Energy and electron transfer between quantum dots and biomolecules

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Quantum dots have been used in biological applications as an alternative to fluorescent dyes because of their stability, brightness, and wide range of colours. However, these semiconductor nanocrystals also possess other properties that make them potentially useful as a whole new class of nanoscale biosensors: those that turn off and on (or change colour) in response to a specific process within a cell. In our previous work, we defined the types of biologically-relevant processes that might result in alterations of quantum dot fluorescence, and illustrated the use of quantum dots as sensors for redox potential within living cells. In this work, we have two specific aims: (1) to use these general principles to create a sensor for cellular membrane potential and ion flux. We will apply this to the specific case of a bacterial sodium channel, with the eventual goal of using the sensor to probe action potentials. We will determine the exact photophysical mechanisms behind the fluorescence changes seen, and thus to enable the easier creation of new classes of nanoparticle-based sensors. (2) To measure quantum dot fluorescence intermittency ("blinking") as the particles encounter living cells, are taken up, travel to different intracellular locations, and are processed. This may allow the phenomenon of blinking to be used as a truly nanoscale probe of intracellular conditions.