A tour de force: Engineers discover new ‘all-optical’ nanoscale sensors of force

New highly responsive nanoscale force sensor

In a paper published today nature, A team led by Columbia Engineering researchers and collaborators reports the invention of a new nanoscale force sensor. They are light-emitting nanocrystals that change intensity and/or color when you push or pull on them. These “all-optical” nanosensors detect using only light, allowing for fully remote readout – no wires or connections required.

Researchers led by associate professor of mechanical engineering Jim Schuck and postdoctoral scholar Natalie Fardian-Melamed, along with the Cohen and Chan groups at Lawrence Berkeley National Laboratory (Berkeley Lab), developed nanosensors that have been implemented in The most sensitive force response and the largest dynamic range achieved among similar nanoprobes. Their force sensitivity is 100 times greater than existing optically responsive nanoparticles that use rare earth ions, and their operating range spans more than four orders of magnitude of force, a wider range – 10-100 times larger – than any All previous optical nanosensors are better.

“We anticipate that our discovery will revolutionize the sensitivity and dynamic range achievable with optical force sensors and will immediately disrupt technology in fields ranging from robotics to cellular biophysics to medicine to space travel,” Shook said.

New nanosensors can operate in previously inaccessible environments

The new nanosensor is the first to achieve high-resolution, multi-scale functionality using the same nanosensor. This is important because it means that just this nanosensor, rather than a suite of different classes of sensors, can be used in engineering and biological systems, such as developing embryos, from subcellular to whole Continuous study of forces at the system level, migration cells, batteries or integrated NEMS, very sensitive nanoelectromechanical systems where the physical movement of nanoscale structures is controlled by electronic circuits and vice versa.

“In addition to their unparalleled multi-scale sensing capabilities, these force sensors are unique in that they operate with benign, biocompatible and deeply penetrating infrared light,” said Fardian-Melamed. “This enables Being able to gain in-depth understanding of various technical and physiological systems and monitor their health remotely will enable early detection of faults or malfunctions in these systems, which will have a profound impact on areas such as human health, energy, and sustainable development.” .

Using the photon avalanche effect to build nanosensors

The team was able to construct these nanosensors by exploiting the photon avalanche effect within nanocrystals. In photon avalanche nanoparticles, first discovered by Shook’s team at Columbia Engineering, the absorption of a single photon within the material triggers a chain reaction that ultimately results in the emission of many photons. So: one photon is absorbed, many photons are emitted. This is an extremely nonlinear and unstable process. Shuke likes to use the word “avalanche” to describe it as “dramatic nonlinearity.”

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

The team investigated a surprising observation

The researchers found that the photon avalanche process is very, very sensitive to several factors, including the spacing between the lanthanide ions. With this in mind, they whacked some photon avalanche nanoparticles (ANPs) with an atomic force microscope (AFM) tip and found that avalanche behavior was greatly affected by these mild forces – far more than they expected.

“We discovered this almost by accident,” Shook said. “We suspected that these nanoparticles were force sensitive, so we measured their emission when we tapped them. It turned out they were much more sensitive than expected! We actually didn’t believe it at first; we thought the tip might have a But then Natalie took all the control measurements and found that the responses were all due to this extreme force sensitivity.

After understanding ANP’s sensitivity, the team designed new nanoparticles that could respond to force in different ways. In a new design, nanoparticles change the color of their glow depending on the force applied. In another design, they created nanoparticles that did not exhibit photon avalanches under ambient conditions, but did begin to avalanche when force was applied — and it turned out that these nanoparticles were extremely sensitive to force.

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

what’s next

The team now aims to implement these force sensors into an important system where they can have a significant impact, such as a developing embryo, as Columbia University mechanical engineering professor Karen Kasza ) as studied. In terms of sensor design, the researchers hope to add self-calibration capabilities to the nanocrystals so that each nanocrystal can act as an independent sensor. Shook believes this could be easily accomplished by adding another thin shell during the nanocrystal synthesis process.

“The importance of developing new force sensors has recently been emphasized by 2021 Nobel Prize winner Ardem Patapoutian, who highlighted the difficulties in detecting environmentally sensitive processes in multiscale systems – that is, in most physical and biological processes. . Cell Biology, 18, 771 (2017)),” Schuck noted. “We are excited to be part of these discoveries that change the sensing paradigm, enabling sensitive and dynamic mapping of critical changes in force and pressure in real-world environments that are not possible with current technology.