Okinawa Institute of Science & Technology Promotion Corp.

Organic electrochemical transistors (OECTs) allow current to flow in devices like implantable biosensors. But scientists long knew about a quirk of OECTs that no one could explain: When an OECT is switched on, there is a lag before current reaches the desired operational level. When switched off, there is no lag. Current drops immediately. Researchers report that they have discovered the reason for this activation lag, and in the process are paving the way to custom-tailored OECTs for a growing list of applications in biosensing, brain-inspired computation and beyond. Researchers who want to bridge the divide between biology and technology spend a lot of time thinking about translating between the two different "languages" of those realms. "Our digital technology operates through a series of electronic on-off switches that control the flow of current and voltage," said Rajiv Giridharagopal, a research scientist at the University of Washington. "But our bodies operate on chemistry. In our brains, neurons propagate signals electrochemically, by moving ions -- charged atoms or molecules -- not electrons." Implantable devices from pacemakers to glucose monitors rely on components that can speak both languages and bridge that gap. Among those components are OECTs -- or organic electrochemical transistors -- which allow current to flow in devices like implantable biosensors. But scientists long knew about a quirk of OECTs that no one could explain: When an OECT is switched on, there is a lag before current reaches the desired operational level. When switched off, there is no lag. Current drops almost immediately. A UW-led study has solved this lagging mystery, and in the process paved the way to custom-tailored OECTs for a growing list of applications in biosensing, brain-inspired computation and beyond. "How fast you can switch a transistor is important for almost any application," said project leader David Ginger, a UW professor of chemistry, chief scientist at the UW Clean Energy Institute and faculty member in the UW Molecular Engineering and Sciences Institute. "Scientists have recognized the unusual switching behavior of OECTs, but we never knew its cause -- until now." In a paper published April 17 in Nature Materials, Ginger's team at the UW -- along with Professor Christine Luscombe at the Okinawa Institute of Science and Technology in Japan and Professor Chang-Zhi Li at Zhejiang University in China -- report that OECTs turn on via a two-step process, which causes the lag. But they appear to turn off through a simpler one-step process. In principle, OECTs operate like transistors in electronics: When switched on, they allow the flow of electrical current. When switched off, they block it. But OECTs operate by coupling the flow of ions with the flow of electrons, which makes them interesting routes for interfacing with chemistry and biology. The new study illuminates the two steps OECTs go through when switched on. First, a wavefront of ions races across the transistor. Then, more charge-bearing particles invade the transistor's flexible structure, causing it to swell slightly and bringing current up to operational levels. In contrast, the team discovered that deactivation is a one-step process: Levels of charged chemicals simply drop uniformly across the transistor, quickly interrupting the flow of current. Knowing the lag's cause should help scientists design new generations of OECTs for a wider set of applications. "There's always been this drive in technology development to make components faster, more reliable and more efficient," Ginger said. "Yet, the 'rules' for how OECTs behave haven't been well understood. A driving force in this work is to learn them and apply them to future research and development efforts." Whether they reside within devices to measure blood glucose or brain activity, OECTs are largely made up of flexible, organic semiconducting polymers -- repeating units of complex, carbon-rich compounds -- and operate immersed in liquids containing salts and other chemicals. For this project, the team studied OECTs that change color in response to electrical charge. The polymer materials were synthesized by Luscombe's team at the Okinawa Institute of Science and Technology and Li's at Zhejiang University, and then fabricated into transistors by UW doctoral students Jiajie Guo and Shinya "Emerson" Chen, who are co-lead authors on the paper. "A challenge in the materials design for OECTs lies in creating a substance that facilitates effective ion transport and retains electronic conductivity," said Luscombe, who is also a UW affiliate professor of chemistry and of materials science and engineering. "The ion transport requires a flexible material, whereas ensuring high electronic conductivity typically necessitates a more rigid structure, posing a dilemma in the development of such materials." Guo and Chen observed under a microscope -- and recorded with a smartphone camera -- precisely what happens when the custom-built OECTs are switched on and off. It showed clearly that a two-step chemical process lies at the heart of the OECT activation lag. Past research, including by Ginger's group at the UW, demonstrated that polymer structure, especially its flexibility, is important to how OECTs function. These devices operate in fluid-filled environments containing chemical salts and other biological compounds, which are more bulky compared to the electronic underpinnings of our digital devices. The new study goes further by more directly linking OECT structure and performance. The team found that the degree of activation lag should vary based on what material the OECT is made of, such as whether its polymers are more ordered or more randomly arranged, according to Giridharagopal. Future research could explore how to reduce or lengthen the lag times, which for OECTs in the current study were fractions of a second. "Depending on the type of device you're trying to build, you could tailor composition, fluid, salts, charge carriers and other parameters to suit your needs," said Giridharagopal. OECTs aren't just used in biosensing. They are also used to study nerve impulses in muscles, as well as forms of computing to create artificial neural networks and understand how our brains store and retrieve information. These widely divergent applications necessitate building new generations of OECTs with specialized features, including ramp-up and ramp-down times, according to Ginger. "Now that we're learning the steps needed to realize those applications, development can really accelerate," said Ginger. Guo is now a postdoctoral researcher at the Lawrence Berkeley National Laboratory and Chen is now a scientist at Analog Devices. Other co-authors on the paper are Connor Bischak, a former UW postdoctoral researcher in chemistry who is now an assistant professor at the University of Utah; Jonathan Onorato, a UW doctoral alum and scientist at Exponent; and Kangrong Yan and Ziqui Shen of Zhejiang University. The research was funded by the U.S. National Science Foundation, and polymers developed at Zhejiang University were funded by the National Science Foundation of China.

A new study that combines genetic and molecular techniques helps solve the riddle of sea star (commonly called starfish) body plans, and how sea stars start life with bilateral body symmetry -- just like humans -- but grow up to be adults with fivefold 'pentaradial' symmetry. If you put a hat on a starfish, where would you put it? On the center of the starfish? Or on the point of an arm and, if so, which one? The question is silly, but it gets at serious questions in the fields of zoology and developmental biology that have perplexed veteran scientists and schoolchildren in introductory biology classes alike: Where is the head on a starfish? And how does their body layout relate to ours? Now, a new Stanford study that used genetic and molecular tools to map out the body regions of starfish -- by creating a 3D atlas of their gene expression -- helps answer this longstanding mystery. The "head" of a starfish, the researchers found, is not in any one place. Instead, the headlike regions are distributed with some in the center of the sea star as well as in the center of each limb of its body. "The answer is much more complicated than we expected," said Laurent Formery, lead author and postdoc in the labs of Christopher Lowe at the Stanford School of Humanities and Sciences and Daniel S. Rokhsar at the University of California, Berkeley. "It is just weird, and most likely the evolution of the group was even more complicated than this." Starfish (sea stars) belong to a group of animals called echinoderms. Echinoderms and humans are closely related, yet the life cycle and anatomy of sea stars are very different from ours. Sea stars begin life as fertilized eggs that hatch into a free-floating larva. The larvae bob in the ocean in a plankton form for weeks to months before settling to the ocean floor to perform a magic trick of sorts -- transforming from a bilateral (symmetric across the midline) body plan into an adult with a five-point star shape called a pentaradial body plan. "This has been a zoological mystery for centuries," said Lowe, who is also a researcher at Hopkins Marine Station and senior author of the paper that published Nov. 1 in Nature. "How can you go from a bilateral body plan to a pentaradial plan, and how can you compare any part of the starfish to our own body plan?" Mapping stars For puzzles such as this one, researchers often conduct comparative studies to identify similar structures in related groups of animals to glean clues about the evolutionary events that prompted the trait of interest. "The problem with starfish is there is nothing on a starfish anatomically that you can relate to a vertebrate," said Lowe. "There is just nothing there." At least, nothing on the outside of a starfish. And that is where genetic and molecular techniques come in. During his graduate research, Formery studied early development in sea urchins -- echinoderms, like sea stars, that also start their life as bilateral larvae before transforming into adults with fivefold symmetry. When Formery joined Lowe's lab, Formery's knowledge of echinoderm development combined with Lowe's expertise in molecular biology techniques to help tackle the mystery of sea stars' baffling body plan. The team used a group of well-studied molecular markers (Hox genes are an example) that act as blueprints for an organism's body plan by "telling" each cell which body region it belongs to. "If you strip away the skin of an animal and look at the genes involved in defining a head from a tail, the same genes code for these body regions across all groups of animals," said Lowe. "So we ignored the anatomy and asked: Is there a molecular axis hidden under all this weird anatomy and what is its role in a starfish forming a pentaradial body plan?" To investigate this question, the researchers used RNA tomography, a technique that pinpoints where genes are expressed in tissue, and in situ hybridization, a technique that zeroes in on a specific RNA sequence in a cell. "First we sectioned sea star arms into thin slices from tip to center, top to bottom, and left to right," said Formery, noting that sea stars regenerate missing limbs. "We used RNA tomography to determine which genes were expressed in each slice and then 'reassembled' the slices using computer models. This gave us a 3D map of gene expression." "In the second method, in situ hybridization chain reaction, we stained sea star tissue and visually inspected the samples to see where a gene was expressed," said Formery. This enabled the researchers to examine anterior-posterior (head to tail) body patterning in the outermost layer of cells called the ectoderm. "This was made possible by the recent, big, technical improvement in in situ hybridization, known as in situ hybridization chain reaction, Formery said. "This new method provides better resolution of where the gene is expressed." The research revealed that sea stars have a headlike territory in the center of each "arm" and a tail-like region along the perimeter. In an unexpected twist, no part of the sea star ectoderm expresses a "trunk" genetic patterning program, suggesting that sea stars are mostly headlike. Mining truly diverse biodiversity Research is often centered on groups of animals that look like us, the researchers explained. But if we focus on the familiar, we are less likely to learn something new. "There are 34 different animal phyla living on this planet and in over roughly 600 million years they have all come up with different solutions to the same fundamental biological problems," Lowe said. "Most animals don't have spectacular nervous systems and are out chasing prey -- they are modest animals that live in burrows in the ocean. People are generally not drawn to these animals, and yet they probably represent how much of life got started." This study demonstrates how a comparative approach that uses genetic and molecular techniques can be used to mine biodiversity for insights into why different animals look the way they do and how their body plans evolved. "Even in recent molecular papers there's a question mark near echinoderms on the evolutionary tree because we don't know much about them," Formery said. "It was nice to show that -- at least at the molecular level -- we have a new piece of the puzzle that can now be put on the tree." Formery, Lowe, and Rokhsar are also researchers at the Chan Zuckerberg BioHub. Rokhsar is also a researcher at the Okinawa Institute of Science and Technology. Additional Stanford co-authors are Ian Kohnle, Judith Malnick, and Kevin Uhlinger of Hopkins Marine Station. Additional authors are from Pacific Biosciences in Menlo Park, California, and Columbia Equine Hospital in Gresham, Oregon. This research was funded by NASA, the National Science Foundation, and the Chan Zuckerberg BioHub.

Researchers have developed one of the world's fastest cameras capable of detecting fluorescence from single molecules. Researchers at Kyoto University, Okinawa Institute of Science and Technology Graduate University (OIST), and Photron Limited in Japan have developed the world's fastest camera capable of detecting fluorescence from single molecules. They describe the technology and examples of its power in two articles published in the same issue of the Journal of Cell Biology. "Our work with this camera will help scientists understand how cancer spreads and help develop new drugs for treating cancer," says bio-imaging expert Takahiro Fujiwara, who led the research at the Institute for Integrated Cell-Material Sciences (iCeMS). Single fluorescent-molecule imaging (SFMI) uses a fluorescent molecule as a reporter tag that can bind to molecules of interest in a cell and reveal where they are and how they are moving and binding to each other. The team's ultra-fast camera allows the highest resolution in time ever achieved by SFMI. It can detect single molecule movements that are 1,000 times faster than the normal video frame rate. Specifically, it can detect a molecule with an attached fluorescent tag every 33 microseconds with 34 nanometre precision in position, or every 100 microseconds at 20 nanometre precision. "We can now observe how individual molecules dance within living cells, as if we are watching a ballet performance in a theatre," says Fujiwara. He emphasises that previous SFMI techniques were like watching the ballet once every 30 seconds, so the audience had to guess the story from such sparse observations. It was extremely difficult and the guesses were often entirely wrong. Furthermore, the ultrafast camera that the team developed tremendously improved the time resolution of a previous super spatial resolution method, which was recognized with the Nobel award in Chemistry in 2014. In this earlier method, the positions of individual molecules are recorded as small dots of approximately 20 nm, forming images like the pointillism paintings by the new impressionists, led by Georges Seurat. However, the problem of the pointillism under the microscope has been that the image formation is extremely slow and it often takes more than 10 minutes to obtain a single image, and thus the specimens had to be chemically fixed dead cells. With the developed ultrafast camera, the image can be formed in 10 seconds, about 60 times faster, allowing observations of live cells. The team further demonstrated the power of their camera by examining the localization and movement of a receptor protein involved in cancers and a cellular structure called the focal adhesion. The focal adhesion is a complex of protein molecules that connects bundles of structural proteins inside cells to the material outside cells called the extracellular matrix. It can play a significant role in the cellular mechanical interactions with its environment, allowing cancer cells to move and metastasize. "In one investigation we found that a cancer-promoting receptor that binds to signalling molecules is confined within a specific cellular compartment for a longer time when it is activated. In another, we revealed ultrafine structures and molecular movements within the focal adhesion that are involved in cancer cell activities," says Akihiro Kusumi, the corresponding author, who is a professor at OIST and professor emeritus of Kyoto University. The results allowed the team to propose a refined model of focal adhesion structure and activity. Many research teams worldwide are interested in developing drugs that can interfere with the role of focal adhesions in cancer. The ultrafast camera developed by the team in collaboration with Mr. Takeuchi of Photron Limited, a camera manufacturer in Japan, will assist these efforts by revealing deeper understanding of how these structures move and interact with other structures inside and outside of cells.