Development of All-Plastic Microvalve Array for Multiplexed Immunoassay

There is a need for low-cost immunoassays that measure the presence and concentration of multiple harmful agents in one device. Currently, comparable immunoassays employ a one-analyte-per-test format that is time consuming and not cost effective for the requirement of detecting multiple analytes in a single sample. For instance, if a spectrum of harmful agents, including E. coli O157, cholera toxin, and Salmonella typhimurium, should be simultaneously monitored in foods and drinking water, then a one-analyte-per-test would be inefficient. This work demonstrates a platform capable of simultaneous detection of multiple analytes in a single, low-cost, microvalve array-enabled multiplexed immunoassay. This multiplexed immunoassay platform is demonstrated in a prototype COC (cyclic olefin copolymer) device with a 2×3 array in which 6 analytes can be detected simultaneously. In order to contain and regulate the flow of reagents in the multichannel device, an array of microfluidic valves actuated by a thermally expandable material and microfabricated resistors have been developed to direct the flow to the necessary assay sites. The microvalve-based immunoassay is shown to be reliable, easy to operate, and compatible with large-scale integration. The all-plastic microvalves use paraffin wax as the thermally sensitive material which drastically reduces power consumption by latching upon closing so that pulsed power is required only to close and latch the microvalve until it is necessary to re-open the valve. The multiplexed detection scheme has been demonstrated by using three proteins, C reactive protein (CRP) and transferrin, both of which are biomarkers associated with traumatic brain injury (TBI) as well as bovine serum albumin (BSA) as the negative control. Since there are no external bulky pneumatic accessories required to operate/latch the microvalves in the device, this compact, thermally actuated and latching microvalve-enabled multiplexed immunoassay has the potential to realize a portable, low power, battery operated microfluidic device for biological assays.

Improvement of Thermal Conductivity of Electroplated Copper Thin-Film Interconnections by Controlling Their Micro Texture

Copper thin films are indispensable for the interconnections in the advanced electronic products, such as TSV (Trough Silicon Via), fine bumps, and thin-film interconnections in various devices and interposers. However, it has been reported that both electrical and mechanical properties of the films vary drastically comparing with those of conventional bulk copper. The main reason for the variation can be attributed to the fluctuation of the crystallinity of grain boundaries in the films. Porous or sparse grain boundaries show very high resistivity and brittle fracture characteristic in the films. Thus, the thermal conductivity of the electroplated copper thin films should be varied drastically depending on their micro texture based on the Wiedemann-Franz’s law. Since the copper interconnections are used not only for the electrical conduction but also for the thermal conduction, it is very important to quantitatively evaluate the crystallinity of the polycrystalline thin-film materials and clarify the relationship between the crystallinity and thermal properties of the films. The crystallinity of the interconnections were quantitatively evaluated using an electron back-scatter diffraction method. It was found that the porous grain boundaries which contain a significant amount of vacancies increase the local electrical resistance in the interconnections, and thus, cause the local high Joule heating. Such porous grain boundaries can be eliminated by control the crystallinity of the seed layer material on which the electroplated copper thin film is electroplated.

Static Analysis of a Microscale Cricket Filiform Hair Socket

Filiform hairs of crickets are of great interest to engineers because of their highly sensitive response to low velocity air currents. In this study, the cercal sensory system of a common house cricket has been analyzed. The sensory system consists of two antennae like appendages called cerci that are situated at the rear of the cricket’s abdomen. Each cercus is covered with 500–750 flow sensitive hairs that are embedded in a complex viscoelastic socket that acts as a spring -dashpot system and guides the movement of the hair. When the hair deflects due to the drag force induced on its length by a moving air-current, the spiking activity of the neuron and the combined spiking activity of all hairs are extracted by the cercal sensory system. The hair has been experimentally studied by few researchers though its characteristics are not fully understood. The socket structure has not been analyzed experimentally or theoretically from a mechanical standpoint. Therefore, this study aims to understand the socket’s behavior and its interaction with the filiform hair by conducting static analysis. First, a 3D Finite Element Analysis (FEA) model, representing hair and hair-socket, has been developed. Then the static analysis is conducted utilizing the appropriate load and boundary conditions based on the physical conditions that an insect experiences. These numerical analyses aid to understand the deformation mechanism the hair and hair-socket system. The operating principles of the hair and hair-socket could be used for the design of highly responsive MEMS devices such as fluid flow sensors or micro-manipulators.

Solvent-Based Polymer Swelling Characterization for the Development of the Nano/Micro-Particle Polymer Composite MEMS Corrosion Sensor

The concept of using Micro-Electro-Mechanical Systems (MEMS) for in-situ corrosion sensing and for long-term applications has been proposed and is currently under development by our research lab. This is a new type of sensing using MEMS technology and, to the knowledge of our team, has not been explored previously. The MEMS corrosion sensor is based on the oxidation of metal nano/micro-particle embedded in elastomeric polymer to form a composite sensing element. The polymer controls the diffusion into and out of the sensor while the corrosion of the metal particles inhibits electrical conduction which is used as the detection signal. The work presented here is based on part of the methods developed for the removal of native and process-induced metal oxides. A major aspect is the study of the swelling dynamics of the polymer matrix (polydimethylsiloxane, PDMS) intended for enhancing material transport of etchants into and reaction products out of the composite during oxide removal. More specifically, the characterization of the swelling of copper particles-PDMS composite samples in liquid solvent baths is presented.

Understanding the Impact of Flow Bypass on the Thermal Performance of Air Cooled Heat Sinks

In this effort, theoretical modeling was employed to understand the impact of flow bypass on the thermal performance of air cooled heat sinks. Fundamental mass and flow energy conservation equations across a longitudinal fin heat sink configuration and the bypass region were applied and a generic parameter, referred as the Flow Bypass Factor (α), was identified from the theoretical solution that mathematically captures the effect of flow bypass as a quantifiable parameter on the junction-to-ambient thermal resistance of the heat sink. From the results obtained, it was found that, at least in the laminar regime, the impact of flow bypass on performance can be neglected for cases when the bypass gap is typically less than 5% of the fin height, and is almost linear at high relative bypass gaps (i.e., usually for bypass gaps that are more than 10–15% of the fin height). It was also found that the heat sink thermal resistance is more sensitive to small bypass gaps and the effect of flow bypass decreases with increasing bypass gap.

Simulation of Impaction Between Liquid Droplet and Solid Particles Based on SPH Method

The phenomenon of impaction between liquid droplets and solid particles is involved in many scientific problems and engineering applications, such as impaction between sprayed droplet and solid particles in limestone injection desulfurization system and the collision between a droplet of the liquid to be granulated and a seed particle in fluidized bed spray granulation process. There are a lot of factors affected this phenomenon: droplet and particle size, momentum of both liquid droplet and solid particles, materials, surface conditions of the solid particles and so on. However the experimental or numerical researches have been done mostly pay attention to Specific application or process, so the impaction phenomenon has not been through studied, for example how different factors affected the impaction process with its effect on different applications. This paper focuses on the basic issue of interaction between droplet and solid particles. Three main factors were considered: ratio of diameter between the droplet and solid particle, relative velocity and the surface tension (including the contact angle between droplet and solid particle). All the study is based on simulation using SPH (smoothed particle hydrodynamics) method, and the surface tension is simulated by particle-particle interaction.

Stretchable Impedance Spectroscopy Sensor for Mammalian Cells Impedance Measurements

In this paper, an impedance spectroscopy biosensor fabricated on a stretchable substrate has been investigated. A thin stretchable membrane integrated with an impedance biosensor tolerated cyclic strain without cracking. The electric cell-substrate impedance spectroscopy (ECIS) technique has been used to monitor the impedance of the membrane of bovine aortic endothelial cells (BAEC). Integrating mechanical stretching and ECIS sensing onto a single platform requires biocompatible, highly flexible, and reversibly stretchable (elastic) materials for device fabrication. In addition, the interfacial impedance of electrode material to electrolyte should be small to improve the sensitivity of the impedance measurements. In this research, the biocompatible and stretchable membrane was fabricated from polydimethylsiloxane (PDMS), and the ECIS sensor was fabricated on pre-stretched PDMS membrane using sputtering microfabrication and pattern-transferring processes. The stretchable membrane, integrated with the ECIS sensor, can be used to simulate the dynamic environment of organisms and enable the analysis of the cell activity in vitro.

Multi-Scale Regular-Fractal Topography Characterization and Modeling

Regular-fractal topography on RF-switch MEMS surface is reported over different scale ranges. Surface topography is crucial in understanding underling physics associated with the surface contacts, switch working performance, and reliability. The complexity of these structures requires new techniques to characterize topography and then replicate the multi-scale regular-fractal structure for analysis. Topography on RF-switch contacting surfaces are scanned by atomic force microscopy (AFM) at different length scales (e.g. 1×1, 10×10 and 60×60 μm2). A sample allocation plan is designed to maximize the spatial representative of the AFM scanning patches with different resolutions and uniformly distributed sample patches. The scanning data are used for characterizing and model estimation. Hexagonal patterns are found on at coarser scales (e.g. 10×10 and 60×60 μm2). They were formed by the remnant (polymer) of etching process. Random irregularity is observed and the fractal structure at finer scales (e.g. 1×1 μm2) is identified. A regular-fractal model is proposed to decompose and characterize the regular and fractal structures with two model components: one for the regular geometric pattern and the other for fractal irregularity. The former uses a 2D cosine functions to characterize dominant modes in the regular (larger scale) patterns. The later summarizes random irregularity in finer scales with a statistical fractal model estimated from the data on the scattered sample patches. The model validation is made through the comparisons of topography and conventional roughness parameters between the results of simulation from the proposed model and that derived from AFM scanned data.

Design and Analysis of Actuated Microneedles for Robotic Manipulation

We present the design of a MEMS based single-unit actuator consisting of a single microneedle with 3D mobility. The four-sided single-unit actuator (4SA) microrobot design can achieve an in-plane actuation (x, y) of 76 μm (±38 μm) at 160 V and an out-of-plane actuation (z) of more than 6.5 μm at 35 V. The mechanical stress developed within the operational range is between 0.08 to 0.5 percent of the yield strength of silicon i.e. 7000 MPa. We discuss both the analytical modeling and finite element analysis (FEA) simulation of the design based on the range of dimensions analyzed for the individual actuator components. Our primary goal is to integrate multiple actuators into a parallel architecture for independent actuation of multiple microneedles for targeted micro- and nano-robotic manipulation tasks, such as single-cell analyses. We have also successfully fabricated sample 4SA microrobot without the microneedle as a pre-cursor to experimenting with our future advanced design of microrobots. We demonstrate successfully the 3D actuation of the 4SA microrobot of up to 10 μm at 120 V (in-plane) and more than 0.5 μm at 600 V (out-of-plane) with minimum decoupling.