Synthetic systems cannot easily mimic the color-changing abilities of animals such as cephalopods. Soft machines, machines fabricated from soft polymers and flexible reinforcing sheets, are rapidly increasing in functionality. This manuscript describes simple microfluidic networks that can change the color, contrast, pattern, apparent shape, luminescence, and surface temperature of soft machines for camouflage and display. The color of these microfluidic networks can be changed simultaneously in the visible and infrared-a capability that organisms do not have. These strategies begin to imitate the functions, although not the anatomies, of color-changing animals.Main Text: Cephalopods (e.g., squid and cuttlefish) have amazing control over their appearance (color, contrast, pattern, and shape) (1, 2). These animals use dynamic body patterns for disguise, for protection, and for warning. Other animals (e.g., chameleons and many insects) can also actively change their coloration for camouflage or display (3, 4). Yet others (e.g., jellyfish and fireflies) use bioluminescence to communicate (5). The color-changing capabilities of these animals have not been replicated using soft synthetic systems, but such systems could enhance the function of certain machines (e.g., robots or prosthetics). This paper describes our initial approaches to change the color, contrast, pattern, apparent shape, luminescence, and infrared (IR) emission (that is, surface temperature) of soft machines 2 fabricated from elastomers and flexible reinforcing sheets (6-8) by changing the color and pattern of microfluidic networks. These systems are first steps toward imitating the functions, although not the anatomies, of cephalopods (9, 10) and other color-changing animals (4). These animals typically change color using specialized cells, such as chromatophores or iridophores (4, 9, 10), not simple microchannels. The near-perfect matching of environments used by colorchanging organisms with highly developed nervous systems is not required for camouflage to be effective.Nature offers countless examples of camouflage and display (3,11, 12). While specific demonstrations of camouflage vary among species, the strategies used have common themes: background matching, disruptive coloration, and disguise (3,11, 12). In background matching,

This paper describes an inexpensive, handheld device that couples the most common forms of electrochemical analysis directly to "the cloud" using any mobile phone, for use in resource-limited settings. The device is designed to operate with a wide range of electrode formats, performs on-board mixing of samples by vibration, and transmits data over voice using audio-an approach that guarantees broad compatibility with any available mobile phone (from low-end phones to smartphones) or cellular network (second, third, and fourth generation). The electrochemical methods that we demonstrate enable quantitative, broadly applicable, and inexpensive sensing with flexibility based on a wide variety of important electroanalytical techniques (chronoamperometry, cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, and potentiometry), each with different uses. Four applications demonstrate the analytical performance of the device: these involve the detection of (i) glucose in the blood for personal health, (ii) trace heavy metals (lead, cadmium, and zinc) in water for in-field environmental monitoring, (iii) sodium in urine for clinical analysis, and (iv) a malarial antigen (Plasmodium falciparum histidine-rich protein 2) for clinical research. The combination of these electrochemical capabilities in an affordable, handheld format that is compatible with any mobile phone or network worldwide guarantees that sophisticated diagnostic testing can be performed by users with a broad spectrum of needs, resources, and levels of technical expertise.electrochemistry | mHealth | point-of-care diagnostics | low-cost potentiostat | telemedicine E lectrochemistry provides a broad array of quantitative methods for detecting important analytes (e.g., proteins, nucleic acids, metabolites, metals) for personal and public health, clinical analysis, food and water quality, and environmental monitoring (1, 2). Although useful in a variety of settings, these methodswith the important exception of blood glucose meters (3, 4)-are generally limited to well-resourced laboratories run by skilled personnel. If simplified and made inexpensive, however, these versatile methods could become broadly applicable tools in the hands of healthcare workers, clinicians, farmers, and military personnel who need accurate and quantitative results in the field, especially in resource-limited settings. Furthermore, if results of testing were directly linked to "the cloud" through available mobile technology, expertise (and archiving of information) could be geographically decoupled from the site of testing. To enable electrochemical measurements to be performed and communicated in any setting, a useful technology must be (i) able to perform complete electrochemical analyses while remaining low in cost, simple to operate, and as independent of infrastructure as possible; and (ii) compatible with any generation of mobile telecommunications technology, including the low-end phones and 2G networks that continue to dominate communications in much o...

All matter has density. The recorded uses of density to characterize matter date back to as early as ca. 250 BC, when Archimedes was believed to have solved “The Puzzle of The King's Crown” using density.[1] Today, measurements of density are used to separate and characterize a range of materials (including cells and organisms), and their chemical and/or physical changes in time and space. This Review describes a density‐based technique—magnetic levitation (which we call “MagLev” for simplicity)—developed and used to solve problems in the fields of chemistry, materials science, and biochemistry. MagLev has two principal characteristics—simplicity, and applicability to a wide range of materials—that make it useful for a number of applications (for example, characterization of materials, quality control of manufactured plastic parts, self‐assembly of objects in 3D, separation of different types of biological cells, and bioanalyses). Its simplicity and breadth of applications also enable its use in low‐resource settings (for example—in economically developing regions—in evaluating water/food quality, and in diagnosing disease).

Optical metasurfaces-patterned arrays of plasmonic nanoantennas that enable the precise manipulation of light-matter interactions-are emerging as critical components in many nanophotonic materials, including planar metamaterials, chemical and biological sensors, and photovoltaics. The development of these materials has been slowed by the difficulty of efficiently fabricating patterns with the required combinations of intricate nanoscale structure, high areal density, and/or heterogeneous composition. One convenient strategy that enables parallel fabrication of periodic nanopatterns uses self-assembled colloidal monolayers as shadow masks; this method has, however, not been extended beyond a small set of simple patterns and, thus, has remained incompatible with the broad design requirements of metasurfaces. This paper demonstrates a technique-shadow-sphere lithography (SSL)-that uses sequential deposition from multiple angles through plasma-etched microspheres to expand the variety and complexity of structures accessible by colloidal masks. SSL harnesses the entire, relatively unexplored, space of shadow-derived shapes and-with custom software to guide multiangled deposition-contains sufficient degrees of freedom to (i) design and fabricate a wide variety of metasurfaces that incorporate complex structures with small feature sizes and multiple materials and (ii) generate, in parallel, thousands of variations of structures for high-throughput screening of new patterns that may yield unexpected optical spectra. This generalized approach to engineering shadows of spheres provides a new strategy for efficient prototyping and discovery of periodic metasurfaces.

This paper presents methods that use Magnetic Levitation (MagLev) to measure very small differences in density of solid diamagnetic objects suspended in a paramagnetic medium.Previous work in this field has shown that, while it is a convenient method, standard MagLev cannot resolve differences in density < 0.0001 g/mm 3 for macroscopic objects (> mm) because i) objects close in density prevent each other from reaching equilibrium height due to hard contact and excluded volume and ii) using weaker magnets or reducing the magnetic susceptibility of the medium destabilizes the magnetic trap. The present work investigates ways to increase the sensitivity of MagLev without destabilization by i) rotating the standard configuration relative to the gravitational field, and therefore, exploiting the weak magnetic gradients along alternative axes of measurement, and ii) tuning the sensitivity by manipulating the geometries of the magnets. These modifications enable an improvement in the resolution up to 1300 over the standard configuration, and measurements with resolution down to 10 -6 g/cm 3 . Three examples of characterizing the small differences density among "identical" samples of materials-Nylon spheres, PMMA spheres, and drug spheres-demonstrate the applicability of high-sensitivity, rotated Maglev to measure the density of small (0.1 -1 mm) objects with high sensitivity, for use in materials science, separations, and quality control of manufactured products.2