H. Thurman Henderson

An integrated microfluidic biochemical detection system for protein analysis with magnetic bead-based sampling capabilities

This paper presents the development and characterization of an integrated microfluidic biochemical detection system for fast and low-volume immunoassays using magnetic beads, which are used as both immobilization surfaces and bio-molecule carriers. Microfluidic components have been developed and integrated to construct a microfluidic biochemical detection system. Magnetic bead-based immunoassay, as a typical example of biochemical detection and analysis, has been successfully performed on the integrated microfluidic biochemical analysis system that includes a surface-mounted biofilter and electrochemical sensor on a glass microfluidic motherboard. Total time required for an immunoassay was less than 20 min including sample incubation time, and sample volume wasted was less than 50 microl during five repeated assays. Fast and low-volume biochemical analysis has been successfully achieved with the developed biofilter and immunosensor, which is integrated to the microfluidic system. Such a magnetic bead-based biochemical detection system, described in this paper, can be applied to protein analysis systems.

A new magnetic bead-based, filterless bio-separator with planar electromagnet surfaces for integrated bio-detection systems

Abstract A new filterless bio-separator separating magnetic microbeads from a carrier fluid has been designed, fabricated, and characterized as a core component of biological cell sampling and detecting systems. To maximize the sampling capability, a planar electromagnet surface with a serpentine coil and semi-encapsulated permalloy has been realized. Using this bio-separator, antibody-coated magnetic beads have been successfully separated from the bio-buffer suspension solution and characterized in dynamic fluid flow. The magnetic characteristics of the bio-separator have been simulated and experimentally studied to establish and validate the design rules for fabrication. The realized filterless bio-separator has a high potential in biomedical and biological detection systems. It is especially useful in selective sampling and separation of small amounts of bio-molecules (e.g., antigen) for on-chip micro total analysis systems (μ-TAS) or remote detection systems.

Development and Characterization of Microfluidic Devices and Systems for Magnetic Bead-Based Biochemical Detection

This paper presents the development and characterization of a generic microfluidic system for magnetic bead-based biochemical detection. Microfluidic and electrochemical detection devices such as microvalves, flow sensors, biofilters, and immunosensors have been successfully developed and individually characterized in this work. Magnetically driven microvalves, pulsed-mode microflow sensors, magnetic particle separators as biofilters, and electrochemical immunosensors have been sep-arately fabricated and tested. The fabricated microfluidic components have been surface-mounted on the microfluidic motherboard for fully integrated microfluidic biochemical detection system. A magnetic bio-bead approach has been adopted for both sampling and manipulating target biological molecules. Magnetic beads were used as both substrate of antibodies and carriers of target antigens for magnetic bead-based immunoassay, which was chosen as a proof-of-concept for the generic microfluidic bio-chemical detection system. The microfluidic and electrochemical immunosensing experiment results obtained from this work have shown that the biochemical sensing capability of the complete microfluidic subsystem is suitable for portable biochemical detection of bio-molecules. The methodology and system, which has been developed in this work, can be extended to generic bio-molecule detection and analysis systems by replacing antibody/antigen with appropriate bio receptors/reagents such as DNA fragments or oligonucleotides for application towards DNA analysis and/or high throughput protein analysis.

Ultra-deep anisotropic etching of (110)silicon

The anisotropic etching behavior of (110) silicon wafers in KOH and TMAH was studied with emphasis on ultra-deep microchannels. Effects which degrade the etching behavior when etching to a depth of the order of a millimeter were encountered and investigated. In particular, oxygen precipitates and their growth during high temperature processing apparently strongly affect the etching of the (111) and (110) planes and reduce the achievable anisotropy ratio. A new 1300 °C high temperature step significantly reduces these negative effects by dissolving oxygen precipitates back into the crystal. Additionally, the influence of pattern alignment, solution concentration and the solution dissolved silicon content as well as the influence of varying masking layers on the achievable anisotropy ratio were investigated and optimized.

Resolving chemical/bio-compatibility issues in microfluidic MEMS systems

We are currently developing a generic microfluidic system (on chip) for the detection of bio-organisms. Numerous bio/chemical compatibility issues arise in development of these chip based microfluidic systems. The resolution of bio/compatibility issues often necessitates a change in materials and, on occasion, leads to redesigning of the system itself. We have successfully decoupled the fabrication and compatibility issues that arose in the fabrication of a generic microfluidic system for chemical detection. We have successfully developed techniques for coating the offending surfaces with a TeflonTM-like amorphous fluorocarbon polymer CYTOPTM and assembling the coated components. In this paper we briefly discuss the microfluidic system being developed by us and the bio/chemical compatibility issues that need to be addressed in this system. Next we discuss the material CYTOP and its application to surfaces and devices. The bonding technique developed to bond the polymer coated structures and some of the components fabricated using this material are also discussed.

A low temperature biochemically compatible bonding technique using fluoropolymers for biochemical microfluidic systems

A new low temperature biochemically compatible bonding technique using fluoropolymers has been developed in this work and characterized in terms of mechanical bonding strength and biochemical resistance. This bonding technique uses a spin-on Teflon-like amorphous fluorocarbon polymer (CYTOP/sup TM/) as a bonding interface layer. The developed bonding process requires a bonding temperature of 160/spl deg/C and the bonding strength attained from the process shows 4.3 Mpa in silicon-to-silicon. Furthermore, the bonding technique achieves reliable and leak-proof bonding in various substrates and provides excellent chemical resistance and biocompatibility for some specific immunoassays. The bonding technique developed in this work has been successfully applied to the development of a microfluidic motherboard system with surface mountable microfluidic components.

MEMS loop heat pipe based on coherent porous silicon technology

This paper discusses the theory, modeling, design, fabrication and preliminary test results of the MEMS loop heat pipe being developed at the Center for Microelectronic Sensors and MEMS at the University of Cincinnati. The emphasis is placed upon the silicon micro wick and its production through a novel technique known as Coherent Porous Silicon (CPS) Technology.

Etching of self-sharpening (338) tips in (100) silicon

Numerous papers have appeared in recent years describing various methods of achieving nanoscale tips for vacuum microelectronics. In single-crystalline (100) silicon, wet anisotropic etching (KOH in this case) has been affected by the truncation, or blunting, of the tip when the masking oxide or nitride is completely underetched, which exposes the quickly etching (100) surface plane. This paper reports for the first time the activation of (338) type sidewalls, which under our conditions results in an etching effect along the (100) direction that exceeds the ordinary etching rate of the (100) plane, thus resulting in a self-sharpening tip. Secondary planes reported in the literature have traditionally been of low index, such as (122), (112), (113), or (133), although (114) and even (225) have also been reported. Comparison of the relevant angles of each of these planes reveals similarities that may lead to ambiguities found in the literature. A statistical analysis of the data presented in this paper lends confidence to the assertion that the (338) family defines the sidewalls of the tips. Also, a novel and highly promising double tip (tip on a tip) is herein reported preliminarily, in (110) oriented silicon; this is currently under analysis.

Test Cell for a Novel Planar MEMS Loop Heat Pipe Based on Coherent Porous Silicon

Work towards the development of an innovative, potentially high power density, MEMS loop heat pipe is in progress at the Center for Microelectronic Sensors and M E M S at the University of Cincinnati. The design of the loop heat pipe is based upon the very unique coherent porous silicon technology, a technique in which vast arrays of micrometer ‐ sized through ‐ holes are photo ‐ electrochemically etched into a silicon wafer perpendicular to the (100) surface. The initial mathematical model, the design, fabrication and characterization of the device in the open loop configuration were previously reported at this conference, STAIF 2002. This paper begins with a very brief explanation of the device and its theory of operation. The design of the device components and their production utilizing the various techniques of microelectronic and microelectromechanical fabrication are presented. The modifications made to the photon ‐ induced, electrochemical etch process, which significantly increase the etch rate o...

Probing human skin as an information-rich smart biological interface using MEMS sensors

Abstract This paper describes our approach of studying the dynamic, information rich, molecular structure of the ultimate smart interface — human skin — by coupling the advances in biological, microsystems, and information technology. The outer layer of human skin, the stratum corneum is a biologically complex thin film that has unique molecular mechanisms that allow it to function simultaneously as a structural and as a perceptual interface. It is continuously ‘sampled’ by the brain in terms of visual, tactile, and olfactory cues. It interfaces the organism with its environment and has unique micro/nano architecture from an engineering standpoint, e.g. it simultaneously retains and uses water to plasticize the membrane for flexibility. This paper focuses on the development of a sampling interface and MEMS components for a freestanding, multifunctional, multimode, microfluidics-based sensor system for real time physiological monitoring. This research will enable us to gain an insight into the functioning of the human at a fundamental level (from cellular to population) that has not been possible before.