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 β-mercaptoethanol, have been posited as antiblinking agents to help mitigate this challenge. We have examined the effect of β-mercaptoethanol on the luminescence intermittency of CdSe/ZnS quantum dots using fluorescence correlation spectroscopy. We find that β-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 β-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.