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. Author manuscript; available in PMC: 2012 Oct 12.
Published in final edited form as: Nano Lett. 2011 Sep 13;11(10):4074–4078. doi: 10.1021/nl201225r

Figure 2.

Figure 2

Two-photon excitation response of Quantum Dots. (a) An Image of 2P excited individual QD525. Scale bar is 500 nm. QDs were conjugated to streptavidin and tethered to a BSA-biotin coated surface. Imaging buffer (DPBS, pH7.5) was supplemented with 50 mM DTT. (b) The log average emission intensity of individual QDs plotted versus log excitation power. Slope of linear fit is 1.93, indicating QDs have a predominant quadratic dependence of fluorescence on laser power, in agreement with quadratic power law dependence of two-photon excitation. At higher two-photon excitation power QDs emission is saturated and fast photobleaching occurs. (c) Blinking is near completely eliminated by adding in 50 mM DTT. (d) DTT enhances the QD emission more as its concentration increases.