Individual spot sizes for high density arrays down to 80 microns in diameter are possible using reservoir pins manufactured by laser micromachining technique
The Human Genome Project is currently providing vital insights into our human genetic structure.
The number of different genes controlling growth, metabolism, reproduction and other aspects of human life is around 40,000+, a quantity that gives rise to vast amounts of data.
In order to look at the behaviour of many thousands of genes at the same time, micro-array technology is required.
Oxford Lasers, in collaboration with the University of Cambridge and BioRobotics, has developed a new, fast and highly precise method of fabricating capillary reservoir pins for use in microarrays.
The MicroSpot pins are used in BioRobotics MicroGrid premier platforms for the robotic creation of genomic arrays. These machines feature a high level of automation, a large capacity, and fast throughput in a very compact design.
One method of making arrays is by precisely depositing liquid containing cDNA (cloned DNA) on to a flat accepting surface, such as a glass microscope slide, using a capillary reservoir pin.
The substrate is patterned with a regular 2D pattern of cDNA by first dipping the pin tips into the microtitre plate, one pin for each sample well.
The pin tool is then brought into contact with the glass substrate and the liquid transferred from the pins.
The properties of the pins determine the quality of the array that is produced.
The target area of an array on the glass substrate should be as small as possible, since the arrays are tested against very expensive chemicals.
Oxford Lasers can produce pins giving individual spot sizes for high density arrays down to 80 microns in diameter.
The new MicroSpot pins manufactured by Oxford Lasers have several micro features.
In particular, a 15 micron wide capillary slot leading to a reservoir 1000 microns long and 100 microns wide.
The narrow kerf of laser micro machining also allows designs with more complex geometries.
To make a capillary reservoir pin, a 1mm tungsten rod is used with a 2mm long point at one end.
The point has a flat tip (typically 0.05mm in diameter) into which the capillary slot is cut by laser micro machining.
Slot widths down to 5 microns can be achieved and, as the pin geometry is reduced, so denser arrays can be produced.
Although the impact force of the capillary reservoir pin onto the substrate surface is minimised by the use of precision robotic systems, a small force is inevitable and can damage the pins.
Fabrication of slots in tips of this diameter would generally weaken the tip of the finished pin, but at 15 microns the slot produced by laser micro machining is much smaller than any produced by electro-discharge (EDM), and consequently the pin is less fragile.
This, combined with the inherent strength of the tungsten, produces pins with exceptional robustness and very long lifetimes.
A further advantage of laser micro machining is its ability to perform at very high speeds. The process time for the production of capillary reservoir pins is 10 - 20 times faster than EDM, making it more cost effective for high volume production.
Unlike EDM cutting which is limited to conductive, pliable materials, the copper laser micro machining process can be equally successful in a wide variety of other materials including metals, ceramics, diamond and polymers. Martyn Knowles, Oxford Lasers's technology manager, commented that for this particular application, the copper laser has several key advantages over other laser types.
"CO2 and fundamental Nd:Yag lasers can cut rapidly, but they lack precision for the capillary slot and reservoir features" he said.
"Also the fine geometry of the tip of the pin means that it is easily damaged or distorted if there is any significant heat input - another reason why CO2 and Nd:Yag lasers can't be used".
Knowles pointed out that, while Excimer lasers may be able to produce the required feature sizes without thermal distortion of the pin, its poor focusability and low pulse repetition rate means that the process speed is unacceptably slow, especially considering the depth of the reservoir.
New component designs can be rapidly prototyped and volume produced at Oxford Lasers's facility in Abingdon where it claims to have some of the best applications laboratories in the world.
Access to UV and other very high powered lasers, with all the necessary expertise to refine and develop designs gives customers the means to produce top quality, new components out the most difficult materials.
David Moore, University of Cambridge, commented that this direct laser machining approach to microsystem technology may be applied to sensor fabrication and micro opto-electronic packaging.
