Researchers at Delft University of Technology have demonstrated for the first time that nano-antennas can enhance the fluorescence of proteins in living human and other mammalian cells. Scientists already use smart fluorescent proteins that light up when the electrical voltage across a nerve cell changes. By placing nano-antennas close to these light-emitting proteins, researchers can monitor processes inside cells with much greater precision. The discovery adds a new tool for revealing electrical signals in the brain: through nanotechnology as well as genetic engineering. The research has been published in Advanced Materials .
Monitoring signals in the brain requires both high resolution and rapid imaging. "Existing methods for visualising voltage changes in cells often do not produce enough light, or they do not respond quickly or strongly enough to the small electrical pulses that occur at synapses," says principal investigator Daan Brinks.
First authors Marco Locarno and Qiangrui Dong achieved a breakthrough by placing nano-antennas extremely close to fluorescent voltage-sensitive proteins. This made the proteins up to six times brighter, allowing researchers to monitor processes in living mammalian cells with much greater precision. Importantly, the cells remained alive and continued to function normally throughout the measurements.
An idea from nanotechnology
"It has long been known in nanophotonics that metallic nanoparticles, known as plasmonic nano-antennas, can enhance light extremely locally," says Brinks. "So we started with a simple question: what happens if you place such a nano-antenna very close to a fluorescent protein?"
Achieving the precise positioning required to enhance fluorescence had not previously been accomplished in more complex living systems. "The nanoparticles need exactly the right shape and size to enhance light without disturbing the cell," Brinks explains. "They must be chemically stable and end up in precisely the right place in a living cell, close to the protein that detects electrical signals. Achieving that requires a delicate combination of simulations, chemistry and biological experiments."
Enhancing light in living cells
After extensive design work and experimentation, researchers in the Brinks Lab succeeded in demonstrating brighter protein fluorescence in living, functioning mammalian cells for the first time. "Scientists had previously only achieved this in single-molecule measurements, not with proteins that functionally respond to processes inside the cell," says Brinks. "We can now perform biological measurements involving multiple protein molecules."
Brighter and faster
The voltage-sensitive proteins did more than simply become brighter. They also responded around ten times faster to changes in electrical voltage. This came as a surprise. For years, researchers had attempted to optimise these proteins through genetic engineering, achieving only limited improvements in response speed. It turned out that the proximity of a nanoparticle made an entirely new level of acceleration possible.
A new nanotechnology tool
The discovery introduces a new tool: light-sensitive proteins can now be modified not only through genetic engineering, but also through smart nanostructures. This offers a new way to manipulate protein function. "In the case of the protein we use in this study, our approach enables faster recording of signals in the brain," says Brinks. "But the same principle could potentially be applied to proteins involved in signalling in the eye, for example in the presence of defects, or to proteins that can be programmed to transport substances within cells."
What began as a curiosity-driven idea in nanotechnology also proves valuable for brain research. Faster and locally enhanced signals make it possible to measure electrical activity at the scale of synapses, the sites where neurons exchange information. In the longer term, this technology could help address fundamental questions about the brain: how does it process information? What happens at the microscopic level during learning and memory formation? And how are these processes disrupted in neurological disorders?
For this research, the Brinks Lab collaborated with the TU Delft Reactor Institute , the Liedewij Laan Lab , and the Chien Lab at Erasmus MC.
