Northern blot

The Northern Blot test is used to identify tissue specific protein expression by detecting mRNA in a sample.
Steps:
#RNA samples are separated via. gel electrophoresis
#RNA samples that have now been separated by size are transferred to a nylon membrane
#Once RNA is transferred it is fixed to the nylon membrane using heat or UV light.
#Once RNA is fixed to the nylon sheet the hybridization probes are applied to the membrane.
#Prior to imaging, the membrane is washed to remove any additional probe.
#Hybrid signals are then detected by X-ray film.
This can help to determine if gene expression is tissue specific or to determine when certain genes are expressed.
Reference:
Wikipedia. Northern Blot. Last modified: Sep 19 2012. http://en.wikipedia.org/wiki/Northern_blot