Detecting Neural Activity in Near-Infrared Light

Detecting Neural Activity in Near-Infrared Light
This image shows overlay of near-infrared fluorescence of calcium biosensor (purple pseudocolor) and blood oxygenation (rainbow pseudocolor) in the brain of a living mouse. It was made using a hybrid fluorescence and photoacoustic microscope developed by Dr. Verkhusha and Dr. Junjie Yao from Duke University, a co-author on the paper. Oxygenation levels range from low (blue) to high (red).

The ability of fluorescent proteins (FPs) to serve as building blocks of biosensors allows scientists to observe normal and pathological biological processes in live cells in real time. FPs that emit visible light were previously available, but only recently have FPs glowing in the near-infrared spectrum been developed by Vladislav Verkhusha, Ph.D., and his group.

In a study published online on October 26 in Nature Biotechnology, Dr. Verkhusha and colleagues report the next advance in optical imaging. Using two near-infrared FPs, they have engineered a calcium biosensor that can detect evoked and spontaneous calcium fluxes in the brain, which is an indicator of neural activity. The biosensor is stimulated by and emits near-infrared light, which penetrates deeply in biological tissues with minimally scatter; this allows scientists to non-invasively observe activity in neurons deep within living animals. It is the only calcium biosensor developed so far that operates in the near-infrared range.

The near-infrared calcium biosensor can be combined with biosensors functioning in visible light, allowing for spectral “crosstalk-free” imaging of several simultaneous biochemical intracellular processes. In addition, so called all-optical assays can be conducted in which a photoreceptor uses light of one wavelength to activate an intracellular biochemical process, and the biosensor detects the resulting cellular perturbation in another wavelength range.

Dr. Verkhusha and his team constructed a hybrid microscope combining fluorescence and photoacoustic imaging. The hybrid microscope can “see through” the skulls of living mice, simultaneously using the near-infrared calcium biosensor to monitor neuronal activity and photoacoustics to track blood-oxygen levels in the brain. The new calcium biosensor should prove useful in pre-clinical studies involving animal models.

Moreover, to detect extremely fast changes in neuronal electrical activity, Dr. Verkhusha used the same pair of near-infrared FPs to develop the first near-infrared fluorescent membrane voltage biosensor, described online on October 16 in ACS Chemical Neuroscience.

Dr. Verkhusha is a professor of anatomy & structural biology.