluorescence (0.7 ns).
- Tip signal intensity and anisotropy were geometry-dependent, highest at edges/corners.
Conclusions:
- AFM tip optical properties, including scatter and fluorescence, vary significantly with material and geometry.
- Understanding these properties is essential for optimizing combined optical and force spectroscopy techniques.
- Confocal illumination presents an alternative to total internal reflection for such applications.