Tag Archives: glass blowing

Nanoparticle detection with whispers and bubbles

Caption: A magnified photograph of a glass Whispering Gallery Resonator. The bubble is extremely small, less than the width of a human hair. Credit: OIST (Okinawa Institute of Science and Technology Graduate University)

It was the reference to a whispering gallery which attracted my attention; a July 11, 2018 news item on Nanowerk is where I found it,

Technology created by researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) [Japan] is literally shedding light on some of the smallest particles to detect their presence – and it’s made from tiny glass bubbles.

The technology has its roots in a peculiar physical phenomenon known as the “whispering gallery,” described by physicist Lord Rayleigh (John William Strutt) in 1878 and named after an acoustic effect inside the dome of St Paul’s Cathedral in London. Whispers made at one side of the circular gallery could be heard clearly at the opposite side. It happens because sound waves travel along the walls of the dome to the other side, and this effect can be replicated by light in a tiny glass sphere just a hair’s breadth wide called a Whispering Gallery Resonator (WGR).

A July 11, 2018 OIST press release by Andrew Scott (also on EurekAlert), provides more details,

When light is shined into the sphere, it bounces around and around the inner surface, creating an optical carousel. Photons bouncing along the interior of the tiny sphere can end up travelling for long distances, sometimes as far as 100 meters. But each time a photon bounces off the sphere’s surface, a small amount of light escapes. This leaking light creates a sort of aura around the sphere, known as an evanescent light field. When nanoparticles come within range of this field, they distort its wavelength, effectively changing its color. Monitoring these color changes allows scientists to use the WGRs as a sensor; previous research groups have used them to detect individual virus particles in solution, for example. But at OIST’s Light-Matter Interactions Unit, scientists saw they could improve on previous work and create even more sensitive designs. The study is published in Optica.

Today, Dr. Jonathan Ward is using WGRs to detect minute particles more efficiently than ever before. The WGRs they have made are hollow glass bubbles rather than balls, explains Dr. Ward. “We heated a small glass tube with a laser and had air blown down it – it’s a lot like traditional glass blowing”. Blowing the air down the heated glass tube creates a spherical chamber that can support the sensitive light field. The most noticeable difference between a blown glass ornament and these precision instruments is the scale: the glass bubbles can be as small as 100 microns- a fraction of a millimeter in width. Their size makes them fragile to handle, but also malleable.

Working from theoretical models, Dr. Ward showed that they could increase the size of the light field by using a thin spherical shell (a bubble, in other words) instead of a solid sphere. A bigger field would increase the range in which particles can be detected, increasing the efficacy of the sensor. “We knew we had the techniques and the materials to fabricate the resonator”, said Dr. Ward. “Next we had to demonstrate that it could outperform the current types used for particle detection”.

To prove their concept, the team came up with a relatively simple test. The new bubble design was filled with a liquid solution containing tiny particles of polystyrene, and light was shined along a glass filament to generate a light field in its liquid interior. As particles passed within range of the light field, they produced noticeable shifts in the wavelength that were much more pronounced than those seen with a standard spherical WGR.

With a more effective tool now at their disposal, the next challenge for the team is to find applications for it. Learning what changes different materials make to the light field would allow Dr Ward to identify and target them, and even control their activity.

Despite their fragility, these new versions of WGRs are easy to manufacture and can be safely transported in custom made cases. That means these sensors could be used in a wide verity of fields, such as testing for toxic molecules in water to detect pollution, or detecting blood borne viruses in extremely rural areas where healthcare may be limited.

For Dr. Ward however, there’s always room from improvement: “We’re always pushing to get even more sensitivity and find the smallest particle this sensor can detect. We want to push our detection to the physical limits.”

Here’s a link to and a citation for the paper,

Nanoparticle sensing beyond evanescent field interaction with a quasi-droplet microcavity by Jonathan M. Ward, Yong Yang, Fuchuan Lei, Xiao-Chong Yu, Yun-Feng Xiao, and Síle Nic Chormaic. Optica Vol. 5, Issue 6, pp. 674-677 (2018) https://doi.org/10.1364/OPTICA.5.000674

This paper is open access.

SiO2: The Science of Glass; glassblowing and glory holes

The SiO2: The Science of Glass traveling exhibit from the Montreal Science Centre opened at the Canada Science and Technology Museum on Nov. 5, 2011 and can be seen until April 9, 2012.

I wonder if there’s any chance the exhibit will travel to the West Coast? I have a longstanding interest in glass and notice the images from the Montreal Science Centre website look quite interesting. Here’s a sample,

Glass from the Libyan Desert (Verre du désert Libyen) © Denis Farley

Here’s a synopsis of the show from the Montreal Science Centre website,

Discover the origins and surprising physical and chemical properties of glass. SiO2: The Science of Glass tells us about the various types of glass, their properties, and about the many methods used in producing glass on an industrial scale. It also explains the role glass has played in the history of civilisation and reminds us of its daily uses. From its production at an industrial scale to its leading-edge innovations, glass will shine through its ubiquitous brilliance and contrasts.

In a Nov. 1, 2010 posting I featured an essay about glass (Heavenly illumination: The science and magic of stained glass [link to original essay on Guardian science blog]) by Andy Connelly, here’s an excerpt about the science of glass from my posting which includes a comment from me,

So what is a glass? Why can we see through it when other materials are opaque? Glasses exist in a poorly understood state somewhere between solids and liquids. [If I ever knew that interesting fact, I’ve long since forgotten it.] In general, when a liquid is cooled there is a temperature at which it will “freeze”, becoming a crystalline solid (eg. water into ice at 0C). Most solid inorganic materials are crystalline and are made up of many millions of crystals, each having an atomic structure which is highly ordered, with atomic units tessellating throughout. The shape of these units can be observed in the shape of single crystals (eg. hexagonal quartz crystals).

Glass is different: it is not crystalline but made up of a continuous network of atoms that are not ordered but irregular and liquid-like. This difference in atomic structure occurs because the liquid glass is cooled so quickly that the atoms do not have time to arrange themselves into regular, crystal-like patterns.

If cooled fast enough almost any liquid can form glass, even water. However, the rate of cooling must be very fast. Fortunately for us, liquids composed primarily of silicon oxide [SiO2] can be cooled slowly and still form a glass.

A few months later I found a brief bit accompanied by  a video about glass on the Guardian science blogs, this time about scientific and art glass blowing, from the news bit by Alex Rappaport and Kiva Ford highlighting Ford’s video of his work,

Aside from Mr Ford’s pastime of creating miniature distillation vessels and delicately curlicued glass jewelry, his day job is as a scientific glassblower, creating extractors, reactors, condensers, and a variety of custom flasks. The vessels used in chemical research cannot be mass produced; each piece has been meticulously handcrafted for thousands of years.

Here’s the video,

I found the information about the decline of science glass blowing a little saddening although Ford seems to feel that there’ll always be a demand for custom work. Amazingly, he works during the day as a scientific glass blower and then goes home to create art glass. I loved his animal series (the detail is amazing).

Years ago, I came across a new media piece about glass and the glory hole. I gather it’s a furnace where you finish your glass. The term exerts a fascination for me and I found this video about glass and glory holes (there is a commercial at the beginning but if you persist I think you’ll find the video amusing),

Happy Weekend!