Figure 1.

Schematics of different Nano-Biophotonics techniques. A) Near-field optical microscopy based on tapered, metal-coated fiber probes. Typical aperture diameters range from 50 – 100 nm. The photograph shows emission from an actual near-field tip. The white scale bar is 100 µm. B) Tip-enhanced spectroscopy uses a confocal laser spot in which a gold or silver metal tip is positioned and which enhances the electromagnetic field between tip and sample. C) Single molecule localization: the intensity distribution of a single molecule can be fit with a Gaussian fit function to achieve localization of the centroid to approximately 1.5 nm. D) Plasmon-resonant particles can be detected by dark-field white light scattering, or if they are coated with Raman active molecules, by their surface-enhanced Raman response (shown in the spectrum for Rhodamine 6G molecules attached to a 60 nm silver particle). The scale bar in the electron micrograph of a gold nanoparticle is 25 μm. E) Nano-apertures restrict the probe volume of a confocal laser spot and permit single molecule analysis at micromolar concentration. The scale bar in the electron micrograph of a square nano-aperture is 50 nm. F) SHG or upconverting particles can act as nanoscale light sources. G) Principle of structured illumination microscopy. Sample features that are smaller than the wavelength of light become visible as beat frequencies in a pattern with known periodicity. H) Principle of stimulated emission depletion microscopy. Red-shifted laser beams that overlap with the emission spectrum of the excited fluorophore deplete the emission except for the very center of the excitation beam (green).