Dominic Reali with Maureen McEnery (Medical School)

Quantum Dots in Biological Imaging

 At the present, most biological imaging is done using organic fluorescent molecules (known as fluorophores).  These are coupled to antibodies which then attach to the specific protein or sample that the scientist wishes to study.  Through fluorescent microscopy, the scientist shines a light on the sample, exciting the fluorophores, which then emit a photon in order to return to ground state.  This emitted photon is has a lower energy and thus a different color from excitation photon provided by the scientist.  Thus, through the use of filters, the background light from the excitation photon can be eliminated and the scientist sees only the light from the fluorophores attached to the desired sample.

       This system, however, has some drawbacks.  For one, fluorophores are subject to photobleaching.  Over time, exposure to light will destroy the fluorophores.  Also, each fluorophore only emits a broad spectrum with a continuous range of wavelengths, potentially overlapping with the emission or absorption spectra of other fluorophores.  These problems can be resolved using quantum dots.  Semiconductor quantum dots contain a finite number of “free” electrons that can act like the electron cloud of an atom.  These electrons can be excited just like the electrons of atoms, and like those electrons, they will emit photons to return to the ground state.  The advantages here over fluorophores are that this excitation/emission interaction is not destructive and the emitted photons have discrete wavelengths due to the nature of the interaction.  In addition, quantum dots can be synthesized to emit photons of virtually any wavelength.

       Here, we are attempting to exploit these and many other advantages of quantum dots over fluorophores by coupling them to antibodies instead of fluorophores for use in biological imaging and the detection of biological toxins.