Publications

2014
Savo S, Zhou Y, Castaldi G, Moccia M, Galdi V, Ramanathan S, Sato Y. Reconfigurable anisotropy and functional transformations with metamaterial electric circuits [Internet]. arxiv.org 2014; Publisher's VersionAbstract

We demonstrate an innovative multifunctional artificial material that combines exotic metamaterial properties and the environmentally responsive nature of phase change media. The tunable metamaterial is designed with the aid of two interwoven coordinate-transformation equations and implemented with a network of thin film resistors and vanadium dioxide (VO2). The strong temperature dependence of VO2 electrical conductivity results in a relevant modification of the resistor network behavior, and we provide experimental evidence for a reconfigurable metamaterial electric circuit (MMEC) that not only mimics a continuous medium but is also capable of responding to thermal stimulation through dynamic variation of its spatial anisotropy. Upon external temperature change the overall effective functionality of the material switches between a "truncated-cloak" and "concentrator" for electric currents. Possible applications may include adaptive matching resistor networks, multifunctional electronic devices, and equivalent artificial materials in the magnetic domain. Additionally, the proposed technology could also be relevant for thermal management of integrated circuits

2014_savo_physics_optics.pdf
Vickers DAL, Ouyang M, Choi CH, Hur SJC. Direct drug cocktail analyses using microscale vortex-assisted electroporation. Analytical Chemistry 2014;86:10099-10105.Abstract

Combination therapy has become one of the leading approaches for treating complex diseases because it coadministers clinically proven drugs to concurrently target multiple signaling pathways of diseased cells. Identification of synergic drug combinations at their respective effective doses without unwanted accumulative side effects is the key to success for such therapy. In this work, we demonstrate the feasibility of the vortex-assisted microfluidic electroporation system for direct drug cocktail analyses where drug substances were individually delivered into cytosols in a sequential and dosage-controlled manner. Through quantitative analyses, the synergic combinational dosage ratios of the chemotherapeutic drug and the anticancer flavonoid were identified. When integrated with high-throughput label-free rare cell purification techniques, the presented system has the potential for development of personalized medicines as the system would be capable of comprehensively assessing drug combinations directly on patients’ cellular samples.

Vickers DAL, Hur SJC. Microscale vortex-assisted electroporator for sequential molecular delivery. JoVE 2014;90(e51702)Abstract

Electroporation has received increasing attention in the past years, because it is a very powerful technique for physically introducing non-permeant exogenous molecular probes into cells. This work reports a microfluidic electroporation platform capable of performing multiple molecule delivery to mammalian cells with precise and molecular-dependent parameter control. The system’s ability to isolate cells with uniform size distribution allows for less variation in electroporation efficiency per given electric field strength; hence enhanced sample viability. Moreover, its process visualization feature allows for observation of the fluorescent molecular uptake process in real-time, which permits prompt molecular delivery parameter adjustments in situ for efficiency enhancement. To show the vast capabilities of the reported platform, macromolecules with different sizes and electrical charges (e.g., Dextran with MW of 3,000 and 70,000 Da) were delivered to metastatic breast cancer cells with high delivery efficiencies (>70%) for all tested molecules. The developed platform has proven its potential for use in the expansion of research fields where on-chip electroporation techniques can be beneficial.

Chen A, Sanchez A, Dai L, Gore J. Dynamics of a producer-parasite ecosystem on the brink of collapse. [Internet]. Nature Communications 2014;5:3713. Publisher's VersionAbstract

Ecosystems can undergo sudden shifts to undesirable states, but recent studies with simple single-species ecosystems have demonstrated that advance warning can be provided by the slowing down of population dynamics near a tipping point. However, it is unclear how this ‘critical slowing down’ will manifest in ecosystems with strong interactions between their components. Here we probe the dynamics of an experimental producer-freeloader ecosystem as it approaches a catastrophic collapse. Surprisingly, the producer population grows in size as the environment deteriorates, highlighting that population size can be a misleading measure of ecosystem stability. By analysing the oscillatory producer-freeloader dynamics for over 100 generations in multiple environmental conditions, we find that the collective ecosystem dynamics slow down as the tipping point is approached. Analysis of the coupled dynamics of interacting populations may therefore be necessary to provide advance warning of collapse in complex communities.

2014_chen_nature_communications.pdf
Moccia M, Castaldi G, Savo S, Sato Y, Galdi V. Independent manipulation of heat and electrical current via bifunctional metamaterials. Physical Review X 2014;4Abstract

Spatial tailoring of the material constitutive properties is a well-known strategy to mold the local flow of given observables in different physical domains. Coordinate-transformation-based methods (e.g., trans-formation optics) offer a powerful and systematic approach to design anisotropic, spatially inhomogeneous artificial materials (metamaterials) capable of precisely manipulating wave-based (electromagnetic, acoustic, elastic) as well as diffusion-based (heat) phenomena in a desired fashion. However, as versatile as these approaches have been, most designs have thus far been limited to serving single-target functionalities in a given physical domain. Here, we present a step towards a “transformation multiphysics” framework that allows independent and simultaneous manipulation of multiple physical phenomena. As a proof of principle of this new scheme, we design and synthesize (in terms of realistic material constituents) a metamaterial shell that simultaneously behaves as a thermal concentrator and an electrical “invisibility cloak.” Our numerical results open up intriguing possibilities in the largely unexplored phase space of multifunctional metadevices, with a wide variety of potential applications to electrical, magnetic, acoustic, and thermal scenarios.

2014_moccia_pr.pdf
Schonbrun E, Möller G, Caprio GD. Polarization encoded color camera [Internet]. Optics Letters [Internet] 2014;39(6):1433-1436. Publisher's VersionAbstract

Digital cameras would be colorblind if they did not have pixelated color filters integrated into their image sensors. Integration of conventional fixed filters, however, comes at the expense of an inability to modify the camera’s spectral properties. Instead, we demonstrate a micropolarizer-based camera that can reconfigure its spectral response. Color is encoded into a linear polarization state by a chiral dispersive element and then read out in a single exposure. The polarization encoded color camera is capable of capturing three-color images at wavelengths spanning the visible to the near infrared.

2014_schonbrun_cytometry.pdf
Sato Y. Sagnac-based rotation sensing with superfluid helium quantum interference devices. Comptes Rendus de l’Academie des Sciences 2014;15(10):898-906.Abstract

The Sagnac effect has played an instrumental role for the fundamental studies of relativity, and various devices that utilize this effect have been applied to many disciplines ranging from inertial navigation to geodesy and to seismology. In this context we present an overview of recent developments related to superfluid helium quantum interference devices. With the discovery of superfluid Josephson phenomena in View the MathML source, the device technology has been rapidly developing in the past 10 years. We discuss the underlying working principles of these interference devices and their applications. We focus on their use as sensitive rotation sensors based on the Sagnac effect coupled with the existence of a macroscopic quantum phase via particle–wave duality.

Harrington KI, Sanchez A. Eco-evolutionary dynamics of complex social strategies in microbial communities. [Internet]. Communicative & Integrative Biology 2014;7(1) Publisher's VersionAbstract

Microbial communities abound with examples of complex social interactions that shape microbial ecosystems. One particularly striking example is microbial cooperation via the secretion of public goods. It has been suggested by theory, and recently demonstrated experimentally, that microbial population dynamics and the evolutionary dynamics of cooperative social genes take place with similar timescales, and are linked to each other via an eco-evolutionary feedback loop. We overview this recent evidence, and discuss the possibility that a third process may be also part of this loop: phenotypic dynamics. Complex social strategies may be implemented at the single-cell level by means of gene regulatory networks. Thus gene expression plasticity or stochastic gene expression, both of which may occur with a timescale of one to a few generations, can potentially lead to a three-way coupling between behavioral dynamics, population dynamics, and evolutionary dynamics

Schonbrun E, Malka R, Caprio GD, Schaak D, Higgins JM. Quantitative absorption cytometry for measuring red blood cell hemoglobin mass and volume [Internet]. Journal of Cytometry 2014; Publisher's Version 2014_schonbrun_cytometry.pdf
Packard R, Sato Y. Superfluid helium quantum interference devices: principles & performance. In: Journal of Physics: Conference Series. 2014 2014_packard_27th_int._conference_on_low_temp._physics.pdf
Sato Y. Manipulation of heat flow. In: McGraw-Hill Yearbook of Science & Technology. McGraw-Hill Education; 2014Abstract

Artificial materials engineered to exhibit properties that do not typically exist in nature are often called metamaterials, and these unique materials have attracted a significant amount of scientific interest in recent years. Just as conventional materials owe their properties to the average response from an ensemble of atoms and molecules, in “artificial” materials, each structural unit plays the role of an atom. The material properties are controlled not only by what elements are used and their individual properties, but also by the way they are arranged collectively in lattice-like geometrical patterns with prescribed spatial variations. This immense flexibility is one of the main reasons why material engineering has become such an explosive catalyst in so many scientific disciplines. For example, metamaterials applied to the manipulation of electromagnetic waves have demonstrated some counterintuitive concepts such as a negative index of refraction, which allows light to bend at the interface of materials in a direction opposite to what you would observe from any ordinary materials. The concept of artificial material engineering has extended beyond conventional material science and it has now started to be applied to the manipulation of heat flow.

Webster A, Vollmer F, Sato Y. Probing biomechanical properties with a centrifugal force quartz crystal microbalance. Nat. Commun. 2014;5:5284.Abstract

Application of force on biomolecules has been instrumental in understanding biofunctional behaviour from single molecules to complex collections of cells. Current approaches, for example, those based on atomic force microscopy or magnetic or optical tweezers, are powerful but limited in their applicability as integrated biosensors. Here we describe a new force-based biosensing technique based on the quartz crystal microbalance. By applying centrifugal forces to a sample, we show it is possible to repeatedly and non-destructively interrogate its mechanical properties in situ and in real time. We employ this platform for the studies of micron-sized particles, viscoelastic monolayers of DNA and particles tethered to the quartz crystal microbalance surface by DNA. Our results indicate that, for certain types of samples on quartz crystal balances, application of centrifugal force both enhances sensitivity and reveals additional mechanical and viscoelastic properties.

2014_webster_.pdf
2013
Hausmann BJM, Shields BJ, Quan Q, Chu Y, de Leon NP, Evans M, Burek J, Zibrov AS, Markham M, Twitchen DJ, Park H, Lukin MD, Loncar M. Coupling of NV centers to photonic crystal nanobeams in diamond. Nano Letters 2013;13:5791.Abstract
Abstract Image

The realization of efficient optical interfaces for solid-state atom-like systems is an important problem in quantum science with potential applications in quantum communications and quantum information processing. We describe and demonstrate a technique for coupling single nitrogen vacancy (NV) centers to suspended diamond photonic crystal cavities with quality factors up to 6000. Specifically, we present an enhancement of the NV center’s zero-phonon line fluorescence by a factor of ∼7 in low-temperature measurements.

nl402174g.pdf
Liang F, Clarke NA, Patel R, Loncar M, Quan Q. Scalable nanobeam photonic sensors for high sensitivity protein detection [Internet]. Optics Express 2013;21:32306. Publisher's VersionAbstract

Scalable microfabrication technology has enabled semiconductor and microelectronics industries, among other fields. Meanwhile, rapid and sensitive bio-molecule detection is increasingly important for drug discovery and biomedical diagnostics. In this work, we designed and demonstrated that photonic crystal sensor chips have high sensitivity for protein detection and can be mass-produced with scalable deep-UV lithography. We demonstrated label-free detection of carcinoembryonic antigen from pg/mL to μg/mL, with high quality factor photonic crystal nanobeam cavities.

oe-21-26-32306.pdf
Quan Q, Floyd D, Burgess IB, Deotare PB, Frank IW, Yang SKY, Ilic R, Loncar M. Single particle detection in CMOS compatible photonic crystal nanobeam cavities [Internet]. Optics Express 2013;2013(21):32225. Publisher's VersionAbstract

We report the label-free detection of single particles using photonic crystal nanobeam cavities fabricated in silicon-on-insulator platform, and embedded inside microfluidic channels fabricated in poly-dimethylsiloxane (PDMS). Our system operates in the telecommunication wavelength band, thus leveraging the widely available, robust and tunable telecom laser sources. Using this approach, we demonstrated the detection of polystyrene nanoparticles with dimensions down to 12.5nm in radius. Furthermore, binding events of a single streptavidin molecule have been observed.

oe-21-26-32225.pdf
Wilson LG, Carter LM, Reece SE. High-speed holographic microscopy of malaria parasites reveals ambidextrous flagellar waveforms. Proceedings of the National Academy of Sciences 2013;110 (47):18769-18774.Abstract

Axonemes form the core of eukaryotic flagella and cilia, performing tasks ranging from transporting fluid in developing embryos to the propulsion of sperm. Despite their abundance across the eukaryotic domain, the mechanisms that regulate the beating action of axonemes remain unknown. The flagellar waveforms are 3D in general, but current understanding of how axoneme components interact stems from 2D data; comprehensive measurements of flagellar shape are beyond conventional microscopy. Moreover, current flagellar model systems (e.g., sea urchin, human sperm) contain accessory structures that impose mechanical constraints on movement, obscuring the "native" axoneme behavior. We address both problems by developing a high-speed holographic imaging scheme and applying it to the (male) microgametes of malaria (Plasmodium) parasites. These isolated flagella are a unique, mathematically tractable model system for the physics of microswimmers. We reveal the 3D flagellar waveforms of these microorganisms and map the differential shear between microtubules in their axonemes. Furthermore, we overturn claims that chirality in the structure of the axoneme governs the beat pattern [Hirokawa N, et al. (2009) Ann Rev Fluid Mech 41:53-72], because microgametes display a left- or right-handed character on alternate beats. This breaks the link between structural chirality in the axoneme and larger scale symmetry breaking (e.g., in developing embryos), leading us to conclude that accessory structures play a critical role in shaping the flagellar beat.

2013_wilson_pnas.pdf
Moccia M, Castaldi G, Galdi V, Savo S, Sato Y. Transformation Multiphysics. In: Transformation Wave Physics. Pan Stanford Publishing; 2013Abstract
Spatial tailoring of the material constitutive properties is a well-known strategy to mold the local flow of given observables in different physical domains. Coordinate transformation-based methods (e.g., transformation optics) offer a powerful and systematic approach to design anisotropic, spatially-inhomogeneous artificial materials (“metamaterials”) capable of precisely manipulating wave-based (electromagnetic, acoustic, elastic) as well as diffusion-based (heat) phenomena in a desired fashion. However versatile these approaches have been, most designs have so far been limited to serving single-target functionalities in a given physical domain. Here we present a “transformation multi physics” framework that allows independent and simultaneous manipulation of multiple physical phenomena. As a proof of principle of this new scheme, we design and synthesize (in terms of realistic material constituents) a metamaterial shell that simultaneously behaves as a thermal concentrator and an electrical “invisibility cloak”. Our numerical results open up intriguing possibilities in the largely unexplored phase space of multi- functional metadevices, with a wide variety of potential applications to electrical, magnetic, acoustic, and thermal scenarios
00b495302213fc9c33000000.pdf
Gorthi SS, Schaak D, Schonbrun E. Fluorescence imaging of flowing cells using a temporally coded excitation [Internet]. Optics Express 2013;21:5164-517. Publisher's Version
Clemente CJ, Richards CT. Built for rowing: frog muscle is tuned to limb morphology to power swimming. Journal of the Royal Society Interface 2013;10Abstract

Rowing is demanding, in part, because drag on the oars increases as the square of their speed. Hence, as muscles shorten faster, their force capacity falls, whereas drag rises. How do frogs resolve this dilemma to swim rapidly? We predicted that shortening velocity cannot exceed a terminal velocity where muscle and fluid torques balance. This terminal velocity, which is below Vmax, depends on gear ratio (GR ¼ outlever/inlever) and webbed foot area. Perhaps such properties of swimmers are ‘tuned’, enabling shortening speeds of approximately 0.3Vmax for maximal power. Predictions were tested using a ‘musculo-robotic’ Xenopus laevis foot driven either by a living in vitro or computational in silico plantaris longus muscle. Experiments verified predictions. Our principle finding is that GR ranges from 11.5 to 20 near the predicted optimum for rowing (GR 11). However, gearing influences muscle power more strongly than foot area. No single morphology is optimal for producing muscle power. Rather, the ‘optimal’ GR decreases with foot size, implying that rowing ability need not compromise jumping (and vice versa). Thus, despite our neglect of additional forces (e.g. added mass), our model predicts pairings of physiological and morphological properties to confer effective rowing. Beyond frogs, the model may apply across a range of size and complexity from aquatic insects to human-powered rowing.

2013_clemente_j_r_soc_interface.pdf
Caprio GD, Schaak D, Schonbrun E. Hyperspectral fluorescence microfluidic microscopy [Internet]. Biomedical Optics Express 2013;4:1486-1493. Publisher's Version 2013_di_caprio_biomed._optics_express.pdf

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