Nano News: 06/24/15

Artifical neuron mimicks function of human cells (w/video)

Scientists at Sweden’s Karolinska Institutet have managed to build a fully functional neuron by using organic bioelectronics ("An organic electronic biomimetic neuron enables auto-regulated neuromodulation"). This artificial neuron contain no ‘living’ parts, but is capable of mimicking the function of a human nerve cell and communicate in the same way as our own neurons do. Neurons are isolated from each other and communicate with the help of chemical signals, commonly called neurotransmitters or signal substances. Inside a neuron, these chemical signals are converted to an electrical action potential, which travels along the axon of the neuron until it reaches the end. Here at the synapse, the electrical signal is converted to the release of chemical signals, which via diffusion can relay the signal to the next nerve cell. To date, the primary technique for neuronal stimulation in human cells is based on electrical stimulation. However, scientists at the Swedish Medical Nanoscience Centre (SMNC) at Karolinska Institutet in collaboration with collegues at Linköping University, have now created an organic bioelectronic device that is capable of receiving chemical signals, which it can then relay to human cells. “Our artificial neuron is made of conductive polymers and it functions like a human neuron”, says lead investigator Agneta Richter-Dahlfors, professor of cellular microbiology. “The sensing component of the artificial neuron senses a change in chemical signals in one dish, and translates this into an electrical signal. This electrical signal is next translated into the release of the neurotransmitter acetylcholine in a second dish, whose effect on living human cells can be monitored.“

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The research team hope that their innovation, presented in the journal Biosensors & Bioelectronics, will improve treatments for neurologial disorders which currently rely on traditional electrical stimulation. The new technique makes it possible to stimulate neurons based on specific chemical signals received from different parts of the body. In the future, this may help physicians to bypass damaged nerve cells and restore neural function. “Next, we would like to miniaturize this device to enable implantation into the human body”, says Agneta Richer-Dahlfors. “We foresee that in the future, by adding the concept of wireless communication, the biosensor could be placed in one part of the body, and trigger release of neurotransmitters at distant locations. Using such auto-regulated sensing and delivery, or possibly a remote control, new and exciting opportunities for future research and treatment of neurological disorders can be envisaged.”

Using lasers to see the shape of molecules

A scientist in a crisp, white lab coat and protective eye goggles sits behind a safety shield, controller in hand. In front of him is a powerful titanium-sapphire laser, aimed at a crystal lens. His thumb gently squeezes the trigger on the controller. There is an imperceivable wisp of gas that is escaping from a nozzle and crossing the laser’s path. Before he can even blink his eye the laser is capable of firing more than a trillion times. On the screen a line of alternating pairs of glowing, amorphous spots appear. For the first time ever, someone has been able to peer down into the molecular level to observe simultaneously in two dimensions. Professor Hyeok Yun and his team from the Institute for Basic Science (IBS) and Gwangju Institute of Science and Technology (GIST) in Korea have gotten a step closer to fully understanding the complicated relationship of form and motion of molecules ("Resolving Multiple Molecular Orbitals Using Two-Dimensional High-Harmonic Spectroscopy"). Using Lasers to See the Shape of Molecules

(click on image to enlarge) The structure and movement of molecules is not feasible to observe via conventional microscopic methods. In order to get information about molecular shape and the orientation of their orbits, researchers use a process called high harmonic generation (HHG). To do this, a laser pulse tuned to a specific high frequency is directed into a jet of gas of the molecule being studied. When the pulse meets the jet of gas, plasma is generated which emits specific color light. This interaction with the molecule and light generation reveals what is called the highest-occupied molecular orbital (HOMO). The HOMO can be envisioned as the “shape” of the outside molecular orbits. The pulsed laser beam is converted to a high harmonic frequency which reaches the sensor where data from the interaction can be collected. What the researchers see allow them to gather information about the characteristics of molecule’s structure and dynamics. As useful as this technology is, researchers have been limited in what information they can obtain because they have been confined to observing the high harmonic frequency from a single laser pulse on a one-dimensional plane each time. To gather more information from the molecules during each test, Professor Yu’s team, have devised a method for resolving multiple molecular orbitals by using two-dimensional high-harmonic spectroscopy (HHS). This HHS process involves pulsing a laser at an ultra-fast interval through a polarizing lens which splits the beam in two. The team focused the laser through a thin crystal which split the beam into two polarized waves traveling in the same direction but now perpendicular to each other. When one beam traveling up and down while the other is moving side to side, the beams are moving orthogonally. When the two beams interacted with the gas sample, they revealed not only the HOMO, but simultaneously the HOMO-1, a lower lying molecular orbit. In the past these two orbits have been difficult to distinguish from one another, because HOMO-1 has been overshadowed by the more energetic HOMO. According to Yun, “In this work, we approached molecules in two dimensions. HOMO-1 can be revealed with relative ease in the orthogonal direction to the molecular axis, while HOMO does it in a parallel direction. Orthogonally polarized two waves enable us to probe both orbitals in two dimensions and to separate signals to different harmonic frequencies. Thus, we could resolve the signals from the two orbitals and could simultaneously obtained information on both orbitals.” After combining the data collected from each laser pulse the researchers were able to use a clever technique called tomography to piece the two-dimensional images together into a three-dimensional approximation. With the three-dimensional approximation, they were able to discern the shape and relative alignment of the HOMO and HOMO-1 orbitals, something that had never been done before. There is no loud applause, nobody waiting to congratulate Professor Yun on this achievement. “The ultimate goal” he says, “is to follow a chemical reaction in its own time scale. It leads us to have direct insight and to understand fundamental mechanism about transformations in molecular scale. We expect this method can be a route or be of help to achieve the goal.” This new method will advance future molecular research by allowing for independent and simultaneous observation of the structures and dynamics of multiple molecular orbitals. It will enable the observation of multi-orbital dynamics during chemical reactions of more complicated molecules.

Nanostructure design enables pixels to produce two different colors

Through precise structural control, A*STAR researchers have encoded a single pixel with two distinct colors and have used this capability to generate a three-dimensional stereoscopic image ("Three-dimensional plasmonic stereoscopic prints in full colour"). Figuring out how to include two types of information in the same area was an enticing challenge for Xiao Ming Goh, Joel Yang and their colleagues at the A*STAR Institute of Materials Research and Engineering. They knew such a capability could help a range of applications, including ultrahigh-definition three-dimensional color displays and state-of-the-art anti-counterfeiting measures. So they set about designing a nanostructure architecture that could provide more ‘bang for the buck’. Having previously used plasmonic materials to generate color prints at the optical diffraction limit by carefully varying the nanostructure size and spacing, Yang thought polarization would be a promising direction to pursue. “We decided to extend our research to prints that would exhibit different images depending on the polarization of the incident light,” he explains. The main challenge to overcome was the mixing of colors between polarizations, a phenomenon known as cross-talk. Goh and Yang trialed two aluminum nanostructures as pixel arrays: ellipses and two squares separated by a very small space (known as coupled nanosquare dimers). Each pixel arrangement had its own pros and cons. While the ellipses offered a broader color range and were easier to pattern than the nanosquare dimers, they also exhibited a slightly higher cross-talk. In contrast, the coupled nanosquare dimers had a lower cross-talk but suffered from a very narrow color range. Because of their lower cross-talk, the coupled nanosquare dimers were deemed better candidates for encoding two overlaid images on the same area that could be viewed by using different incident polarizations. While the coupled nanosquare dimers’ color palette could be expanded by varying the width and spacing between adjacent squares in each nanosquare dimer, the ellipses were better for demonstrating the wide color range achievable. Furthermore, the researchers used these pixel arrays to generate a three-dimensional stereoscopic image. They achieved this by using ellipses as pixel elements, carefully offsetting the images and choosing background colors that minimized cross-talk. “Being able to print two images onto the same area and, further, generating a three-dimensional stereoscopic image opens up many new avenues for applications,” remarks Goh. But the possibilities do not end there. Complex nanostructures, including circularly asymmetric shapes, offer many more options. “By employing additional circular polarizations, we could encode multiple images — that is, not just two, but three or more images in a single area,” Goh explains.