Arrayers

Arrayers are available from a number of companies at a cost of approximately $60,000. However the construction of arrayers is possible in the laboratory, but it is not easy to do. Some laboratories have relied on professional engineers.
The first arrayer used by Vivian Cheung at the University of Pennsylvania was put together in four months. However, it is more likely that these arrayers will become more affordable as the technology improves.

Here is an arrayer produced by BioRobotics; their MicroGrid II.

BioRobotics' MicroGrid II

Here is a close-up of the arraying equipment:

BioRobotics' MicroGrid II

Building an Arrayer

Instructions for building an arrayer can be found at the website of Patrick Brown, of Stanford University: http://cmgm.stanford.edu/pbrown

It is difficult to know how best to invest the funds available though; whilst the technology is changing at the rate it currently is.

Scanners

Affymetrix's GeneArray Scanner

The principle of scanners is to detect the different levels of fluorescence between the spots on the microarray. This produces a ratio of fluorescence, representing a ratio of hybridisation, for the different mRNA or cDNA sequences. This gives an indication of the expression of the genes under study in the tissue or cell samples.

A light source inside the scanner excites the fluorescently labelled samples. This is then detected, measured and recorded.

Most image capture instruments use a scanning detector similar to the line-scanning detectors that are present in DNA sequencing instruments.

For the continued progression of microarray techniques, the technology behind scanners must keep pace. In the last year probe cells have decreased in size from 50 microns to approximately 25 microns. This means that an increase in the resolution of the scanners is needed to ensure this decrease in size continues.

Also important to the results produced by the scanners is the signal-to-noise ratio of the final image. Inadequate fluorescent labelling or concentration of the DNA being studied can significantly weaken the fluorescent signal produced. This can also occur when the probe cells do not have enough molecules to get a sufficient signal during hybridisation.