Saturation of two-photon excitation provides insight into the effects of a quantum dot blinking suppressant: A fluorescence correlation spectroscopy study

Abstract

Quantum dots are now extensively used as luminescent tags for biological and chemical applications; however, their propensity to display intermittent luminescence (aka blinking) has limited their use in quantitative assays. Various surface active redox agents, such as ss-mercaptoethanol, have been posited as antiblinking agents to help mitigate this challenge. We have examined the effect of ss-mercaptoethanol on the luminescence intermittency of CdSe/ZnS quantum dots using fluorescence correlation spectroscopy. We find that ss-mercaptoethanol lowers the quantum dot brightness and therefore lowers the probability of observing blinking but does not otherwise inhibit intermittent luminescence. Based on changes in fluorescence correlation data and excited-state lifetimes, we propose that the partitioning of ss-mercaptoethanol onto the quantum dot surfaces increases nonradiative de-excitation rates. This behavior appears to be independent of the quantum dot surface passivation layer or the solution contents.