BLOGS

The study of quantum dots began in the 1980s. Quantum dots are very small amounts of semiconductor material (nanoparticles) whose size affects the allowed energy levels of the material. The electrons of the material usually reside in the lowest band of energy levels called the valence band. When the electron absorbs energy it is excited to a higher band of energy levels, levels called the conduction band, leaving behind an empty spot known as a hole. When the electron returns to the lower valence energy level it emits energy. How far apart the valence band and conduction band are depends on the size of the particle. The size of the particle controls what is known as the confinement energy, Figure 1. This means that the size of the particle can be used to control the different types of light the particles absorb and emit. Quantum dots have been created that absorb ultraviolet light and emit all of the colors of the rainbow depending on their size, rather than just what it is made of.

Quantum Dots and Cells

How does the quantum dot make a neuron fire? When a quantum dot is excited by light shining on it, it becomes polarized so that one part of the material is more positive and the other is more negative. This in turn sets up an electric field, which can interact with a neuron or other cell of interest. How strong that interaction is depends on how close the polarized quantum dot is to the cell. The closer it is, the stronger the interaction. The strength of the interaction also depends on the type of ion channel on the cell membrane. If the field set up by the quantum dot is strong enough, it can cause the ion channels to open and a transfer of ions out of and into the cell. For a neuron, this is "firing" the neuron or switching it on.