Suppressing background noise in STED optical nanoscopy

Super-resolution microscopy or optical nanoscopy has enabled all-optical observation of nanoscopic objects with resolution beyond Abbe’s diffraction limit. STimulated Emission Depletion (STED) nanoscopy achieves diffraction-unlimited resolution by employing a de-excitation laser with a hollow core in addition to the conventional excitation laser in confocal microscopy. One of the strong unexpected adverse effects in resolution improvement in STED nanoscopy is a structured, systematic background noise, which deteriorates the desired super-resolved image. Suppressing background noise, therefore, has been an important challenge in STED nanoscopy. Here, we introduce the characteristics of the background noise in STED nanoscopy and review several recent approaches that tackle this problem. The methods will be examined in comparison to one another and the advantages and disadvantages of each method will be highlighted.