New “all-optical” nanoscale force sensor accesses previously inaccessible environments

Mechanical forces are an essential feature of many physical and biological processes. Telemetry of mechanical signals with high sensitivity and spatial resolution is required for a wide range of applications, from robotics to cell biophysics and medicine, and even space travel. Nanoscale luminescent force sensors are excellent for measuring piconewton forces, and larger sensors have proven powerful for investigating micronewton forces.

However, large gaps remain in the magnitude of forces that can be studied remotely from subsurface or interfacial sites, and discrete non-invasive sensors that can make measurements over the wide dynamic range needed to understand many systems are not yet available. .

New, highly responsive nanoscale force sensors

In a paper published today in Nature, a team led by Columbia Engineering researchers and collaborators reports that they have invented a new nanoscale force sensor. These are luminescent nanocrystals that change intensity and color when pushed or pulled. These “all-optical” nanosensors are probed with light only, allowing for fully remote reading and requiring no wiring or connections.

The researchers, led by Jim Shack, associate professor of mechanical engineering, and Nathalie Fardian Melamed, a postdoctoral fellow in his group, collaborated with the Cohen group at Lawrence Berkeley National Laboratory (Berkeley Lab) and Chan Together with the group, they developed a nanosensor that met both conditions. The most sensitive force response and largest dynamic range ever achieved with similar nanoprobes.

They have 100 times better force sensitivity than existing nanoparticles that utilize rare earth ions for their optical response, with force operating ranges spanning more than four orders of magnitude and a much wider range than nanoparticles (10 to 100 times ). Conventional optical nanosensor.

“Our discovery revolutionizes the sensitivity and dynamic range achievable with optical force sensors, and we expect it to immediately disrupt the technology in fields ranging from robotics to cellular biophysics, medicine to space travel.” ,” Shook said.

New nanosensors can operate in previously inaccessible environments

The new nanosensor enables high-resolution, multiscale capabilities for the first time in the same nanosensor. This means that this nanosensor alone, rather than a series of different classes of sensors, can be used for the continuous study of forces from the subcellular level to the whole system level in engineered and biological systems such as embryonic development. It is important because it means , moving cells, batteries, or integrated NEMS, highly sensitive nanoelectromechanical systems in which the physical movement of nanometer-scale structures is controlled by electronic circuits and vice versa.

“What makes these force sensors unique, apart from their unparalleled multiscale sensing capabilities, is that they are benign, biocompatible, and operate with deep-penetrating infrared light,” says Fardian-Melamed. “This allows us to peer deeply into various technical and physiological systems and monitor health conditions from a distance. These sensors, which enable early detection of malfunctions and failures in these systems, are It will have a huge impact on areas ranging from health to energy and sustainability.” ”

Construction of nanosensor using photon avalanche effect

The research team was able to construct these nanosensors by exploiting the photon avalanche effect within nanocrystals. In photon avalanche nanoparticles, first discovered by Schuck’s group at Columbia Engineering, the absorption of a single photon within a material sets off a chain reaction that ultimately leads to the emission of many photons.

Therefore, one photon is absorbed and many photons are emitted. This is a highly nonlinear and unstable process, which Schuck likes to describe as “steeply nonlinear,” a play on the word “avalanche.”

The optically active components within the nanocrystals studied are atomic ions from the lanthanide series of elements of the periodic table, also known as rare earth elements, doped into the nanocrystals. In this paper, the team used thulium.

The researchers found that the photon avalanche process is very sensitive to several things, including the spacing between lanthanide ions. With this in mind, they tapped a piece of a photon avalanche nanoparticle (ANP) with an atomic force microscope (AFM) tip and found that the avalanche behaved much more strongly than previously expected due to these gentle forces. I discovered that I was greatly affected by this.

“We discovered this almost by accident,” Shook says. “We suspected that these nanoparticles might be sensitive to force, so we measured their release while tapping the nanoparticles, and found that they were much more sensitive than we expected. We actually couldn’t believe it at first. We thought there might be a protrusion on the tip.”But when Natalie did all the control measurements, the reactions were all this extreme. It turns out that it is due to force sensitivity. ”

Knowing how sensitive ANPs were, the team designed new nanoparticles that responded to forces in different ways. In one new design, nanoparticles change the color of their emitted light depending on the applied force. In another design, they created nanoparticles that do not exhibit photon avalanches under ambient conditions, but start avalanching when a force is applied. These turned out to be very sensitive to forces.

For this research, Schuck, Fardian-Melamed, and other members of the Schuck nano-optics team collaborated with researchers at Lawrence Berkeley National Laboratory’s Molecular Foundry (Berkeley Lab), led by Emory Chan and Bruce Cohen. I worked closely with the team. The Berkeley research team developed custom ANPs based on feedback from Columbia and synthesized and characterized dozens of samples to understand and optimize the particles’ optical properties.

what’s next

The research team is now looking to apply these force sensors to critical systems that can have significant effects, such as developing embryos, such as the one studied by Karen Kaza, a professor of mechanical engineering at Columbia University. I’m aiming for it. In terms of sensor design, the researchers hope to add self-calibration capabilities to the nanocrystals, allowing each nanocrystal to function as a standalone sensor. Schuck believes this could be easily accomplished by adding another thin shell during nanocrystal synthesis.

“The importance of developing new force sensors was recently highlighted by 2021 Nobel Prize Laureate Erdem Patapoutian. “It highlighted the difficulty of investigating biological processes,” Shook said.

“We are excited to be part of these discoveries that transform the sensing paradigm and allow us to sensitively and dynamically map significant changes in forces and pressures in real-world environments that are unreachable with today’s technology.” ”