Energy Transfer Sensing
Our group has a variety of emissive QDs and methods to impart functional elements to their surfaces. What can we develop with this technology? It turns out that the excitation energy of a QD may be transferred to a surface bound organic fluorophore if the dye is closely bound to the QD and has an absorption profile that closely matches the emission of the QD. An interesting aspect of this work is that many dyes have absorption profiles that are environmentally sensitive- thus the local chemical environment may influence the efficiency of energy transfer from QD to dye. Shown here is a QD / dye coupled sensor for an environmentally hazardous element- mercury.
As the levels of mercury rise, the dye become more absorptive which causes energy transfer from the QD to the dye to occur. What is interesting about this work is that we have avoided the problem of the mercury ion reacting with the QD itself which quenches the QD fluorescence. Note that the sensing is ratiometric- or “self-calibrating,” which is much more useful than single response sensing elements that merely “turn-on” in the presence of selected analytes. This work was recently accepted for publication in the journal Chemical Communications. We are presently designing several types of ratiometric sensing QDs for harmful environmental contaminants.
We also have a strong interest in detecting species that are indicative of cancer. So far, we have developed sensors for pH and recently found a novel way to sense oxygen levels in a celluar media. These technologies may assist us in diagnosing the development of cancer as tumors reside in acidic, hypoxic environments. We have also imaged cancer tumors developing in mouse models.
Non-labeled Protein Sensors
Whats next? We are concerned with worldwide health epidemics where the cost of treatment is so great that it becomes prohibitive to help the ones that need it most. What do you do? Make the treatment cheaper and easier; case in point, we are developing on our energy transfer technology to develop a sensor for HIV and Cholera where the expense of synthesizing the sensor and analysis of the result are very low. So far, we have had a major breakthrough where we have been able to detect picomolar quantities of un-labeled proteins using nanocrystals that can change color in the presence of the target. Shown here is a preview of the results; there is a change in the energy transfer efficiency from a QD to a dye as a fuQDtion of protein concentration. This effect only occurs in the presence of the protein of interest.