Jacob Hoogenboom, TUE

Title: Photo-darkening and photo-brightening of bio-conjugated colloidal quantum dots after electron-beam irradiation
Session: Tuesday 6 October, 17:15


We investigate fluorescence imaging of bio-functionalized colloidal quantum dots (qdots) using a focused electron beam for excitation. Qdots were conjugated to epidermal growth factor and imaged in whole cells fixated after uptake and intracellular transport. We show that the qdots can be imaged with cathodoluminescence using low-energy (<5keV) electron excitation to reduce the background signal from the underlying glass substrate. However, high-dose electron exposure leads to a darkening of the qdots, which makes it impossible to perform high magnification cathodoluminescence imaging and visualize single qdots. We use in-situ photon excitation and fluorescence detection during electron beam irradiation to monitor the state (on/off) of the quantum dots in the electron microscope. This reveals a complicated on-off switching under electron-beam exposure. Interestingly, low-dose exposures, insufficient to generate detectable cathodoluminescence signal, are found to lead to fluorescence enhancement. Higher dose exposures lead to reversible darkening and, eventually, bleaching. These results can be partly understood in terms of charge carrier dynamics and electron trapping in the quantum dot core-shell geometry, which is also linked to quantum dot fluorescence blinking.





 to be announced


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