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Engineering conductive 3D cell scaffoldings offer unique advantages towards the creation of physiologically relevant platforms with integrated real-time sensing capabilities. Toward this goal, rat dopaminergic neural cells were encapsulated into graphene-laden alginate microfibers using a microfluidic fiber fabrication approach, which is unmatched for creating continuous, highly tunable microfibers. Incorporating graphene increases the conductivity of the alginate microfibers 148%, creating a similar conductivity to native brain tissue. Graphene leads to an increase in the cross-sectional sizes and porosities of the fibers, while reducing the roughness of the fiber surface. The cell encapsulation procedure has an efficiency rate of 50%, and of those cells, approximately 30% remain for the entire 6-day observation period. To understand how encapsulation effects cell genetics, the genes IL-1β, TH, TNF-α, and TUBB-3 are analyzed, both after manufacturing and after encapsulation for six days. The manufacturing process and combination with alginate leads to an upregulation of TH, and the introduction of graphene further increases its levels; however, the inverse trend is true of TUBB-3. Long-term encapsulation shows continued upregulation of TH and of TNF-α, and six-day exposure to graphene leads to the upregulation of TUBB-3 and IL-1β, which indicates increased inflammation.

Fibrous scaffolds have shown promise in tissue engineering due to their ability to improve cell alignment and migration. In this paper, poly(e-caprolactone) (PCL) fibers are fabricated in different sizes using a microfluidic platform. By using this approach, we demonstrated considerable flexibility in ability to control the size of the fibers. It was shown that the average diameter of the fibers was obtained in the range of 2.6–36.5 μm by selecting the PCL solution flow rate from 1 to 5 μL min–1 and the sheath flow rate from 20 to 400 μL min–1 in the microfluidic channel. The microfibers were used to create 3D microenvironments in order to investigate growth and differentiation of adult hippocampal stem/progenitor cells (AHPCs) in vitro. The results indicated that the 3D topography of the PCL substrates, along with chemical (extracellular matrix) guidance cues supported the adhesion, survival, and differentiation of the AHPCs. Additionally, it was found that the cell deviation angle for 44–66% of cells on...

Microbial fuel cells have gained popularity as a viable, environmentally friendly alternative for the production of energy. However, the challenges in miniaturizing the system for application in smaller devices as well as the short duration of operation have limited the application of these devices. Here, the capillary motion was employed to design a self-pumped paper-based microbial fuel cell operating under continuous flow condition. A proof-of-concept experiment ran approximately 5 days with no outside power or human interference required for the duration of operation. Shewanella oneidensis MR-1 was used to create a maximum current of 52.25 µA in a 52.5 µL paper-based microfluidic device. SEM images of the anode following the experiment showed biofilm formation on the carbon cloth electrode. The results showed a power density of approximately 25 W/m3 and proved unique capabilities of the paper-based microbial fuel cells to produce energy for an extended period of time.

This work reports on the discovery of a high thermal conductivity (κ) switch-on phenomenon in high purity graphene paper (GP) when its temperature is reduced from room temperature down to 10 K. The κ after switch-on (1732 to 3013 W m−1 K−1) is 4–8 times that before switch-on. The triggering temperature is 245–260 K. The switch-on behavior is attributed to the thermal expansion mismatch between pure graphene flakes and impurity-embedded flakes. This is confirmed by the switch behavior of the temperature coefficient of resistance. Before switch-on, the interactions between pure graphene flakes and surrounding impurity-embedded flakes efficiently suppress phonon transport in GP. After switch-on, the structure separation frees the pure graphene flakes from the impurity-embedded neighbors, leading to a several-fold κ increase. The measured κ before and after switch-on is consistent with the literature reported κ values of supported and suspended graphene. By conducting comparison studies with pyrolytic graphite, graphene oxide paper and partly reduced graphene paper, the whole physical picture is illustrated clearly. The thermal expansion induced switch-on is feasible only for high purity GP materials. This finding points out a novel way to switch on/off the thermal conductivity of graphene paper based on substrate-phonon scattering.

Paper-based analytical devices are lightweight, inexpensively produced, effective, and easily disposable; allowing for their suitable implementation in resource-limited areas. They allow effective handling of quantitative analysis in a diverse range of areas, from standard healthcare and environmental monitoring to water quality monitoring. Nonetheless, such devices often require an energy source for their complex assays or readings, preventing their effective use. Most commonly, conventional batteries are integrated into the device to serve as an energy source. However, considering its non-environmentally friendly approach to energy generation and its difficulty of being effectively disposed, a search for a new power source has begun. In light of the newly found potential of cellulose-based entities in the energy field, attention has been drawn towards a supposedly unlikely material: paper. Considering the potentials of such technology, this manuscript aims to describe the benefits of current and future technologies of paper-based devices in the energy sector. Here, we discuss the role of paper as a main platform or part of energy storage and conversion devices such as fuel cells, lithium-ion batteries, and alkaline batteries thoroughly.

Transient electronics is a class of electronic devices designed to maintain stable operation for a desired and preset amount of time; and, undergo fast and complete degradation and deconstruction once transiency is triggered. Controlled and programmed transiency in solvent-triggered devices is strongly dependent on chemical and physical interactions between the solvent and the device, as well as those within the device itself, among its constituent components. Mechanics of transiency of prototypical transient circuits demonstrate strong dependence of the transiency characteristics on that of the substrate. In the present study, we demonstrate the control of transiency through the dissolution behavior of a substrate for the devices with electronic parts composed of colloidal units. It is observed that the physical circuit–substrate interactions are the dominating factors in defining the overall transiency behavior of the device. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 517–524

Transient soft bioelectronics are capable of forming conformal contacts with curvilinear surfaces of biological host tissues and organs. Such systems are often subject to continu- ous static and dynamic loads from the biological host. In this article, we present investigation of electronic attributes of tran- sient soft bioelectronic circuits subjected to mechanical force and influence of substrate's transiency on the transiency of the whole device; also, characterize and quantify loss of functional- ity in triggered devices. Variations in the electrical conductivity of circuits as a function of applied mechanical load was used as a means to deduce electronic characteristics under stress. The experimental results suggest that there exists a correlation between electronic properties of circuits and applied mechani- cal strain; no clear correlation was, however, observed between electronic properties of circuits and frequency of the applied dynamic load. Control over transiency rate of identical circuits utilizing the transiency characteristics of the poly(vinyl alcohol)l-based substrates is also studied and demonstrated. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 00, 000-000

Microfluidic technology has provided innovative solutions to numerous problems, but the cost of designing and fabricating microfluidic channels is impeding its expansion. In this work, Shrinky-Dink thermoplastic sheets are used to create multilayered complex templates for microfluidic channels. We used inkjet and laserjet printers to raise a predetermined microchannel geometry by depositing several layers of ink for each feature consecutively. We achieved feature heights over 100 μm, which were measured and compared with surface profilometry. Templates closest to the target geometry were then used to create microfluidic devices from soft-lithography with the molds as a template. These microfluidic devices were in turn used to fabricate polymer microfibers using the microfluidic focusing approach to demonstrate the potential that this process has for microfluidic applications. Finally, an economic analysis was conducted to compare the price of common microfluidic template manufacturing methods. We showed that multilayer microchannels can be created significantly quicker and cheaper than current methods for design prototyping and point-of-care applications in the biomedical area.

Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m(-1) K(-1) due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed "thermal reffusivity": Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C× e(-θ/2T) and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m(-2) for the studied GF and 43-112 s m(-2) for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene.

Objectives: In recent years, there is some evidence that adipokins play an important role in autoimmunity and inflammation. Resistin is the novel adipocyte-derived peptid and the aim of this study was to compare its serum values in lupus patients and controls. Methods: A cross sectional study was carried out on 73 patients with the definite diagnosis of SLE. Resistin and other proinflammatory markers were compared between patients and normal age and sex match individuals. Results: There was no significant difference in serum resistin, concentrations, between patients and healthy individuals (6.88 ± 4.53 and 6.74 ± 3.74 ng/mL respectively, P = 0.704). Statistical analysis showed a positive correlation between serum, levels of resistin with CRP and ESR (P ≤ 0.008 and P ≤ 0.037 respectively), in SLE patients. Higher serum levels of resistin in patients with proteinuria were found in comparison with normal kidney patients (P = 0.022). But there was no relationship between resistin like SLEDAI score. Conclusions: Resistin was associated with in inflammatory markers but not a notable association with markers of disease activity has been detected.

We have developed a facile low-temperature synthetic method for the preparation of NaMnF3 nanocubes with Er3+ and Yb3+ ions homogeneously incorporated in the host lattice. The effects of the reaction temperature, and the volume ratio between ethanol and DI water on the morphology of NaMnF3 nanocubes are systematically investigated. The NaMnF3 nanocubes can be produced in the low temperature range (25–80 °C), and the higher reaction temperature (80 °C) is favorable for the formation of a smooth surface. The formation of NaMnF3 nanocubes strongly depends on the ethanol solvent. The morphology and single-phase of the obtained samples could be well maintained by controlling the doping concentration (Yb3+ ≤ 20 mol%). Single-band red upconversion emission can be generated in Er3+/Yb3+ codoped NaMnF3 nanocubes due to the energy transfer between host Mn2+ and dopant Er3+ ions. It is revealed that our NaMnF3:Er3+/Yb3+ nanocubes irradiate the brightest red luminescence at the dopant concentrations of Er3+ (2 mol%) and Yb3+ (15 mol%), which is stronger than that of the hexagonal-phase NaYF4:Er3+/Yb3+ phosphor.

The first step in curing a disease is being able to detect the disease effectively. Paper-based microfluidic devices are biodegradable and can make diagnosing diseases cost-effective and easy in almost all environments. We created a three-dimesnional (3D) paper device using wax printing fabrication technique and basic principles of origami. This design allows for a versatile fabrication technique over previously reported patterning of SU-8 photoresist on chromatography paper by employing a readily available wax printer. The design also utilizes multiple colorimetric assays that can accommodate one or more analytes including urine, blood, and saliva. In this case to demonstrate the functionality of the 3D paper-based microfluidic system, a urinalysis of protein and glucose assays is conducted. The amounts of glucose and protein introduced to the device are found to be proportional to the color change of each assay. This color change was quantified by use of Adobe Photoshop. Urine samples from participants with no pre-existing health conditions and one person with diabetes were collected and compared against synthetic urine samples with predetermined glucose and protein levels. Utilizing this method, we were able to confirm that both protein and glucose levels were in fact within healthy ranges for healthy participants. For the participant with diabetes, glucose was found to be above the healthy range while the protein level was in the healthy range.

Transient Li-ion batteries based on polymeric constituents are presented, exhibiting a twofold increase in the potential and approximately three orders of magnitude faster transiency rate compared to other transient systems reported in the literature. The battery takes advantage of a close variation of the active materials used in conventional Li-ion batteries and can achieve and maintain a potential of >2.5 V. All materials are deposited form polymer-based emulsions and the transiency is achieved through a hybrid approach of redispersion of insoluble, and dissolution of soluble components in approximately 30 min. The presented proof of concept has paramount potentials in military and hardware security applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2021–2027

Polymer-based interpenetrating networks (IPNs) with controllable and programmable degradation and release kinetics enable unique opportunities for physisorption and controlled release of therapeutic proteins or vaccines while their chemical and structural integrities are conserved. This paper presents materials, a simple preparation method, and release kinetics of a series of long-term programmable, biocompatible, and biodegradable polymer-based IPN controlled release platforms. Release kinetics of the gp41 protein was controlled over a 30-day period via tuning and altering the chemical structure of the IPN platforms. Post-release analysis confirmed structural conservation of the gp41 protein throughout the process. Cell viability assay confirmed biocompatibility and non-cytotoxicity of the IPNs.

Varying bead concentrations over the course of experiments have been reported by many scientists. A new device was designed and developed to eliminate bead aggregation in a syringe pump prior to flowing through a microchannel. We have modeled the effects of rotation in the absence of longitudinal flow by evenly populating the cross section of a syringe with particles, then tracking their movement due to rotation, gravity, and centripetal forces. We have shown both experimentally and numerically that the concentration of the beads remains constant over the course of experiments once the rotational device is used. However, the concentration of the beads drops significantly once no rotation is applied during the experiment.

Analysis of the intrinsic fluorescence profiles of individual marine algae can be used in general classification of organisms based on cell size and fluorescence properties. We describe the design and fabrication of a Microflow Cytometer on a chip for characterization of phytoplankton. The Microflow Cytometer measured distinct side scatter and fluorescence properties of Synechococcus sp., Nitzschia d., and Thalassiosira p.; measurements were confirmed using the benchtop Accuri C6 flow cytometer. The Microflow Cytometer proved sensitive enough to detect and characterize picoplankton with diameter approximately 1 μm and larger phytoplankton of up to 80 μm in length. The wide range in size discrimination coupled with detection of intrinsic fluorescent pigments suggests that this Microflow Cytometer will be able to distinguish different populations of phytoplankton on unmanned underwater vehicles.

Cationic molecules can interact with anionic and other cationic species in solutions. Electrostatic and hydrophobic interactions between two series of cationic antimicrobial dyes and several surfactants were studied using a UV−vis spectrophotometer. The dye containing more cationic charges with a short alkyl chain showed stronger binding power with surfactants than the one with less positive charge, while the ones with longer chains exhibited lower binding energy. These dyes could form complex structures with anionic surfactant species in solutions at very low concentrations of the surfactant (far below critical-micelle-forming concentrations of the surfactants), which was revealed from the changes in absorbance and wavelength of the maximum absorbance (λmax) of photospectrometry. However, when the concentrations of surfactants were above their critical micelle concentrations, the dyes could redissolve and dissociate into molecular or ionic forms. Such results were confirmed by conductivity and antimicrob...

We have developed an optofluidic biosensor to study microscale particles and different species of microalgae. The system is comprised of a microchannel with a set of chevron-shaped grooves. The chevrons allows for hydrodynamic focusing of the core stream in the center using a sheath fluid. The device is equipped with a new generation of highly sensitive photodetectors, multi-pixel photon counter (MPPC), with high gain values and an extremely small footprint. Two different sizes of high intensity fluorescent microspheres and three different species of algae (Chlamydomonas reinhardtii strain 21 gr, Chlamydomonas suppressor, and Chlorella sorokiniana) were studied. The forward scattering emissions generated by samples passing through the interrogation region were carried through a multimode fiber, located in 135 degree with respect to the excitation fiber, and detected by a MPPC. The signal outputs obtained from each sample were collected using a data acquisition system and utilized for further statistical analysis. Larger particles or cells demonstrated larger peak height and width, and consequently larger peak area. The average signal output (integral of the peak) for Chlamydomonas reinhardtii strain 21 gr, Chlamydomonas suppressor, and Chlorella sorokiniana falls between the values found for the 3.2 and 10.2 μm beads. Different types of algae were also successfully characterized.

Using a significant quantity of fossil fuels has adverse impacts on our lives and will affect future generations. Additionally, there are limited and decreasing numbers of nonrenewable resources around the world. In contrast, renewable resources are not depleted and provide energy with negligible pollution. Wind energy is one of the more common renewable energy resources. This project aims to evaluate Iowa's wind energy potential and to provide suggestions to improve the future well‐being of this state. A preliminary analysis shows that Iowa has great potential for wind energy. Based on the preliminary analysis, Ames, Iowa, is selected as a case study of its potential in terms of wind energy. Some important characteristics of wind energy, such as mean wind speed, wind distribution, and wind direction are evaluated for Ames. It is observed that although Iowa has the greatest wind power capacity density in the U.S., there are some untapped places in Iowa that can be utilized to harvest wind power. Results indicate that the city of Ames is one of the places that have strong wind speeds. According to the results, if a wind farm is installed in the city of Ames, reliance on non-renewable energy resources will be considerably decreased

Microbial fuel cell (MFC) technology is a promising area in the field of renewable energy because of their capability to use the energy contained in wastewater, which has been previously an untapped source of power. Microscale MFCs are desirable for their small footprints, relatively high power density, fast start-up, and environmentally-friendly process. Microbial fuel cells employ microorganisms as the biocatalysts instead of metal catalysts, which are widely applied in conventional fuel cells. MFCs are capable of generating electricity as long as nutrition is provided. Miniature MFCs have faster power generation recovery than macroscale MFCs. Additionally, since power generation density is affected by the surface-to-volume ratio, miniature MFCs can facilitate higher power density. We have designed and fabricated a microscale microbial fuel cell with a volume of 4 μL in a polydimethylsiloxane (PDMS) chamber. The anode and cathode chambers were separated by a proton exchange membrane. Carbon cloth was used for both the anode and the cathode. Shewanella Oneidensis MR-1 was chosen to be the electrogenic bacteria and was inoculated into the anode chamber. We employed Ferricyanide as the catholyte and introduced it into the cathode chamber with a constant flow rate of approximately 50 μL/hr. We used trypticase soy broth as the bacterial nutrition and added it into the anode chamber approximately every 15 hours once current dropped to base current. Using our miniature MFC, we were able to generate a maximum current of 4.62 μA.

Microbial fuel cells (MFCs) have been a potential green energy source for a long time but one of the problems is that either the technology must be used on a large scale or special equipment have been necessary to keep the fuel cells running such as syringe pumps. Paper-based microbial fuel cells do not need to have a syringe pump to run and can run entirely by themselves when placed in contact with the fluids that are necessary for it to run. Paper-based microbial fuel cells are also more compact than traditional MFCs since the device doesn’t need any external equipment to run. The goal of this paper is to develop a microbial fuel cell that does not require a syringe pump to function. This is done by layering chromatography paper with wax design printed onto it. This restricts the fluids to a specific flow path allowing it to act like the tubes in a typical microbial fuel cell device by delivering the fluids to the chamber. The fluids are picked up by tabs that sit in the fluid and use capillary attraction to flow up the tab and into the device. The fluids are directed to the chambers where the chemical and biological processes take place. These flows are then directed out of the device so that they are taken to a waste container and out of the system. Our microliter scale paper-based microbial fuel cell creates a significant current that is sustained for a period of time and can be repeated. A paper-based microbial fuel cell also has a fast response time. These results mean that it could be possible for a set of paper-based microbial fuel cells to create a power density capable of powering small, low power circuits when used in series or parallel. In this paper, we discuss the fabrication and experimental results of our paper-based microbial fuel cell. Also there will be a discussion of how paper-based microbial fuels cells compare to the traditional microbial fuel cells and how they could be used in the future.

As interest in and potential uses for microfluidic and optofluidic analytical techniques grows, the need for on-chip, automated sample processing becomes increasingly important because this aspect is critical to allowing the devices to be commercially feasible and practical. One such design that implements on-chip processing is using ionic electroactive polymer (IEAP) actuators to perform mixing of particles in the microchannel and using a single magnet positioned beneath the channel to trap the magnetic beads. IEAP actuators consist of a central ionic membrane with conductive network composite (CNC) layers on either side. Gold electrodes placed on the outside of CNC layers are connected to a metal anode and cathode. When subjected to an electric field, the ions in the actuator move, electromechanically causing the entire length of the actuator to flex [1]. Although most actuators to date have been developed for use in air rather than in solutions, we have adapted previously developed actuators by optimizing their electromechanical functions to suit our needs and coating them in a protective film. The actuators are embedded in a microchannel in different configurations, which are then tested to determine which configuration most effectively trapped, mixed, and released the magnetic beads. The most effective configuration will subsequently be used to perform automated sample processing for an assay.

We have shown the design and fabrication of a microfluidic flow cytometer. The microfluidic flow cytometer has been used to characterize microspheres of different sizes. The device is consisted of a microchannel, electronics, and integrated optics. The microchannel has three inlets. Two inlets are used to introduce sheath flows and one middle inlet is assigned as sample inlet. The sample flow is hydrodynamically focused at the center of the microchannel by two side streams (sheath flows). Also arrays of four chevron grooves compress the sample flow from the top and bottom of the microchannel. The core flow contains microspheres at a certain concentration. Detection of the microspheres at the interrogation region of the channel is performed by integrated optics and electronics. The scattered light emitted from the microspheres is collected by a multi-plex photo diode (MPPC). The results are recorded using data acquisition (DAQ) unit. The MPPCs employed in the setup is the new generation of photon counter devices with an excellent detection limit, a compact size, and capability of recording data at high gain compared to previous generation of photodetectors such as photomultipliers or avalanche photon diodes. The flow cytometer was sensitive enough to collect data from 3 μm microspheres using such mentioned sensitive photon counting unit. We have also used COMSOL Multiphysics software to investigate velocity and pressure distribution as well as concentration distribution along the microchannel. The average voltage collected by MPPC was 1.9 V for 10.2 μm and 1.6 V for 3.2 μm microsphere.Copyright © 2013 by ASME

This paper discusses the fundamentals and developments of miniaturized fuel cells, both biological and electrochemical. An overview of microfluidic fuel cells, miniaturized microbial fuel cells, enzymatic biofuel cells, and implanted biofuel cells in an attempt to provide green energy and to power implanted microdevices is provided. Also, the challenges and applications of each type of fuel cell are discussed in detail. Most recent developments in fuel cell technologies such as novel catalysts, compact designs, and fabrication methods are reviewed.

Analysis of the intrinsic scatter and fluorescence profiles of marine algae can be used for general classification of organisms based on cell size and fluorescence properties. We describe the design and fabrication of a Microflow Cytometer on a chip for characterization of phytoplankton. The Microflow Cytometer measured distinct side-scatter and fluorescence properties of Synechococcus sp., Nitzschia d., and Thalassiosira p. Measurements were confirmed using the benchtop Accuri C6 flow cytometer. The Microflow Cytometer proved sensitive enough to detect and characterize picoplankton with diameter approximately 1 mm and larger phytoplankton of up to 80 mm in length. The wide range in size discrimination coupled with detection of intrinsic fluorescent pigments suggests that this Microflow Cytometer will be able to distinguish different populations of phytoplankton on unmanned underwater vehicles. Reversing the orientation of the grooves in the channel walls returns the sample stream to its original unsheathed position allowing separation of the sample stream from the sheath streams and the recycling of the sheath fluid.

The utility of pathogen and toxin detection systems depends not only upon sensitivity, specificity and capability for multiplexed recognition, but also on access at the point of need, ease of use, and response time. Combining microfluidics and optical biosensors facilitates miniaturization and automation, while careful design makes it possible to test variable quantities of complex matrices such as food (mL) and clinical samples (µL). We report on progress towards an optofluidic system that combines a rotating magnet trap for automated sample processing and a microflow cytometer capable of 4-color analysis to achieve multi-analyte diagnostics. Sample and antibody-coated magnetic beads are introduced into a moving magnetic field created by magnets rotating in the opposite direction of the flow. The color-coded magnetic beads with captured target remain in suspension while fluorescent tracer reagents are introduced to the flow, thus optimizing the binding kinetics and minimizing aggregation. Magnetic beads with bound target and tracer reagents are released for multiplexed analysis by reversing the direction of spinning magnets.

The phenomenon of "unmixing" has been demonstrated in microfluidic mixers, but here we manipulate laminar flow streams back to their original positions in order to extend the operational utility of an analytical device where no mixing is desired. Using grooves in the channel wall, we passively focus a sample stream with two sheath streams to center it in a microchannel for optical analysis. Even though the sample stream is completely surrounded by sheath fluid, reversing the orientation of the grooves in the channel walls returns the sample stream to its original position with respect to the sheath streams. We demonstrate the separation of the sample stream from the contiguous sheath streams and the recycling of the sheath fluid using the reversibility of laminar flow. Polystyrene microspheres and fluorescent dye were used to quantify the performance of the unsheathing process. We found that the maximum numbers of microspheres and all of the fluorescent dye were recaptured at sheath recycling levels

A rapid, automated, multi-analyte Microflow Cytometer is being developed as a portable, field-deployable sensor for onsite diagnosis of biothreat agent exposure and environmental monitoring. The technology relies on a unique method for ensheathing a sample stream in continuous flow past an interrogation region where optical fibers provide excitation and collect emission. This approach efficiently focuses particles in the interrogation region of the fluidic channel, avoids clogging and provides for subsequent separation of the core and sheath fluids in order to capture the target for confirmatory assays and recycling of the sheath fluid. Fluorescently coded microspheres provide the capability for highly multiplexed assays. Optical analysis at four different wavelengths identified six sets of the coded microspheres recognizing Escherichia coli, Listeria, and Salmonella as well as cholera toxin, staphylococcal enterotoxin B (SEB), and ricin, and assay results were compared with those of a commercial Luminex analysis system.

Using grooves in the walls of a microchannel and two sheath streams, we have passively focused a sample stream in the center of the microchannel for optical analysis. Even though the sample stream is completely surrounded by sheath fluid, reversing the orientation of the grooves in the channel walls returns the sample stream to its original position with respect to the sheath streams. The use of this sheathing technique has already been demonstrated in a sensitive microflow cytometer; the unsheathing capability now provides the opportunity to recover particles from the sensor with minimal dilution or to recycle the sheath fluid for long-term unattended operation. The ability to reverse focused laminar flows opens a variety of options for combining target transport, processing and analysis procedures.Copyright © 2010 by ASME

We present a novel method for investigating a nanometric cluster of water molecules, which includes the formation and manipulation of nanometric water, and the measurement of its mechanical properties. The atomic force microscope based on the quartz tuning-fork sensor is employed to form and manipulate the nanometric water, and the theoretical tool of amplitude-modulation atomic force microscopy is used to obtain the elasticity, viscosity and dissipation energy of it. With high vertical resolution less than approximately 0.1 nm and high force sensitivity of approximately 0.01 N m(-1), this tool facilitates the stable formation and manipulation of a nano-water cluster (approximately 10(4) molecules) in air without 'jump-to-contact' instability, as well as quantitative measurements of its physico-chemical properties. PACS numbers: 47.55.nk, 62.10.+s, 68.37.Ps

We study the power dissipated by the tip of an oscillating micron-scale cantilever as it interacts with a sample using a nonlinear model of the tip-surface force interactions that includes attractive, adhesive, repulsive, and capillary contributions. The force interactions of the model are entirely conservative and the dissipated power is due to the hysteretic nature of the interaction with the capillary fluid layer. Using numerical techniques tailored for nonlinear and discontinuous dynamical systems we compute the exact dissipated power over a range of experimentally relevant conditions. This is accomplished by computing precisely the fraction of oscillations that break the fluid meniscus. We find that the dissipated power as a function of the equilibrium cantilever-surface separation has a characteristic shape that we directly relate to the cantilever dynamics. Even for regions where the cantilever dynamics are highly irregular the fraction of oscillations breaking the fluid meniscus exhibits a simple trend. Using our results we also explore the accuracy of the often used harmonic approximation in determining dissipated power. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2980057]

We study the nonlinear dynamics of a tapping mode atomic force microscope with tip-surface interactions that include attractive, repulsive, and capillary force contributions using numerical techniques tailored for hybrid or discontinuous dynamical systems that include forward-time simulation with event handling and numerical pseudo-arclength continuation. We find four branches of periodic solutions that are separated by windows of complex and irregular dynamics. The branches of periodic solutions end where the cantilever comes into grazing contact with event surfaces in state space, corresponding to the onset of capillary interactions and the onset of repulsive forces associated with contact. These windows of irregular dynamics are found to coexist with the periodic branches of solutions as well as exist beyond the termination of the periodic solution. Finally, we show that these details can be overlooked unless one is careful to sample the dynamics appropriately. (C) 2008 American Institute of Physics.

We numerically explore the nonlinear dynamics of the oscillating cantilever tip in tapping mode atomic force microscopy. The cantilever dynamics are determined by complex force interactions between the sample surface and the oscillating cantilever tip which are dominated by attractive, adhesive, and repulsive contributions depending on the instantaneous position of the cantilever. We use a model proposed by Zitzler et al that includes a capillary force interaction due to the thin film of water that covers all surfaces as a result of ambient humidity. As the cantilever approaches the surface a meniscus is formed and as the cantilever retracts this water layer forms a neck and eventually breaks. This introduces hysteresis since the formation of the meniscus and the breaking of the water neck occur at different spatial locations during an oscillation of the cantilever. Using forward-time simulation with event handling techniques tailored for situations with rapid changes in force interactions we find three classes of steady-state dynamics: (i) a branch of solutions with periodic dynamics and large amplitude of oscillation; (ii) a branch of solutions with periodic dynamics and small amplitude of oscillation; (iii) windows of irregular aperiodic dynamics. We quantify the global basins of attraction for these solutions by performing a large set of numerical simulations over a wide range of initial conditions. Our findings provide a useful framework for further studies interested in controlling these dynamics.

Many micro and nano-technologies rely upon the complicated motion of objects immersed in a viscous fluid. It is often the case that for such problems analytical theory is not available to quantitatively describe and predict the device dynamics. In addition, the numerical simulation of such devices involves moving boundaries and use of the standard Eulerian computational approaches are often difficult to implement. In order to address this problem we use and validate a fully Lagrangian finite element approach that treats the moving boundaries in a natural manner. We validate the method for use in calculating the dynamics of oscillating objects in a viscous fluid. Specifically, the dynamics of a micron-scale cylinder oscillating in water are studied numerically. The fluid dynamics generated by an infinitely long cylinder are a good approximation for the flow field around an oscillating cantilever. The numerical results agree well with analytical theory. It is anticipated that further development of the fully Lagrangian numerical approach for fluid-solid interaction problems will be useful in the development of micro and nano-technologies.Copyright © 2007 by ASME

We have employed the easy-to-scale-up method of spray-coating in combination with layer-by-layer self-assembly technique to fabricate ionic electroactive polymer actuators (IEAPAs). IEAPAs with spray-coated silver microparticle electrodes demonstrate enhanced strain and response time when compared to nearly identical, optimized conventional IEAPA with gold leaf electrodes. The results demonstrate that strain of these IEAPAs increases with the decrease of thickness of the outer silver microparticle electrodes. In addition, the response time of the actuators at frequencies of 1 and 10 Hz improves compared to optimized conventionally fabricated IEAPA. It was found that samples consisting of spray-coated silver electrodes can charge up to ∼3 times faster than conventional actuators at 1 Hz frequency. Faster charging/discharging results in higher mobility of ions within the actuator and thus, faster actuation. Given the relatively large thickness of the silver microparticle electrodes (∼50× gold leaf), similar strain was observed due to the lower Young's modulus of spray-coated layers compared to that of bulk material.

Er3+/Yb3+ doped MnF2 nanostructures have been prepared via a solvothermal method. The morphology of the nanocrystals could be well controlled from nanoparticles to nanoclusters and nanolanterns by varying the volume ratio between oleic acid and ethanol in the solvent. Moreover, the size is tuned from 200 nm to 1.5 μm with the increase of reaction temperature from 110 to 200 °C. It is shown that controlling the doping concentration (Yb3+ ≤ 20 mol%) is essential to preserve the single phase and morphology of the MnF2 host. Single-band red upconversion (UC) emission can be generated in Er3+ single and Er3+/Yb3+ codoped MnF2 nanoclusters due to the energy transfer between host Mn2+ and dopant Er3+ ions. The detailed studies suggest that our MnF2:Er3+/Yb3+ nanocrystals have the strongest single-band luminescence feature at the dopant concentrations of Er3+ (2 mol%) and Yb3+ (20 mol%). The brighter red emission from the current nanostructure compared with those from NaYF4:Er3+/Yb3+ has shown its suitability as an efficient UC luminescence host. It is expected that the achieved intense pure red emission may have potential application in in vivo bioimaging.

The effects of global warming, pollution in river effluents, and changing ocean currents can be studied by characterizing variations in phytoplankton populations. We demonstrate the design and fabrication of a Microflow Cytometer for characterization of phytoplankton. Guided by chevron-shaped grooves on the top and bottom of a microfluidic channel, two symmetric sheath streams wrap around a central sample stream and hydrodynamically focus it in the center of the channel. The lasers are carefully chosen to provide excitation light close to the maximum absorbance wavelengths for the intrinsic fluorophores chlorophyll and phycoerythrin, and the excitation light is coupled to the flow cytometer through the use of an optical fiber. Fluorescence and light scatter are collected using two multimode optical fibers placed at 90-degree angles with respect to the excitation fiber. Light emerging from these collection fibers is directed through optical bandpass filters into photomultiplier tubes. The cytometer measured the optical and side scatter properties of Karenia b., Synechococcus sp., Pseudo-Nitzchia, and Alexandrium. The effect of the sheath-to-sample flow-rate ratio on the light scatter and fluorescence of these marine microorganisms was investigated. Reducing the sample flow rate from 200 μL/min to 10 μL/min produced a more tightly focused sample stream and less heterogeneous signals.

We perform a large number of simulations over a wide range of system parameters to approximate the basins of attraction of steady oscillating solutions. We find that the basins of attraction vary as a function of system parameters and initial conditions. For large equilibrium separations, the basin of attraction is dominated by the low-amplitude solution. The location of the fixed point is shifted toward the higher values of instantaneous displacement and velocity for larger equilibrium separations. We show that the basin of attraction in the neighborhood of the fixed point is dominated by low-amplitude solutions as relative humidity is increased.