European researchers have recently conducted a study showcasing the potential of highly sensitive sensors utilizing color centers in diamonds to capture electrical activity from neurons within living brain tissue. Published in Scientific Reports, this research aims to delve into the subtle changes occurring in the brain before noticeable symptoms of diseases like dementia manifest.
Prior to the onset of brain disease symptoms, subtle alterations take place in the brain tissue, such as swelling or the formation of protein clumps. These minute changes can impact how nerve cells signal and communicate, influencing information processing and memory.
Medical scientists aspire to investigate these early-stage changes to gain deeper insights into disease causes and develop more effective treatments. Presently, microscopic brain studies employ two primary strategies: optical examination of brain tissue samples from either animals or deceased patients affected by the studied disease, or measurements of nerve cell signals using wires, coloring, or light.
However, these methods have limitations. They may potentially damage tissue, alter signals, or operate differently based on the tissue being studied. Some signals from specific parts of nerve cells involved in a particular disease might prove challenging to measure using existing techniques.
Measuring the field, not the sample
Collaborative efforts from scientists at DTU, the University of Copenhagen, Copenhagen University Hospital, Université Sorbonne, and Leipzig University have yielded a groundbreaking method to measure brain tissue signals without the need for invasive procedures like needle probes. Instead, they detect weak magnetic fields generated by nerve cells during communication, exploiting the fact that these magnetic fields travel through the tissue unaltered.
The non-invasive nature of this approach eliminates the necessity for inserting electrodes or probes into the tissue or applying stains for analysis. Alexander Huck, Associate Professor at DTU Physics and project supervisor, highlights that by capturing the induced magnetic field, valuable information about activity can be obtained without physically altering the system.
While measuring induced magnetic fields in the human body is not entirely new, traditional methods involve bulky equipment requiring cryogenic cooling, rendering them unsuitable for small living tissue samples, especially those from the human brain. In this innovative project, scientists leverage minute, purposeful imperfections in synthetic diamond crystals known as color centers or nitrogen-vacancy centers (NV centers). These NV centers, created by replacing a carbon atom with a nitrogen atom adjacent to a vacancy in the diamond lattice, enable light absorption and emission.
Huck explains that these NV color centers possess an effective unpaired electron with a spin. In the presence of a magnetic field, the electron's spin oscillates around that field. Consequently, changes in the magnetic field result in corresponding changes in the oscillation speed, which can be measured through the light emission of the NV color centers. This novel technique opens doors to studying brain tissue with unprecedented precision and minimal intrusion.
Still at an early stage
The experimental configuration involves placing a slice of mouse brain tissue on insulating layers of aluminum foil within a centimeter-scale chamber. Beneath these layers, a diamond with color centers is positioned in a cavity at the chamber's bottom. To initiate the experiment, a green laser and a microwave antenna target the diamond's color center, and the ensuing light emission is recorded. Despite the brain tissue being the focus, neither the laser light nor the microwaves directly reach it; instead, changes in the magnetic field are monitored through the NV color centers.
“When neurons in the brain tissue sample fire, they induce a magnetic field that alters the light emission and the diamond's brightness. We capture this as an optical signal,” explains Huck.
The researchers demonstrate their ability to discern signals from various types of nerve cells in the experiments. To validate their findings, they cross-checked measurements with a conventional technique involving direct contact with the tissue, measuring electricity. Additionally, they illustrate their capability to artificially modify neuron activity using a drug that blocks specific channels in nerve cells.
The ultimate vision is to apply methods derived from these experiments to diagnose specific neurodegenerative diseases in patients. However, Huck underscores the need for considerable additional work before this becomes a reality, acknowledging the current superiority of established techniques over this nascent field. While the potential for using NV centers in clinical settings exists, the research is in its early stages, demanding further exploration and refinement.