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A Molecule-Thick Coating Changes What a Surface Does, Thanks to Nanoscience
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MLA Full: | "A Molecule-Thick Coating Changes What a Surface Does, Thanks to Nanoscience." YouTube, uploaded by SciShow, 1 November 2022, www.youtube.com/watch?v=otCcg8CfheQ. |
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This episode was made in partnership with The Kavli Prize. The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience and neuroscience — transforming our understanding of the big, the small, and the complex.
From removing glare in windows to making pacemakers safer, monolayers hold a number of possibilities for advances in future technology.
Hosted by: Hank Green (he/him)
SciShow is on TikTok! Check us out at https://www.tiktok.com/@scishow
----------
Support SciShow by becoming a patron on Patreon: https://www.patreon.com/scishow
----------
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:
Matt Curls, Alisa Sherbow, Dr. Melvin Sanicas, Harrison Mills, Adam Brainard, Chris Peters, charles george, Piya Shedden, Alex Hackman, Christopher R, Boucher, Jeffrey Mckishen, Ash, Silas Emrys, Eric Jensen, Kevin Bealer, Jason A Saslow, Tom Mosner, Tomás Lagos González, Jacob, Christoph Schwanke, Sam Lutfi, Bryan Cloer
----------
Looking for SciShow elsewhere on the internet?
SciShow Tangents Podcast: https://scishow-tangents.simplecast.com/
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Sources:
https://doi.org/10.1146/annurev.physchem.52.1.107
https://doi.org/10.1126/science.89.2299.60
https://doi.org/10.1021/ed061p437
https://www.sciencehistory.org/distillations/magazine/the-invisible-woman
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https://doi.org/10.1063/1.436844
https://www.cd-genomics.com/blog/introduction-to-dna-microarray-technology/
https://doi.org/10.1021/bm050180a
https://www.kavliprize.org/prizes/nanoscience/2022
http://lee.chem.uh.edu/1998/Langmv14p3815.pdf
https://doi.org/10.1016/j.progsurf.2003.12.001
https://doi.org/10.1039/D0TC00388C
https://www.sciencedirect.com/science/article/pii/S1566119918300387
https://doi.org/10.1364/OE.24.027184
https://doi.org/10.1021/ja00019a011
https://doi.org/10.1002/admi.201700316
https://link.springer.com/article/10.1007/s00253-013-5232-z
Images:
https://www.gettyimages.com/detail/video/artist-applying-red-color-on-canvas-stock-footage/1368075329
https://www.gettyimages.com/detail/video/man-sculptor-creates-sculpt-bust-clay-human-woman-stock-footage/1376840189
https://www.gettyimages.com/detail/video/scientist-is-preparation-of-nanomaterials-for-scanning-stock-footage/1196111142
https://www.gettyimages.com/detail/video/abstract-corporate-architecture-stock-footage/1338052026
https://en.wikipedia.org/wiki/File:Katharine_Burr_Blodgett_(1898-1979),_demonstrating_equipment_in_lab.jpg
https://commons.wikimedia.org/wiki/File:Langmuir-sitting.jpg
https://en.wikipedia.org/wiki/File:LBcompression.jpg
https://commons.wikimedia.org/wiki/File:Ksv-nima-medium-lb01.jpg
https://www.gettyimages.com/detail/photo/graphene-royalty-free-image/112039080
https://commons.wikimedia.org/wiki/File:Sony_oled.jpg
https://commons.wikimedia.org/wiki/File:Oled_display_alterung.jpg
https://www.gettyimages.com/detail/video/pixels-of-a-liquid-crystal-display-stock-footage/1057452344
https://www.youtube.com/watch?v=kpbPvWucNEg
https://www.youtube.com/watch?v=LZqv7Jl4iTo
https://commons.wikimedia.org/wiki/File:Surface_of_copper_oxide_(II).png
https://www.gettyimages.com/detail/video/arduino-nano-electronic-component-small-single-board-stock-footage/1368509819
https://www.gettyimages.com/detail/video/concept-video-contact-lenses-with-chip-inside-stock-footage/1312058054
https://www.gettyimages.com/detail/video/graphene-sheet-stock-footage/483199685
https://commons.wikimedia.org/wiki/File:Mixed_monolayer.jpg
https://en.wikipedia.org/wiki/File:From_spit_to_DNA-sample.webm
https://en.wikipedia.org/wiki/PDMS_stamp#/media/File:Sarfus.SoftLitho.Streptavidin.jpg
https://www.gettyimages.com/detail/video/dna-stock-footage/186901379
https://www.gettyimages.com/detail/video/ray-image-of-chest-with-artificial-cardiac-pacemaker-stock-footage/1187251785
https://www.kavliprize.org/prizes/nanoscience/2022
From removing glare in windows to making pacemakers safer, monolayers hold a number of possibilities for advances in future technology.
Hosted by: Hank Green (he/him)
SciShow is on TikTok! Check us out at https://www.tiktok.com/@scishow
----------
Support SciShow by becoming a patron on Patreon: https://www.patreon.com/scishow
----------
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:
Matt Curls, Alisa Sherbow, Dr. Melvin Sanicas, Harrison Mills, Adam Brainard, Chris Peters, charles george, Piya Shedden, Alex Hackman, Christopher R, Boucher, Jeffrey Mckishen, Ash, Silas Emrys, Eric Jensen, Kevin Bealer, Jason A Saslow, Tom Mosner, Tomás Lagos González, Jacob, Christoph Schwanke, Sam Lutfi, Bryan Cloer
----------
Looking for SciShow elsewhere on the internet?
SciShow Tangents Podcast: https://scishow-tangents.simplecast.com/
Facebook: http://www.facebook.com/scishow
Twitter: http://www.twitter.com/scishow
Instagram: http://instagram.com/thescishow
#SciShow #science #education
----------
Sources:
https://doi.org/10.1146/annurev.physchem.52.1.107
https://doi.org/10.1126/science.89.2299.60
https://doi.org/10.1021/ed061p437
https://www.sciencehistory.org/distillations/magazine/the-invisible-woman
https://lemelson.mit.edu/resources/katherine-blodgett
https://www.nanoscience.com/techniques/langmuir-films/
https://doi.org/10.1016/j.ces.2005.05.064
https://doi.org/10.1021/la00017a030
https://www.nature.com/articles/nprot.2009.234
https://doi.org/10.1166/jnn.2006.503
https://doi.org/10.1002/adma.201302283
https://doi.org/10.1021/la053152m
https://doi.org/10.1016/j.progsurf.2003.12.001
http://dx.doi.org/10.1007/s10965-006-9078-2
https://pubs.acs.org/doi/pdf/10.1021/la100956w
https://link.springer.com/article/10.1007/s10854-019-02527-y
https://www.nanoscience.com/techniques/langmuir-films/
https://doi.org/10.1039/B410027C
https://www.kavliprize.org/jacob-sagiv-autobiography
http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/J%20Ame%20Che%20Soc102,%2092.pdf
https://doi.org/10.1063/1.436844
https://www.cd-genomics.com/blog/introduction-to-dna-microarray-technology/
https://doi.org/10.1021/bm050180a
https://www.kavliprize.org/prizes/nanoscience/2022
http://lee.chem.uh.edu/1998/Langmv14p3815.pdf
https://doi.org/10.1016/j.progsurf.2003.12.001
https://doi.org/10.1039/D0TC00388C
https://www.sciencedirect.com/science/article/pii/S1566119918300387
https://doi.org/10.1364/OE.24.027184
https://doi.org/10.1021/ja00019a011
https://doi.org/10.1002/admi.201700316
https://link.springer.com/article/10.1007/s00253-013-5232-z
Images:
https://www.gettyimages.com/detail/video/artist-applying-red-color-on-canvas-stock-footage/1368075329
https://www.gettyimages.com/detail/video/man-sculptor-creates-sculpt-bust-clay-human-woman-stock-footage/1376840189
https://www.gettyimages.com/detail/video/scientist-is-preparation-of-nanomaterials-for-scanning-stock-footage/1196111142
https://www.gettyimages.com/detail/video/abstract-corporate-architecture-stock-footage/1338052026
https://en.wikipedia.org/wiki/File:Katharine_Burr_Blodgett_(1898-1979),_demonstrating_equipment_in_lab.jpg
https://commons.wikimedia.org/wiki/File:Langmuir-sitting.jpg
https://en.wikipedia.org/wiki/File:LBcompression.jpg
https://commons.wikimedia.org/wiki/File:Ksv-nima-medium-lb01.jpg
https://www.gettyimages.com/detail/photo/graphene-royalty-free-image/112039080
https://commons.wikimedia.org/wiki/File:Sony_oled.jpg
https://commons.wikimedia.org/wiki/File:Oled_display_alterung.jpg
https://www.gettyimages.com/detail/video/pixels-of-a-liquid-crystal-display-stock-footage/1057452344
https://www.youtube.com/watch?v=kpbPvWucNEg
https://www.youtube.com/watch?v=LZqv7Jl4iTo
https://commons.wikimedia.org/wiki/File:Surface_of_copper_oxide_(II).png
https://www.gettyimages.com/detail/video/arduino-nano-electronic-component-small-single-board-stock-footage/1368509819
https://www.gettyimages.com/detail/video/concept-video-contact-lenses-with-chip-inside-stock-footage/1312058054
https://www.gettyimages.com/detail/video/graphene-sheet-stock-footage/483199685
https://commons.wikimedia.org/wiki/File:Mixed_monolayer.jpg
https://en.wikipedia.org/wiki/File:From_spit_to_DNA-sample.webm
https://en.wikipedia.org/wiki/PDMS_stamp#/media/File:Sarfus.SoftLitho.Streptavidin.jpg
https://www.gettyimages.com/detail/video/dna-stock-footage/186901379
https://www.gettyimages.com/detail/video/ray-image-of-chest-with-artificial-cardiac-pacemaker-stock-footage/1187251785
https://www.kavliprize.org/prizes/nanoscience/2022
This episode was made in partnership with the Kavli Prize The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience and neuroscience, transforming our understanding of the big, the small and the complex. [♪ INTRO] The phrase “surface-level” usually means something… at least mildly insulting.
If something’s surface-level, it’s superficial. It’s not interesting. Well, there’s an entire field of science that begs to differ. It’s the science of coating a thing with another thing, and making that thing do something wildly different.
These coatings are called monolayers, because each layer of the material is just a single molecule thick, spread out over a surface. Coating glass with certain monolayers can make it easier, not harder, to see through, and that’s just the start. From TVs to pacemakers, from engineering microscopic circuits to studying and controlling the behavior of cells, we’re here today to show that surfaces are more than skin-deep. Some optical, electrical and even biological processes are easier to deal with on thin surfaces than they are in big, bulky volumes. Think about painting complicated designs on a canvas compared to sculpting something in the round.
You can more easily manipulate stuff on a flat plane than in big blobs. That’s true even for tiny stuff, and layers can be a great way to manipulate things down to the scale of nanometers. Scientists first got a handle on monolayers in the early 20th century, after noticing that certain kinds of glass actually transmitted more light when they were tarnished. It all comes down to how light waves transmit and reflect off surfaces. If a wave of light heads straight towards a pane of glass, most of it will go through the material, but some small amount will also be reflected back. That reflected light makes up the glare that can make it harder to see through. One way of dealing with this is with a film.
As in a thin layer of material rather than the theatrical movie kind, although we’ll come to those in a moment too! If you put a transparent film with precisely the right refractive index and width on the glass, it lets incoming light enter the material as normal, but it has another effect as well. Light will be reflected from the surface of the glass like before, but it will also be reflected from the surface of the film. That sounds like it ought to increase the total amount of reflected light, making things worse. But this is the part where we remember that light is a wave, with peaks and troughs.
If the film is just the right width, the peaks and troughs of the reflected light from the glass and the film interfere and align to cancel out! In short, the film actually winds up with getting rid of the reflections and reducing the glare, which makes the glass super clear and transparent. Sounds convenient, but creating these films isn’t easy. That was the problem facing scientists around the 1930s. Enter star physicist Katherine Blodgett. Building on the work of her mentor Irving Langmuir, she developed a process involving a chemical reaction between acids and other compounds inside a container.
After the reaction, a film would form on top of the liquid solution, consisting of a thin layer of something called cadmium arachidate. This is a type of molecule with one end that dissolves readily in water, and one that doesn’t. Blodgett’s process lined them all up neatly across the water, all pointing the same direction, since the water-loving ends would end up facing the water’s surface. If a piece of glass was dunked into this water beforehand, you could carefully pull it out so that the film, just a single molecule wide, neatly transfers itself onto the glass.
Kind of like pulling out a strawberry from a pot of melted chocolate so it's all coated evenly. After that, voila, you’ve got yourself a layer of molecules on a piece of glass. The resulting films are called Langmuir-Blodgett monolayers, or LBMs, named after their inventors. The specialized container used for creating them is called a Langmuir-Blodgett trough.
The trough, along with the method they used for lifting monolayers out intact, is what allowed them to apply LBMs onto solid surfaces, like glass. By repeating this process as many times as needed to get the right thickness, Blodgett managed to create a film of material on glass capable of reflecting less than one percent of white light falling on it. That made the glass amazingly clear and was extremely useful. For example, glass developed using her process produced crystal clear lenses used for movie projectors in the late 1930s. The same kind of lenses were even used in the periscopes built for submarines and spy planes in the second world war!
But Blodgett and Lamguir’s research on monolayers wasn’t just confined to glass, or even a particular chemical process. Using Langmuir-Blodgett troughs with different chemical reactions, researchers could apply even, molecule-sized layers onto materials for all kinds of uses. Basically, a kind of Swiss army knife of nano-scale engineering! For instance, you might be familiar with OLED TVs or computer monitors.
They use organic light emitting diodes to create a picture. But they’re pretty inefficient, especially the blue kind. Because of the crystal structure inside the OLED, the light kind of bounces around inside it before escaping, getting absorbed by the material and losing energy instead of coming out as visible light. But if we could control the thickness, pattern and shape of the OLED layers, we might be able to make them more efficient at releasing light. A 2016 study by French researchers found that constructing these layers with LBMs did make them super efficient, and that by carefully tweaking the different layers, they could even understand why.
Which means LBMs could help us save energy when using those big old screens we like looking at so much. But as incredible as LBMs are, they’re not always the best way of neatly arranging a layer of molecules onto a surface. In some cases, they’re chemically unstable on the surface they’re applied to, meaning they won’t stick around in their organized, layered structure for long. And what’s more, using a Langmuir-Blodgett trough can be a slow and delicate process. It only works on flat surfaces, and it’s one and done.
No tweaking once you’ve pulled your surface out. But, as is often the case in chemistry, there’s more than one way to arrange an organized layer of molecules onto a surface. You know, as they say. By 1946, chemists had seen that in some cases they could simply dunk a surface into a solution, and have the molecules arrange themselves onto it in a neat layer. In 1980 chemist Jacob Sagiv, at the Max Planck Institute in Germany, showed that it was possible to create monolayers on certain kinds of surfaces without all that messing around with a water trough. In Sagiv’s version, the molecules in the solution were individually attracted onto the solid surface, sticking themselves onto it in a particular direction.
In a short amount of time, they arranged themselves into a monolayer, firmly stuck onto the material. In fact, by mixing and matching specific molecules and organizing different surfaces, it was possible to create patterns – something you couldn’t get with the pull-out-the-strawberry method. Since these monolayers assemble themselves, they’re called, no awards for guessing, self-assembled monolayers or SAMs. Sagiv’s work on SAMs was a huge step, allowing him to create monolayers on a variety of surfaces. Specifically, solids with a layer of oxides on their surfaces were especially well suited to the process. That might seem super specific, but lots of materials exposed to air react with oxygen and end up with oxides on their surface, so the ability to make SAMs on them opens a lot of doors. For example, this made it possible to make electrical circuits at the nano-scale, as in, technology that’s only dozens of molecules or so in size.
Using SAMs, Sagiv was able to create monolayers that could conduct currents through them, which is a crucial step for engineering electrical circuits that are only a few molecules thick! Which you’d want for things like transparent displays or smart contact lenses – things where you don’t want the electronics getting in the way. But while this works for things like electronics, SAMs would have even more potential if they could be put onto materials without oxides, like bare metal surfaces. A few years later in 1983, the chemists Ralph Nuzzo and David Allara reported in the Journal of the American Chemical Society that they’d created a SAM on a surface of bare gold. These kinds of SAMs were a game changer.
Like Blodgett and Langmuir had shown forty years earlier, covering the surface of a thing with something else can vastly change what you can do with that thing. The SAMs based on Nuzzo and Allara’s design could be made from lots of different organic materials and made as precise as a few atoms in width. Researchers have since used them to change the electrical properties of metals, make them more resistant to corrosion, and in particular, study biological processes. See, long before humans got into the molecular engineering game, nature was chock-full of microbiological processes carrying out different functions at the nanoscale. And a lot of these happen at some kind of boundary, like the surface of a cell. Which makes SAMs a great model system for studying such processes. For instance, in one 1991 study, German researchers embedded molecules of biotin onto an SAM, which itself was bonded onto gold.
In nature, biotin has particularly strong reactions with a protein called streptavidin, that plays a key role in biochemical processes. The SAM basically gave the researchers a nanoscale hotbed for studying the chemical interactions between the two in a well-controlled way! As well as studying nature, researchers also quickly realized they could use the microbiological tools it provided. One instance is what’s called a DNA microarray.
These are a sort of fancy chip with a lot of DNA stuck on them. Since a strand of DNA will connect with its complementary strand, a microarray can tell you how much of that complementary DNA is present in a given sample. Like, the level of certain genes expressed in samples from patients who do or don’t have a particular sort of cancer can be very different, and so a DNA array can be a kind of genetic magnifying glass to help diagnose a patient. Early on, SAMs were a promising way of creating microarrays like these because they could be used to hold a bunch of molecules, like DNA, in place. The challenge was placing each strand of DNA in a particular location on the array, since you have to know what location on the chip corresponds to what DNA sequence. Which meant finding a way of creating SAMs with specific and intricate patterns. By 1992, a team of Harvard researchers led by the chemist George Whitesides had cracked the problem using what’s called soft lithography. The solution was basically drawing a particular pattern onto gold with the substance that the SAM would be made out of.
That laid the foundation for another idea. Instead of drawing it out, they created the pattern they wanted on a kind of stamp, covered it in the substance the monolayer would be made of and stamped it on a surface to create an SAM. Later, Whitesides’ team came up with another way to achieve the same effect, only this time, the idea was to make a kind of mold in the shape of the film you wanted to create and put it on top of a surface, like gold, and fill it with the substance of the film. After a short while, remove the mold and you’ve got yourself an SAM with a particular shape! There’s a lot going on here, so to recap, by controlling the exact shape and structure of a SAM, we can create surfaces which hold specific biological molecules in place.
That makes it easier to study them, but also to use them, like in a DNA array. Better still, SAMs made with particular patterns can hold all kinds of useful and important molecules on surfaces. Pacemakers, for instance, can often be attacked by the body at the point where the electrical contacts are in touch with your organs, because the immune system identifies it as something foreign to the body. And the resulting inflammation does a lot more harm than good. But, by coating the contact points with SAMs, they can be cloaked with anti-inflammatory molecules that prevent the body from going haywire. A little like an invisibility cloak for medical equipment.
Nothing to see here, just normal heart things. I could keep going, but hopefully you’ve seen that the ability to stick a thing to a surface has an incredible range of applications from medical devices to consumer electronics. In 2022 Sagiv, Nuzzo, Allara and Whitsides were all awarded the Kavli Prize in Nanoscience for the remarkable tools they worked to develop in creating and studying SAMs. At the time of this video, there are already ten thousand patents involving SAMs, from chemical sensors to solar cells. So at least on the nanoscale, we’ve only begun to scratch the surface… or at least build on it. Thanks to the Kavli Prize Foundation for partnering with us on this video.
The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience and neuroscience, transforming our understanding of the big, the small and the complex. Now that you’ve learned about the nanoscience award, you can check out the research that earned a 2022 Kavli Prize in neuroscience and astrophysics. [♪ OUTRO]
If something’s surface-level, it’s superficial. It’s not interesting. Well, there’s an entire field of science that begs to differ. It’s the science of coating a thing with another thing, and making that thing do something wildly different.
These coatings are called monolayers, because each layer of the material is just a single molecule thick, spread out over a surface. Coating glass with certain monolayers can make it easier, not harder, to see through, and that’s just the start. From TVs to pacemakers, from engineering microscopic circuits to studying and controlling the behavior of cells, we’re here today to show that surfaces are more than skin-deep. Some optical, electrical and even biological processes are easier to deal with on thin surfaces than they are in big, bulky volumes. Think about painting complicated designs on a canvas compared to sculpting something in the round.
You can more easily manipulate stuff on a flat plane than in big blobs. That’s true even for tiny stuff, and layers can be a great way to manipulate things down to the scale of nanometers. Scientists first got a handle on monolayers in the early 20th century, after noticing that certain kinds of glass actually transmitted more light when they were tarnished. It all comes down to how light waves transmit and reflect off surfaces. If a wave of light heads straight towards a pane of glass, most of it will go through the material, but some small amount will also be reflected back. That reflected light makes up the glare that can make it harder to see through. One way of dealing with this is with a film.
As in a thin layer of material rather than the theatrical movie kind, although we’ll come to those in a moment too! If you put a transparent film with precisely the right refractive index and width on the glass, it lets incoming light enter the material as normal, but it has another effect as well. Light will be reflected from the surface of the glass like before, but it will also be reflected from the surface of the film. That sounds like it ought to increase the total amount of reflected light, making things worse. But this is the part where we remember that light is a wave, with peaks and troughs.
If the film is just the right width, the peaks and troughs of the reflected light from the glass and the film interfere and align to cancel out! In short, the film actually winds up with getting rid of the reflections and reducing the glare, which makes the glass super clear and transparent. Sounds convenient, but creating these films isn’t easy. That was the problem facing scientists around the 1930s. Enter star physicist Katherine Blodgett. Building on the work of her mentor Irving Langmuir, she developed a process involving a chemical reaction between acids and other compounds inside a container.
After the reaction, a film would form on top of the liquid solution, consisting of a thin layer of something called cadmium arachidate. This is a type of molecule with one end that dissolves readily in water, and one that doesn’t. Blodgett’s process lined them all up neatly across the water, all pointing the same direction, since the water-loving ends would end up facing the water’s surface. If a piece of glass was dunked into this water beforehand, you could carefully pull it out so that the film, just a single molecule wide, neatly transfers itself onto the glass.
Kind of like pulling out a strawberry from a pot of melted chocolate so it's all coated evenly. After that, voila, you’ve got yourself a layer of molecules on a piece of glass. The resulting films are called Langmuir-Blodgett monolayers, or LBMs, named after their inventors. The specialized container used for creating them is called a Langmuir-Blodgett trough.
The trough, along with the method they used for lifting monolayers out intact, is what allowed them to apply LBMs onto solid surfaces, like glass. By repeating this process as many times as needed to get the right thickness, Blodgett managed to create a film of material on glass capable of reflecting less than one percent of white light falling on it. That made the glass amazingly clear and was extremely useful. For example, glass developed using her process produced crystal clear lenses used for movie projectors in the late 1930s. The same kind of lenses were even used in the periscopes built for submarines and spy planes in the second world war!
But Blodgett and Lamguir’s research on monolayers wasn’t just confined to glass, or even a particular chemical process. Using Langmuir-Blodgett troughs with different chemical reactions, researchers could apply even, molecule-sized layers onto materials for all kinds of uses. Basically, a kind of Swiss army knife of nano-scale engineering! For instance, you might be familiar with OLED TVs or computer monitors.
They use organic light emitting diodes to create a picture. But they’re pretty inefficient, especially the blue kind. Because of the crystal structure inside the OLED, the light kind of bounces around inside it before escaping, getting absorbed by the material and losing energy instead of coming out as visible light. But if we could control the thickness, pattern and shape of the OLED layers, we might be able to make them more efficient at releasing light. A 2016 study by French researchers found that constructing these layers with LBMs did make them super efficient, and that by carefully tweaking the different layers, they could even understand why.
Which means LBMs could help us save energy when using those big old screens we like looking at so much. But as incredible as LBMs are, they’re not always the best way of neatly arranging a layer of molecules onto a surface. In some cases, they’re chemically unstable on the surface they’re applied to, meaning they won’t stick around in their organized, layered structure for long. And what’s more, using a Langmuir-Blodgett trough can be a slow and delicate process. It only works on flat surfaces, and it’s one and done.
No tweaking once you’ve pulled your surface out. But, as is often the case in chemistry, there’s more than one way to arrange an organized layer of molecules onto a surface. You know, as they say. By 1946, chemists had seen that in some cases they could simply dunk a surface into a solution, and have the molecules arrange themselves onto it in a neat layer. In 1980 chemist Jacob Sagiv, at the Max Planck Institute in Germany, showed that it was possible to create monolayers on certain kinds of surfaces without all that messing around with a water trough. In Sagiv’s version, the molecules in the solution were individually attracted onto the solid surface, sticking themselves onto it in a particular direction.
In a short amount of time, they arranged themselves into a monolayer, firmly stuck onto the material. In fact, by mixing and matching specific molecules and organizing different surfaces, it was possible to create patterns – something you couldn’t get with the pull-out-the-strawberry method. Since these monolayers assemble themselves, they’re called, no awards for guessing, self-assembled monolayers or SAMs. Sagiv’s work on SAMs was a huge step, allowing him to create monolayers on a variety of surfaces. Specifically, solids with a layer of oxides on their surfaces were especially well suited to the process. That might seem super specific, but lots of materials exposed to air react with oxygen and end up with oxides on their surface, so the ability to make SAMs on them opens a lot of doors. For example, this made it possible to make electrical circuits at the nano-scale, as in, technology that’s only dozens of molecules or so in size.
Using SAMs, Sagiv was able to create monolayers that could conduct currents through them, which is a crucial step for engineering electrical circuits that are only a few molecules thick! Which you’d want for things like transparent displays or smart contact lenses – things where you don’t want the electronics getting in the way. But while this works for things like electronics, SAMs would have even more potential if they could be put onto materials without oxides, like bare metal surfaces. A few years later in 1983, the chemists Ralph Nuzzo and David Allara reported in the Journal of the American Chemical Society that they’d created a SAM on a surface of bare gold. These kinds of SAMs were a game changer.
Like Blodgett and Langmuir had shown forty years earlier, covering the surface of a thing with something else can vastly change what you can do with that thing. The SAMs based on Nuzzo and Allara’s design could be made from lots of different organic materials and made as precise as a few atoms in width. Researchers have since used them to change the electrical properties of metals, make them more resistant to corrosion, and in particular, study biological processes. See, long before humans got into the molecular engineering game, nature was chock-full of microbiological processes carrying out different functions at the nanoscale. And a lot of these happen at some kind of boundary, like the surface of a cell. Which makes SAMs a great model system for studying such processes. For instance, in one 1991 study, German researchers embedded molecules of biotin onto an SAM, which itself was bonded onto gold.
In nature, biotin has particularly strong reactions with a protein called streptavidin, that plays a key role in biochemical processes. The SAM basically gave the researchers a nanoscale hotbed for studying the chemical interactions between the two in a well-controlled way! As well as studying nature, researchers also quickly realized they could use the microbiological tools it provided. One instance is what’s called a DNA microarray.
These are a sort of fancy chip with a lot of DNA stuck on them. Since a strand of DNA will connect with its complementary strand, a microarray can tell you how much of that complementary DNA is present in a given sample. Like, the level of certain genes expressed in samples from patients who do or don’t have a particular sort of cancer can be very different, and so a DNA array can be a kind of genetic magnifying glass to help diagnose a patient. Early on, SAMs were a promising way of creating microarrays like these because they could be used to hold a bunch of molecules, like DNA, in place. The challenge was placing each strand of DNA in a particular location on the array, since you have to know what location on the chip corresponds to what DNA sequence. Which meant finding a way of creating SAMs with specific and intricate patterns. By 1992, a team of Harvard researchers led by the chemist George Whitesides had cracked the problem using what’s called soft lithography. The solution was basically drawing a particular pattern onto gold with the substance that the SAM would be made out of.
That laid the foundation for another idea. Instead of drawing it out, they created the pattern they wanted on a kind of stamp, covered it in the substance the monolayer would be made of and stamped it on a surface to create an SAM. Later, Whitesides’ team came up with another way to achieve the same effect, only this time, the idea was to make a kind of mold in the shape of the film you wanted to create and put it on top of a surface, like gold, and fill it with the substance of the film. After a short while, remove the mold and you’ve got yourself an SAM with a particular shape! There’s a lot going on here, so to recap, by controlling the exact shape and structure of a SAM, we can create surfaces which hold specific biological molecules in place.
That makes it easier to study them, but also to use them, like in a DNA array. Better still, SAMs made with particular patterns can hold all kinds of useful and important molecules on surfaces. Pacemakers, for instance, can often be attacked by the body at the point where the electrical contacts are in touch with your organs, because the immune system identifies it as something foreign to the body. And the resulting inflammation does a lot more harm than good. But, by coating the contact points with SAMs, they can be cloaked with anti-inflammatory molecules that prevent the body from going haywire. A little like an invisibility cloak for medical equipment.
Nothing to see here, just normal heart things. I could keep going, but hopefully you’ve seen that the ability to stick a thing to a surface has an incredible range of applications from medical devices to consumer electronics. In 2022 Sagiv, Nuzzo, Allara and Whitsides were all awarded the Kavli Prize in Nanoscience for the remarkable tools they worked to develop in creating and studying SAMs. At the time of this video, there are already ten thousand patents involving SAMs, from chemical sensors to solar cells. So at least on the nanoscale, we’ve only begun to scratch the surface… or at least build on it. Thanks to the Kavli Prize Foundation for partnering with us on this video.
The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience and neuroscience, transforming our understanding of the big, the small and the complex. Now that you’ve learned about the nanoscience award, you can check out the research that earned a 2022 Kavli Prize in neuroscience and astrophysics. [♪ OUTRO]