Using a new type of low-power, compact, fluid-based prism to steer the beam in a laser scanning microscope could transform brain imaging and help researchers learn more about neurological conditions such as Alzheimer’s disease.

The “electrowetting prism” utilized was developed by a team led by Juliet Gopinath from the electrical, computer and energy engineering and physics departments at the University of Colorado at Boulder (CU Boulder) and Victor Bright from CU Boulder’s mechanical engineering department, as part of their ongoing collaboration on electrically controllable optical elements for improving microscopy techniques.

“We quickly became interested in biological imaging, and work with a neuroscience group at University of Colorado Denver Anschutz Medical Campus that uses mouse models to study neuroscience,” Gopinath tells Physics World. “Neuroscience is not well understood, as illustrated by the neurodegenerative diseases that don’t have good cures. So a great benefit of this technology is the potential to study, detect and treat neurodegenerative diseases such as Alzheimer’s, Parkinson’s and schizophrenia,” she explains.

The researchers fabricated their patented electrowetting prism using custom deposition and lithography methods. The device consists of two immiscible liquids housed in a 5 mm tall, 4 mm diameter glass tube, with a dielectric layer on the inner wall coating four independent electrodes. When an electric field is produced by applying a potential difference between a pair of electrodes on opposite sides of the tube, it changes the surface tension and therefore the curvature of the meniscus between the two liquids. Light passing through the device is refracted by a different amount depending on the angle of tilt of the meniscus (as well as on the optical properties of the liquids chosen), enabling beams to be steered by changing the voltage on the electrodes.

Beam steering for scanning in imaging and microscopy can be achieved via several means, including mechanically controlled mirrors, glass prisms or acousto-optic deflectors (in which a sound wave is used to diffract the light beam). But, unlike the new electrowetting prisms, these methods consume too much power and are not small or lightweight enough to be used for miniature microscopy of neural activity in the brains of living animals.

In tests detailed in Optics Express, the researchers integrated their electrowetting prism into an existing two-photon laser scanning microscope and successfully imaged individual 5 µm-diameter fluorescent polystyrene beads, as well as large clusters of those beads.

They also used computer simulation to study how the liquid–liquid interface moved, and found that when a sinusoidal voltage is used for actuation, at 25 and 75 Hz, standing wave resonance modes occur at the meniscus – a result closely matched by a subsequent experiment that showed resonances at 24 and 72 Hz. These resonance modes are important for enhancing device performance since they increase the angle through which the meniscus can tilt and thus enable optical beams to be steered through a greater range of angles, which helps minimize distortions when raster scanning in two dimensions.

Bright explains that this research built on previous work in which an electrowetting prism was used in a benchtop microscope to image a mouse brain. He cites seeing the individual neurons as a standout moment that, coupled with the current results, shows their prism is now “proven and ready to go”.

Gopinath and Bright caution that “more work is needed to allow human brain scans, such as limiting voltage requirements, allowing the device to operate at safe voltage levels, and miniaturization of the device to allow faster scan speeds and acquiring images at a much faster rate”. But they add that miniaturization would also make the device useful for endoscopy, robotics, chip-scale atomic clocks and space-based communication between satellites.

The team has already begun investigating two other potential applications: LiDAR (light detection and ranging) systems and optical coherence tomography (OCT). Next, the researchers “hope to integrate the device into a miniaturized microscope to allow imaging of the brain in freely moving animals in natural outside environments,” they say. “We also aim to improve the packaging of our devices so they can be integrated into many other imaging systems.”

The post Fluid-based laser scanning technique could improve brain imaging appeared first on Physics World.

It’s Halloween today and so what better time than to bring you a couple of spooky stories from the world of physics.

First up is researchers at the University of Georgia in the US who have confirmed that six different species of bats found in North America emit a ghoulish green light when exposed to ultraviolet light.

The researchers examined 60 specimens from the Georgia Museum of Natural History and exposed the bats to UV light.

They found that the wings and hind limbs of six species – big brown bats, eastern red bats, Seminole bats, southeastern myotis, grey bats and the Brazilian free-tailed bat – gave off photoluminescence with the resulting glow being a shade of green.

While previous research found that some mammals, like pocket gophers, also emit a glow under ultraviolet light, this was the first discovery of such a phenomenon for bats located in North America.

The colour and location of the glow on the winged mammals suggest it is not down to genetics or camouflage and as it is the same between sexes it is probably not used to attract mates.

“It may not seem like this has a whole lot of consequence, but we’re trying to understand why these animals glow,” notes wildlife biologist Steven Castleberry from the University of Georgia.

Given that many bats can see the wavelengths emitted, one option is that the glow may be an inherited trait used for communication.

“The data suggests that all these species of bats got it from a common ancestor. They didn’t come about this independently,” adds Castleberry. “It may be an artifact now, since maybe glowing served a function somewhere in the evolutionary past, and it doesn’t anymore.”

Thread lightly

In other frightful news, spider webs are a classic Halloween decoration and while the real things are marvels of bioengineering, there is still more to understand about these sticky structures.

Many spider species build spiral wheel-shaped webs – orb webs – to capture prey, and some incorporate so-called “stabilimenta” into their web structure. These “extra touches” look like zig-zagging threads that span the gap between two adjacent “spokes,” or threads arranged in a circular “platform” around the web’s centre.

The purpose of stabilimenta is unknown and proposed functions include as a deterrence for predatory wasps or birds.

Yet Gabriele Greco of the Swedish University of Agricultural Sciences and colleagues suggest such structures might instead influence the propagation of web vibrations triggered by the impact of captured prey.

Greco and colleagues observed different stabilimentum geometries that were constructed by wasp spiders, Argiope bruennichi. The researchers then performed numerical simulations to explore how stabilimenta affect prey impact vibrations.

For waves generated at angles perpendicular to the threads spiralling out from the web centre, stabilimenta caused negligible delays in wave propagation.

However, for waves generated in the same direction as the spiral threads, vibrations in webs with stabilimenta propagated to a greater number of potential detection points across the web – where a spider might sense them – than in webs without stabilimenta.

This suggests that stabilimenta may boost a spider’s ability to pinpoint the location of unsuspecting prey caught in its web.

Spooky.

The post Spooky physics: from glowing green bats to vibrating spider webs appeared first on Physics World.