What is the technological differences between the DNA microarray and RNA microarray, specifically when gene expression is measured by each? Wikipedia says "Scientists use DNA microarrays to measure the expression levels of large numbers of genes simultaneously or to genotype multiple regions of a genome.". RNA microarray also can be used to measure the expression levels of large numbers of genes simultaneously, I think. So, is the difference of the two technologies only about genotyping genomic regions?
If you need to measure mRNA abundance or expression in cell (which I will assume that this is what you mean by RNA microarray), first mRNA transformed to more stable cDNA. Other than that I do not know what do you mean by RNA microarray.
This is a nice review, that may help to make the idea clear.
DNA microarrays: Types, Applications and their future
Do you mean Expression arrays Vs Genotyping arrays (for CNV detection, LOH, genotyping, SNV etc)?
For Expression arrays, RNA (mostly mRNA) is the starting material and probes are designed to detect RNA (qualitative and quantitative).
For SNP/genotyping arrays, starting material is DNA and probes are designed to detect genome level events.