Arnspang Christensen, E., Kulatunga, P., & Lagerholm, B. C.
Department of Physics and Chemistry and MEMPHYS – Centre for Bio-membrane Physics, University of Southern Denmark, Odense M, Denmark, Department of Physics, Hobart and William Smith Colleges, Geneva, New York, United States of America.
Quantum dots (QDs) are very attractive probes for multi-colour fluorescence imaging in biological applications because of their immense brightness and reported extended photo-stability. We report here however that single QDs, suitable for biological applications, that are subject to continuous blue excitation from a conventional 100 W mercury arc lamp will undergo a continuous blue-switching of the emission wavelength eventually reaching a permanent dark, photo-bleached state. We further show that β-mercaptoethanol has a dual stabilizing effect on the fluorescence emission of QDs: 1) by increasing the frequency of time that a QD is in its fluorescent state, and 2) by decreasing the photo-bleaching rate. The observed QD colour spectral switching is especially detrimental for multi-colour single molecule applications, as we regularly observe spectral blue-shifts of 50 nm, or more even after only ten seconds of illumination. However, of significant importance for biological applications, we find that even small, biologically compatible, concentrations (25 µM) of β-mercaptoethanol has a significant stabilizing effect on the emission colour of QDs, but that greater amounts are required to completely abolish the spectral blue shifting or to minimize the emission intermittency of QDs.
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