A repository & source of cutting edge news about emerging terahertz technology, it's commercialization & innovations in THz devices, quality & process control, medical diagnostics, security, astronomy, communications, applications in graphene, metamaterials, CMOS, compressive sensing, 3d printing, and the Internet of Nanothings. NOTHING POSTED IS INVESTMENT ADVICE! REPOSTED COPYRIGHT IS FOR EDUCATIONAL USE.
High-resolution and fast-paced optical microscopy is a requirement for current trends in biotechnology and materials industry. The most reliable and adaptable technique so far to obtain higher resolution than conventional microscopy is near-field scanning optical microscopy (NSOM), which suffers from a slow-paced nature. Stemming from the principles of diffraction imaging, we present fast-paced graphene-based scanning-free wide-field optical microscopy that provides image resolution that competes with NSOM. Instead of spatial scanning of a sharp tip, we utilize the active reconfigurable nature of graphene’s surface conductivity to vary the diffraction properties of a planar digitized atomically thin graphene sheet placed in the near field of an object. Scattered light through various realizations of gratings is collected at the far-field distance and postprocessed using a transmission function of surface gratings developed on the principles of rigorous coupled wave analysis. We demonstrate image resolutions of the order of 𝜆0/16 using computational measurements through binary graphene gratings and numerical postprocessing. We also present an optimization scheme based on the genetic algorithm to predesign the unit cell structure of the gratings to minimize the complexity of postprocessing methods. We present and compare the imaging performance and noise tolerance of both grating types. While the results presented in this article are at terahertz frequencies (𝜆0=10μm), where graphene is highly plasmonic, the proposed microscopy principle can be readily extended to any frequency regime subject to the availability of tunable materials.
A polaritonic photonic crystal made by DNA-programmable assembly. (A) Three-dimensional illustration of a plasmonic PPC, in the shape of a rhombic dodecahedron, assembled from DNA-modified gold nanoparticles. Red arrows indicate light rays normal to the underlying substrate, impinging on and backscattering through a top facet of the crystal (FPMs). The blue ones represent light rays entering through the slanted side facets and leaving the PPC through the opposite side, not contributing to the FPMs (Fig. S2). The top right inset shows the top view of the crystal with two sets of arrows defining two polarization bases at the top and side facets. The bottom right inset shows an SEM image of a representative single crystal corresponding to the orientation of the top right inset. (Scale bar, 1 μm.) (B) A 2D scheme showing the geometric optics approximation of backscattering consistent with the explanation in A. The hexagon outline is a vertical cross-section through the gray area in the top right inset of A parallel to its long edge. The box enclosed by a dashed line depicts the interaction between localized surface plasmons and photonic modes (red arrows; FPMs) with a typical near-field profile around gold nanoparticles. The contribution of backscattering through the side facets (blue arrows) to FPMs is negligible. (C) Scheme of plasmon polariton formation. The localized surface plasmons (yellow bar) strongly couple to the photonic modes (red bars; FPMs). Credit: Park DJ, et al. (2014) Plasmonic photonic crystals realized through DNA-programmable assembly. Proc Natl Acad Sci USA Published online before print on December 29, 2014.
(Phys.org)—As biotechnology and nanotechnology continue to merge, DNA-programmable methods have emerged as a way to provide unprecedented control over the assembly of nanoparticles into complex structures, including customizable periodic structures known as superlattices that allow fine tuning the interaction between light and highly organized collections of particles. Lattice structures have historically been two-dimensional because fabricating three-dimensional DNA lattices has been too difficult, while three-dimensional dielectric photonic crystals have well-established enhanced light–matter interactions. However, the dearth of synthetic means of creating plasmonic crystals (those that exploit surface plasmons produced from the interaction of light with metal-dielectric materials) based on arrays of nanoparticles has prevented them from being experimentally studied. At the same time, it has been suggested that polaritonic photonic crystals (PPCs) – plasmonic counterparts of photonic crystals – can prohibit light propagation and open a photonic band gap (also known as a polariton gap) by strong coupling between surface plasmons and photonic modes if the crystal is in a deep subwavelength size regime. (Polaritons are quasiparticles resulting from strong coupling of electromagnetic waves with an electric or magnetic dipole-carrying excitation.)
To that end, scientists at Northwestern University recently reported strong light-plasmon interactions within 3D plasmonic photonic crystals that have lattice constants and nanoparticle diameters that can be independently controlled in the deep subwavelength size regime by using a DNA-programmable assembly technique – the first devices prepared by DNA-guided colloidal crystallization. The researchers have shown that they can tune the interaction between light and the collective electronic modes of gold nanoparticles by independently adjusting lattice constants and gold nanoparticle diameters, adding that their results in tuning interactions between light and highly-organized nanoscale collections of particles suggest the possibility of applications that include lasers, quantum electrodynamics and biosensing.
Prof. George C. Schatz discussed the paper that he, Prof. Chad A. Mirkin, lead author Daniel J. Park and their co-authors published in Proceedings of the National Academy of Sciences by first addressing the main challenges the scientists encountered in tuning the interaction between light and the collective electronic modes of gold nanoparticles by independently adjusting lattice constants and gold nanoparticle diameters. "The wavelength associated with photonic resonance modes" – such as the Fabry-Pérot interactions that occur with interferometers of the same name – "is defined by an interference condition that depends on geometry of the microstructure, as well as on the effective index of refraction of the material in the microstructure," Schatz tellsPhys.org. "At the same time, the wavelength of plasmon resonances in a gold nanoparticle is determined by collective electron excitation in the particle and depends on the size and shape of the nanoparticle as well as on gold's refraction index." The researchers addressed this by fabricating superlattice materials that allow for independently tuning these two wavelengths, and therefore to study the interactions between the resonance modes. Moreover, he adds, the researchers found a range of superlattice and nanoparticle parameters where the photonic modes could be observed both below and above the plasmon energy – that is, its resonance wavelength – enabling them to observe a band gap that indicates strong coupling between the modes.
A second key aspect of their research was using DNA-guided colloidal crystallization to independently control strong light-plasmon interactions within 3D plasmonic photonic crystals that have lattice constants and nanoparticle diameters, as well as synthesizing plasmonic PPCs (polaritonic photonic crystals) from gold nanoparticles. "Prior to our paper and work published last year1by our colleagues at Northwestern in Prof. Mirkin's group, the DNA-guided crystallization method had been developed for making superlattice materials with variable gold particle size and lattice spacing," Schatz explains.
Experimental and theoretical backscattering spectra of PPC1–3. (A) SEM image (Top) and optical bright field reflection mode image (Bottom) of PPC1 on a silicon substrate. (Scale bar, 1 μm.) (B) Measured backscattering spectrum (red solid …more
"However," he continues, "the materials were polycrystalline, and therefore did not exhibit well-defined photonic modes that can allow for probing the interaction between light and surface plasmons. A key advance was the discovery1 of a method for making superlattice single crystals with a well-defined crystal habit – that is, a rhombic dodecahedral shape – and variable size on the order of a few microns." Nevertheless, it was still unclear that there would be optical modes of high enough quality for Fabry-Pérot resonances to be observed and be tuned across the plasmon resonance. "It took several months to theoretically and experimentally probe and confirm the presence of Fabry-Pérot resonances," Schatz adds.
Schatz and his colleagues addressed these challenges by using measurements of backscattering – the reflection of waves, particles, or signals back to the source direction – to probe Fabry-Pérot modes. "Although backscattering measurements have been used in other contexts, this was the first application of this technology to DNA superlattice crystals, and it wasn't immediately clear to us that Fabry-Pérot resonances could be observed for this crystal habit and choice of material," Schatz notes. However, as detailed in their current paper, the scientists developed a realistic theoretical model of this experiment that predicted the existence of Fabry-Pérot modes and the possibility of observing them via backscattering while doing the experiments. "This stimulated us to do the experiments and persist with this work even though the early results were of poor quality. Furthermore, we used the computational model to guide in optimizing the experiment – including the work in which we coated PPCs with silver."
In their paper, the researchers discussed further photonic studies and possible applications in lasers, cavity quantum electrodynamics, quantum optics, quantum many-body dynamics, biosensing and other areas suggested by tuning nanoscale light-plasmon interactions. "Past work has observed quantum electrodynamics behavior in dielectric optical cavities, including enhanced and suppressed fluorescence from emitters in these cavities. The present experiments suggest that this type of measurement can be extended to cavities where hybrid plasmonic/photonic modes occur." He emphasizes that while quantum electrodynamics phenomena via 2D hybrid plasmonic/photonic modes have already been observed for the last several years, their system opens a unique opportunity to utilize 3D crystal modes that contain plasmonic properties. "As a possible application, since plasmon-enhanced lasers have been observed with 2D lattices, the successful observation of 3D hybrid photonic-plasmonic modes suggests that such lasers can be prepared for 3D lattices."
Another interesting finding is the tunability of DNA interconnects and the corresponding volume fraction of the plasmonic elements. "Tunability of the DNA interconnects provides the ability to change the lattice constant," Schatz explains," and with a certain size of nanoparticle, by varying the lattice constant we can tune the gold volume."
A schematic description of the backscattering signal detection setup. The blue arrows indicate the light incident on the sample and the red arrows the reflected light. Only the reflection mode, not the transmission mode, is reflected. Credit: …more
When asked if their findings might interact with or contribute to developments in synthetic biology and synthetic genomics, as well as the accelerating integration of biotechnology and nanotechnology in translational medicine, Schatz pointed out that DNA provides a synthetic 'hook' that can be connected to synthetic biology. "We can therefore envision using the genetic programmability of DNA as input to the synthesis of fluorescent proteins in precise locations," adding that the medical applications of DNA-programmed superlattice materials are only at the concept stage. "From earlier work in the Mirkin group, we know how to use gold nanoparticles coated with DNA in medical diagnostics and therapeutics, so one can imagine future applications where these applications are extended to superlattices. A key point is that the superlattices provide a systematic tool for building structures that combine together inorganic components, such as metal or semiconductor nanoparticles with biomolecules."
Moving forward, Schatz says, the researchers need to generalize the menu of superlattice crystals. "The micron-scale crystal habits exhibit other photonic modes – that is, functionalities – such as whispering gallery resonance and light focusing. In addition, other nanoparticle components such as silver nanoparticles and quantum dots can be incorporated into superlattices." This means that the scientists can play with a large number of photonic/electronic degrees of freedom within the framework of a DNA superlattice. "Therefore, we need to establish a well-defined set of photonic applications and studies utilizing and combining those physical degrees of freedom – and theory will play an important role in this process."
PPC silver coating process. (A) A PPC on a glass slide. (B) A silver layer is deposited on the PPC. (C) The uncoated bottom side of the PPC is exposed after sticking the PPC to the top surface of a PDMS pillar. (D) Another layer of silver is …more
In terms of additional innovations, Schatz tells Phys.org that "now that we know that plasmon-photonic interactions can exhibit strong coupling, we need to expand this research, probably with different nanoparticles and with different types of photonic resonances. For example, we can incorporate anisotropic nanoparticles that exhibit more interesting plasmonic response to polarization of light – and utilizing other available photonic modes that exhibit light focusing features, we can think about developing optical components such as a plasmonic microlens. Finally, synthesizing quantum dot nanoparticle superlattices, we can perform fundamental physics studies related to the collective exciton emission."
Schatz concludes that other areas of research might also benefit from their study. "We're excited about the possibility of using superlattice materials not just in photonics, but also in energy-related applications, including photovoltaics, photocatalysis, and batteries."
More information: Plasmonic photonic crystals realized through DNA-programmable assembly, Proceedings of the National Academy of Sciences published online before print December 29 2014, doi:10.1073/pnas.1422649112
Related:
1DNA-mediated nanoparticle crystallization into Wulff polyhedral, Nature (2014)505(7481):73–77, doi:10.1038/nature12739
Wearable companies all over the world are racing to create devices that tell you what’s going on in your body. They’re on sports bras, wristwatches, necklaces and even cocktail rings. They can be stuck on wounded areas to measure pain. And then there’s WiseWear, whose tiny platform promises to “See Inside” the body and “collect contextually aware data that is automated and derived from multiple sources.”WiseWear’s tiny sensor platform monitors heart rate, movement—including what your exercise regime is producing–and dehydration, and its Bluetooth device lets it communicate with other devices to monitor health.
“Sensor technology empowers individuals to live a happy, healthy and productive life,” said CEO and Founder Jerry Wilmink. “This lets you really see everything that happens in the body. The first generation of wearables only measured one or two things and in many cases it was highly inaccurate. This is a platform and there are several use cases ranging from a patch to a watch version…. It’s highly accurate monitoring captures and gives you a really good pulse on what’s happening inside your body.”
WiseWear plans to launch a crowdfunding campaign in August for pre-sales of its first wearable device, called “Evolve,” according to a company press release. The device “adheres directly to the user’s chest with ultrathin, ultra soft, transfer-printed micro-circuitry and sensors.” The device collects biometric data that is then transmitted wirelessly to a smartphone or tablet for data analysis.
Wilmink’s Background
Wilmink got his bachelor’s and master’s in biochemical engineering at Vanderbilt then, he said “Snuck into the Ph.D. program.” When he graduated, he was a research associate with the National Academy of Sciences and then moved to the Department of Defense where he founded the first Terahertz bioeffects research laboratory where he began to develop WiseWear. “I hand picked the talent and grew it from nothing to a pretty big laboratory. We were connecting the dots, being creative, finding the talent, building a rock star team with tremendous potential.” For the first time, he said, he wasn’t competing on pure IQ but on creativity. That became his prime criteria for teammates.
Wilmink also received his Executive MBA from the McCombs School of Business at the University of Texas at Austin, class of 2014.
Creating WiseWear
His interest in biotechnology, Wilmink said, came from growing up with his grandparents. Once his grandfather—a Sicilian with a black Cadillac who smoked cigars and listened to Sinatra—fell. He seemed fine on Thanksgiving and ended up dying the day after Christmas. The fall, it turns out, was because of a change in his grandfather’s gait, which is an indication of dehydration.
“If we had noticed he had changes in his gait, we could have prevented him from falling,” Wilmink said. “Our initial product was a line sensor system to pick up when a senior was dehydrated and his gait was changing. Fifty percent of seniors over the age of 65 who fall end up passing away in the next six months. And that’s not connected to the severity of the fall.”
Keeping track of what’s going on inside the body before it manifests in a negative way is a big step toward prevention, according to WiseWear advisor, Dr. David Katz Head of Yale Health & Preventative Medicine.
“WiseWear is designed to … provide personalized, real-time feedback about an individual’s daily activities fully integrated with accurate heart rate, respiration, hydration, and by providing direction, motivation, and even a kind of oversight and accountability. This kind of feedback is known to encourage healthy behaviors- and now you can get it from something that’s practically a part of you.”
“This allows a user to take a proactive kind of action to treat health and wellness rather than treat disease, “ Wilmink said. And running this company, after his long journey is “all, absolutely exhilarating.”
Founded in March of 2013, WiseWear is based in both San Antonio and Austin. The company recently moved into Geekdom, a coworking space and technology incubator in downtown San Antonio. Wilmink has raised more than $1 million in seed stage funding, and the company plans to raise a Series A round of funding next year. Wilmink has put together a team of experts including Ph.Ds, MBAs, C-Level executives and others. The company has also licensed its intellectual property from the University of Texas, according to a company release.
WiseWear plans to release its consumer products and then pursue clinical trials and FDA approval for a line of medical products. The company has plans for a device called WiseDoctor to accurately record a patient’s vital signs, hydration and activity in a hospital setting. Future products will be targeted at monitoring babies, seniors, diabetics and even pets.
Editor’s note: THis article appears in the Silicon Hills News print edition on the Life Sciences industry in central Texas.
