Wireless, battery-free optoelectronic systems as subdermal implants for local tissue oximetry

Monitoring regional tissue oxygenation in animal models and potentially in human subjects can yield insights into the underlying mechanisms of local O2-mediated physiological processes and provide diagnostic and therapeutic guidance for relevant disease states. Existing technologies for tissue oxygenation assessments involve some combination of disadvantages in requirements for physical tethers, anesthetics, and special apparatus, often with confounding effects on the natural behaviors of test subjects. This work introduces an entirely wireless and fully implantable platform incorporating (i) microscale optoelectronics for continuous sensing of local hemoglobin dynamics and (ii) advanced designs in continuous, wireless power delivery and data output for tether-free operation. These features support in vivo, highly localized tissue oximetry at sites of interest, including deep brain regions of mice, on untethered, awake animal models. The results create many opportunities for studying various O2-mediated processes in naturally behaving subjects, with implications in biomedical research and clinical practice.Center for Bio-Integrated Electronics at Northwestern University; Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF) [ECCS-1542205]; Materials Research Science and Engineering Center [DMR-1720139]; State of Illinois; Northwestern University; Developmental Therapeutics Core at Northwestern University; Robert H. Lurie Comprehensive Cancer Center [NCI CA060553]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Superchiral Light Generation On Degenerate Achiral Surfaces

A novel route of superchiral near-field generation is demonstrated based on geometrically achiral systems supporting degenerate and spatially superimposed plasmonic modes. Such systems generate a single-handed chiral near field with simultaneous zero far-field circular dichroism. The phenomenon is theoretically elucidated with a rotating dipole model, which predicts a uniform single-handed chiral near field that flips handedness solely by reversing the handedness of the source. This property allows detection of pure background free molecular chirality through near-field light-matter interaction, which is experimentally demonstrated in the precise identification of both handedness of a chiral molecule on a single substrate with about four orders of magnitude enhancement in detection sensitivity compared to its conventional volumetric counterpart

Superchiral Light Generation On Achiral Nanostructured Surfaces

In this work, we demonstrate superchiral light generation based on achiral plasmonic surfaces. At resonance, the symmetric cavity-coupled plasmonic system generates single-sign chiral near-field whose helicity is determined solely by the handedness of the incident light. We elucidate the mechanism for such unique superchiral near field generation and find its origin in coherent and synergetic interactions between plasmonic and photonic cavity modes. The cavity-coupling enhances otherwise weak plasmonic chiral near-field by many folds. Furthermore, the system in a unique way suppresses the far field chirality due to its totally symmetric geometry providing a route for surface-enhanced chiroptic spectroscopy on a single surface

Broadband angle-independent antireflection coatings on nanostructured light trapping solar cells

Backscattering from nanostructured surfaces greatly diminishes the efficacy of light trapping solar cells. While the analytical design of broadband, angle-independent antireflection coatings on nanostructured surfaces proved inefficient, numerical optimization proves a viable alternative. Here, we numerically design and experimentally verify the performance of single and bilayer antireflection coatings on a 2D hexagonal diffractive light trapping pattern on crystalline silicon substrates. Three well-known antireflection coatings, aluminum oxide, silicon nitride, and silicon oxide, which also double as high-quality surface passivation materials, are studied in the 400-1000 nm band. By varying thickness and conformity, the optimal parameters that minimize the broadband total reflectance (specular and scattering) from the nanostructured surface are obtained. The design results in a single-layer antireflection coating with normal-angle wavelength-integrated reflectance below 4% and a bilayer antireflection coating demonstrating reflection down to 1.5%. We show experimentally an angle-averaged reflectance of ∼5.2% up to 60° incident angle from the optimized bilayer antireflection-coated nanostructured surface, paving the path toward practical implementation of the light trapping solar cells

Broadband Angle-Independent Antireflection Coatings On Nanostructured Light Trapping Solar Cells

Backscattering from nanostructured surfaces greatly diminishes the efficacy of light trapping solar cells. While the analytical design of broadband, angle-independent antireflection coatings on nanostructured surfaces proved inefficient, numerical optimization proves a viable alternative. Here, we numerically design and experimentally verify the performance of single and bilayer antireflection coatings on a 2D hexagonal diffractive light trapping pattern on crystalline silicon substrates. Three well-known antireflection coatings, aluminum oxide, silicon nitride, and silicon oxide, which also double as high-quality surface passivation materials, are studied in the 400-1000 nm band. By varying thickness and conformity, the optimal parameters that minimize the broadband total reflectance (specular and scattering) from the nanostructured surface are obtained. The design results in a single-layer antireflection coating with normal-angle wavelength-integrated reflectance below 4% and a bilayer antireflection coating demonstrating reflection down to 1.5%. We show experimentally an angle-averaged reflectance of ∼5.2% up to 60° incident angle from the optimized bilayer antireflection-coated nanostructured surface, paving the path toward practical implementation of the light trapping solar cells

Multi-Spectral Infrared Spectroscopy For Robust Plastic Identification

The identification and classification of plastics plays an important role in waste management and recycling processes. Present electrical and optical sorting techniques lack the required resolution for accurate identification in a high throughput manner for a diverse set of plastics commonly found in municipal waste. In this work a multispectral infrared spectroscopic technique is employed to construct a unique fingerprint library of 12 plastic resin groups that are commonly encountered in municipal waste. We test the proposed method in a blind plastic identification experiment, which shows excellent unbiased identification accuracy. This simple optical technique in combination with the multi-spectral library will enable high throughput and accurate detection of various plastics from recovered solid waste

Dynamically Tunable Extraordinary Light Absorption In Monolayer Graphene

The high carrier mobility of graphene makes it an attractive material for electronics, however, graphene\u27s application for optoelectronic systems is limited due to its low optical absorption. We present a cavity-coupled nanopatterned graphene absorber designed to sustain temporal and spatial overlap between localized surface plasmon resonance and cavity modes, thereby resulting in enhanced absorption up to an unprecedented value of theoretically (60%) and experimentally measured (45%) monolayer graphene in the technologically relevant 8-12-μm atmospheric transparent infrared imaging band. We demonstrate a wide electrostatic tunability of the absorption band (∼2μm) by modifying the Fermi energy. The proposed device design allows enhanced absorption and dynamic tunability of chemical vapor deposition grown low carrier mobility graphene which provides a significant advantage over previous strategies where absorption enhancement was limited to exfoliated high carrier mobility graphene. We developed an analytical model that incorporates the coupling of the graphene electron and substrate phonons, providing valuable and instructive insights into the modified plasmon-phonon dispersion relation necessary to interpret the experimental observations. Such gate voltage and cavity tunable enhanced absorption in chemical vapor deposited large area monolayer graphene paves the path towards the scalable development of ultrasensitive infrared photodetectors, modulators, and other optoelectronic devices

Covert Infrared Image Encoding Through Imprinted Plasmonic Cavities

Functional surfaces that can control light across the electromagnetic spectrum are highly desirable. Plasmonic nanostructures can assume this role by exhibiting dimension-tunable resonances that span multiple electromagnetic regimes. However, changing these structural parameters often impacts the higher-order resonances and spectral features in lower-wavelength domains. In this study, we discuss a cavity-coupled plasmonic system with resonances that are tunable across the 3–5 or 8–14 μm infrared bands while retaining near-invariant spectral properties in the visible domain. This result is accomplished by regime-dependent resonance mechanisms and their dependence on independent structural parameters. Through the identification and constraint of key parameters, we demonstrate multispectral data encoding, where images, viewable in the infrared spectral domain, appear as uniform areas of color in the visible domain—effectively hiding the information. Fabricated by large area nanoimprint lithography and compatible with flexible surfaces, the proposed system can produce multifunctional coatings for thermal management, camouflage, and anti-counterfeiting

Polyimide For Silicon Solar Cells With Double-Sided Textured Pyramids

Silicon solar cells incorporating double-sided pyramidal texture are capable of superior light trapping over cells with front-side only texture. However, increased surface area, roughness and exposed \u3c111\u3e crystal planes of textured surfaces not only causes increased recombination, but also makes cells susceptible to shunting through pinholes in the dielectric at the sharp peaks and valleys of the textured pyramids. A polyimide film as an insulating interlayer film is investigated to circumvent the tradeoff between improved light trapping, increased recombination and increased shunt paths. When applied at the rear of the interdigitated back contact silicon solar cell structure, the polyimide film provides an excellent electrical insulation (\u3e 1000 MΩ of insulation resistance) and increases photocurrent (~ 1.1 mA/cm2) owing to an increased rear internal reflectance. The polyimide is also compatible with metal annealing of passivating dielectrics such as silicon nitride. Optical simulation and experimental results are combined in a 3D semiconductor simulation (Quokka) to quantify the possible gain of implementing the double-sided texture in high efficiency silicon solar cells

Covert infrared image encoding through imprinted plasmonic cavities

Undercover images: Hiding in plasmonic sight A new device employing the science of ‘plasmonics’ allows control over the interaction of various wavelengths of light with its components, with implications for camouflage and anti-counterfeit applications. The device, designed by Debashis Chanda and colleagues of the University of Central Florida, is formed of a dielectric layer patterned with regularly-spaced nano-sized holes, sandwiched between a reflective metallic mirror and a thin upper gold layer with holes corresponding to the middle layer’s discs. Images are encoded onto the surface in spun coat films of thermoplastic. Changing the diameters and depths of the holes changes how different wavelengths of light react with the materials. The team was able to tune the device’s parameters in a way that made the surface appear as a uniform block of colour unless viewed through an infrared camera over a specific band, when the image can be seen