Nano Lett. 15, 6848–6854 (2015)

Semiconductor nanocrystals could potentially be used to study the electrical activity of neurons by monitoring their luminescence during a firing event. The basic principle is that an electric field affects the spatial separation of electrons and holes in nanocrystals (a phenomenon known as the quantum confined Stark effect) and, therefore, affects the time it takes for these charges to recombine and ultimately the intensity of the luminescence emitted. To put this principle into practice, however, it is essential to understand the exact mechanism of luminescence variation and, above all, whether these variations occur on a timescale comparable to the firing events. James Delehanty and colleagues at the Naval Research Laboratory in the US have now explored these issues by experimentally simulating the action of neurons on nanocrystals.

The researchers fabricated a device in which an electric field can be applied in a controlled way to a film of nanocrystals. Increasing the applied electric field leads to a reduction of the luminescence intensity. However, the time variation of the luminescence, and hence the electron–hole recombination speeds, is barely affected. According to the team, this means that the luminescence is reduced by the electric-field-induced charging of the nanocrystals, rather than by the Stark effect. It is, in fact, known that in charged nanocrystals, the recombination of electrons and holes happens primarily through a non-radiative phenomenon known as the Auger effect.

Delehanty and colleagues also simulated a realistic neuron firing event by applying to the device an electric voltage pulse recorded independently from a murine cortical neuron. The intensity of the luminescence followed the voltage profile accurately, with a total variation of up to 5% in luminescence.