Chemistry: analytical and immunological testing – Involving an insoluble carrier for immobilizing immunochemicals – Carrier is inorganic
Reexamination Certificate
2000-10-17
2004-09-28
Chin, Christopher L. (Department: 1641)
Chemistry: analytical and immunological testing
Involving an insoluble carrier for immobilizing immunochemicals
Carrier is inorganic
C436S518000, C436S525000, C436S527000, C436S528000, C436S529000, C436S164000, C436S806000, C435S006120, C435S007100, C435S007200, C435S007210, C435S007230, C435S007930, C435S007940, C435S007950, C427S002120, C427S002130, C427S483000, C427S059000, C427S077000
Reexamination Certificate
active
06797524
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of materials science and analytical chemistry.
The present invention specifically relates to the realization of a complete, functionally integrated system for the implementation of biochemical analysis in a planar, miniaturized format on the surface of a conductive and/or photoconductive substrate, with applications in pharmaceutical and agricultural drug discovery and in in-vitro or genomic diagnostics. In addition, the method and apparatus of the present invention may be used to create material surfaces exhibiting desirable topographical relief and chemical functionality, and to fabricate surface-mounted optical elements such as lens arrays.
BACKGROUND OF THE INVENTION
I—Ions, Electric Fields and Fluid Flow: Field-induced Formation of Planar Bead Arrays
Electrokinesis refers to a class of phenomena elicited by the action of an electric field on the mobile ions surrounding charged objects in an electrolyte solution When an object of given surface charge is immersed in a solutionaping ions, a diffuse ion cloud forms to screen the object's surface charge. This mrrangement of a layer of (immobile) charges associated with an immersed object and the screening cloud of (mobile) counterions in solution is referred to as a “double layer”. In this region of small but finite thickness, the fluid is not electroneutral. Consequently, electric fields acting on this region will set in motion ions in the diffluse layer, and these will in turn entrain the surrounding fluid. The resulting flow fields reflect the spatial distribution of ionic current in the fluid. Electroosmosis represents the simplest example of an electrokinetic phenomenon. It arises when an electric field is applied parallel to the surface of a sample container or electrode exhibiting fixed surface charges, as in the case of a silicon oxide electrode (in the range of neutral pH). As counterions in the electrode double layer are accelerated by the electric field, they drag along solvent molecules and set up bulk fluid flow. This effect can be very substantial in narrow capillaries and may be used to advantage to devise fluid pumping systems.
Electrophoresis is a related phenomenon which refers to the field-induced transport of charged particles immersed in an electrolyte. As with electroosmosis, an electric field accelerates mobile ions in the double layer of the particle. If, in contrast to the earlier case, the particle itself is mobile, it will compensate for this field-induced motion of ions (and the resulting ionic current) by moving in the opposite direction. Electrophoresis plays an important role in industrial coating processes and, along with electroosmosis, it is of particular interest in connection with the development of capillary electrophoresis into a mainstay of modern bioanalytical separation technology.
In confined geometries, such as that of a shallow experimental chamber in the form of a “sandwich” of two planar electrodes, the surface charge distribution and topography of the bounding electrode surfaces play a parcay important role in determining the nature and spatial structure of electroosmotic flow. Such a “sandwich” electrochemical cell may be formed by a pair of electrodes separated by a shallow gap. Typically, the bottom electrode will be formed by an oxide ed silicon wafer, while the other electrode is formed by optically transparent, conducting indium tin oxide (ITO). The silicon (Si) wafer represents a thin slice of a single crystal of silicon which is doped to attain suitable levels of electrical conductivity and insulated from the electrolyte solution by a thin layer of silicon oxide (SiOx).
The reversible aggregation of beads into planar aggregates adjacent to an electrode surface may be induced by a (DC or AC) electric field is applied normal to the electrode surface. While the phenomenon has been previously observed in a cell formed by a pair of conductive ITO electrodes (Richetti, Prost and Barois, J. Physique Lettr. 45, L-1137 through L1143 (1984)), the contents of which are incorporated herein by reference, it has been only recently demonstrated that the underlying attractive interaction between beads is mediated by electrokinetic flow (Yeh, Seul and Shraiman, “Assembly of Ordered Colloidal Aggregates by Electric Field Induced Fluid Flow”, Nature 386, 57-59 (1997), the contents of which are incorporated herein by reference. This flow reflects the action of lateral non-uniformities in the spatial distribution of the current in the vicinity of the electrode. In the simplest case, such non-uniformities are introduced bv the very presence of a colloidal bead near the electrode as a result of the fact that each bead interferes with the motion of ions in the electrolyte. Thus, it has been observed that an individual bead, when placed near the electrode surface, generates a toroidal flow of fluid centered on the bead. Spatial non-uniformities in the properties of the electrode can also be introduced deliberately by several methods to produce lateral fluid flow toward regions of low impedance. These methods are described in subsequent sections below.
Particles embedded in the electrokinetic flow are advected regardless of their specific chemical or biological nature, while simultaneously altering the flow field. As a result, the electric field-induced assembly of planar aggregates and arrays applies to such diverse particles as: colloidal polymer lattices (“latex beads”), lipid vesicles, whole chromosomes, cells and biomolecules including proteins and DNA, as well as meal or semiconductor colloids and clusters.
Important for the applications to be described is the fact that the flow-mediated attractive interaction between beads extends to distances far exceeding the characteristic bead dimension. Planar aggregates are formed in resonse to an eternally applied electric field and disassemble when the field is removed. The strength of the applied field determines the strength of the attractive interaction that underlies the array assembly process and thereby selects the specific arrangement adopted by the beads within the array. That is, as a function of increasing applied voltage, beads first form planar aggregates in which particles are mobile and loosely packed, then assume a tighter packing, and finally exhibit a spatial arrangement in the form of a crystalline, or ordered, array resembling a raft of bubbles. The sequence of transitions between states of increasing internal order is reversible, including complete disassembly of planar aggregates when the applied voltage is removed. In anoter arrangement, at low initial concentration, beads form small clusters which in turn assume positions within an ordered “superstructure”.
II—Patterning of Silicon Oxide Electrode Surfaces
Electrode patterning in accordance with a predetermined design facilitates the quasi-permanent modification of iie electrical impedance of the EIS (Electrolyte-Insulator-Semiconductor) structure of interest here. By spatially modulating the EIS impedance, electrode-patterning determines the ionic current in the vicinity of the electrode. Depending on the frequency of the applied electric field, beads either seek out, or avoid, regions of high ionic current. Spatial patterning therefore conveys explicit external control over the placement and shape of bead arrays.
While patterning may be achieved in many ways, two procedures offer particular advantages. First, UV-mediated re-growth of a thin oxide layer on a properly prepared silicon surface is a convenient methodology that avoids photolithographic resist patterning and etching. In the presence of oxygen, UV illumination mediates the conversion of exposed silicon into oxide. Specifically, the thickness of the oxide layer depends on the exposure time and may thus be spatially modulated by placing patterned masks into the UV illumination path. This modulation in thickness, with typical variations of approximately 10 Angstroms, translates into spatial modulations in the impedance of the Si/SiOx inte
Bioarray Solutions Ltd.
Bowker Julie
Chin Christopher L.
Do Pensee T.
Mirabel Eric P.
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