It can be performed on total cellular RNA or poly(A)-selected mRNA as a target. RPA is an extremely sensitive technique for the quantitation of specific RNAs in solution.
Northern blotting involves the use of electrophoresis to separate RNA samples by size, then detect the mRNA with a hybridization probe complementary to part of the target sequence. Among these techniques, Northern blot analysis remains a standard method for detection and quantitation of mRNA levels despite the advent of more robust techniques. There are several methods available to determine gene expression, such as northern blot analysis, ribonuclease protection assay (RPA), serial analysis of gene expression (SAGE), reverse transcription-polymerase chain reaction (RT-PCR), quantitative real-time polymerase chain reaction (qRT-PCR), PCR arrays, and microarrays.
Gene expression assays, for example, gene profiling, are an important tool and are widely used in nanotoxicity studies.
The study of gene expression in a cell or tissue at a particular moment gives an insight into the capacity of the cell for protein synthesis.