Molecular Fluorescence in the Vicinity of a Nanoscopic Probe

Published

May 1, 2001

Author(s)

H F. Hamann, M Kuno, Alan Gallagher, David Nesbitt

Abstract

The dramatic modifications of molecular fluorescence in the proximity of a sharp nanoscopic probe is investigated by an apertureless or antenna-based near-field scanning optical microscope, which exploits the interactions between a fluorescent sample and a laser illuminated Si atomic force microscope probe. Specifically, luminescence is monitored from evanscently excited, dye-doped polystyrene nanospheres (R_s = 20-80 nm) on a fused silica prism surface as a function of probe-sample geometry. The incident laser is enhanced in the near-field of the probe tip, resulting in images with high sensitivity (ς_minnearly equal to} 2 ² in a 1 Hz detection bandwidth) and strongly subdiffraction-limited spatial resolution. At probe-sample distances greater than nearly equal to}λ/2, the images are dominated by far-field interference between (i) direct fluorescence from the molecular sample and (ii) indirect fluorescence from image dipoles induced in the atomic force microscope probe. Near-field shadowing of the molecular fluorescence by the probe also occurs and is studied as a function of probe-sample detector geometry. Finally, effects of probe-sample proximity on the fluorescence emission spectrum are investigated. In summary, the data elucidate several novel near and far-field molecular fluorescence enhancement effects relevant to further development of molecular and nonostructural spectroscopic methods with spatial resolution well below the diffraction limit.

Citation

Journal of Chemical Physics

Volume

114

Issue

No. 19

Pub Type

Journals

Keywords

apertureless scanning fluorescence micro, fluorescence, spectroscopy

Citation

Hamann, H. , Kuno, M. , Gallagher, A. and Nesbitt, D. (2001), Molecular Fluorescence in the Vicinity of a Nanoscopic Probe, Journal of Chemical Physics (Accessed October 27, 2025)