Figure 5: Bleaching of QDs in STED nanoscopy.

(a) Fluorescence intensity against the number of scan repetitions for repeated scanning of QD images acquired with the excitation beam only (confocal), the excitation plus the STED laser and the excitation plus the STED laser alternating with the STED laser only, as necessary for later subtraction of the background owing to direct excitation by the STED laser. Excitation laser power was 21.8 μW, STED laser power was 344 mW and dwell time was 30 μs. (b) Summation of 70 scans from 1 to 70 (upper panel) and from 1,001 to 1,071 (lower panel) for all three laser settings, without subtraction of the direct excitation by the STED laser. Scale bar, 100 nm.