Micro & Nanotech : Microarrays

Micro & Nanotech Portfolios


Patch Clamp Providing On-Chip Thermal Control

A UW–Madison researcher has developed a patch clamp chip providing precise, localized temperature control of cell membranes.

The chip’s temperature system uses a Peltier device, which is capable of heating or cooling depending on the direction of current flow. It is a semiconducting membrane and can be etched on a silicon wafer, separated and then bonded to the substrate of the patch clamp. Using techniques previously developed by the researcher, the sandwiched structure is exposed to laser radiation to drill a nanoscale pore.

Laser Drilling Quartz to Make Patch Clamp Plate Arrays

UW–Madison researchers have developed a technique to form pores as small as 200 nanometers in single crystal quartz. The process can employ UV-emitting excimer lasers or other types of lasers.

In the new technique, the quartz substrate is backed by an energy absorbing material like acetone and/or fluorescent immersion oil, which absorbs UV radiation. When the laser is directed into the quartz, it passes through and strikes this absorbing material. The material increases in temperature, melting a small pore or crater in the overlying quartz.

Improved Nanoscale Aperture Fabrication Technique for Mass Production of Patch Clamp Plate Arrays

UW-Madison researchers have developed an improved laser ablation technique to manufacture glass plates with an array of nanoscale apertures having smooth contact surfaces.  The method involves backing the plate substrate with a thermally expanding material that may either be a solid or a thin layer of liquid.  A first ablation period is used to burn a crater in the plate substrate that does not extend all the way through the material.  During the final stage of ablation the laser is applied in such a fashion that heat generates a shock wave in the thermally expanding substance, creating a smaller counter-facing concave crater in the plate substrate and completing the aperture.  Specific laser parameters also are controlled during the final stage of ablation such that etching via laser produces a smooth finish around the pore.

The improved method can be used to produce smooth pores less than 500 nanometers in diameter, making it ideal for production of patch clamp plate arrays.  The use of transparent substrates, such as glass, permits the use of both optical and electrical measurements of cell membranes.  With respect to the thin liquid layer method, the volatilizable substance provides a pressure wave to improve aperture formation and adjustment of the liquid layer thickness also permits precise control of the shock wave formation parameters.

Robust and Improved Surfaces for Biological Microarrays That Reduce Nonspecific Binding

A UW-Madison researcher has developed a robust coating for use in microarrays. This reactive polymer coating has a high mechanical stability, binding-site density and signal-to-noise ratio. It can be formed readily on many substrates and may also be patterned to control the localization and density of the target molecules.

The coating consists of a cross-linked epoxy-functional copolymer film. The copolymers incorporate at least two sets of polymerized monomers. The first set, which contains epoxide groups, reacts with the target molecules to immobilize them on the film. The second set contains photo-cross-linkable groups, which are used to cross-link the copolymers into a stable film. Using different monomers to provide the cross-linking and target binding functions allows each function to be controlled and optimized independently.

Plasma-Enhanced Functionalization of Carbon-Containing Substrates

UW-Madison researchers have developed an efficient, dry plasma technique for functionalizing surfaces that holds several advantages over traditional wet chemical approaches. The technique involves two steps. First, a carbon containing substrate is exposed to an inert plasma (e.g., argon or hydrogen) that generates reactive active sites, such as free radicals or ions, on the surface of the substrate. Next, the surface is exposed to volatile compounds in the absence of plasma. The compounds react with the active sites to produce surface-bound spacer chain molecules containing one or more functional groups. These functional groups, in turn, can react with molecules of DNA or protein.

Methods and Devices for Precisely Dispensing Microvolumes of Fluids

UW-Madison researchers have developed a microplotter device that can deposit spots or lines on the order of 5 micrometers in size for several applications, including biological microarrays and polymer-based circuits. The device consists of a nozzle for depositing fluid, which is connected to a positioning system that is controlled by customized software on a desktop computer. The nozzle, composed of a micropipette fastened to a piece of piezoelectric, deposits small features through ultrasonics.

Minimizing Cross-Talk Between Photodiodes in Array

UW–Madison researchers have developed a method to essentially eliminate leakage current by isolating very close diodes using narrow, vertically walled trenches etched in the array.

The photodiodes are formed of spaced regions in a base layer, each region having an impurity type opposite of the base to create a semiconducting p-n junction. The base layer meets a more heavily doped substrate of the same material, such as crystalline silicon, at a boundary. Minority carriers generated by absorption of light photons in the base layer can only migrate to an adjacent diode through the substrate—their lifetime and corresponding diffusion length are so short that they recombine in the substrate before reaching an adjacent diode.