Optical far-field microscopy of single molecules with 3.4 nm lateral resolution.

Optical far-field imaging of single molecules in a frozen solution at 1.2 K with a lateral resolution of 3.4 nm is reported. The mechanical stability of the fluorescence microscope, especially of the low-temperature insert, allows for the localization of fluorescing molecules with a reproducibility of better than 5 nm within observation times up to 10 min. For observation times of 9 h the reproducibility of the lateral position is limited to about 20 nm due to mechanical drift. Lateral position and orientation of 314 single molecules, present within the confocal detection volume of approximately 10 microm(3), are obtained. The possibility to correct for mechanical drift by monitoring the position of a spatial reference in the sample is demonstrated.

High-Frequency/High-field electron spin echo envelope modulation study of nitrogen hyperfine and quadrupole interactions on a disordered powder sample

High-frequency/high-field (95 GHz/3.4 T) electron spin echo envelope modulation (ESEEM) experiments on single crystals and disordered samples of dianisyl-nitroxide (DANO) radicals are reported. At these high microwave frequencies (W-band), the anisotropic g-matrix of the nitroxide radical is resolved in the EPR spectrum. Additionally ESEEM modulations from other than nitrogen nuclei, such as protons, are highly suppressed at these frequencies, because they are too far from the cancellation condition for effective mixing of the nuclear spin functions. Therefore the nitrogen (14N) hyperfine and quadrupole coupling tensors could be determined without ambiguity from powder measurements. The results obtained were checked by ESEEM measurements on single crystals. Advantages and disadvantages of high-field ESEEM on nitrogen couplings are briefly discussed and compared with electron nuclear double resonance (ENDOR) and X-band ESEEM. Copyright 1998 Academic Press.