MIT's new multiphoton, photoacoustic, label free microscope system. Tatsuya Osaki/MIT Picower Institute
For decades, scientists have pushed the limits of microscopy to capture sharper and deeper views of the brain. Traditional light-based systems can map the cortex in detail but struggle to reach deeper regions like the hippocampus without losing resolution.
The challenge is even greater when imaging molecular activity inside single cells, which is an essential step in understanding brain function and diseases.
MIT scientists and engineers have now built a microscope that overcomes this barrier by combining ultrafast light pulses with sound detection.
The system can image at depths more than five times greater than existing methods without using dyes, chemicals, or genetic modification. Researchers believe it could transform neuroscience research and surgical applications.
Seeing deeper into the brain
The study shows the system can detect NAD(P)H, a molecule linked to cell metabolism and neuronal activity, through dense brain samples. Tests included a 1.1 millimetre thick human stem cell-derived cerebral organoid and a 0.7 millimetre slice of mouse brain tissue.
“That’s when we hit the glass on the other side,” said W. David Lee, the postdoctoral researcher who designed the system, explaining that the samples were not large enough to push the technology’s true limits.
The device uses a three-photon excitation method, firing ultrashort light bursts at triple the molecule’s normal absorption wavelength. These longer wavelengths scatter less and penetrate deeper into tissue.
Most of the absorbed energy creates a rapid, microscopic thermal expansion inside the cell, generating sound waves.
A sensitive ultrasound microphone detects these waves, and software turns them into sharp images. This process is called three-photon photoacoustic imaging.
Merging advanced imaging techniques
The team combined three-photon excitation, photoacoustic detection, and label-free imaging into a platform they call “Multiphoton-In and Acoustic-Out.” This setup allows precise molecular detection without altering the tissue.
The system can also identify other molecules, such as GCaMP, a calcium indicator used to track neural activity. Additionally, “third-harmonic generation” imaging maps cellular structures, giving structural and molecular detail in the same scan.
Co-lead author Tatsuya Osaki from The Picower Institute said the aim was to combine advanced techniques into one efficient process.
This capability could help study conditions where NAD(P)H levels change, including Alzheimer’s disease, Rett syndrome, and seizures.
Because it works without labels, it could also guide brain surgeries by mapping activity in real time.
The next goal is to test the system in living animals. In this case, both the light source and microphone will need to be on the same side of the tissue instead of opposite sides.
Lee expects the system could image up to 2 millimetres deep in live brains. “In principle it should work,” he said.
Lee’s earlier work through Precision Healing Inc. showed that NAD(P)H imaging can guide wound treatment. Now, the same approach may prove valuable for neurosurgery and brain research.
The project was funded by the National Institutes of Health, the Simon Center for the Social Brain, The Picower Institute, and other sources.
MasterCard
