Smaller Than Stippling : Quantum Dots

With an article out in UDaily, we are connecting the last of the dots in putting Art in Science together.

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Sleeping Girl, Roy Lichtenstein, Legion of Andy

Dot Techniques in Art

Dots are featured in many different art techniques.The dot technique that may be the most familiar is the Ben-Day dots most frequently seen in comic books. Ben-Day dots are characterized as a series of large unicolor dots with of uniform size and spacing.

Although they were created by and named after Benjamin Henry Day, Ben-Day dots are most iconic in the work of Roy Lichtenstein during the pop art movement in 1950-1960. Lichtenstein used the dots to create different tones in his pieces while still largely using only primary colors. The close up of Lichtenstein’s sleeping girl to the right demonstrates the use of red dots to develop the peach tone of skin and the deeper red of the lip.

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Femmes au bord de l’eau, Georges Seurat, Wikimedia

Pointillism is another dot related art technique. Developed by Georges Seurat and Paul Signac in the 1880s as a derivative of impressionism, pointillism overlays small colored dots.  Similarly to impressionism, pointillism does not blend any colors together but uses the overlaid colors to create the impression of a new color.

This concept of overlaying colors to create the impression of a new color is used on a much smaller scale in color printers. Color printers follow four color model, also known as the CMYK model. The CMYK model overlays dots of cyan (C), magenta (M), yellow (Y), and black/key (K) to create the full spectrum of colors.

Example of Stippling

While there are more art techniques that feature dots, the last technique we will discuss is stippling. Stippling differs from Ben-Day dots and pointillism in that the dots are small, uniform in size, but shading is created by altering the spacing between dots. The denser the dots, the darker the color appears. Because stippling relies only on the changes in spacing between dots, it is often found in monochromatic works.

Quantum Dots

Quantum dots are spherical nanosized semiconductors. A semiconductor is characterized by a material with a specific set of electrical properties. Semiconductors have a resistance between that of conductive materials (metals, low resistance) and insulators (high resistance). Hence, the material is somewhat or “semi-” conducive.

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Cadmium Telluride Quantum Dots, PlasmaChem GmbH, Wikimedia

Quantum dots absorb white light and emit colored light. The color of quantum dots depends on the size of the dot. 2-3 nanometer quantum dots emit short wavelengths colors such as blue while larger quantum dots (5-6 nanometers in radius) emit longer wavelength colors such as red. The control over quantum dot size and the resulting optical effect is useful in many technologies.

Electronic Displays

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LCD vs Quantum dot display, Engadget

Similar to organic light-emitting diode (OLED) displays, using quantum dots would create flexible electronic displays. However, large quantum dot displays will be easier to create than large OLED displays and also have longer lifetimes. Additionally, quantum dot-based LEDs have very narrow bandwidths, which means that the colors emitted by the quantum dot based LEDs are very bright, pure, and efficient. Compared to current liquid crystal displays (LCD), quantum dot displays can display 50% more color. Using the optical properties of quantum dots, quantum dot displays would allow for brighter, more colorful, and more efficient electronic displays.

Although quantum dot displays can improve on current electronic display technology, there are a few obstacles hindering its widespread use.These obstacles include, but are not limited to: difficulties manufacturing the very small blue quantum dots, and unequal quantum yields across different quantum dots. Quantum yield is a ratio that compares how much light is emitted for each unit of light used for excitation. Different quantum yields among quantum dots means that although the light absorbed by individual quantum dots are the same intensity, the light emitted by the quantum dots will differ in intensity. However, quantum dot displays are already available in selected devices, and there will likely be more to come.

Cancer Imaging

One of the difficulties in tumor removal is that there is no clear boundary between the tumor and the surrounding healthy tissue. Additionally, there may be satellite tumors hidden in the surrounding tissue several centimeters away from the primary tumor. It is difficult for surgeons to completely remove all cancerous tissue while leaving all of the healthy tissue. Quantum dots can be modified to target cancerous tissue allowing surgeons to visualize both the boundary of the primary tumor and also any satellite tumors. For images and more information, please read this ActaNaturae paper.

Gene Detection

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Schematic of resonance energy transfer

The emission of quantum dots, similar to fluorophores, can be used to excite other quantum dots of a different size and color. This effect, called resonance energy transfer, only occurs when the two quantum dots are in close proximity.

To detect specific genes, a specific sequence of DNA is attached to one size of quantum dot. Called a complementary strand, this sequence of DNA will pair perfectly with DNA from a specific gene and reveal whether that specific gene is expressed. Then, DNA from a cell or person is attached to a second size of quantum dot. If the specific gene is expressed, it will bind to the complementary strand. The binding of the specific gene DNA and complementary strand DNA brings the two quantum dots into close proximity. Analyzing the quantity and location of the colors emitted reveals any resonance energy transfer, and therefore, whether the specific gene is expressed.

From art to science, dots are used to create beautiful and useful images. In the end, dots all we need to know!

Until Next Time

Green Fluorescent Protein : Illuminating Molecular Level Processes

Steel Jellyfish, Julian Voss-Andreae

We are incentivizing entries in Art in Science by offering a monetary prize – and who doesn’t love a good prize? Specifically speaking, who doesn’t love the Nobel Prize?

In 2008, Martin Chalfie, Osamu Shimomura, and Roger Tsien won the Nobel Prize in Chemistry for the discovery and subsequent development of green fluorescent protein (GFP) as a microbiology tool. A sculpture of the protein entitled “Steel Jellyfish” is on display at Friday Harbor Laboratories in Washington where GFP was discovered.

GFP as a Microbiology Tool

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GFP protein structure, Wikimedia

GFP is composed of 238 amino acids, or protein building blocks. These amino acids associated with each other using hydrogen bonding into 11 secondary structures known as beta sheets or beta pleated sheets. These 11 beta pleated sheets form the barrel shape called a beta-can. Because the beta-can shape is very compact, GFP is a relatively stable protein able to withstand temperatures up to 90C and a pH range of 4-12 with little denaturation. Additionally, the beta-can structure gives GFP a low reactivity, which allows scientists to introduce GFP to other types of cells or organisms with few negative effects.

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Transgenic Mouse, Wikimedia

While the mouse expressing GFP is possibly the most iconic animal, many transgenic GFP organisms exists. In addition to a wide varieties of plants and bacteria, transgenic GFP organisms include zebrafish, rabbits, cats and even pigs. Transgenic GFP zebrafish and mice are even available to purchase commercially as pets.

In addition to transgenic organisms expressing solitary GFP, scientists can create sequences that attach GFP to another protein. When this hybrid protein is expressed, GFP acts as a reporter, allowing scientists to track and observe how these proteins behave within the cell or organism.

Fluorescence vs Bioluminescence

Crystal Jelly, Aequorea victoria.
Aequorea victoria, Wikimedia

GFP was discovered in Aequorea victoria, a species of jellyfish. Also known as the crystal jelly, Aequorea victoria lives in the Pacific waters off the coast of North America. Aequorea victoria is known not only for producing GFP, but also a bioluminescent protein called aequorin.

Bioluminescence occurs from proteins that react with molecules such as calcium ions, oxygen, or ATP, the energy source of living cells. Conversely, fluorescence occurs when the fluorophore, or glowing portion, of proteins or molecules interacts with a specific color of light. Colors of light are characterized by their wavelength and only a very narrow range is absorbed by the fluorophore. The chemical bonds of the fluorophore give the energy from the light a temporary home. The electrons in the chemical bonds are moved to an excited stage with the light energy, and will fall back to their non-excited states and emit light. Since some of the energy from the original light has been dissipated in the chemical bonds, the color of light emitted from the fluorophore is a lower energy color, or higher wavelength. Although there is a range of wavelengths where both the fluorophore excites and the fluorophore emits, there is a narrow range of where there is the maximum amount of excitation and emission occur. Fluorophores exist in many different colors, with different excitation and emission wavelengths, but only GFP is depicted below.

Excitation and Emission of GFP, Thermofisher Spectraviewer

GFP found in jellyfish has a maximum excitation around a wavelength of 395 nanometers and a maximum excitation around 509 nanometers. However, modifications made to GFP by scientists to create enhanced green fluorescent protein (EGFP ) has an excitation at 488 nanometers.

Because fluorophores require a source of light for excitation, one might wonder where the crystal jellyfish finds a light source in the dark waters. The answer is above – aequorin! Aequorin is a bioluminescent protein that interacts with calcium ions to produces a blue light around 365 nanometers. While 365 nanometers is not a perfect match to the 395 nanometer maximum excitation of GFP, it is well within the range of excitation wavelengths for GFP. How amazing is it that this organism not only has proteins to produce light, but also a complementary one to transform light?

From its origins in a humble jellyfish, GFP has revolutionized research in microbiology.  As my high school calculus teacher always said, “bright kids see things differently.” Now, thanks to GFP, bright proteins help scientists see things differently.

Until next time.

Now Accepting Submissions!!

Thank you to everyone for your patience.

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Science in Art : Dichroic Glass

As with any good event, we hope to have open communication while hosting Art in Science. In short, we will do our best to maintain transparency- and what in our lives is iconic for being transparent so much as glass?

Dichroic beads, Wikimedia

Glass is a material that has a wide variety of uses, from the practical drinking glasses to beautifully crafted opalescent stained glass windows to optical fibers. Today’s post focuses on glass with dichroic optical properties : where the glass has two (“di”) or more distinct behaviors depending on the angle or color of light with which it interacts, usually relating to the color (“chroic”) that can be observed.

Dichroic Glass

Dichroic glass is named because the glass changes colors depending on the lighting conditions. In modern times, this effect is created using the same metals, metal oxides and/or nitrides that are used to color glass, but in a different treatment. Instead of incorporating the coloring agents into the bulk glass, thin layers of coloring agent are applied to the glass. Because there are multiple nanoscale layers, interactions of dichroic glass with different angles of light will create different colors, giving the glass a distinct iridescent quality.

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Schematic of Filter Cube

Filter Cubes in Fluorescence Microscopy

The most common scientific application of dichroic optical effects is in fluorescence microscopy as filter cubes. Filter cubes in fluorescence microscopy are composed of two filters and a dichroic mirror. Similarly to dichroic glass, a dichroic mirror is made by applying thin layers to a glass.

During fluorescence microscopy the light enters through the first filter, known as an excitation filter, which only allows one color of light to pass. The excitation filter is calibrated to the color of light with which the sample will have the greatest interaction, or excitation. Then, this first color of light bounces off of the dichroic mirror and interacts with the sample. The sample momentarily absorbs this light, dissipates some of the light energy, and emits the light with a lower energy color. This second color of light is separated from other light by the second filter in the filter cube, known as the emission filter, passes through the dichroic mirror, and can then be observed by the microscope’s user. Dichroic mirrors make fluorescence microscopy possible because of their ability to selectively reflect and transmit different colors of light.

The Lycurgus Cup

Although it was not created using thin films, the most famous piece of glass with a dichroic optical effect is the Lycugrus Cup which is on display at the British Museum. The Lycurgus Cup is a carved glass cup from the Roman era depicting the myth of King Lycurgus who expelled the god Dionysus from his kingdom and persecuted his followers. One of Dionysus’ followers is later transformed into a vine that traps Lycurgus. While the history is very interesting, the most notable feature of the Lycurgus cup is the dichroic optical effect.

The Lycurgus Cup viewed under transmitted (left) and reflected (right) light, British Museums

When viewed under reflected light the Lycurgus cup appears green. Conversely, when the Lycurgus is viewed under transmitted light it appears red. This effect is a result of incorporating trace nanoscopic gold and silver particles in the glass when it was forged. While this effect is spectacular, it is under debate whether the incorporation of nanoparticles was intentional or merely a happy result of contamination. Mistakes or otherwise, glass has been used in expressions of art throughout history, but today, we have viewed it in a different light.

Until next time.

Art in Science Is a Go!

We are pleased to announce that we have a finalized date and location for the Art in Science symposium : April 16th 2016, 12-5 pm, ISE Laboratories. Submissions will be opening soon.

Additionally, to help create excitement for our symposium, we are happy to announce a series of weekly blog posts on topics at the intersection of art and science starting next week. Stay tuned!