Three-dimensional nano-localization of single fluorescent emitters

Spectral domain fluorescence coherence phase microscopy

Spectral domain phase microscopy (SDPM) has been reported in the literature as a functional extension to low-coherence interferometry, which enables nanoscale measurement of a scatter's displacement. The signal in SDPM is generated from structural images that lack molecular specificity. This paper investigates the expansion of phase analysis to fluorescence self-interference signals to provide functional information about a sample. Spectral domain fluorescence coherence phase microscopy is demonstrated for nanoscale resolution motion detection of fluorescent particles with a signal-to-noise ratio limited resolution of ~10 nm. This paper demonstrates the feasibility of combining phase processing with fluorescence self-interference, which may be useful for future applications such as cell rheology.

Comparison between SOFI and STORM

A straightforward method to achieve super-resolution consists of taking an image sequence of stochastically blinking emitters using a standard wide-field fluorescence microscope. Densely packed single molecules can be distinguished sequentially in time using high-precision localization algorithms (e.g., PALM and STORM) or by analyzing the statistics of the temporal fluctuations (SOFI). In a face-to-face comparison of the two post-processing algorithms, we show that localization-based super-resolution can deliver higher resolution enhancements but imposes significant constraints on the blinking behavior of the probes, which limits its applicability for live-cell imaging. SOFI, on the other hand, works more consistently over different photo-switching kinetics and also delivers information about the specific blinking statistics. Its suitability for low SNR acquisition reveals SOFI's potential as a high-speed super-resolution imaging technique.