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Nemiroski, Alex

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Nemiroski

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Alex

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Nemiroski, Alex
Author's Publications: search.filters.isAuthorOfPublication.e530b7d4-e79b-4222-8e45-f94e27c162d2

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Now showing 1 - 9 of 9
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    Engineering Shadows to Fabricate Optical Metasurfaces
    (American Chemical Society (ACS), 2014) Nemiroski, Alex; Gonidec, Mathieu; Fox, Jerome Michael; Jean-Remy, Philip; Turnage, Evan; Whitesides, George
    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.
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    Universal mobile electrochemical detector designed for use in resource-limited applications
    (Proceedings of the National Academy of Sciences, 2014) Nemiroski, Alex; Christodouleas, Dionysios; Hennek, J. W.; Kumar, Ashok Ashwin; Maxwell, E. J.; Fernandez-Abedul, M. T.; Whitesides, George
    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.
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    Noncontact orientation of objects in three-dimensional space using magnetic levitation
    (Proceedings of the National Academy of Sciences, 2014) Subramaniam, A. B.; Yang, Dian; Yu, H.-D.; Nemiroski, Alex; Tricard, S.; Ellerbee, A. K.; Soh, S.; Whitesides, George
    This paper describes several noncontact methods of orienting objects in 3D space using Magnetic Levitation (MagLev). The methods use two permanent magnets arranged coaxially with like poles facing and a container containing a paramagnetic liquid in which the objects are suspended. Absent external forcing, objects levitating in the device adopt predictable static orientations; the orientation depends on the shape and distribution of mass within the objects. The orientation of objects of uniform density in the MagLev device shows a sharp geometry-dependent transition: an analytical theory rationalizes this transition and predicts the orientation of objects in the MagLev device. Manipulation of the orientation of the levitating objects in space is achieved in two ways: (i) by rotating and/or translating the MagLev device while the objects are suspended in the paramagnetic solution between the magnets; (ii) by moving a small external magnet close to the levitating objects while keeping the device stationary. Unlike mechanical agitation or robotic selection, orienting using MagLev is possible for objects having a range of different physical characteristics (e.g., different shapes, sizes, and mechanical properties from hard polymers to gels and fluids). MagLev thus has the potential to be useful for sorting and positioning components in 3D space, orienting objects for assembly, constructing noncontact devices, and assembling objects composed of soft materials such as hydrogels, elastomers, and jammed granular media.
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    Camouflage and Display for Soft Machines
    (American Association for the Advancement of Science (AAAS), 2012) Morin, Stephen A.; Shepherd, Robert F.; Kwok, Sen Wai; Stokes, Adam A.; Nemiroski, Alex; Whitesides, George
    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.
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    Using Magnetic Levitation for Non-Destructive Quality Control of Plastic Parts
    (Wiley-Blackwell, 2015) Hennek, Jonathan; Nemiroski, Alex; Subramaniam, Anand; Bwambok, David K.; Yang, Dian; Harburg, Daniel V.; Tricard, Simon; Ellerbee, Audrey K.; Whitesides, George
    Magnetic levitation (MagLev) enables rapid and non-destructive quality control of plastic parts. The feasibility of MagLev as a method to: i) rapidly assess injection-molded plastic parts for defects during process optimization, ii) monitor the degradation of plastics after exposure to harsh environmental conditions, and iii) detect counterfeit polymers by density is demonstrated.
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    Broadly Available Imaging Devices Enable High-Quality Low-Cost Photometry
    (American Chemical Society (ACS), 2015) Christodouleas, Dionysios; Nemiroski, Alex; Kumar, Ashok Ashwin; Whitesides, George
    This paper demonstrates that, for applications in resource-limited environments, expensive microplate spectrophotometers that are used in many central laboratories for parallel measurement of absorbance of samples can be replaced by photometers based on inexpensive and ubiquitous, consumer electronic devices (e.g., scanners and cell-phone cameras). Two devices, (i) a flatbed scanner operating in transmittance mode and (ii) a camera-based photometer (constructed from a cell phone camera, a planar light source, and a cardboard box), demonstrate the concept. These devices illuminate samples in microtiter plates from one side and use the RGB-based imaging sensors of the scanner/camera to measure the light transmitted to the other side. The broadband absorbance of samples (RGB-resolved absorbance) can be calculated using the RGB color values of only three pixels per microwell. Rigorous theoretical analysis establishes a well-defined relationship between the absorbance spectrum of a sample and its corresponding RGB-resolved absorbance. The linearity and precision of measurements performed with these low-cost photometers on different dyes, which absorb across the range of the visible spectrum, and chromogenic products of assays (e.g., enzymatic, ELISA) demonstrate that these low-cost photometers can be used reliably in a broad range of chemical and biochemical analyses. The ability to perform accurate measurements of absorbance on liquid samples, in parallel and at low cost, would enable testing, typically reserved for well-equipped clinics and laboratories, to be performed in circumstances where resources and expertise are limited.
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    An implantable wireless biosensor for the immediate detection of upper GI bleeding: a new fluorescein-based tool for diagnosis and surveillance (with video)
    (Elsevier BV, 2011) Ryou, Marvin; Nemiroski, Alex; Azagury, Dan; Shaikh, Sohail N.; Ryan, Michele B.; Westervelt, Robert; Thompson, Christopher C.
    Background: Early recurrent hemorrhage after endoscopic intervention for acute upper GI bleeding (UGIB) can approach 20% and leads to increased morbidity and mortality. Little has changed over the past several decades regarding immediate posthemorrhage surveillance, and there has likewise been no significant improvement in outcomes. Objective: To develop and test an endoscopically implantable wireless biosensor for real-time detection of fluorescein-labeled blood in ex vivo and in vivo porcine models of UGIB. Setting: Animal laboratory. Design: Benchtop and acute animal studies. Subjects: Five pigs. Interventions: UGIB models were surgically created in living pigs. Biosensors were endoscopically deployed in the stomach using standard endoscopic clips. The ability to detect acute UGIB and estimated blood loss leading to biosensor activation were recorded. Feasibility of wireless data transmission out of the body to an external computer and cell phone was assessed. Main Outcome Measurements: Technical feasibility and immediate complications. Results: A porcine UGIB model was successfully created. Biosensors were able to detect all acute bleeding events and wirelessly transmit out of the body, and successfully sent an emergency text message to the intended cell phone in all cases. Average estimated blood loss leading to biosensor activation was 30 mL (10 –75 mL). Limitations: Animal study; small numbers. Conclusions: An endoscopically implantable wireless biosensor successfully detected acute hemorrhage in a porcine UGIB model and sent an emergency cell-phone alert in real time.
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    Tilted Magnetic Levitation Enables Measurement of the Complete Range of Densities of Materials with Low Magnetic Permeability
    (American Chemical Society (ACS), 2016) Nemiroski, Alex; Soh, Siowling; Kwok, Sen Wai; Yu, Hai-Dong; Whitesides, George
    Magnetic levitation (MagLev) of diamagnetic or weakly paramagnetic materials suspended in a paramagnetic solution in a magnetic field gradient provides a simple method to measure the density of small samples of solids or liquids. One major limitation of this method, thus far, has been an inability to measure or manipulate materials outside of a narrow range of densities (0.8 g/cm3 <  < 2.3 g/cm3) that are close in density to the suspending, aqueous medium. This paper explores a simple method—“tilted MagLev”—to increase the range of densities that can be levitated magnetically. Tilting the MagLev device relative to the gravitational vector enables the magnetic force to be decreased (relative to the magnetic force) along the axis of measurement. This approach enables many practical measurements over the entire range of densities observed in matter at ambient conditions—from air bubbles ( ≈ 0) to osmium and iridium ( ≈ 23 g/cm3). The ability to levitate, simultaneously, objects with a broad range of different densities provides an operationally simple method that may find application to forensic science (e.g., for identifying the composition of miscellaneous objects or powders), industrial manufacturing (e.g., for quality control of parts), or resource-limited settings (e.g., for identifying and separating small particles of metals and alloys).
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    Automating Microfluidics: Reconfigurable Virtual Channels for Cell and Droplet Transport
    (2012-07-17) Floryan, Caspar Jerzy; Nemiroski, Alex; Westervelt, Robert
    The emerging field of digital microfluidics promises to solve many shortcomings of traditional continuous-flow fluidics. This technology has a few incarnations, including EWOD (eletrowetting on dielectric) and DEP (dielectrophoresis) chips. Both consist of large arrays of electrical pixels which move droplets and cells. They actuate fluids actively, have error feedback, are programmable, perform operations in parallel, and do not rely on external pumps. For these reasons we foresee the increased use of digital microfluidics in the near future. We also foresee a gradual shift away from purpose-built microfluidic devices, towards multi-purpose platforms with specific applications encoded in software. To this extent we present here a new paradigm of encoding and automating microfluidic operations using video files. We use this technology to create several configurations of virtual microfluidic channels and to play film clips using living cells on a DEP chip.