Microscale Bioanalytical Systems

Abstract

M icrofluidic phenomena are present in all of nature's exquisitely designed biological systems (1). A complex oxygen transport network consisting of plasma, red blood cells ~6 to 8 gm in diameter, and capillaries -8 gm in diameter carries sustenance to cells throughout the body, including the eyes through which you are reading this article. Without microfluidic channels and diffusion transport systems, life as we know it would not be possible (1).Most microfluidic systems draw their advantages from low thermal mass and efficient mass transport, as well as from large channel surface area-to-channel volume ratios. Manmade microfluidic systems have been made possible by microfabrication methods developed for the electronics industry. Microfluidic systems are of intense interest because of their characteristic controlled mixing that expedites chemical reactions, reduced consumption of expensive materials, high sensitivity, and efficient product yields. Here, we aim to share a summary of the applications and design of microfluidic devices. Welcome to an expansive world of the very small.Microfluidic systems are composed of fluid channels and chambers with critical dimensions of tens to hundreds of micrometers (for reference, a relatively fine human hair is about 80 gm in diameter). Integrated systems of microfluidic channels combined with pumps, valves, and detectors are known as Micro Total Analysis Systems (gTAS) or "lab-on-a-chip" systems (2, 3). Modern microfluidic devices are generally hybrids of various materials and processes integrated with electro-optical components for detection and, importantly, manipulation of molecules of interest (2).Rapid and efficient mixing of components is critical in the control of chemical reactions. In nature, the limit of diffusion has determined, in part, how single-cell organisms evolved and how they behave (4). Microfluidic channels provide specialized environments for controlling mixing. Only laminar flow exists in confined spaces such as microchannels, because fluid viscosity, not inertia, dominates fluid behavior. Therefore, fluid flow in these systems is not turbulent or random. In macrofluidic systems, a much larger fluid mass is in motion and inertial forces can dominate and lead to turbulent conditions (see figure, this page). In laminar flow, two nonreacting fluids that merge will flow smoothly next to each other as diffusion brings the two solutions into a well-mixed equilibrium. This is achieved by layering the fluid or minimizing the channel dimensions (see figure, next page). The equilibration time is proportional to the square of the diffusion distance, in this case the microchannel dimension in the direction of the concentration gradient.The small dimensions of microfluidic devices cause the ratio of surface area-to-volume to be large. Capture of specific molecules and particles is achieved by exploiting the binding affinity of these substances to specialty coatings of the wall surfaces. Captured molecules and particles can be released all at (D.M.); holl@u.washi...

A bubble-driven microfluidic transport element for bioengineering

“…The flow of liquid in these devices is regulated by a large variety of applied forces (3), such as pressure differences, electrophoresis (4), capillary forces (5), or Marangoni forces (6). In biology-related applications, the flows are often used for cytometry and sorting of cells (7)(8)(9). In the overwhelming majority of microfluidic setups, the flow is confined to microchannels or microcapillaries that have been etched into or grafted onto a substrate.…”

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

“…In recent years, the field of microfluidics has seen major conceptual advances, and, enabled by the progress in methodology and technology, the number of applications has grown substantially [197][198][199][200]. In particular, it has been recognized that microfluidic devices can be beneficial − or instrumental − in a much greater range of applications as one moves away from utilizing homogeneous liquids as the transport medium.…”

“…It has evolved as the major technological platform on which bio-technology, material science and other related fields have seen a tremendous growth in the last decade [197][198][199][200]. In contrast to the flows at macro scales, flow within microchannels is fundamentally different due to the drastic reduction of the intertial effects, resulting in very low Reynolds numbers [201].…”

A New Mathematical Model for Calculating the Electronic Coupling of a B-DNA Molecule

“…Also, because of its self-assembly and self-recognition characteristics, DNA can easily adopt to various states and conformations, thereby providing the possibility of producing nanostructures with very high precision, beyond what is achievable with traditional silicon-based technologies [2]. Equally important is the understanding of charge transport in DNA in relation to damage and mutation throughout the macromolecule [7][8][9], the detecting, manipulating, and sequencing of DNA [10][11][12], and the transport properties of other systems with π π − interactions, such as molecular crystals and discotic materials [13,14].…”