To effectively treat a variety of neurological ailments and make further advancements in our understanding of the brain depends on our ability to examine thethe brain in ever-greater detail. Imaging the voltage generated from the firing of neurons on the micron scale can helps us understand how neural networks grow, alter, and function over time. Unfortunately, the smallest electrodes currently available cannot reliably distinguish signal from individual neurons, which are about 20 millionths of a meter in size. Therefore it remains challenging to understand the networks of connections between them. For more than 2 decades, no significant technological improvement has been made in this regard.
Diamond voltage microscope
A novel high-speed, high-resolution, and scalable voltage imaging platform called a diamond voltage imaging microscope using diamond-based quantum sensors was introduced in a recent study published in Nature Photonics. The device, which was created by a team of physicists from the Universities of Melbourne and RMIT, uses the nitrogen vacancy (NV) color center to convert voltage signals directly into optical signals, allowing the observation of electrical activity as it takes place. A high-density thin layer of NV centers at the diamond surface is highly sensitive to voltage outside the diamond. These near-surface NV centers are strongly affected by the surface of the diamond. The crystal structure of the diamond usually ends with hydrogen and oxygen atoms at the surface.
Surface control and modification
There is a “Goldilock’s” amount of hydrogen that should be at the surface. If there is too much, the optical signals from NV centers are too dark to be seen. When there is insufficient hydrogen, the NV centers become so intense that they produce too much background. The Australian team created an electrochemical technique for carefully removing hydrogen in order to reach this zone. This allowed them to obtain voltage sensitivities that were two orders of magnitude higher than those that had previously been reported.
Another technology they took advantage of was nanostructuring. Creating “nanopillars” on the surface guides the light from the fluorescent NV centers to high-speed recording cameras which greatly amplifies the optical signal they receive. To test their device, they used a minuscule wire that was 10 times smaller than a human hair to generate small voltages at the diamond surface in salty water.
Spatial-resolution on the neuron level
The spatial resolution, sensitivity, and stability of the device is unprecedented. The next step will be to record activity from cultured neuron. This device will be a powerful tool for researchers in the development of treatments for neurological and neurodegenerative diseases.
To understand more about the biological applications of quantum sensing, reach out to our technology specialist Fleming Bruckmaier!